Abstract 211: A new class of sequence-selective DNA cross-linking ADC payloads with increased in vivotolerability

Abstract

Although five Antibody-Drug Conjugates (ADCs) have been approved and over eighty others are in development, the majority contain payloads belonging to two classes: tubulin inhibitors and DNA interactive agents. Most DNA cross-linking payloads (e.g., the PBD dimers) have potent cytotoxicity but ADCs containing them have high hydrophobicity and a narrow therapeutic window. Thus, there is interest in developing novel payloads which benefit from a potency similar to the PBD dimers but that possess lower hydrophobicity and produce ADCs with a wider Therapeutic Index (TI). The pyridinobenzodiazepines (PDDs) are a new class of guanine-alkylating payloads, and these have been coupled to an adenine-alkylating CXI/duocarmycin pharmacophore to generate molecules that can form G-A DNA cross-links. The lead PDD-CXI payload (FGX-8-46) has a sequence-selectivity profile that differs from other DNA cross-linking agents in that it spans seven to eight base-pairs compared to six to seven for a typical PBD dimer. DNA cleavage experiments have indicated that it cleaves at discrete Adenine-containing sequences of the type 5’-XGXWWWW-3’ (X is any base; W is A/T, and the underlined bases show the cleavage points), and Transcription Factor (TF) Array studies show that it is a potent TF inhibitor, down-regulating several key oncogenic TFs (e.g., NF-κB). In in vitro cell line studies, the G-A cross-linkers have low pM cytotoxicity comparable to the PBD dimers in a wide and diverse range of cell lines, including those from both solid and haematological cancers (e.g., IC50 of ~2 pM in SW-48). This payload class is also compatible with a wide variety of linker technologies, and attachment can be made through either the PDD or CXI units. Importantly, these payloads are significantly less hydrophobic than other equivalent payload classes. ADCs have been generated by conjugating these new payloads to the EGFR-targeting antibody Cetuximab with DARs of between 1.8 and 2.2. The ADCs exhibit potent cytotoxicity in vitro, significant in vivo efficacy and substantially increased tolerability compared to other DNA cross-linking payloads (e.g., the PBD dimer Tesirine). While the G-A cross-linkers retain the cytotoxic potency of the PBD dimers, the “softer” cross-link formed compared to the G-G cross-linking PBD dimers may contribute to the enhanced tolerability profile of this molecular class. The favourable hydrophobicity profile of the PDD-CXI payloads and their ease of conjugation to antibodies, along with their significant in vitro cytotoxicity, in vivo efficacy and tolerability of ADCs produced from them, suggest that they represent a promising new class of ADC payloads. Citation Format: George Procopiou, Jennifer Auer, Daniella di Mascio, Keith R. Fox, Paolo Andriollo, Ilona Pysz, Francesco Cascio, Nicolas Veillard, K. Miraz Rahman, Paul J. Jackson, David E. Thurston. A new class of sequence-selective DNA cross-linking ADC payloads with increased in vivotolerability [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 211.