Abstract 3912: Towards development of next-generation biparatopic ADCs using a novel linker-toxin with expanded therapeutic window
Authors: Davies Rupert H. , Barnscher Stuart D. , Chan Peter W. , Madera Laurence , Rich Jamie R. , Vallejo Marylou , Wickman Grant R. , Yin Kevin , Fung Vincent , Hamblett Kevin J. , Kaminker Patrick G. , Babcook John S. 
Published: August 2018

Abstract
Antibody drug conjugate (ADC) therapies such as Kadcyla® and Adcetris® have significantly improved outcomes for patients. Despite these early advances, many ADCs have failed due to tolerability and efficacy concerns; therefore, there is a need to develop ADCs with a greater therapeutic window. We have previously reported the increased tolerability of a novel N-acyl sulfonamide auristatin payload conjugated to trastuzumab via a protease cleavable linker. In non-human primates (NHPs), the HNSTD for this ADC was 18 mg/kg compared to 3 mg/kg for the MMAE conjugate control. Separately, we have also reported that a biparatopic antibody targeting a tumor associated antigen (e.g. anti-HER2 bispecific antibody ZW25) can lead to enhanced receptor clustering and improved internalization, thereby increasing the efficiency of payload delivery. Our aim is to develop a series of novel biparatopic ADCs with expanded therapeutic windows against multiple targets. Here we present the proof-of-concept in vitro and in vivo characterization of benchmark ADCs against 3 different targets with improved tolerability and equivalent efficacy. Benchmark antibodies against 3 known clinical targets were conjugated to our N-acyl sulfonamide auristatin (mAb-ADCs) or to MMAE or DM4 controls (mAb-control ADCs) via cleavable linkers and were assessed for in vitro binding affinity and cytotoxicity. The therapeutic windows of mAb-ADCs and mAb-control ADCs were compared by assessing efficacy in mouse xenograft models and tolerability and pharmacokinetics in NHPs. mAb-ADCs had similar binding affinities to recombinant targets and/or to cancer cells expressing low to high levels of target antigen compared to the mAb-control ADCs. mAb-ADCs demonstrated similar in vitro cytotoxicity compared to mAb-control ADCs and this was recapitulated in vivo with similar tumor growth inhibition in mouse xenograft models. In a NHP tolerability/PK study, mAb-ADCs for all 3 targets were tolerated at doses up to 18 mg/kg (single dose IV infusion) compared to the mAb-control ADCs that showed severe to life-threatening neutropenia at lower doses. The increase in maximum tolerated dose for the mAb-ADCs over the mAb-control ADCs, together with comparable efficacy across 3 different targets, demonstrates the broad applicability of the novel N-acyl sulfonamide auristatin payload to expand the therapeutic window. This strategy, together with ongoing efforts to identify synergistic antibody paratopes that more efficiently deliver payload, could lead to next-generation biparatopic ADCs with improved activity.
Citation Format: Rupert H. Davies, Stuart D. Barnscher, Peter W. Chan, Laurence Madera, Jamie R. Rich, Marylou Vallejo, Grant R. Wickman, Kevin Yin, Vincent Fung, Kevin J. Hamblett, Patrick G. Kaminker, John S. Babcook. Towards development of next-generation biparatopic ADCs using a novel linker-toxin with expanded therapeutic window [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3912.