preclinical activity and safety of stro-002, a novel adc
TRANSCRIPT
Preclinical Activity and Safety of STRO-002, a Novel ADC Targeting Folate Receptor Alpha for Ovarian CancerCristina Abrahams, Stellanie Krimm, Xiaofan Li, Sihong Zhou, Jeffrey Hanson, Mary Rose Masikat, Krishna Bajjuri, Tyler Heibeck, Dharti Kothari, Abigail Yu, Robert Henningsen, Cuong Tran, Gang Yin, James Zawada, Julie Hang, Maureen Bruhns, Willy Solis, Alexander Steiner, Joy Chen, Adam Galan, Toni Kline, Ryan Stafford, Alice Yam, Venita I. De Almeida, Mark Lupher, Jr., Trevor Hallam. Sutro Biopharma, South San Francisco, CA, USA
Sutro’s proprietary XpressCF+TM cell-free expression system includes:• incorporationofpAMF,thatenablessite-specificconjugation• anorthogonaltRNAsynthetasewhichenableshighfidelitypAMFincorporation• engineeredXpressCF+TMextractsthatutilizeanengineered,attenuatedRF-1whichenables:a.EfficientandmultipleinsertionpointsofpAMFinthesametranslationproductb.PreciseDARrangingfrom1-8inawell-definedmolecularspeciesADCc.ADCproductioninafewdaysallowingforrapiditerativestructure-activityoptimization
Generation of STRO-002, A Well-Defined FolRa-Targeting ADC Through Cell-Free Antibody Synthesis And Site-Specific Conjugation
Cell Killing Activity of STRO-002 Is Highly Specific for FolRa Expressing Cells
Summary
•STRO-002showedpotentactivityinacellkillingassayonFolRαpositiveIgrov-1andOVSAHOcells,butnoeffectonFolRαnegativeA549cells
•CytotoxicactivityofSTRO-002wasspecificforcellsexpressingFolRα;andwascompetedwithexcessSP8166(H01)
• anti-FolRαantibodiesisolatedusingFab-basedribosomedisplaywereoptimizedfor - Linkerandwarheadattributes - Antibody moiety - Drugantibodyratio - Sitepairsfordrug-linkerattachment
• Folatereceptoralpha(FolRa)isacell-surfaceproteinoverexpressedinovarianandendometrialcancer• FolRaexpressionishighlyrestrictedonnormaltissues,makingitahighlyrelevanttargetforcancer
therapyusingantibodydrugconjugates(ADCs).
• WehaveusedaplatformbasedonSutro’sproprietary XpressCF+TM cell-free expression system and site specificconjugationtodesignanovel,FolRa-targetingADC,STRO-002.
• STRO-002containstheanti-FolRahumanIgG1antibodySP8166(H01)conjugatedtoanovelproprietarycleavabledrug-linker(SC239)atspecificsitesY180andF404ontheantibodyheavychain.
• SP8166(H01)wasdiscoveredandoptimizedusingaFabribosomedisplayselectionandhasfour non-naturalaminoacid,p-azido-phenylalanine(pAMF)residuesincorporatedatpositionsY180andF404oneachheavychain.
• SC239iscomposedofatubulin-targeting3-aminophenylhemiasterlinwarhead,SC209,andacleavablevalinecitrullinep-aminobenzylcarbamatelinkerfunctionalizedwithdibenzocyclooctyne(DBCO).
• TherapidandselectivereactionofDBCOonSC239andpAMFresiduesinSP8166resultsinahomogenousADCwiththepredominantspecieshavingadrug-antibodyratio(DAR)of4.
• WehaveleveragedSutro’sXpressCF+TMcell-freetechnologyforrapidinterrogationandoptimizationofparametersforaFolRαtargetingADC,includingchoiceofantibody,conjugationsites,DAR,andlinkerwarhead.
• STRO-002demonstratedgoodpharmacologicalpropertiessuchasspecificityandastabledruglinkagewiththecatabolite,SC209,thatisclearedrapidlyfromcirculationandisaweaksubstratefordrug-resistanceeffluxpumps.
• STRO-002exhibitsdose-dependenttumorgrowthinhibitioninovarianandendometrialtumorxenografts,withefficacyappearingtocorelatewithexpressionlevelsofFolRainthexenograftmodel.Inaddition,STRO-002whencombinedwithcarboplatinsignificantlyimprovesefficacycomparedtocarboplatinaloneinIgrov-1tumors.
• FavorablesafetyprofilesforbothSC209andSTRO-002wereobservedinsafetystudiesinratsandincynomolgousmonkeys,respectively.
• STRO-002thereforehasthepotentialforanimprovedsafetyandactivityprofile,andareducedriskoftumordrugresistance,makingitanidealcandidateforclinicaldevelopment.
• IND-enablingstudiessupportingSTRO-002asapotentialtreatmentofFolRaexpressingmalignanciessuchasovarianandendometrialcancerareongoingandINDsubmissionisplannedforsecondhalfof2018.
References•Zimmerman,E.S.,etal.;(2014)Productionofsite-specificantibody−drugconjugatesusingoptimizednon-naturalaminoacidsinacell-freeexpressionsystem.BioconjugateChemistry2014,25,351−361.
•Yin,G.,et.al.;(2017)RF1attenuationenablesefficientnon-naturalaminoacidincorporationforproductionofhomogeneousantibodydrugconjugates.ScientificReports7(1):3026.
STRO-002 is Highly Stable In Vitro and In Vivo
• STRO-002ishighlystablein vitro (PBS,cynomolgusorhumanplasmaat50mg/mL)andin vivo (plasmafrommicetreatedwithsingledoseof5mg/kg),withaDARof~4beingretaineduntilday21.
