Abstract 1618: New peptide-linked anilino-maytansinoid antibody-drug conjugates (ADCs) for the treatment of cancer (2014)

Abstract A number of ADCs consisting of a maytansinoid cytotoxic agent linked to an antibody via a cleavable disulfide linker or a non-cleavable thioether linker are in the clinic. In preclinical models, antibody-maytansinoid conjugates (AMCs) utilizing a cleavable disulfide linker have been shown to be able to kill both the targeted antigen-positive (Ag+) cancer cells and also adjacent Ag- “bystander” cancer cells because of intra-cellular generation of maytansinoid catabolites that can travel out of the Ag+ cells, into adjacent Ag- cells, and kill these cells when they divide. Such bystander killing of Ag- cancer cells can be advantageous for some tumor types, such as those with heterogeneous target expression on the cancer cells. We thus developed a new dipeptide linker designed to promote bystander killing more efficiently than current disulfide linkers. It is used to attach an aniline-bearing maytansinoid to the targeting antibody. To determine the effect of amino acid stereochemistry on the therapeutic index, dipeptide-anilino AMCs (dpa-AMCs) were prepared with the four possible L- and D-alanine configurations using an anti-EGFR antibody. These were compared to a dpa-AMC containing the L-Val-L-Cit dipeptide, which is a commonly utilized dipeptide for ADC linkage. Dipeptide stereochemistry had a significant effect on the in vitro potency and bystander killing activity of the AMCs. Based on the results, the three most potent designs - those bearing the L-Ala-L-Ala, D-Ala-L-Ala, and L-Val-L-Cit peptides - were further investigated. In tolerability experiments in mice, with AMC dosing based on linked maytansinoid, the MTDs of the D-Ala-L-Ala dpa-AMCs and a disulfide linked control AMC were both approximately 1.4 mg/kg, while the L-Val-L-Cit and L-Ala-L-Ala dpa-AMCs were not as well tolerated. The AMC with the disulfide linker and the three most potent dpa-AMCs had similar in vivo efficacy in tumor xenograft models in mice where the antigen was expressed homogeneously. The D-Ala-L-Ala dpa-AMC however was selected as the lead based on its favorable MTD and because its anti-CanAg conjugate had 2-3 fold greater efficacy in vivo than a disulfide linked anti-CanAg AMC in a HT-29 tumor model, where the antigen is expressed heterogeneously. Cellular processing studies revealed that the anti-CanAg D-Ala-L-Ala dpa-AMC produced a unique, highly potent anilino-maytansinoid catabolite that can diffuse into, and kill, bystander cells. In conclusion, we have developed a promising new type of maytansinoid ADC, one that provides a high degree of bystander killing, improved activity in a heterogeneous tumor model in vivo, and a different mechanism of cytotoxic catabolite release than current AMC designs. Citation Format: Wayne C. Widdison, Joe Ponte, Jennifer Coccia, Yulius Setiady, Ling Dong, Anja Skaletskaya, Nathan Fishkin, Yelena Kovtun, Rui Wu, Rajeeva Singh, Luke Harris, Greg Jones, Leanne Lanieri, Erin Maloney, Charlene Audette, Andre Dandeneau, Ravi Chari, Juliet Costoplus, Karen Veale, Sharon Wilhelm. New peptide-linked anilino-maytansinoid antibody-drug conjugates (ADCs) for the treatment of cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1618. doi:10.1158/1538-7445.AM2014-1618