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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_McCarthyMember_lbl" xml:lang="en-US">McCarthyMember</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MorrisonAndFoersterMember_lbl" xml:lang="en-US">MorrisonAndFoersterMember</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DesjardinsMember_lbl" xml:lang="en-US">DesjardinsMember</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InvestorRelationServicesMember_lbl" xml:lang="en-US">InvestorRelationServicesMember</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesAPreferredStockMember_lbl" xml:lang="en-US">SeriesAPreferredStockMember</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xml:lang="en-US">Statement Class Of Stock [Axis]</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_DesjardinsSecuritiesIncMember_lbl" xml:lang="en-US">LegalEntityAxis</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_McCarthyTetraultLLPMember_lbl" xml:lang="en-US">LegalEntityAxis</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_MorrisonAndFoersterLLPMember_lbl" xml:lang="en-US">LegalEntityAxis</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesAMember" xlink:to="us-gaap_SeriesAMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesAMember_lbl" xml:lang="en-US">SeriesAMember</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis" xlink:label="us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis" xlink:to="us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AuctionMarketPreferredSecuritiesStockSeriesAxis_lbl" xml:lang="en-US">AuctionMarketPreferredSecuritiesStockSeries [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinimumMember" xlink:to="us-gaap_MinimumMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MinimumMember_lbl" xml:lang="en-US">MinimumMember</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MaximumMember" xlink:to="us-gaap_MaximumMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MaximumMember_lbl" xml:lang="en-US">MaximumMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PreModificationMember" xlink:label="VSTA_PreModificationMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationMember" xlink:to="VSTA_PreModificationMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreModificationMember_lbl" xml:lang="en-US">Pre-Modification [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShortTermDebtTypeAxis" xlink:label="us-gaap_ShortTermDebtTypeAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShortTermDebtTypeAxis" xlink:to="us-gaap_ShortTermDebtTypeAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShortTermDebtTypeAxis_lbl" xml:lang="en-US">Short-term Debt, Type [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PostModificationMember" xlink:label="VSTA_PostModificationMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationMember" xlink:to="VSTA_PostModificationMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PostModificationMember_lbl" xml:lang="en-US">Post-Modification [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CatoBioVenturesMember" xlink:label="VSTA_CatoBioVenturesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoBioVenturesMember" xlink:to="VSTA_CatoBioVenturesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CatoBioVenturesMember_lbl" xml:lang="en-US">CatoBioVentures [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_USNationalInstitutesOfHealthMember" xlink:label="VSTA_USNationalInstitutesOfHealthMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_USNationalInstitutesOfHealthMember" xlink:to="VSTA_USNationalInstitutesOfHealthMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_USNationalInstitutesOfHealthMember_lbl" xml:lang="en-US">USNationalInstitutesOfHealth [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsAxis" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsAxis" xlink:to="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsAxis_lbl" xml:lang="en-US">Collaborative Arrangements and Non-collaborative Arrangements [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NIHGrantRevenueMember" xlink:label="VSTA_NIHGrantRevenueMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NIHGrantRevenueMember" xlink:to="VSTA_NIHGrantRevenueMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NIHGrantRevenueMember_lbl" xml:lang="en-US">NIHGrantRevenueMember</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredRevenueArrangementTypeAxis" xlink:label="us-gaap_DeferredRevenueArrangementTypeAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenueArrangementTypeAxis" xlink:to="us-gaap_DeferredRevenueArrangementTypeAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredRevenueArrangementTypeAxis_lbl" xml:lang="en-US">DeferredRevenueArrangementType [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CatoResearchLtdMember" xlink:label="VSTA_CatoResearchLtdMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoResearchLtdMember" xlink:to="VSTA_CatoResearchLtdMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CatoResearchLtdMember_lbl" xml:lang="en-US">CatoResearchLtdMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" xlink:label="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_lbl" xml:lang="en-US">IssuedToPlatinumOnTwoJulyTwoThousandTwelve [Member]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2_lbl" xml:lang="en-US">Related Party [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" xlink:label="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_lbl" xml:lang="en-US">IssuedToPlatinumOnThirtyAugustTwoThousandTwelve [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SeniorNotesNonCurrentMember" xlink:label="VSTA_SeniorNotesNonCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNotesNonCurrentMember" xlink:to="VSTA_SeniorNotesNonCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNotesNonCurrentMember_lbl" xml:lang="en-US">SeniorNotesNonCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NoteDiscountMember" xlink:label="VSTA_NoteDiscountMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountMember" xlink:to="VSTA_NoteDiscountMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountMember_lbl" xml:lang="en-US">NoteDiscount [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:to="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_lbl" xml:lang="en-US">SevenPercentNotesPayableAprilTwoThousandEleven [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" xlink:label="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" xlink:to="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_lbl" xml:lang="en-US">SevenPercentNotesPayableAugustTwoThousandTwelve [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SevenPercentNotesPayableMember" xlink:label="VSTA_SevenPercentNotesPayableMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableMember" xlink:to="VSTA_SevenPercentNotesPayableMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableMember_lbl" xml:lang="en-US">SevenPercentNotesPayable [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CurrentPortionMember" xlink:label="VSTA_CurrentPortionMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionMember" xlink:to="VSTA_CurrentPortionMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionMember_lbl" xml:lang="en-US">CurrentPortion [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SevenPercentNotesPayableNonCurrentPortionMember" xlink:label="VSTA_SevenPercentNotesPayableNonCurrentPortionMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableNonCurrentPortionMember" xlink:to="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_lbl" xml:lang="en-US">SevenPercentNotesPayableNonCurrentPortion [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_BurrPilgerMayerMember" xlink:label="VSTA_BurrPilgerMayerMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerMayerMember" xlink:to="VSTA_BurrPilgerMayerMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BurrPilgerMayerMember_lbl" xml:lang="en-US">BurrPilgerMayer [Member]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DesjardinsMember" xlink:to="VSTA_DesjardinsMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_DesjardinsMember_2_lbl" xml:lang="en-US">Desjardins [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_McCarthyTetraultMember" xlink:label="VSTA_McCarthyTetraultMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultMember" xlink:to="VSTA_McCarthyTetraultMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_McCarthyTetraultMember_lbl" xml:lang="en-US">McCarthyTetrault [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:to="VSTA_MayTwoThousandElevenMorrisonFoersterMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember_lbl" xml:lang="en-US">MayTwoThousandElevenMorrisonFoerster [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_lbl" xml:lang="en-US">AugustTwoThousandTwelveMorrisonAndFoersterNoteA [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_lbl" xml:lang="en-US">AugustTwoThousandTwelveMorrisonAndFoersterNoteB [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NoteDiscountOneMember" xlink:label="VSTA_NoteDiscountOneMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountOneMember" xlink:to="VSTA_NoteDiscountOneMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountOneMember_lbl" xml:lang="en-US">NoteDiscountOne [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SevenPointFivePercentNotesPayableMember" xlink:label="VSTA_SevenPointFivePercentNotesPayableMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPointFivePercentNotesPayableMember" xlink:to="VSTA_SevenPointFivePercentNotesPayableMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPointFivePercentNotesPayableMember_lbl" xml:lang="en-US">SevenPointFivePercentNotesPayable [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CurrentPortionOneMember" xlink:label="VSTA_CurrentPortionOneMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionOneMember" xlink:to="VSTA_CurrentPortionOneMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionOneMember_lbl" xml:lang="en-US">CurrentPortionOne [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NonCurrentPortionAndDiscountMember" xlink:label="VSTA_NonCurrentPortionAndDiscountMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountMember" xlink:to="VSTA_NonCurrentPortionAndDiscountMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionAndDiscountMember_lbl" xml:lang="en-US">NonCurrentPortionAndDiscount [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" xlink:label="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" xlink:to="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_lbl" xml:lang="en-US">FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" xlink:label="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" xlink:to="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_lbl" xml:lang="en-US">TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayable [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CurrentPortionTwoMember" xlink:label="VSTA_CurrentPortionTwoMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionTwoMember" xlink:to="VSTA_CurrentPortionTwoMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionTwoMember_lbl" xml:lang="en-US">CurrentPortionTwo [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NonCurrentPortionMember" xlink:label="VSTA_NonCurrentPortionMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionMember" xlink:to="VSTA_NonCurrentPortionMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionMember_lbl" xml:lang="en-US">NonCurrentPortion [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" xlink:label="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" xlink:to="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_lbl" xml:lang="en-US">TenPercentNotesPayableToUnrelatedParties [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CurrentPortionThreeMember" xlink:label="VSTA_CurrentPortionThreeMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionThreeMember" xlink:to="VSTA_CurrentPortionThreeMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionThreeMember_lbl" xml:lang="en-US">CurrentPortionThree [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NonCurrentPortionAndDiscountOneMember" xlink:label="VSTA_NonCurrentPortionAndDiscountOneMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountOneMember" xlink:to="VSTA_NonCurrentPortionAndDiscountOneMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionAndDiscountOneMember_lbl" xml:lang="en-US">NonCurrentPortionAndDiscountOne [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SevenPercentNotePayableToCatoHoldingMember" xlink:label="VSTA_SevenPercentNotePayableToCatoHoldingMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotePayableToCatoHoldingMember" xlink:to="VSTA_SevenPercentNotePayableToCatoHoldingMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotePayableToCatoHoldingMember_lbl" xml:lang="en-US">SevenPercentNotePayableToCatoHolding [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NoteDiscountTwoMember" xlink:label="VSTA_NoteDiscountTwoMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountTwoMember" xlink:to="VSTA_NoteDiscountTwoMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountTwoMember_lbl" xml:lang="en-US">NoteDiscountTwo [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesPayableToRelatedPartiesMember" xlink:label="VSTA_NotesPayableToRelatedPartiesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableToRelatedPartiesMember" xlink:to="VSTA_NotesPayableToRelatedPartiesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableToRelatedPartiesMember_lbl" xml:lang="en-US">NotesPayableToRelatedParties [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CurrentPortionFourMember" xlink:label="VSTA_CurrentPortionFourMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionFourMember" xlink:to="VSTA_CurrentPortionFourMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionFourMember_lbl" xml:lang="en-US">CurrentPortionFour [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NonCurrentPortionAndDiscountTwoMember" xlink:label="VSTA_NonCurrentPortionAndDiscountTwoMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountTwoMember" xlink:to="VSTA_NonCurrentPortionAndDiscountTwoMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionAndDiscountTwoMember_lbl" xml:lang="en-US">NonCurrentPortionAndDiscountTwo [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" xlink:label="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" xlink:to="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_lbl" xml:lang="en-US">FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" xlink:label="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" xlink:to="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_lbl" xml:lang="en-US">TwelvePercentConvertibleNotesNetNnonCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ShareBasedCompensationWarrantsMember" xlink:label="VSTA_ShareBasedCompensationWarrantsMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsMember" xlink:to="VSTA_ShareBasedCompensationWarrantsMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationWarrantsMember_lbl" xml:lang="en-US">ShareBasedCompensationWarrantsMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_DocumentAndEntityInformationAbstract" xlink:label="VSTA_DocumentAndEntityInformationAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DocumentAndEntityInformationAbstract" xlink:to="VSTA_DocumentAndEntityInformationAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DocumentAndEntityInformationAbstract_lbl" xml:lang="en-US">Document And Entity Information</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityRegistrantName" xlink:to="dei_EntityRegistrantName_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityRegistrantName_lbl" xml:lang="en-US">Entity Registrant Name</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCentralIndexKey" xlink:to="dei_EntityCentralIndexKey_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCentralIndexKey_lbl" xml:lang="en-US">Entity Central Index Key</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentType" xlink:label="dei_DocumentType" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentType" xlink:to="dei_DocumentType_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentType_lbl" xml:lang="en-US">Document Type</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentPeriodEndDate" xlink:to="dei_DocumentPeriodEndDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentPeriodEndDate_lbl" xml:lang="en-US">Document Period End Date</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_AmendmentFlag" xlink:to="dei_AmendmentFlag_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_AmendmentFlag_lbl" xml:lang="en-US">Amendment Flag</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CurrentFiscalYearEndDate" xlink:to="dei_CurrentFiscalYearEndDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xml:lang="en-US">Current Fiscal Year End Date</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityWellKnownSeasonedIssuer" xlink:label="dei_EntityWellKnownSeasonedIssuer" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityWellKnownSeasonedIssuer" xlink:to="dei_EntityWellKnownSeasonedIssuer_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xml:lang="en-US">Is Entity a Well-known Seasoned Issuer?