• MinimalreleaseoftheSTRO-002catabolite,SC209,wasobservedaftera4-dayincubationofSTRO-002inPBS,cynoorhumanplasmaat100mg/mL.
• SC209wasaccumulatedintumors,but undetectable in circulation of treatedmicebearingIgrov1tumors.
• STRO-002wasisolatedfromplasmasamplesbyaffinitypull-downandDARmeasuredbyLC-MS.ReleasedSC209wasquantitated by LC-MS.
C In VitroSC209Release
A In VitroDARMeasurement
Introduction
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Igrov1FolRa Copy # = 1,375,828
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STRO-002 Demonstrates Dose-Dependent Tumor Killing In Igrov-1 Ovarian Tumor Model
A.Igrov-1tumorgrowthcurvesinresponsetoasingledoseofSTRO-002at2.5,5,10and15mg/kg.B.Scatterplotofindividualtumorsizeonday21whencontroltumorsreachedstudyendpoint.C.Tumorgrowthdelayisdefinedastheaveragetime(indays)oftreatmentgrouptoreach300mm3minustimeforvehiclecontrolgrouptoreachthesameendpoint.Statisticalanalysiswasperformedonfinaltumorsizesonday21anddelaytoreach300mm3usingone-wayANOVAwithDunn’sorDunnett’smultiplecomparisonstest,respectively.
STRO-002 Co-administration with Carboplatin Confers Added Benefit in Igrov-1 Ovarian Tumor Xenografts Compared to Carboplatin Alone
A.Igrov-1tumorgrowthcurvesinresponseto2.5mg/kgSTRO-002withandwithout60mg/kgcarboplatin.B.Scatterplotofindividualtumorsizeonday21whencontroltumorsreachedstudyendpoint.Statisticalanalysiswasperformedonfinaltumorsizesonday21usingone-wayANOVAwithTukey’smultiplecomparisonstest.
STRO-002 Showed Significant Anti-Tumor Activity in Established and Large OVCAR-3 Ovarian Tumor Xenografts
OVCAR-3tumorgrowthcurvesinresponsetoindicateddoseofSTRO-002administeredoncewhenwhentumorswere150mm3(A)or400mm3(B).C.Scatterplotofindividualtumorsizeonday55whencontroltumorsreachedstudyendpoint.Statisticalanalysiswasperformedontumorsizeonday55usingone-wayANOVAwithDunnett’smultiplecomparisonstest.
SC209 is a Poor Substrate for Permeability Glycoprotein 1 (PgP) Efflux Pumps
• MES-SA/MX2amitoxantroneresistantderivativeoftheMES-SAcellline,overexpressP-gp.
• ThecytotoxiceffectsofthethreedrugsonMES-SA/MX2andMES-SAcellsweremeasured in the presence or absence of 5mMofP-gpinhibitorGF120918.
• MES-SA/MX2cellsshoweddifferentlevelsofresistancetothefreewarheadsSC209,DM4andMMAE.ComparedtoDM4andMMAE,MES-SA/MX2cellsshowedmuchlowerresistancetoSC209.
• AdditionofthePgPInhibitorGF120918reversedthedrugresistanceinMES-SA/MX2cellsindicatingthatdrugresistancewasmediatedbyP-gp.
STRO-002 Demonstrates Optimal Stability and a Favorable Safety Profile in Cynomolgus Monkeys
STRO-002wastoleratedat0.9,2.9,and8.7mg/kgfollowingtwoIVdosesonDays1and22.Arepresentativeexposureprofileat8.7mg/kgisshown.TotalAbandADClevelsweresimilaronDay1andDay22andSC209levelsweredetectedatlowlevelsincirculation(<10ng/mL),indicatingoptimalinvivostability.ThemostprominentSTRO-002-relatedtoxicityconsistedofdose-relatedhematologicaltoxicity(neutropenia),thatwasreversible.Nooculartoxicitywasobservedfollowingtwodosesatalltolerateddoses,asassessedbyslitlampmicroscopyandhistopathology.Thesefindingsareconsideredantigen-independent(attributedtothecytotoxiccomponentofSTRO-002),reversible,andclinicallymanageable.0 10 20 30 40
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SC209 Catabolite has Similar Safety and TK Profiles to Other Tubulin-Targeting Drugs in Rats Following a Single IV Dose
Toxicokineticanalysisshowsafastclearanceandlargevolumeofdistribution(notshown).SC209exposuresat1mg/kgcorrespondto~102-foldhigherCmaxand~10.3-foldhigherAUCthanthoseofSTRO-002-derivedSC209atthetolerateddoseof8.7mg/kginmonkeys.Themostprominentdose-relatedtoxicityfindingattolerateddoseswasslighttoseverebonemarrowhypocellularitywhichcorrelatedwithhematologicaltoxicity.
SC209 Dose (mg/kg) Tolerated? Cmax (ng/mL) AUC0-24
(ng.hr/mL) Half-life (hr) CL (mL/hr/kg)
0.33 Yes 25.3 64.4 2.52 6930 1.10 Yes 73.6 244 4.30 6000 2.84 No 267 756 NC NC 7.95 No 2210 NC NC NC
NC–notcalculatedduetomissingTKsamplesduetomortalitiesand/orinabilitytoestimaterateconstants
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AcknowledgementsCrownBioscience:MinxiaWang EnsignaBiosystems:YuChienChouandMichelFaure.ExperimentalPathologyLaboratories,Inc.:W.MichaelPeden.QuintaraDiscovery:JulieRen