Abstract 538: LC-MS based catabolite identification study of an ADC with DM21-C, a novel maytansinoid linker-payload

ImmunoGen’s newest antibody-drug conjugate (ADC) design uses the novel maytansinoid linker-payload, DM21-C that bears a peptidase/protease cleavable linker. These ADCs show good bystander killing of proximal antigen negative cells, suggesting the generation of cell-permeable catabolites. The goal of this study was to identify the catabolites generated upon incubation in antigen-positive cancer cells (both cell pellet and media), in mouse plasma, as well as in in vitro catabolic systems. Upon incubation with a cysteine-conjugated DM21-C ADC, the small molecule fraction was extracted with an organic solvent and analyzed by high resolution mass spectrometry after chromatographic separation. Through comparison to reference standards, mass spectral signal extraction of possible products, and database search of unknown peaks, the potential in vitro catabolite products of DM21-C conjugate were identified. Information on linker-payload stability in these model systems, including plasma stability, in vitro metabolism of the ADC, and catabolic products that were both retained and effluxed from cancer cells was obtained. As a result, we identified DM51 (the thiol- resulting from self-immolation of the cleaved linker-payload) as a major catabolite of the DM21-C ADC. Citation Format: Janet Lau, Paulin Salomon, Kerstin Sinkevicius, Juliet Costoplus, Megan Fuller, Raymond Xu, Stuart Hicks, Ravi Chari, Wayne Widdison, Nicholas Yoder, Thomas Keating. LC-MS based catabolite identification study of an ADC with DM21-C, a novel maytansinoid linker-payload [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 538.