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityVoluntaryFilers" xlink:label="dei_EntityVoluntaryFilers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityVoluntaryFilers" xlink:to="dei_EntityVoluntaryFilers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityVoluntaryFilers_lbl" xml:lang="en-US">Is Entity a Voluntary Filer?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityCurrentReportingStatus" xlink:label="dei_EntityCurrentReportingStatus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCurrentReportingStatus" xlink:to="dei_EntityCurrentReportingStatus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCurrentReportingStatus_lbl" xml:lang="en-US">Is Entity's Reporting Status Current?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFilerCategory" xlink:to="dei_EntityFilerCategory_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityFilerCategory_lbl" xml:lang="en-US">Entity Filer Category</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityPublicFloat" xlink:label="dei_EntityPublicFloat" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityPublicFloat" xlink:to="dei_EntityPublicFloat_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityPublicFloat_lbl" xml:lang="en-US">Entity Public Float</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCommonStockSharesOutstanding" xlink:to="dei_EntityCommonStockSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xml:lang="en-US">Entity Common Stock, Shares Outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalPeriodFocus" xlink:to="dei_DocumentFiscalPeriodFocus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xml:lang="en-US">Document Fiscal Period Focus</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalYearFocus" xlink:to="dei_DocumentFiscalYearFocus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalYearFocus_lbl" xml:lang="en-US">Document Fiscal Year Focus</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementOfFinancialPositionAbstract" xlink:label="us-gaap_StatementOfFinancialPositionAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfFinancialPositionAbstract" xlink:to="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xml:lang="en-US">Statement of Financial Position [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsAbstract_lbl" xml:lang="en-US">ASSETS</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xml:lang="en-US">Current assets:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xml:lang="en-US">Cash and cash equivalents</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ReceivablesNetCurrent" xlink:label="us-gaap_ReceivablesNetCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ReceivablesNetCurrent" xlink:to="us-gaap_ReceivablesNetCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ReceivablesNetCurrent_lbl" xml:lang="en-US">Unbilled contract payments receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PrepaidExpenseCurrent" xlink:label="us-gaap_PrepaidExpenseCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseCurrent" xlink:to="us-gaap_PrepaidExpenseCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidExpenseCurrent_lbl" xml:lang="en-US">Prepaid expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_AssetsCurrent_lbl" xml:lang="en-US">Total current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xml:lang="en-US">Property and equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsNoncurrent" xlink:to="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xml:lang="en-US">Security deposits and other assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Assets_lbl" xml:lang="en-US">Total assets</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_LiabilitiesAndStockholdersDeficitAbstract" xlink:label="VSTA_LiabilitiesAndStockholdersDeficitAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LiabilitiesAndStockholdersDeficitAbstract" xlink:to="VSTA_LiabilitiesAndStockholdersDeficitAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LiabilitiesAndStockholdersDeficitAbstract_lbl" xml:lang="en-US">LIABILITIES AND STOCKHOLDERS' DEFICIT</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xml:lang="en-US">Current liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableCurrent" xlink:to="us-gaap_AccountsPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xml:lang="en-US">Accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xml:lang="en-US">Accrued expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NotesAndLoansPayableCurrent" xlink:label="us-gaap_NotesAndLoansPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NotesAndLoansPayableCurrent" xlink:to="us-gaap_NotesAndLoansPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NotesAndLoansPayableCurrent_lbl" xml:lang="en-US">Notes payable and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedParties_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties_lbl" xml:lang="en-US">Notes payable and accrued interest to related parties</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeaseObligationsCurrent" xlink:label="us-gaap_CapitalLeaseObligationsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsCurrent" xlink:to="us-gaap_CapitalLeaseObligationsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsCurrent_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_DeferredRevenues" xlink:label="VSTA_DeferredRevenues" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DeferredRevenues" xlink:to="VSTA_DeferredRevenues_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DeferredRevenues_lbl" xml:lang="en-US">Deferred revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xml:lang="en-US">Total current liabilities.</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xml:lang="en-US">Non-current liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:to="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_lbl" xml:lang="en-US">Senior secured convertible promissory notes and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" xlink:label="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" xlink:to="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_lbl" xml:lang="en-US">Convertible promissory notes, net of discount of $481,300 at September 30, 2012 and $499,300 at March 31, 2012, and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesPayableAndAccruedInterest" xlink:label="VSTA_NotesPayableAndAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterest" xlink:to="VSTA_NotesPayableAndAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterest_lbl" xml:lang="en-US">Notes payable, net of discount of $1,600,400 at September 30, 2012 and $228,900 at March 31, 2012</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_lbl" xml:lang="en-US">Notes payable to related parties, net of discount of $18,000 at September 30, 2012 and $24,300 at March 31, 2012</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent_lbl" xml:lang="en-US">Non-current accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AccruedOfficersCompensation" xlink:label="VSTA_AccruedOfficersCompensation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedOfficersCompensation" xlink:to="VSTA_AccruedOfficersCompensation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedOfficersCompensation_lbl" xml:lang="en-US">Accrued officers' compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeaseObligationsNoncurrent" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsNoncurrent" xlink:to="us-gaap_CapitalLeaseObligationsNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent_lbl" xml:lang="en-US">Capital lease obligations.</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesNoncurrent" xlink:label="us-gaap_LiabilitiesNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrent" xlink:to="us-gaap_LiabilitiesNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesNoncurrent_lbl" xml:lang="en-US">Total non-current liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Liabilities_lbl" xml:lang="en-US">Total liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingencies" xlink:to="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xml:lang="en-US">Commitments and contingencies</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xml:lang="en-US">Stockholders' deficit:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockValue" xlink:to="us-gaap_PreferredStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockValue_lbl" xml:lang="en-US">Preferred stock, $0.001 par value; 500,000 shares authorized at September 30, 2012 and March 31, 2012; 500,000 and 437,055 Series A shares issued and outstanding at September 30, 2012 and March 31, 2012, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockValue" xlink:to="us-gaap_CommonStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockValue_lbl" xml:lang="en-US">Common stock, $0.001 par value; 200,000,000 shares authorized at September 30, 2012 and March 31, 2012; 20,056,558 and 18,704,267 shares issued at September 30, 2012 and March 31, 2012, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapital" xlink:to="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xml:lang="en-US">Additional paid-in capital</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_TreasuryStockValue" xlink:label="us-gaap_TreasuryStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockValue" xlink:to="us-gaap_TreasuryStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_TreasuryStockValue_lbl" xml:lang="en-US">Treasury stock, at cost, 2,713,308 and 2,083,858 shares of common stock held at September 30, 2012 and March 31, 2012, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_lbl" xml:lang="en-US">Notes receivable from sale of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xml:lang="en-US">Deficit accumulated during development stage</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_StockholdersEquity_lbl" xml:lang="en-US">Total stockholders' deficit</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xml:lang="en-US">Total liabilities and stockholders' deficit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesPayableDiscount" xlink:label="VSTA_NotesPayableDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscount" xlink:to="VSTA_NotesPayableDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableDiscount_lbl" xml:lang="en-US">Notes payable, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesPayableDiscountRelatedParties" xlink:label="VSTA_NotesPayableDiscountRelatedParties" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscountRelatedParties" xlink:to="VSTA_NotesPayableDiscountRelatedParties_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableDiscountRelatedParties_lbl" xml:lang="en-US">Notes payable to related parties, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConvertibleNotesDiscount" xlink:label="VSTA_ConvertibleNotesDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertibleNotesDiscount" xlink:to="VSTA_ConvertibleNotesDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertibleNotesDiscount_lbl" xml:lang="en-US">Convertible promissory notes, net of discount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StockholdersEquityAbstract_2_lbl" xml:lang="en-US">Stockholders deficit:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PreferredStockSeriesPerValue1" xlink:label="VSTA_PreferredStockSeriesPerValue1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesPerValue1" xlink:to="VSTA_PreferredStockSeriesPerValue1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesPerValue1_lbl" xml:lang="en-US">Preferred Stock, par value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PreferredStockSeriesASharesAuthorized" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesAuthorized" xlink:to="VSTA_PreferredStockSeriesASharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized_lbl" xml:lang="en-US">Preferred Stock, Authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PreferredStockSeriesASharesIssued" xlink:label="VSTA_PreferredStockSeriesASharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesIssued" xlink:to="VSTA_PreferredStockSeriesASharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesIssued_lbl" xml:lang="en-US">PreferredStockSeriesASharesIssued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PreferredStockSeriesASharesOutstanding" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesOutstanding" xlink:to="VSTA_PreferredStockSeriesASharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding_lbl" xml:lang="en-US">PreferredStockSeriesASharesOutstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xml:lang="en-US">Common Stock, Par Value Par Share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesAuthorized" xlink:to="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xml:lang="en-US">Common Stock, Shares Authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesIssued" xlink:to="us-gaap_CommonStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xml:lang="en-US">Common