Abstract 2895: Characterization of payload release from a novel camptothecin drug-linker

Abstract Camptothecins (CPT) are an important class of molecules that have been employed in cancer therapy for the past 20 years. These molecules interact with the DNA-topoisomerase I complex leading to double-strand breaks and cell death. While these molecules are important cancer therapies, they also induce toxicities including diarrhea and myelosuppression. Antibody-drug conjugates (ADCs) have emerged as a method to help mitigate small molecule toxicities by targeting them to tumors via conjugation to tumor-specific antibodies. Recently, encouraging clinical results have been observed with ADCs bearing CPT payloads, demonstrating a potential new utility for this class. The linker that is used to conjugate a payload to an ADC influences its activity, by controlling the identity of the molecular species that can be released, as well as efficiency of drug release. When employed as an ADC, maleimidopropionyl-PEG7-valine-lysine-glycine-7-aminomethyl-10,11-methylenedioxycamptothecin (VKG-AMDCPT), a novel, highly active and enzyme-cleavable tripeptide CPT drug-linker, releases two CPT payloads in cancer cells, as demonstrated both in vitro and in vivo. Using tandem mass spectrometry (LC-MS/MS), the two CPTs have been identified as 7-amino methyl 10,11-methylenedioxy CPT (AMDCPT) and the corresponding glycine adduct of AMDCPT (G-AMDCPT). We have characterized the efficiency of drug release and intracellular retention of the small molecules released from VKG-AMDCPT-conjugated ADCs. This was accomplished through quantification of each species released in vitro and in vivo using multiple cancer cell lines and xenografts. We report here characterization of the biochemical, cellular and bystander killing potencies of each released drug species to further understand their contributions to ADC activity. Citation Format: Julia H. Cochran, Lauren Farr, Ryan Lyski, Peter D. Senter, Scott C. Jeffrey, Shawna M. Hengel, Nicole M. Okeley. Characterization of payload release from a novel camptothecin drug-linker [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2895.