TRAIL and Paclitaxel Synergize to Kill U87 Cells and U87-Derived Stem-Like Cells In Vitro

TRAIL and Paclitaxel Synergize to Kill U87 Cells and U87-Derived Stem-Like Cells In Vitro

Int.J.Mol.Sci.2012,13,9142-9156;

doi:10.3390/ijms13079142InternationalJournalofMolecularSciencesISSN1422-0067www.mdpi.com/journal/ijmsArticleTRAILandPaclitaxelSynergizetoKillU87CellsandU87-DerivedStem-LikeCellsInVitroBoQiu1,XiyangSun2,DongyongZhang1,YongWang1,JunTao1andShaowuOu1,*1DepartmentofNeurosurgery,FirstHospitalofChinaMedicalUniversity,No.155,NorthNanjingStreet,HepingDistrict,Shenyang110001,Liaoning,China;

E-Mails:fhxue2002@sohu.com(B.Q.);dongyong0622@hotmail.com(D.Z.);wangyongdl@126.com(Y.W.);cmu_taojun@yahoo.com(J.T.)2DepartmentofPharmaceutics,SchoolofPharmacy,FudanUniversity,826ZhanghengRoad,Shanghai201203,China;E-Mail:cmu_sunxiyang@yahoo.com*Authortowhomcorrespondenceshouldbeaddressed;E-Mail:cmu_oushaowu@msn.com;Tel.:+86-24-8328-3316;Fax:+86-24-8328-3390.Received:5March2012;

inrevisedform:11July2012/Accepted:11July2012/Published:20July2012Abstract:U87-derivedstem-likecells(U87-SLCs)wereculturedusingserum-freestemcellmediaandidentifiedbybothbiologicalbehaviorsandmarkers.Tumornecrosisfactor(TNF)-relatedapoptosis-inducingligand(TRAIL)andpaclitaxel(PX),incombinationoralone,wasusedtotreatU87-MGhumangliomacells(U87cells)orU87-SLCs.TheresultsshowedthatTRAIL/PXcannotonlysynergisticallyinhibitU87cellsbutalsoU87-SLCs.WeobservedasignificantlyhigherapoptoticrateinU87cellssimultaneouslytreatedwithTRAIL/PXfor24hcomparedtocellstreatedwitheitherdrugalone.Furthermore,therewasaremarkablyhigherapoptosisrateinU87-SLCsinducedbytheTRAIL/PXcombinationcomparedwitheitherdrugalone.UnlikethesimultaneoustreatmentinU87cells,U87-SLCswerepretreatedfor24hwith1μmol/LofPXfollowedby1000ng/mLofTRAIL.ProteinassaysrevealedthatTRAIL/PXsynergywasrelatedtoDR4,cleavedcaspase-8andcleavedcaspase-3upregulation,whereasthemitochondrialpathwaywasnotinvolvedinTRAIL-inducedapoptosis.ThepresentstudyindicatesthatPXcansensitizeU87cellsandU87-SLCstoTRAILtreatmentthroughanextrinsicpathwayofcellapoptosis.ThecombinedtreatmentofTRAILandPXmaybeapromisinggliomachemotherapybecauseofitssuccessfulinhibitionofU87-SLCs,whicharehypothesizedtoinfluencechemotherapeuticoutcomesofgliomas.Keywords:glioma;

gliomastemcells;U87-derivedstem-likecells(U87-SLCs);

tumornecrosisfactor(TNF)-relatedapoptosis-inducingligand(TRAIL);paclitaxel;

apoptosis1.IntroductionMalignantgliomas,e.g.,glioblastomamultiforme(GBM)andanaplasticastrocytomas(AA),arethemostcommonanddevastatingprimarybraintumorsgiventheirdismalprognosis[1,2].Despiteaggressivetherapywithmaximalsafesurgicalresection,radiationandchemotherapy,thesetumorsinvariablyarerefractoryto,orbecomeresistantto,treatmentandoftenrecur[3,4].Thetreatmentofmalignantgliomasiscurrentlyoneofthemostdifficultchallengesinoncology.Althoughcytoreductivesurgeryisalwaystheprimarytreatment[5,6],adjuvanttherapies,suchaschemotherapy,havealsobeenproventobebeneficialformanagingmalignantgliomas[7,8].Asingledrug,however,cannotobtainoptimalefficacybecausetumorcellsoftenexhibitmajorresistancetoonetypeofchemotherapeuticdrug.Therefore,combinedchemotherapymightbearationalandpracticaloption.Recentworksuggeststhattheexistenceofgliomastemcells(GSCs)maybeacriticalfactorinfluencingchemotherapeuticoutcomesofgliomas[10–13].AccordingtotheGSCstheory,gliomasdevelopascellularandfunctionalhierarchiesoriginatingfromGSCsthatareresponsiblefortumorinitiation,maintenance,progressionandrecurrence[14–16].GSCspossessuniquesurvivalmechanismsanddistinctstemcellproperties:theabilityofself-renewalanddifferentiation,amarkedabilitytoproliferatefollowingaprolongedquiescentperiod,andenhancedexpressionofDNArepairgenes.Consequently,GSCscanescapechemotherapy-inducedcelldeathandremaindormantforextendedperiodsaftertreatmentbuteventuallyre-enterthecellcycle,whichleadstotherecurrenceofgliomas[10,13,17,18].ItisnowhypothesizedthatGSCsarethemajorcausesforintractabilityandtherapeuticresistance,andgliomaswillnotbecuredunlesstheGSCsareeliminated[11,12,19,20].Tumornecrosisfactor(TNF)-relatedapoptosis-inducingligand(TRAIL)inducesapoptosisintumorcellsbybindingtodeathreceptorsTRAIL-R1/DR4andTRAIL-R2/DR5.Thesereceptorspossessanintracellulardeathdomain,whichtriggerstheactivationofthecaspasesignalingcascadewithorwithoutt