Stock, Shares, Issued</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_TreasuryStockShares" xlink:label="us-gaap_TreasuryStockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockShares" xlink:to="us-gaap_TreasuryStockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockShares_lbl" xml:lang="en-US">Treasury Stock, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeStatementAbstract" xlink:label="us-gaap_IncomeStatementAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementAbstract" xlink:to="us-gaap_IncomeStatementAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xml:lang="en-US">Income Statement [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="us-gaap_RevenuesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenuesAbstract" xlink:to="us-gaap_RevenuesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenuesAbstract_lbl" xml:lang="en-US">Revenues:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RevenueFromGrants" xlink:label="us-gaap_RevenueFromGrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueFromGrants" xlink:to="us-gaap_RevenueFromGrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenueFromGrants_lbl" xml:lang="en-US">Grant revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_RevenueFromExternalCustomers" xlink:label="VSTA_RevenueFromExternalCustomers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RevenueFromExternalCustomers" xlink:to="VSTA_RevenueFromExternalCustomers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RevenueFromExternalCustomers_lbl" xml:lang="en-US">Collaboration revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherSalesRevenueNet" xlink:label="us-gaap_OtherSalesRevenueNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherSalesRevenueNet" xlink:to="us-gaap_OtherSalesRevenueNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherSalesRevenueNet_lbl" xml:lang="en-US">Other</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Revenues_lbl" xml:lang="en-US">Total revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="us-gaap_OperatingExpensesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingExpensesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingExpensesAbstract_lbl" xml:lang="en-US">Operating expenses:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="us-gaap_ResearchAndDevelopmentExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xml:lang="en-US">Research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AcquiredInProcessResearchAndDevelopment" xlink:label="VSTA_AcquiredInProcessResearchAndDevelopment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AcquiredInProcessResearchAndDevelopment" xlink:to="VSTA_AcquiredInProcessResearchAndDevelopment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AcquiredInProcessResearchAndDevelopment_lbl" xml:lang="en-US">Acquired in-process research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="us-gaap_GeneralAndAdministrativeExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GeneralAndAdministrativeExpense" xlink:to="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xml:lang="en-US">General and administrative</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="us-gaap_OperatingExpenses" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingExpenses_lbl" xml:lang="en-US">Total operating expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xml:lang="en-US">Loss from operations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract_lbl" xml:lang="en-US">Other expenses, net:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_InterestExpense" xlink:label="us-gaap_InterestExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestExpense" xlink:to="us-gaap_InterestExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestExpense_lbl" xml:lang="en-US">Interest expense, net</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xml:lang="en-US">Change in put and note extension option and warrant liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:to="us-gaap_GainsLossesOnExtinguishmentOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt_lbl" xml:lang="en-US">Loss on early extinguishment of debt</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherIncome" xlink:label="us-gaap_OtherIncome" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherIncome" xlink:to="us-gaap_OtherIncome_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherIncome_lbl" xml:lang="en-US">Other income</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_lbl" xml:lang="en-US">Loss before income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxExpenseBenefit" xlink:to="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xml:lang="en-US">Income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetIncomeLoss_lbl" xml:lang="en-US">Net loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareDiluted" xlink:to="us-gaap_EarningsPerShareDiluted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xml:lang="en-US">Basic and diluted net loss per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xml:lang="en-US">Weighted average shares used in computing basic and diluted net loss per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ComprehensiveLoss" xlink:label="VSTA_ComprehensiveLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComprehensiveLoss" xlink:to="VSTA_ComprehensiveLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ComprehensiveLoss_lbl" xml:lang="en-US">Comprehensive loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:label="us-gaap_StatementOfCashFlowsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfCashFlowsAbstract" xlink:to="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xml:lang="en-US">Statement of Cash Flows [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from operating activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProfitLoss" xlink:to="us-gaap_ProfitLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProfitLoss_lbl" xml:lang="en-US">Net loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US">Adjustments to reconcile net loss to net cash used in operating activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="us-gaap_DepreciationAndAmortization" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DepreciationAndAmortization" xlink:to="us-gaap_DepreciationAndAmortization_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xml:lang="en-US">Depreciation and amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" xlink:label="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" xlink:to="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_lbl" xml:lang="en-US">Amortization of imputed discount on non-interest bearing notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmortizationOfDiscountsOn77.5And10Notes" xlink:label="VSTA_AmortizationOfDiscountsOn77.5And10Notes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOn77.5And10Notes" xlink:to="VSTA_AmortizationOfDiscountsOn77.5And10Notes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOn77.5And10Notes_lbl" xml:lang="en-US">Amortization of discounts on 7%, 7.5% and 10% notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmortizationOfDiscountsOnPlatinumNotes" xlink:label="VSTA_AmortizationOfDiscountsOnPlatinumNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnPlatinumNotes" xlink:to="VSTA_AmortizationOfDiscountsOnPlatinumNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOnPlatinumNotes_lbl" xml:lang="en-US">Amortization of discounts on Platinum notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" xlink:label="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" xlink:to="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_lbl" xml:lang="en-US">Amortization of discounts on August 2010 short-term notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" xlink:label="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" xlink:to="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_lbl" xml:lang="en-US">Amortization of discounts on February 2012 12% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_lbl" xml:lang="en-US">Loss on early extinguishment of debt</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_LossOnSettlementsOfAccountsPayable" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnSettlementsOfAccountsPayable" xlink:to="VSTA_LossOnSettlementsOfAccountsPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable_lbl" xml:lang="en-US">Loss on settlements of accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_lbl" xml:lang="en-US">Change in put and note term extension option and warrant liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensation_lbl" xml:lang="en-US">Stock-based compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ExpenseRelatedToModificationOfWarrants" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseRelatedToModificationOfWarrants" xlink:to="VSTA_ExpenseRelatedToModificationOfWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants_lbl" xml:lang="en-US">Expense related to modification of warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:to="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xml:lang="en-US">Fair value of Series C preferred stock, common stock, and warrants granted for services prior to the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_lbl" xml:lang="en-US">Fair value of common stock granted for services following the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_lbl" xml:lang="en-US">Fair value of warrants granted for services following the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_lbl" xml:lang="en-US">Fair value of additional warrants granted pursuant to exercises of modified warrants (May-August 2012) and under Discounted Warrant Exercise Program (2011)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:to="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_lbl" xml:lang="en-US">Fair value of common stock issued for note term modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:to="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_lbl" xml:lang="en-US">Consulting services by related parties settled by issuing promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:to="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xml:lang="en-US">Gain on sale of assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xml:lang="en-US">Changes in operating assets and liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xml:lang="en-US">Unbilled contract payments receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xml:lang="en-US">Prepaid expenses and other current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInDepositOtherAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets_lbl" xml:lang="en-US">Security deposits and other assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xml:lang="en-US">Accounts payable and accrued expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:to="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xml:lang="en-US">Deferred revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xml:lang="en-US">Net cash used in operating activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from investing activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:to="us-gaap_PaymentsToAcquireMachineryAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment_lbl" xml:lang="en-US">Purchases of equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xml:lang="en-US">Net cash used in investing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from financing activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xml:lang="en-US">Net proceeds from issuance of common stock and warrants, including units</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:label="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:to="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock_lbl" xml:lang="en-US">Net proceeds from issuance of preferred stock and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:to="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_lbl" xml:lang="en-US">Proceeds from exercise of modified warrants (May-August 2012) and under Discounted Warrant Exercise Program (2011)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProceedsFromUnsecuredLinesOfCredit" xlink:label="us-gaap_ProceedsFromUnsecuredLinesOfCredit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromUnsecuredLinesOfCredit" xlink:to="us-gaap_ProceedsFromUnsecuredLinesOfCredit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromUnsecuredLinesOfCredit_lbl" xml:lang="en-US">Proceeds from issuance of notes under line of credit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:to="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_lbl" xml:lang="en-US">Proceeds from issuance of 7% note payable to founding stockholder</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:to="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_lbl" xml:lang="en-US">Net proceeds from issuance of 7% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of 10% convertible notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of Platinum notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of 2008/2010 notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of 2006/2007 notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ProceedsFromIssuanceOf7NotesPayable" xlink:label="VSTA_ProceedsFromIssuanceOf7NotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotesPayable" xlink:to="VSTA_ProceedsFromIssuanceOf7NotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromIssuanceOf7NotesPayable_lbl" xml:lang="en-US">Proceeds from issuance of 7% notes payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of August 2010 short-term notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of February 2012 12% convertible notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:to="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xml:lang="en-US">Repayment of capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RepaymentsOfNotesPayable" xlink:label="us-gaap_RepaymentsOfNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfNotesPayable" xlink:to="us-gaap_RepaymentsOfNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfNotesPayable_lbl" xml:lang="en-US">Repayment of notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xml:lang="en-US">Net cash provided by financing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xml:lang="en-US">Net increase in cash and cash equivalents</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xml:lang="en-US">Cash and cash equivalents at beginning of period</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xml:lang="en-US">Cash and cash equivalents at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NotesToFinancialStatementsAbstract" xlink:label="VSTA_NotesToFinancialStatementsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesToFinancialStatementsAbstract" xlink:to="VSTA_NotesToFinancialStatementsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesToFinancialStatementsAbstract_lbl" xml:lang="en-US">Notes