Abstract 1581: KSQ-4279, a first-in-class USP1 inhibitor shows strong combination activity with multiple PARP inhibitors in BRCA mutant cancers

Abstract

Abstract Tumors harboring BRCA1/2 mutations and other homologous recombination deficiencies are sensitive to agents targeting pathways involved in DNA repair including poly (ADP-ribose) polymerase (PARP) inhibitors, which have been approved for the treatment of BRCA mutant cancers. Despite the clinical benefit with these drugs, many patients achieve incomplete disease control and often develop resistance. By employing our CRISPRomics® technology to screen over 600 cancer cell lines, we identified the deubiquitinating enzyme USP1 as one of the top targets that displays selective anti-tumor activity in ovarian and triple negative breast cancers with homologous recombination deficiencies. Subsequent drug discovery efforts identified KSQ-4279 as a potent and highly selective first-in-class small molecule USP1 inhibitor that is now in clinical development. In preclinical models, we previously demonstrated that KSQ-4279 shows therapeutic potential in combination with olaparib for treating patients who are either intrinsically resistant, or have developed acquired resistance to PARP inhibitors. We performed studies to investigate the therapeutic potential of combining KSQ-4279 across a variety of PARP inhibitors with different ‘PARP trapping’ potencies. Clonogenic assays demonstrated synergistic effects of KSQ-4279 across multiple PARP inhibitors regardless of their PARP trapping potency. Second generation PARP1 selective inhibitors such as AZD5305 are currently in clinical development and may provide a safety and efficacy advantage for patients. We have investigated the potential of combining KSQ-4279 with AZD5305 in a PARP refractory patient-derived triple negative breast cancer (TNBC) xenograft model by evaluating tolerability and anti-tumor efficacy. We observed significantly greater and more durable anti-tumor activity, including regressions, with the combination therapy compared to single agents. Our data supports the clinical testing of KSQ-4279 in combination with PARP inhibitors. Citation Format: Erica Tobin, Pamela Sullivan, Morgan Murray, Hugh Gannon, Anne Dodson, Sol Shenker, Frank Stegmeier, Andrew Wylie, Louise Cadzow. KSQ-4279, a first-in-class USP1 inhibitor shows strong combination activity with multiple PARP inhibitors in BRCA mutant cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1581.