ADC单抗偶联药物

Chapter5LinkerTechnologiesforAntibody–DrugConjugatesBirteNoltingAbstractAntibody–drugconjugates(ADCs),whichcombinethespecificity,favorablepharmacokinetics,andbiodis-tributionofamonoclonalantibody(mAb)withthecytotoxicpotencyofadrug,arepromisingnewtherapiesforcancer.Alongwiththedevelopmentofmonoclonalantibodies(mAbs)andcytotoxicdrugs,thedesignofthelinkerisofessentialimportance,becauseitimpactstheefficacyandtolerabilityofADCs.Thelinkerneedstoprovidesufficientstabilityduringsystemiccirculationbutallowfortherapidandefficientreleaseofthecytotoxicdruginanactiveforminsidethetumorcells.ThisreviewprovidesanoverviewoflinkertechnologiescurrentlyusedforADCsandadvancesthathaveresultedinlinkerswithimprovedproperties.Alsoprovidedisabriefsummaryofsomeconsiderationsfortheconjugationofantibodyanddruglinkersuchasdrug-to-antibodyratioandsiteofconjugation.KeywordsAntibody–drugconjugate,Monoclonalantibody,Linker,Cytotoxicdrug,Conjugation,Hydrazone,Disulfide,Peptide,Cleavable,Noncleavable1IntroductionAntibody–drugconjugates(ADCs)offeraunique-targetedthera-peuticstrategycombiningthebestfeaturesofbothantibodiesandsmall-moleculedrugstocreateasinglemoietythatishighlyspecificandcytotoxic.Assuch,theyhavebeenthesubjectofintenseresearchfocusedonoptimizationtoincreasethetherapeuticindicesofADCs.AnidealADCshouldretainthefavorablepharmacoki-neticandfunctionalpropertiesofantibodies,remainintactandnontoxicinsystemiccirculation(blood),andbecomeactiveatthetargetsite,withthedrugreleasedinasufficientamounttokilltumorcells;andtherebycombinethecytotoxicactivityofthedrugwiththeintrinsicantigen-targetingand/orantitumoractiv-itiesoftheantibody.OneofthebiggestchallengesinthedevelopmentofADCshasbeenthegenerationofsuitablelinkersfortheconjugationofantibodyanddrug.Theroleofthelinkerisfundamentalbecause,inadditiontoefficientdeliveryofthecytotoxicdrug,thestabilityofthedrug–antibodylinkageisakeyfactorindeterminingtheefficacyLaurentDucry(ed.),Antibody-DrugConjugates,MethodsinMolecularBiology,vol.1045,DOI10.1007/978-1-62703-541-5_5,#SpringerScience+BusinessMedia,LLC201371andtoxicityofADCandindoingsotheADC’stherapeuticpotential.Thereareseveralimportantconsiderationsregardingthelinkercomponent,includingthesiteofattachmentontheantibody,theaveragenumberofattachmentsitesperantibodymolecule,thecleavabilityofthelinker(abilitytodisintegratereleas-ingthedrug),andthepolarityofthelinker.Sinceakeyadvantageofantibody-basedtherapeuticsovermostchemotherapeuticdrugsistheirlongretentionincirculation,thelinkershouldbeexceedinglystableincirculationasreleaseofthecytotoxicpayloadbeforereachingthetargetwouldleadtononspe-cificcellkillingandassociatedtoxicities.However,uponreachingthetargetcells,thelinkermustalsoallowforefficientreleaseofthecytotoxiccompoundinanactiveformatthetargetsite.Severalstrategieshavebeenemployedtoproducelinkersthatsatisfythesecriteria,someofwhichexploitdifferentialpropertiesbetweentheextracellularandintracellularenvironmentstoreleasedrugonlyafterantigen-specific,antibody-mediatedinternalizationoftheADCintotumorcells(receptor-mediatedendocytosis)hasoccurred[1].MostADCscurrentlyundergoingclinicalevaluationcontainlinkersthatfallintotwobroadcategories:cleavableandnonclea-vable.Cleavablelinkersrelyonprocessesinsidethecelltoliberatethetoxin,suchasreductioninthecytoplasm,exposuretoacidicconditionsinthelysosome,orcleavagebyspecificproteaseswithinthecell.NoncleavablelinkagesrequireproteolyticdegradationoftheantibodyportionoftheADCforreleaseofthecytotoxicmolecule,whichwillretainthelinkerandtheaminoacidbywhichitwasattachedtotheantibody.EarlygenerationADCsoftencontainedunstablelinkerswithshorthalf-lives(1–2days)suchasdisulfides[2–4]andhydrazones[5–7].Morerecently,attentionhasturnedtowardlinkerswithimprovedstabilitycharacteristicswhileinthesystemiccirculation[8].Includedamongthemarepeptidelinkers[9,10],glucuronides[11],andnoncleavablelinkersthatremaincovalentlyattachedtothedrugafterthemAbcarrierishydrolyzedinlysosomesoftargetcells[8,12].Thechoiceoflinkeristargetdependent,basedontheknowl-edgeoftheinternalizationanddegradationoftheantibody–targetantigencomplex,andapreclinicalinvitroandinvivoactivitycomparisonofconjugates.Furthermore,thechoiceofalinkerisalsoinfluencedbywhichcytotoxinisused,aseachmoleculehasdifferentchemicalconstraints,andfrequentlythedrugstructurelendsitselftoaspecificlinker.AnotherfeatureuniquetoADCsthatcanbemanipulatedbythechoiceoflinkeristhebystanderkillingeffect,whichcanincreasethepotencyofthesetherapeutics.SomeADCshavebeenobservedtoeffectkillingofbystanderantigen-negativecellspres-entinthevicinityoftheantigen-positivetumorcells.Studiesto72BirteNoltingelucidatethemechanismofbystandercellkillingbyADCshaveindicatedthatmetabolicproductsformedduringintracellularpro-cessingoftheADCsmayplayarole[9,12,13].NeutralcytotoxicmetabolitesgeneratedbymetabolismoftheADCsinantigen-positivecellscanbereleasedintothemediumandcankilladjacentantigen-negativecells.Chargedmetabolites,however,maybepre-ventedfromdiffusingacrossthemembraneintothemediumandcannoteffectbystanderkilling[12,14].Manipul