to Financial Statements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_HistoryAndOrganizationTextBlock" xlink:label="VSTA_HistoryAndOrganizationTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationTextBlock" xlink:to="VSTA_HistoryAndOrganizationTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_HistoryAndOrganizationTextBlock_lbl" xml:lang="en-US">NOTE 1 - History and Organization</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiquidityDisclosureTextBlock" xlink:label="us-gaap_LiquidityDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiquidityDisclosureTextBlock" xlink:to="us-gaap_LiquidityDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiquidityDisclosureTextBlock_lbl" xml:lang="en-US">NOTE 2 - Basis of Presentation and Going Concern</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SignificantAccountingPoliciesTextBlock" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SignificantAccountingPoliciesTextBlock" xlink:to="us-gaap_SignificantAccountingPoliciesTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock_lbl" xml:lang="en-US">NOTE 3 - Summary of Significant Accounting Policies</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:label="us-gaap_FairValueDisclosuresTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueDisclosuresTextBlock" xlink:to="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xml:lang="en-US">NOTE 4 - Fair Value Measurements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PrepaidExpensesTextBlock" xlink:label="VSTA_PrepaidExpensesTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesTextBlock" xlink:to="VSTA_PrepaidExpensesTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrepaidExpensesTextBlock_lbl" xml:lang="en-US">NOTE 5 - Prepaid Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AccruedExpensesTextBlock" xlink:label="VSTA_AccruedExpensesTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedExpensesTextBlock" xlink:to="VSTA_AccruedExpensesTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedExpensesTextBlock_lbl" xml:lang="en-US">NOTE 6 - Accrued Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtDisclosureTextBlock" xlink:label="us-gaap_DebtDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtDisclosureTextBlock" xlink:to="us-gaap_DebtDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xml:lang="en-US">NOTE 7 - Convertible Promissory Notes and Other Notes Payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_LicensingAndCollaborativeAgreementsTextBlock" xlink:label="VSTA_LicensingAndCollaborativeAgreementsTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LicensingAndCollaborativeAgreementsTextBlock" xlink:to="VSTA_LicensingAndCollaborativeAgreementsTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LicensingAndCollaborativeAgreementsTextBlock_lbl" xml:lang="en-US">NOTE 8 - Licensing and Collaborative Agreements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CapitalStockTextBlock" xlink:label="VSTA_CapitalStockTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalStockTextBlock" xlink:to="VSTA_CapitalStockTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalStockTextBlock_lbl" xml:lang="en-US">NOTE 9 - Capital Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RelatedPartyTransactionsDisclosureTextBlock" xlink:label="us-gaap_RelatedPartyTransactionsDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyTransactionsDisclosureTextBlock" xlink:to="us-gaap_RelatedPartyTransactionsDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RelatedPartyTransactionsDisclosureTextBlock_lbl" xml:lang="en-US">NOTE 10 - Related Party Transactions</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SubsequentEventsTextBlock" xlink:label="us-gaap_SubsequentEventsTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventsTextBlock" xlink:to="us-gaap_SubsequentEventsTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xml:lang="en-US">NOTE 11 - Subsequent Events</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SummaryOfSignificantAccountingPoliciesPoliciesAbstract" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesPoliciesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SummaryOfSignificantAccountingPoliciesPoliciesAbstract" xlink:to="VSTA_SummaryOfSignificantAccountingPoliciesPoliciesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesPoliciesAbstract_lbl" xml:lang="en-US">Summary Of Significant Accounting Policies Policies</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xml:lang="en-US">Basis of Presentation and Going Concern</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_UseOfEstimates" xlink:label="us-gaap_UseOfEstimates" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UseOfEstimates" xlink:to="us-gaap_UseOfEstimates_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UseOfEstimates_lbl" xml:lang="en-US">Use of Estimates</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RevenueRecognitionPolicyTextBlock" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRecognitionPolicyTextBlock" xlink:to="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xml:lang="en-US">Revenue Recognition</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:to="us-gaap_ResearchAndDevelopmentExpensePolicy_lbl" xlink:type="arc" />
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      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xml:lang="en-US">Recent Accounting Pronouncements</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueMeasurementPolicyPolicyTextBlock" xlink:label="us-gaap_FairValueMeasurementPolicyPolicyTextBlock" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueMeasurementPolicyPolicyTextBlock_lbl" xml:lang="en-US">Fair Value Measurements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SummaryOfSignificantAccountingPoliciesTablesAbstract" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesTablesAbstract" />
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      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" />
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesTablesAbstract" xlink:to="VSTA_PrepaidExpensesTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrepaidExpensesTablesAbstract_lbl" xml:lang="en-US">Prepaid Expenses Tables</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesTableTextBlock" xlink:to="VSTA_PrepaidExpensesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrepaidExpensesTableTextBlock_lbl" xml:lang="en-US">Prepaid Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AccruedExpensesTablesAbstract" xlink:label="VSTA_AccruedExpensesTablesAbstract" />
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      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" xml:lang="en-US">Accrued Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" />
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      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock_lbl" xml:lang="en-US">Convertible Promissory Notes and Other Notes Payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_IncrementalValueOfAmendedMfWarrant" xlink:label="VSTA_IncrementalValueOfAmendedMfWarrant" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfAmendedMfWarrant_lbl" xml:lang="en-US">Incremental value of the Amended M&amp;F Warrant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CapitalStockTablesAbstract" xlink:label="VSTA_CapitalStockTablesAbstract" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalStockTablesAbstract_lbl" xml:lang="en-US">Capital Stock Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_BlackscholesOptionPricingModelTableTextBlock" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock_lbl" xml:lang="en-US">Black-Scholes Option Pricing Model</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_WarrantExercisesAndGrantsTableTextBlock" xlink:label="VSTA_WarrantExercisesAndGrantsTableTextBlock" />
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      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_HistoryAndOrganizationDetailsTextualsAbstract" xlink:label="VSTA_HistoryAndOrganizationDetailsTextualsAbstract" />
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      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AwardedByU.S.NationalInstitutes" xlink:label="VSTA_AwardedByU.S.NationalInstitutes" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AwardedByU.S.NationalInstitutes_lbl" xml:lang="en-US">Awarded by U.S. National Institutes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_OutstandingShares" xlink:label="VSTA_OutstandingShares" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingShares_lbl" xml:lang="en-US">Outstanding shares acquired</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareRepurchase" xlink:to="VSTA_ShareRepurchase_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareRepurchase_lbl" xml:lang="en-US">Share repurchase</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SharesOutstandingAtMerger" xlink:label="VSTA_SharesOutstandingAtMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesOutstandingAtMerger" xlink:to="VSTA_SharesOutstandingAtMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesOutstandingAtMerger_lbl" xml:lang="en-US">Shares outstanding at merger</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingShareRepresentation" xlink:to="VSTA_OutstandingShareRepresentation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingShareRepresentation_lbl" xml:lang="en-US">Outstanding share representation</link:label>
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      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" xlink:label="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment_lbl" xml:lang="en-US">Number of Preferred shares authorized following amendment</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesPreferredStockShares_lbl" xml:lang="en-US">Series A Preferred Stock shares</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesPreferredShareParValue_lbl" xml:lang="en-US">Series A Preferred share par value</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_July2012PlantinumNotePrincipalAmount_lbl" xml:lang="en-US">July 2012 Plantinum Note principal amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_August2012PlantinumNotePrincipalAmount" xlink:label="VSTA_August2012PlantinumNotePrincipalAmount" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_August2012PlantinumNotePrincipalAmount_lbl" xml:lang="en-US">August 2012 Plantinum Note principal amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CashExpenditureMaximum" xlink:label="VSTA_CashExpenditureMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CashExpenditureMaximum" xlink:to="VSTA_CashExpenditureMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CashExpenditureMaximum_lbl" xml:lang="en-US">Cash expenditure maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CashExpenditureMinimum" xlink:label="VSTA_CashExpenditureMinimum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CashExpenditureMinimum" xlink:to="VSTA_CashExpenditureMinimum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CashExpenditureMinimum_lbl" xml:lang="en-US">Cash expenditure minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" xlink:to="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract_lbl" xml:lang="en-US">Summary Of Significant Accounting Policies Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="us-gaap_EarningsPerShareAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xml:lang="en-US">Loss per Common Share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xml:lang="en-US">All series of preferred stock issued and outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" xlink:label="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" xlink:to="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_lbl" xml:lang="en-US">Outstanding options under the 2008 and 1999 Stock Incentive Plan and 1998 Scientific Advisory Board Plan</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:to="VSTA_OutstandingWarrantsToPurchaseCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock_lbl" xml:lang="en-US">Outstanding warrants to purchase common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" xlink:label="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" xlink:to="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_lbl" xml:lang="en-US">February 2012 12% convertible promissory notes and accrued interest (1)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_Total" xlink:label="VSTA_Total" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Total" xlink:to="VSTA_Total_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Total_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementTable_lbl" xml:lang="en-US">Statement [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementLineItems_lbl" xml:lang="en-US">Statement [Line Items]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensation_2_lbl" xml:lang="en-US">Share-based compensation costs</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xml:lang="en-US">Granted options to purchase common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePrice" xlink:label="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePrice" xlink:to="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePrice_lbl" xml:lang="en-US">Exercise price of granted options to purchase common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xml:lang="en-US">outstanding options</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xml:lang="en-US">outstanding options, weighted average exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FairValueMeasurementsDetailsTextualsAbstract" xlink:label="VSTA_FairValueMeasurementsDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueMeasurementsDetailsTextualsAbstract" xlink:to="VSTA_FairValueMeasurementsDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueMeasurementsDetailsTextualsAbstract_lbl" xml:lang="en-US">Fair Value Measurements Details Textuals</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ConvertibleNotesPayable" xlink:label="us-gaap_ConvertibleNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertibleNotesPayable" xlink:to="us-gaap_ConvertibleNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConvertibleNotesPayable_lbl" xml:lang="en-US">convertible promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_OriginalPrincipleBalanceOfNotes" xlink:label="VSTA_OriginalPrincipleBalanceOfNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OriginalPrincipleBalanceOfNotes" xlink:to="VSTA_OriginalPrincipleBalanceOfNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OriginalPrincipleBalanceOfNotes_lbl" xml:lang="en-US">Original Principle balance of notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_RepaymentOfDebtInPercentage" xlink:label="VSTA_RepaymentOfDebtInPercentage" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RepaymentOfDebtInPercentage" xlink:to="VSTA_RepaymentOfDebtInPercentage_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RepaymentOfDebtInPercentage_lbl" xml:lang="en-US">Repayment of debt in