Abstract 4289: Discovery of potent RAD51 inhibitors with anticancer activity in preclinical models of non-small cell lung cancer

RAD51 is a protein that plays a key, canonical role in double-strand break (DSB) repair through homologous recombination (HR) and is biologically important for maintaining genome stability. Given its additional, non-canonical role in mitigating the replication stress characteristic of tumor cells, RAD51 has emerged as an attractive therapeutic target in several malignancies including non-small cell lung cancer (NSCLC). Nonetheless, drug discovery endeavors for developing direct RAD51 inhibitors have had limited success. Here, we describe a series of novel RAD51 inhibitors and their cytotoxic activity in preclinical models of NSCLC. We accessed and improved upon a previously discovered series of phenylsulfonyl indolyl isoquinoline derivatives that bind to the hydrophobic pocket of RAD51 preventing its multimerization and interaction with BRCA2. Of these, JKYN-1 and its mesylate salt (patent application # CA3204011A1) displayed potent and selective RAD51 inhibition in cell-free assays. Given the biological importance of replication stress in a subset of NSCLC, we assessed the cytotoxicity of these RAD51 inhibitors in preclinical models of NSCLC. Using the CellTiter-Glo assay, JKYN-1 displayed cytotoxicity in A549 and H1975 cell lines with lower IC50 values compared to the classical RAD51 inhibitor B02 (A549, 4.9 vs >10 μM; H1975, 3.2 vs 8.3 μM). We subsequently assessed the cytotoxicity in a panel of 7 patient-derived organoids (PDOs) of NSCLC with diverse molecular, genetic, and clinical profiles (LPTO308, XDO137, LPTO357, LPTO318, LPTO366, LPTO362, LPTO221). In these models, JKYN-1 and JKYN-1-mesylate displayed a highly potent cytotoxicity with sub-micromolar IC50 values between 0.1-0.87 μM as opposed to B02 that had IC50 values between 3.7 to >10 μM. In conclusion, our data identify JKYN-1 and its mesylate salt as potent and selective RAD51 inhibitors with superior cytotoxic activity compared to classical inhibitors such as B02. These findings highlight the potential of these novel compounds as promising therapeutic agents in a subset of NSCLC. Citation Format: Yifan Yu, Morgan Black, Nikolina Radulovich, Peter Ferguson, James Koropatnick, Ming Tsao, Mark D. Vincent, Geoffrey Liu, Samir H. Barghout. Discovery of potent RAD51 inhibitors with anticancer activity in preclinical models of non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4289.