Percentage</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_IssuedWarrantToPurchaseCommonStock" xlink:label="VSTA_IssuedWarrantToPurchaseCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedWarrantToPurchaseCommonStock" xlink:to="VSTA_IssuedWarrantToPurchaseCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuedWarrantToPurchaseCommonStock_lbl" xml:lang="en-US">Issued warrant to purchase common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ChangeInFairValueOfTheWarrantLiability" xlink:label="VSTA_ChangeInFairValueOfTheWarrantLiability" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInFairValueOfTheWarrantLiability" xlink:to="VSTA_ChangeInFairValueOfTheWarrantLiability_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInFairValueOfTheWarrantLiability_lbl" xml:lang="en-US">Change in Fair value of the warrant liability</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities" xlink:label="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities" xlink:to="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xml:lang="en-US">increase in the put option and note term extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities" xlink:label="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities" xlink:to="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xml:lang="en-US">Remaining put option and note term extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:label="us-gaap_WarrantsAndRightsOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WarrantsAndRightsOutstanding" xlink:to="us-gaap_WarrantsAndRightsOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WarrantsAndRightsOutstanding_lbl" xml:lang="en-US">Aggregated fair value of the warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PrepaidExpensesDetailsAbstract" xlink:label="VSTA_PrepaidExpensesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesDetailsAbstract" xlink:to="VSTA_PrepaidExpensesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrepaidExpensesDetailsAbstract_lbl" xml:lang="en-US">Prepaid Expenses Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PrepaidExpenseCurrentAbstract" xlink:label="us-gaap_PrepaidExpenseCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseCurrentAbstract" xlink:to="us-gaap_PrepaidExpenseCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PrepaidExpenseCurrentAbstract_lbl" xml:lang="en-US">Prepaid Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants" xlink:label="VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants" xlink:to="VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants_lbl" xml:lang="en-US">Investor relations and awareness services paid by issuance of common stock or warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PrepaidInsurance" xlink:label="us-gaap_PrepaidInsurance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidInsurance" xlink:to="us-gaap_PrepaidInsurance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidInsurance_lbl" xml:lang="en-US">Insurance</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_LegalFees1" xlink:label="VSTA_LegalFees1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LegalFees1" xlink:to="VSTA_LegalFees1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LegalFees1_lbl" xml:lang="en-US">Legal fees</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherPrepaidExpenseCurrent" xlink:label="us-gaap_OtherPrepaidExpenseCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherPrepaidExpenseCurrent" xlink:to="us-gaap_OtherPrepaidExpenseCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherPrepaidExpenseCurrent_lbl" xml:lang="en-US">All other</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AccruedExpensesDetailsAbstract" xlink:label="VSTA_AccruedExpensesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedExpensesDetailsAbstract" xlink:to="VSTA_AccruedExpensesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedExpensesDetailsAbstract_lbl" xml:lang="en-US">Accrued Expenses Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" xml:lang="en-US">Accrued Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedProfessionalFeesCurrent" xlink:label="us-gaap_AccruedProfessionalFeesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedProfessionalFeesCurrent" xlink:to="us-gaap_AccruedProfessionalFeesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedProfessionalFeesCurrent_lbl" xml:lang="en-US">Accrued professional services</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AccruedResearchAndDevelopmentExpenses" xlink:label="VSTA_AccruedResearchAndDevelopmentExpenses" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedResearchAndDevelopmentExpenses" xlink:to="VSTA_AccruedResearchAndDevelopmentExpenses_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedResearchAndDevelopmentExpenses_lbl" xml:lang="en-US">Accrued research and development expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedVacationCurrent" xlink:label="us-gaap_AccruedVacationCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedVacationCurrent" xlink:to="us-gaap_AccruedVacationCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedVacationCurrent_lbl" xml:lang="en-US">Accrued vacation pay and other compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AccruedPlacementAgentFees" xlink:label="VSTA_AccruedPlacementAgentFees" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedPlacementAgentFees" xlink:to="VSTA_AccruedPlacementAgentFees_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedPlacementAgentFees_lbl" xml:lang="en-US">Accrued placement agent fees</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AccruedRegistrationRightsPayments" xlink:label="VSTA_AccruedRegistrationRightsPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedRegistrationRightsPayments" xlink:to="VSTA_AccruedRegistrationRightsPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedRegistrationRightsPayments_lbl" xml:lang="en-US">Accrued registration rights payments</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAccruedLiabilitiesCurrent" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xml:lang="en-US">All other</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AccruedLiabilitiesCurrent_2_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_InvestmentOwnedBalancePrincipalAmount" xlink:label="us-gaap_InvestmentOwnedBalancePrincipalAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InvestmentOwnedBalancePrincipalAmount" xlink:to="us-gaap_InvestmentOwnedBalancePrincipalAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InvestmentOwnedBalancePrincipalAmount_lbl" xml:lang="en-US">Principal Balance</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_InvestmentOwnedAccruedInterest1" xlink:label="VSTA_InvestmentOwnedAccruedInterest1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestmentOwnedAccruedInterest1" xlink:to="VSTA_InvestmentOwnedAccruedInterest1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InvestmentOwnedAccruedInterest1_lbl" xml:lang="en-US">Accrued Interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AggregateInvestmentOwnedAmount" xlink:label="VSTA_AggregateInvestmentOwnedAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateInvestmentOwnedAmount" xlink:to="VSTA_AggregateInvestmentOwnedAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_AggregateInvestmentOwnedAmount_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_MarketPricePerShare" xlink:label="VSTA_MarketPricePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MarketPricePerShare" xlink:to="VSTA_MarketPricePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MarketPricePerShare_lbl" xml:lang="en-US">Market price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FairValueAssumptionsExercisePrice1" xlink:label="VSTA_FairValueAssumptionsExercisePrice1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsExercisePrice1" xlink:to="VSTA_FairValueAssumptionsExercisePrice1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueAssumptionsExercisePrice1_lbl" xml:lang="en-US">Exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_FairValueAssumptionsRiskFreeInterestRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsRiskFreeInterestRate" xlink:to="us-gaap_FairValueAssumptionsRiskFreeInterestRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsRiskFreeInterestRate_lbl" xml:lang="en-US">Risk-free interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsExpectedTerm" xlink:label="us-gaap_FairValueAssumptionsExpectedTerm" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedTerm" xlink:to="us-gaap_FairValueAssumptionsExpectedTerm_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedTerm_lbl" xml:lang="en-US">Expected term (years)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:label="us-gaap_FairValueAssumptionsExpectedVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:to="us-gaap_FairValueAssumptionsExpectedVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_FairValueAssumptionsExpectedDividendRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate_lbl" xml:lang="en-US">Dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FairValuePerShare" xlink:label="VSTA_FairValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShare" xlink:to="VSTA_FairValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValuePerShare_lbl" xml:lang="en-US">Fair Value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_DebtInstrumentTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentTable_lbl" xml:lang="en-US">Schedule of Long-term Debt Instruments [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xml:lang="en-US">Debt Instrument [Line Items]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentAxis_2_lbl" xml:lang="en-US">Debt Instrument [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RegistrationPaymentArrangementAccrualCarryingValue" xlink:label="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue" xlink:to="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue_lbl" xml:lang="en-US">Liability under the Registration Rights Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_July2012PlatinumNoteAmount" xlink:label="VSTA_July2012PlatinumNoteAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_July2012PlatinumNoteAmount" xlink:to="VSTA_July2012PlatinumNoteAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_July2012PlatinumNoteAmount_lbl" xml:lang="en-US">July 2012 Platinum Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_August2012PlatinumNote" xlink:label="VSTA_August2012PlatinumNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_August2012PlatinumNote" xlink:to="VSTA_August2012PlatinumNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_August2012PlatinumNote_lbl" xml:lang="en-US">August 2012 Platinum Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_JulyAndAugustNoteRate" xlink:label="VSTA_JulyAndAugustNoteRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_JulyAndAugustNoteRate" xlink:to="VSTA_JulyAndAugustNoteRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_JulyAndAugustNoteRate_lbl" xml:lang="en-US">July and August note Rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ExpectedGrossNoteProceeds" xlink:label="VSTA_ExpectedGrossNoteProceeds" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedGrossNoteProceeds" xlink:to="VSTA_ExpectedGrossNoteProceeds_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedGrossNoteProceeds_lbl" xml:lang="en-US">Expected gross note proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_February2012Note" xlink:label="VSTA_February2012Note" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February2012Note" xlink:to="VSTA_February2012Note_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_February2012Note_lbl" xml:lang="en-US">February 2012 Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FebruaryNoteRate" xlink:label="VSTA_FebruaryNoteRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FebruaryNoteRate" xlink:to="VSTA_FebruaryNoteRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FebruaryNoteRate_lbl" xml:lang="en-US">February Note rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_WarrantValue" xlink:label="VSTA_WarrantValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantValue" xlink:to="VSTA_WarrantValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantValue_lbl" xml:lang="en-US">Warrant value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AggregateShareValue" xlink:label="VSTA_AggregateShareValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateShareValue" xlink:to="VSTA_AggregateShareValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AggregateShareValue_lbl" xml:lang="en-US">Aggregate share value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_RegistrationRightsAgreementLiability" xlink:label="VSTA_RegistrationRightsAgreementLiability" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RegistrationRightsAgreementLiability" xlink:to="VSTA_RegistrationRightsAgreementLiability_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RegistrationRightsAgreementLiability_lbl" xml:lang="en-US">Registration rights agreement liability</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_LegalEntityAxis" xlink:to="dei_LegalEntityAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="dei_LegalEntityAxis_2_lbl" xml:lang="en-US">Legal Entity [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RepaymentsOfDebt" xlink:label="us-gaap_RepaymentsOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfDebt" xlink:to="us-gaap_RepaymentsOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfDebt_lbl" xml:lang="en-US">Repayment of note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AggregatePrincipalAmount" xlink:label="VSTA_AggregatePrincipalAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregatePrincipalAmount" xlink:to="VSTA_AggregatePrincipalAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AggregatePrincipalAmount_lbl" xml:lang="en-US">Aggregate principal amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConvertibleNoteMayConversion" xlink:label="VSTA_ConvertibleNoteMayConversion" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertibleNoteMayConversion" xlink:to="VSTA_ConvertibleNoteMayConversion_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertibleNoteMayConversion_lbl" xml:lang="en-US">May conversion</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ExercisePriceConversionNote" xlink:label="VSTA_ExercisePriceConversionNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePriceConversionNote" xlink:to="VSTA_ExercisePriceConversionNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePriceConversionNote_lbl" xml:lang="en-US">Exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConversionToLongtermNote" xlink:label="VSTA_ConversionToLongtermNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionToLongtermNote" xlink:to="VSTA_ConversionToLongtermNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionToLongtermNote_lbl" xml:lang="en-US">Conversion to long-term note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ConversionInto7Note" xlink:label="VSTA_ConversionInto7Note" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionInto7Note" xlink:to="VSTA_ConversionInto7Note_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionInto7Note_lbl" xml:lang="en-US">Conversion into 7% note</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_UnsecuredLongTermDebt" xlink:label="us-gaap_UnsecuredLongTermDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnsecuredLongTermDebt" xlink:to="us-gaap_UnsecuredLongTermDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnsecuredLongTermDebt_lbl" xml:lang="en-US">New unsecured promissory note</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xml:lang="en-US">Shares Exercisable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xml:lang="en-US">Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award [Line Items]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_AwardTypeAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AwardTypeAxis_2_lbl" xml:lang="en-US">Award Type [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_lbl" xml:lang="en-US">Assumption:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ExercisePricePerShareWeightedAvg" xlink:label="VSTA_ExercisePricePerShareWeightedAvg" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePricePerShareWeightedAvg" xlink:to="VSTA_ExercisePricePerShareWeightedAvg_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePricePerShareWeightedAvg_lbl" xml:lang="en-US">Exercise price per share (weighted average)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:to="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_lbl" xml:lang="en-US">Exercise price per share Upper</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_lbl" xml:lang="en-US">Risk-free interest rate Minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_lbl" xml:lang="en-US">Risk-free interest rate Maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xml:lang="en-US">Expected term (years) Minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ExpectedTermYearsMaximum" xlink:label="VSTA_ExpectedTermYearsMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedTermYearsMaximum" xlink:to="VSTA_ExpectedTermYearsMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedTermYearsMaximum_lbl" xml:lang="en-US">Expected term (years) Maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_lbl" xml:lang="en-US">Volatility Minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_lbl" xml:lang="en-US">Volatility Maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xml:lang="en-US">Dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_WeightedAverageFairValuePerShare" xlink:label="VSTA_WeightedAverageFairValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageFairValuePerShare" xlink:to="VSTA_WeightedAverageFairValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WeightedAverageFairValuePerShare_lbl" xml:lang="en-US">Weighted Average Fair Value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_WarrantsOptionAbstract" xlink:label="VSTA_WarrantsOptionAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsOptionAbstract" xlink:to="VSTA_WarrantsOptionAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsOptionAbstract_lbl" xml:lang="en-US">Warrants option</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ExercisePrice" xlink:label="VSTA_ExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePrice" xlink:to="VSTA_ExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePrice_lbl" xml:lang="en-US">Exercise Price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ExpirationDate" xlink:label="VSTA_ExpirationDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpirationDate" xlink:to="VSTA_ExpirationDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpirationDate_lbl" xml:lang="en-US">Expiration Date</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xml:lang="en-US">Number of Warrants</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_StatementEquityComponentsAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StatementEquityComponentsAxis_2_lbl" xml:lang="en-US">Equity Components [Axis]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_StatementClassOfStockAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StatementClassOfStockAxis_2_lbl" xml:lang="en-US">Class of Stock [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_lbl" xml:lang="en-US">Purchase of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_InvestmentWarrantsExercisePrice" xlink:label="VSTA_InvestmentWarrantsExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestmentWarrantsExercisePrice" xlink:to="VSTA_InvestmentWarrantsExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InvestmentWarrantsExercisePrice_lbl" xml:lang="en-US">Common stock, exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" xlink:label="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" xlink:to="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_lbl" xml:lang="en-US">Fair value of warrant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SharePrice1" xlink:label="VSTA_SharePrice1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharePrice1" xlink:to="VSTA_SharePrice1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_SharePrice1_lbl" xml:lang="en-US">Market price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_lbl" xml:lang="en-US">Common stock exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ContractualTerm1" xlink:label="VSTA_ContractualTerm1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ContractualTerm1" xlink:to="VSTA_ContractualTerm1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ContractualTerm1_lbl" xml:lang="en-US">Contractual term</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate" xlink:label="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate" xlink:to="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_FairValueAssumptionsExpectedDividendRate_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate_2_lbl" xml:lang="en-US">Expected dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1_lbl" xml:lang="en-US">Common stock granted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CommonStockValue1" xlink:label="VSTA_CommonStockValue1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockValue1" xlink:to="VSTA_CommonStockValue1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockValue1_lbl" xml:lang="en-US">Common stock granted value</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharePrice1" xlink:to="VSTA_SharePrice1_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharePrice1_2_lbl" xml:lang="en-US">Common stock granted date market price</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_2_lbl" xml:lang="en-US">Cash proceeds from common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmountsDueForServices" xlink:label="VSTA_AmountsDueForServices" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountsDueForServices" xlink:to="VSTA_AmountsDueForServices_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmountsDueForServices_lbl" xml:lang="en-US">Amounts due for services</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CommonStockPurchseDiscription" xlink:label="VSTA_CommonStockPurchseDiscription" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockPurchseDiscription" xlink:to="VSTA_CommonStockPurchseDiscription_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockPurchseDiscription_lbl" xml:lang="en-US">Common stock purchse discription</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_IncreasedValueOfWarrantsExercised" xlink:label="VSTA_IncreasedValueOfWarrantsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncreasedValueOfWarrantsExercised" xlink:to="VSTA_IncreasedValueOfWarrantsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncreasedValueOfWarrantsExercised_lbl" xml:lang="en-US">Increased value of warrants exercised</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_2_lbl" xml:lang="en-US">common stock at a weighted average exercise price</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PreferredStockSharesIssued_2_lbl" xml:lang="en-US">Preferred stock issued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_CommonStockOwned" xlink:label="VSTA_CommonStockOwned" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockOwned" xlink:to="VSTA_CommonStockOwned_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockOwned_lbl" xml:lang="en-US">Common stock owned</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_SecuredConvertiblePromissoryNote1" xlink:label="VSTA_SecuredConvertiblePromissoryNote1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SecuredConvertiblePromissoryNote1" xlink:to="VSTA_SecuredConvertiblePromissoryNote1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SecuredConvertiblePromissoryNote1_lbl" xml:lang="en-US">Secured convertible promissory note</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertibleNotesPayable" xlink:to="us-gaap_ConvertibleNotesPayable_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ConvertibleNotesPayable_2_lbl" xml:lang="en-US">Convertible promissory note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_FinancingTransactionsGrossProceeds" xlink:label="VSTA_FinancingTransactionsGrossProceeds" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FinancingTransactionsGrossProceeds" xlink:to="VSTA_FinancingTransactionsGrossProceeds_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FinancingTransactionsGrossProceeds_lbl" xml:lang="en-US">Financing transactions gross proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_InvestmentInQualifiedFinancing" xlink:label="VSTA_InvestmentInQualifiedFinancing" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestmentInQualifiedFinancing" xlink:to="VSTA_InvestmentInQualifiedFinancing_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InvestmentInQualifiedFinancing_lbl" xml:lang="en-US">Investment in Qualified Financing</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmountOfCommitmentsFromOtherInvestors" xlink:label="VSTA_AmountOfCommitmentsFromOtherInvestors" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountOfCommitmentsFromOtherInvestors" xlink:to="VSTA_AmountOfCommitmentsFromOtherInvestors_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmountOfCommitmentsFromOtherInvestors_lbl" xml:lang="en-US">Amount of commitments from other investors</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_PeriodOfCommitmentsFromOtherInvestors2" xlink:label="VSTA_PeriodOfCommitmentsFromOtherInvestors2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PeriodOfCommitmentsFromOtherInvestors2" xlink:to="VSTA_PeriodOfCommitmentsFromOtherInvestors2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PeriodOfCommitmentsFromOtherInvestors2_lbl" xml:lang="en-US">Period of commitments from other investors</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_2_lbl" xml:lang="en-US">Securities stated value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesOutstanding" xlink:to="us-gaap_CommonStockSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xml:lang="en-US">Authorized and outstanding shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenueArrangementTypeAxis" xlink:to="us-gaap_DeferredRevenueArrangementTypeAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DeferredRevenueArrangementTypeAxis_2_lbl" xml:lang="en-US">Deferred Revenue Arrangement Type [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_MonthlyPayments" xlink:label="VSTA_MonthlyPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MonthlyPayments" xlink:to="VSTA_MonthlyPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MonthlyPayments_lbl" xml:lang="en-US">Monthly payments</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AmountPaidForUhnRoyalties" xlink:label="VSTA_AmountPaidForUhnRoyalties" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountPaidForUhnRoyalties" xlink:to="VSTA_AmountPaidForUhnRoyalties_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmountPaidForUhnRoyalties_lbl" xml:lang="en-US">Amount paid for UHN royalties</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AwardGivenToSupportDevelopment" xlink:label="VSTA_AwardGivenToSupportDevelopment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AwardGivenToSupportDevelopment" xlink:to="VSTA_AwardGivenToSupportDevelopment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AwardGivenToSupportDevelopment_lbl" xml:lang="en-US">Award given to Support development</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_AwardedAmountIncreasedToSupportDevelopment" xlink:label="VSTA_AwardedAmountIncreasedToSupportDevelopment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AwardedAmountIncreasedToSupportDevelopment" xlink:to="VSTA_AwardedAmountIncreasedToSupportDevelopment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AwardedAmountIncreasedToSupportDevelopment_lbl" xml:lang="en-US">Awarded amount increased to Support development</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ChemicalsRevenue" xlink:label="us-gaap_ChemicalsRevenue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ChemicalsRevenue" xlink:to="us-gaap_ChemicalsRevenue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ChemicalsRevenue_lbl" xml:lang="en-US">Grant revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:to="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_lbl" xml:lang="en-US">Research and development expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts" xlink:label="us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts" xlink:to="us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_lbl" xml:lang="en-US">Business Aquisition</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_UnsecuredPromissoryNoteIssued2" xlink:label="VSTA_UnsecuredPromissoryNoteIssued2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnsecuredPromissoryNoteIssued2" xlink:to="VSTA_UnsecuredPromissoryNoteIssued2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UnsecuredPromissoryNoteIssued2_lbl" xml:lang="en-US">Unsecured promissory note issued value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20120930.xsd#VSTA_WarrantsExercisable" xlink:label="VSTA_WarrantsExercisable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsExercisable" xlink:to="VSTA_WarrantsExercisable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsExercisable_lbl" xml:lang="en-US">Warrants Exercisable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestIncomeExpenseNet" xlink:to="us-gaap_InterestIncomeExpenseNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xml:lang="en-US">Total interest expense on note and the prior line of credit</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:to="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_2_lbl" xml:lang="en-US">Incurred expenses on research and subsequent other projects</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerAndMayerLLCMember" xlink:to="VSTA_BurrPilgerAndMayerLLCMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BurrPilgerAndMayerLLCMember_2_lbl" xml:lang="en-US">BurrPilgerAndMayerLLCMember</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DesjardinsSecuritiesIncMember" xlink:to="VSTA_DesjardinsSecuritiesIncMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DesjardinsSecuritiesIncMember_2_lbl" xml:lang="en-US">DesjardinsSecuritiesIncMember</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultLLPMember" xlink:to="VSTA_McCarthyTetraultLLPMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_McCarthyTetraultLLPMember_2_lbl" xml:lang="en-US">McCarthyTetraultLLPMember</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MorrisonAndFoersterLLPMember" xlink:to="VSTA_MorrisonAndFoersterLLPMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MorrisonAndFoersterLLPMember_2_lbl" xml:lang="en-US">MorrisonAndFoersterLLPMember</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrent_2_lbl" xml:lang="en-US">Assets, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Assets_2_lbl" xml:lang="en-US">Assets</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrent_2_lbl" xml:lang="en-US">Liabilities, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrent" xlink:to="us-gaap_LiabilitiesNoncurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesNoncurrent_2_lbl" xml:lang="en-US">Liabilities, Noncurrent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Liabilities_2_lbl" xml:lang="en-US">Liabilities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockValue" xlink:to="us-gaap_TreasuryStockValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockValue_2_lbl" xml:lang="en-US">Treasury Stock, Value</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquity_2_lbl" xml:lang="en-US">Stockholders' Equity Attributable to Parent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_2_lbl" xml:lang="en-US">Liabilities and Equity</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Revenues_2_lbl" xml:lang="en-US">Revenues</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingExpenses_2_lbl" xml:lang="en-US">Operating Expenses</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingIncomeLoss_2_lbl" xml:lang="en-US">Operating Income (Loss)</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_2_lbl" xml:lang="en-US">ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLoss_2_lbl" xml:lang="en-US">Net Income (Loss) Attributable to Parent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_2_lbl" xml:lang="en-US">LossOnEarlyExtinguishmentOfDebt</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivable_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_2_lbl" xml:lang="en-US">Increase (Decrease) in Accounts Receivable</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInDepositOtherAssets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets_2_lbl" xml:lang="en-US">Increase (Decrease) in Deposit Assets</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:to="us-gaap_IncreaseDecreaseInDeferredRevenue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue_2_lbl" xml:lang="en-US">Increase (Decrease) in Deferred Revenue</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Operating Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:to="us-gaap_PaymentsToAcquireMachineryAndEquipment_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment_2_lbl" xml:lang="en-US">Payments to Acquire Machinery and Equipment</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Investing Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Financing Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_2_lbl" xml:lang="en-US">Cash and Cash Equivalents, Period Increase (Decrease)</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareAbstract_2_lbl" xml:lang="en-US">Earnings Per Share [Abstract]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseCurrentAbstract" xlink:to="us-gaap_PrepaidExpenseCurrentAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidExpenseCurrentAbstract_2_lbl" xml:lang="en-US">Prepaid Expense, Current [Abstract]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_2_lbl" xml:lang="en-US">Prepaid Expense and Other Assets, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrentAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract_2_lbl" xml:lang="en-US">Accrued Liabilities, Current [Abstract]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAccruedLiabilitiesCurrent" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_2_lbl" xml:lang="en-US">Other Accrued Liabilities, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateInvestmentOwnedAmount" xlink:to="VSTA_AggregateInvestmentOwnedAmount_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AggregateInvestmentOwnedAmount_2_lbl" xml:lang="en-US">AggregateInvestmentOwnedAmount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_2_lbl" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate" xlink:to="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate_2_lbl" xml:lang="en-US">Fair Value Assumptions, Weighted Average Volatility Rate</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ChemicalsRevenue" xlink:to="us-gaap_ChemicalsRevenue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ChemicalsRevenue_2_lbl" xml:lang="en-US">Chemicals Revenue</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedParties_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DeferredRevenues" xlink:to="VSTA_DeferredRevenues_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_DeferredRevenues_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterest" xlink:to="VSTA_NotesPayableAndAccruedInterest_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterest_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" xlink:to="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedOfficersCompensation" xlink:to="VSTA_AccruedOfficersCompensation_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedOfficersCompensation_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RevenueFromExternalCustomers" xlink:to="VSTA_RevenueFromExternalCustomers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_RevenueFromExternalCustomers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AcquiredInProcessResearchAndDevelopment" xlink:to="VSTA_AcquiredInProcessResearchAndDevelopment_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AcquiredInProcessResearchAndDevelopment_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComprehensiveLoss" xlink:to="VSTA_ComprehensiveLoss_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ComprehensiveLoss_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOn77.5And10Notes" xlink:to="VSTA_AmortizationOfDiscountsOn77.5And10Notes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOn77.5And10Notes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnPlatinumNotes" xlink:to="VSTA_AmortizationOfDiscountsOnPlatinumNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOnPlatinumNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" xlink:to="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" xlink:to="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseRelatedToModificationOfWarrants" xlink:to="VSTA_ExpenseRelatedToModificationOfWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:to="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:to="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" xlink:to="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:to="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:to="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotesPayable" xlink:to="VSTA_ProceedsFromIssuanceOf7NotesPayable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromIssuanceOf7NotesPayable_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:to="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationTextBlock" xlink:to="VSTA_HistoryAndOrganizationTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_HistoryAndOrganizationTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesTextBlock" xlink:to="VSTA_PrepaidExpensesTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PrepaidExpensesTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedExpensesTextBlock" xlink:to="VSTA_AccruedExpensesTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedExpensesTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LicensingAndCollaborativeAgreementsTextBlock" xlink:to="VSTA_LicensingAndCollaborativeAgreementsTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LicensingAndCollaborativeAgreementsTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalStockTextBlock" xlink:to="VSTA_CapitalStockTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CapitalStockTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesPerValue1" xlink:to="VSTA_PreferredStockSeriesPerValue1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesPerValue1_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesAuthorized" xlink:to="VSTA_PreferredStockSeriesASharesAuthorized_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesIssued" xlink:to="VSTA_PreferredStockSeriesASharesIssued_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesIssued_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesOutstanding" xlink:to="VSTA_PreferredStockSeriesASharesOutstanding_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" xlink:to="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_doc" xml:lang="en-US">Outstanding Options Under 2008 And 1999 Stock Incentive Plan And 1998 Scientific Advisory Board Plan.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:to="VSTA_OutstandingWarrantsToPurchaseCommonStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock_doc" xml:lang="en-US">Outstanding Warrants To Purchase Common Stock.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" xlink:to="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_doc" xml:lang="en-US">February 2012 12 Convertible Promissory Notes And Accrued Interest1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Total" xlink:to="VSTA_Total_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_Total_doc" xml:lang="en-US">Total.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants" xlink:to="VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestorRelationsAndAwarenessServicesPaidByIssuanceOfCommonStockOrWarrants_doc" xml:lang="en-US">Investor Relations And Awareness Services Paid By Issuance Of Common Stock Or Warrants.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LegalFees1" xlink:to="VSTA_LegalFees1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LegalFees1_doc" xml:lang="en-US">Legal Fees1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedResearchAndDevelopmentExpenses" xlink:to="VSTA_AccruedResearchAndDevelopmentExpenses_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedResearchAndDevelopmentExpenses_doc" xml:lang="en-US">Accrued Research And Development Expenses.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedPlacementAgentFees" xlink:to="VSTA_AccruedPlacementAgentFees_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedPlacementAgentFees_doc" xml:lang="en-US">Accrued Placement Agent Fees.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedRegistrationRightsPayments" xlink:to="VSTA_AccruedRegistrationRightsPayments_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedRegistrationRightsPayments_doc" xml:lang="en-US">Accrued Registration Rights Payments.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationWarrantsMember" xlink:to="VSTA_PreModificationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreModificationWarrantsMember_doc" xml:lang="en-US">Pre Modification Warrants Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationWarrantsMember" xlink:to="VSTA_PostModificationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PostModificationWarrantsMember_doc" xml:lang="en-US">Post Modification Warrants Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MarketPricePerShare" xlink:to="VSTA_MarketPricePerShare_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_MarketPricePerShare_doc" xml:lang="en-US">Market Price Per Share.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedTermYearsMaximum" xlink:to="VSTA_ExpectedTermYearsMaximum_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExpectedTermYearsMaximum_doc" xml:lang="en-US">Expected Term Years Maximum.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageFairValuePerShare" xlink:to="VSTA_WeightedAverageFairValuePerShare_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_WeightedAverageFairValuePerShare_doc" xml:lang="en-US">Weighted Average Fair Value Per Share.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsOneMember" xlink:to="VSTA_ShareBasedCompensationWarrantsOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsOneMember_doc" xml:lang="en-US">Share Based Compensation Warrants One Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTwoMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTwoMember_doc" xml:lang="en-US">Share Based Compensation Warrants Two Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsThreeMember" xlink:to="VSTA_ShareBasedCompensationWarrantsThreeMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsThreeMember_doc" xml:lang="en-US">Share Based Compensation Warrants Three Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsFourMember" xlink:to="VSTA_ShareBasedCompensationWarrantsFourMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsFourMember_doc" xml:lang="en-US">Share Based Compensation Warrants Four Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsFiveMember" xlink:to="VSTA_ShareBasedCompensationWarrantsFiveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsFiveMember_doc" xml:lang="en-US">Share Based Compensation Warrants Five Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsSixMember" xlink:to="VSTA_ShareBasedCompensationWarrantsSixMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsSixMember_doc" xml:lang="en-US">Share Based Compensation Warrants Six Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsSevenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsSevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsSevenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Seven Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsEightMember" xlink:to="VSTA_ShareBasedCompensationWarrantsEightMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsEightMember_doc" xml:lang="en-US">Share Based Compensation Warrants Eight Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsNineMember" xlink:to="VSTA_ShareBasedCompensationWarrantsNineMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsNineMember_doc" xml:lang="en-US">Share Based Compensation Warrants Nine Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Ten Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsElevenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsElevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsElevenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Eleven Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTwelveMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTwelveMember_doc" xml:lang="en-US">Share Based Compensation Warrants Twelve Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePrice" xlink:to="VSTA_ExercisePrice_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExercisePrice_doc" xml:lang="en-US">Exercise Price.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotes12PercentFebruary2012Member" xlink:to="VSTA_ConvertiblePromissoryNotes12PercentFebruary2012Member_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConvertiblePromissoryNotes12PercentFebruary2012Member_doc" xml:lang="en-US">Convertible Promissory Notes 12 Percent February 2012 Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Notediscount12PercentConvertiblePromissoryNotesMember" xlink:to="VSTA_Notediscount12PercentConvertiblePromissoryNotesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_Notediscount12PercentConvertiblePromissoryNotesMember_doc" xml:lang="en-US">Note discount 12 Percent Convertible Promissory Notes Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Net12PercentConvertiblePromissoryNotesMember" xlink:to="VSTA_Net12PercentConvertiblePromissoryNotesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_Net12PercentConvertiblePromissoryNotesMember_doc" xml:lang="en-US">Net 12 Percent Convertible Promissory Notes Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RelatedPartiesMember" xlink:to="VSTA_RelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_RelatedPartiesMember_doc" xml:lang="en-US">Related Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotePayabletoCatoHoldingCo.7PercentRelatedPartiesMember" xlink:to="VSTA_NotePayabletoCatoHoldingCo.7PercentRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotePayabletoCatoHoldingCo.7PercentRelatedPartiesMember_doc" xml:lang="en-US">Note Payable to Cato Holding Co. 7 Percent Related Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscount7percentRelatedPartiesMember" xlink:to="VSTA_NoteDiscount7percentRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscount7percentRelatedPartiesMember_doc" xml:lang="en-US">Note Discount 7 percent Related Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TotalNotesPayableto7PercentRelatedPartiesMember" xlink:to="VSTA_TotalNotesPayableto7PercentRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_TotalNotesPayableto7PercentRelatedPartiesMember_doc" xml:lang="en-US">Total Notes Payable to 7 Percent Related Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LessCurrentPortion7PercentRelatedPartiesMember" xlink:to="VSTA_LessCurrentPortion7PercentRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LessCurrentPortion7PercentRelatedPartiesMember_doc" xml:lang="en-US">Less Current Portion 7 Percent Related Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscount7PercentRelatedPartiesMember" xlink:to="VSTA_NonCurrentPortionAndDiscount7PercentRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionAndDiscount7PercentRelatedPartiesMember_doc" xml:lang="en-US">Non Current Portion And Discount 7 Percent Related Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedOfficersCompensationNotesPayableToOfficersForDefferedSalaryRelatedPartiesMember" xlink:to="VSTA_AccruedOfficersCompensationNotesPayableToOfficersForDefferedSalaryRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedOfficersCompensationNotesPayableToOfficersForDefferedSalaryRelatedPartiesMember_doc" xml:lang="en-US">Accrued Officers Compensation Notes Payable To Officers For Deffered Salary Related Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnrelatedPartiesMember" xlink:to="VSTA_UnrelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_UnrelatedPartiesMember_doc" xml:lang="en-US">Unrelated Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayable7PercentAllCurrentUnrelatedPartiesMember" xlink:to="VSTA_NotesPayable7PercentAllCurrentUnrelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayable7PercentAllCurrentUnrelatedPartiesMember_doc" xml:lang="en-US">Notes Payable 7 Percent All Current Unrelated Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayable7Point5PercentToVendorsBurrAndPilgerAndMayerUnrelatedPartiesMember" xlink:to="VSTA_NotesPayable7Point5PercentToVendorsBurrAndPilgerAndMayerUnrelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayable7Point5PercentToVendorsBurrAndPilgerAndMayerUnrelatedPartiesMember_doc" xml:lang="en-US">Notes Payable 7 Point 5 Percent To Vendors Burr And Pilger And Mayer Unrelated Parties Member.</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SecuredConvertiblePromissoryNote1" xlink:to="VSTA_SecuredConvertiblePromissoryNote1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SecuredConvertiblePromissoryNote1_doc" xml:lang="en-US">Secured Convertible Promissory Note1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FinancingTransactionsGrossProceeds" xlink:to="VSTA_FinancingTransactionsGrossProceeds_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FinancingTransactionsGrossProceeds_doc" xml:lang="en-US">Financing Transactions Gross Proceeds.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestmentInQualifiedFinancing" xlink:to="VSTA_InvestmentInQualifiedFinancing_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestmentInQualifiedFinancing_doc" xml:lang="en-US">Investment In Qualified Financing.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountOfCommitmentsFromOtherInvestors" xlink:to="VSTA_AmountOfCommitmentsFromOtherInvestors_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmountOfCommitmentsFromOtherInvestors_doc" xml:lang="en-US">Amount Of Commitments From Other Investors.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February201212PercentConvertibleNotesMember" xlink:to="VSTA_February201212PercentConvertibleNotesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_February201212PercentConvertibleNotesMember_doc" xml:lang="en-US">February 2012 12 Percent Convertible Notes Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoHoldingCompanyMember" xlink:to="VSTA_CatoHoldingCompanyMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoHoldingCompanyMember_doc" xml:lang="en-US">Cato Holding Company Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerAndMayerLLCMember" xlink:to="VSTA_BurrPilgerAndMayerLLCMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_BurrPilgerAndMayerLLCMember_doc" xml:lang="en-US">Burr Pilger And Mayer LLC Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DesjardinsSecuritiesIncMember" xlink:to="VSTA_DesjardinsSecuritiesIncMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_DesjardinsSecuritiesIncMember_doc" xml:lang="en-US">Desjardins Securities Inc Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultLLPMember" xlink:to="VSTA_McCarthyTetraultLLPMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_McCarthyTetraultLLPMember_doc" xml:lang="en-US">McCarthy Tetrault LLP Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MorrisonAndFoersterLLPMember" xlink:to="VSTA_MorrisonAndFoersterLLPMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_MorrisonAndFoersterLLPMember_doc" xml:lang="en-US">Morrison And Foerster LLP Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ContractualTerm1" xlink:to="VSTA_ContractualTerm1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ContractualTerm1_doc" xml:lang="en-US">Contractual Term1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PeriodOfCommitmentsFromOtherInvestors2" xlink:to="VSTA_PeriodOfCommitmentsFromOtherInvestors2_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PeriodOfCommitmentsFromOtherInvestors2_doc" xml:lang="en-US">Period Of Commitments From Other Investors2</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpirationDate" xlink:to="VSTA_ExpirationDate_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExpirationDate_doc" xml:lang="en-US">Expiration Date.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscount" xlink:to="VSTA_NotesPayableDiscount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableDiscount_doc" xml:lang="en-US">Notes Payable Discount.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscountRelatedParties" xlink:to="VSTA_NotesPayableDiscountRelatedParties_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableDiscountRelatedParties_doc" xml:lang="en-US">Notes Payable Discount Related Parties.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertibleNotesDiscount" xlink:to="VSTA_ConvertibleNotesDiscount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConvertibleNotesDiscount_doc" xml:lang="en-US">Convertible Notes Discount.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePricePerShareWeightedAvg" xlink:to="VSTA_ExercisePricePerShareWeightedAvg_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExercisePricePerShareWeightedAvg_doc" xml:lang="en-US">Exercise Price Per Share Weighted Avg.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:to="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnSettlementsOfAccountsPayable" xlink:to="VSTA_LossOnSettlementsOfAccountsPayable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationMember" xlink:to="VSTA_PreModificationMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreModificationMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationMember" xlink:to="VSTA_PostModificationMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PostModificationMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsExercisePrice1" xlink:to="VSTA_FairValueAssumptionsExercisePrice1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueAssumptionsExercisePrice1_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShare" xlink:to="VSTA_FairValuePerShare_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValuePerShare_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoBioVenturesMember" xlink:to="VSTA_CatoBioVenturesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoBioVenturesMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_USNationalInstitutesOfHealthMember" xlink:to="VSTA_USNationalInstitutesOfHealthMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_USNationalInstitutesOfHealthMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NIHGrantRevenueMember" xlink:to="VSTA_NIHGrantRevenueMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NIHGrantRevenueMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoResearchLtdMember" xlink:to="VSTA_CatoResearchLtdMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoResearchLtdMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsExercisable" xlink:to="VSTA_WarrantsExercisable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_WarrantsExercisable_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnsecuredPromissoryNoteIssued2" xlink:to="VSTA_UnsecuredPromissoryNoteIssued2_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_UnsecuredPromissoryNoteIssued2_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfAmendedMfWarrant" xlink:to="VSTA_IncrementalValueOfAmendedMfWarrant_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalValueOfAmendedMfWarrant_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNotesNonCurrentMember" xlink:to="VSTA_SeniorNotesNonCurrentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SeniorNotesNonCurrentMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountMember" xlink:to="VSTA_NoteDiscountMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:to="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" xlink:to="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableMember" xlink:to="VSTA_SevenPercentNotesPayableMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionMember" xlink:to="VSTA_CurrentPortionMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableNonCurrentPortionMember" xlink:to="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerMayerMember" xlink:to="VSTA_BurrPilgerMayerMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_BurrPilgerMayerMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultMember" xlink:to="VSTA_McCarthyTetraultMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_McCarthyTetraultMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:to="VSTA_MayTwoThousandElevenMorrisonFoersterMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountOneMember" xlink:to="VSTA_NoteDiscountOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountOneMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPointFivePercentNotesPayableMember" xlink:to="VSTA_SevenPointFivePercentNotesPayableMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPointFivePercentNotesPayableMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionOneMember" xlink:to="VSTA_CurrentPortionOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionOneMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountMember" xlink:to="VSTA_NonCurrentPortionAndDiscountMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionAndDiscountMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" xlink:to="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" xlink:to="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionTwoMember" xlink:to="VSTA_CurrentPortionTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionTwoMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionMember" xlink:to="VSTA_NonCurrentPortionMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" xlink:to="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionThreeMember" xlink:to="VSTA_CurrentPortionThreeMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionThreeMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountOneMember" xlink:to="VSTA_NonCurrentPortionAndDiscountOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionAndDiscountOneMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotePayableToCatoHoldingMember" xlink:to="VSTA_SevenPercentNotePayableToCatoHoldingMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotePayableToCatoHoldingMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountTwoMember" xlink:to="VSTA_NoteDiscountTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountTwoMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableToRelatedPartiesMember" xlink:to="VSTA_NotesPayableToRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableToRelatedPartiesMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionFourMember" xlink:to="VSTA_CurrentPortionFourMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionFourMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountTwoMember" xlink:to="VSTA_NonCurrentPortionAndDiscountTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionAndDiscountTwoMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestmentOwnedAccruedInterest1" xlink:to="VSTA_InvestmentOwnedAccruedInterest1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestmentOwnedAccruedInterest1_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateInvestmentOwnedAmount" xlink:to="VSTA_AggregateInvestmentOwnedAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AggregateInvestmentOwnedAmount_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" xlink:to="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" xlink:to="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsMember" xlink:to="VSTA_ShareBasedCompensationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsMember_doc" xml:lang="en-US">Custom element.</link:label>
    </link:labelLink>
</link:linkbase>
</XBRL>
