Abstract 365: Indotecan (LMP400), indimitecan (LMP776) and LMP744, a new class of non-camptothecin topoisomerase I inhibitors selective for schlafen11-positive and BRCA-deficient cells that synergize with olaparib

To overcome the limitations of topoisomerase inhibitors, irinotecan and topotecan (chemical instability, drug efflux substrates, short half-life, dose-limiting bone marrow and gastrointestinal toxicity), we have developed the indenoisoquinolines (LMP400, LMP776 and LMP744). To rationally select patients for phase 2 clinical trials, we have taken two approaches. First, we mined the cancer cell lines genomic databases with CellMinerCDB and found that a dominant response determinant to the indenoisoquinolines is Schlafen 11 (SLFN11), a recently identified executor of cells undergoing replication stress. We validated this finding in isogenic cell lines. Second, because the major lesions generated by the trapping of TOP1 are replication-induced DNA double-strand breaks that are repaired by homologous recombination (HR), we determined whether the indenoisoquinolines exhibit a “synthetic lethality” in cells presenting BRCA1, BRCA2 or PALB2 deficiency. In addition, we tested wether this selectivity could be enhanced when combined with the PARP inhibitor, olaparib. Survival and cell cycle alterations were tested after treatment with the indenoisoquinolines as single agents in isogenic DT40, DLD1 and OVCAR cell lines, with BRCA1, BRCA2 or PALB2 deficiencies, and organoids cultured from patient-derived xenografts with BRCA2 loss, as well as in combination with olaparib. We found that BRCA1-, BRCA2- and PALB2-deficient cells are 3 to 5 times more sensitive to the indenoisoquinolines compared to isogenic cell lines. Moreover, combination treatments showed high synergy between all three indenoisoquinolines and olaparib. We also established the synergy between LMP400 (Indotecan) and olaparib in orthotopic allograft models derived from genetically engineered mouse models for serous epithelial ovarian cancer harboring BRCA1 loss. Better efficacy was observed with the combination over single agent treatments of LMP400 or olaparib. Our results provide a rationale for Phase 2 indenoisoquinoline clinical trials with the indenoisoquinolines in HR-deficient cancers as single agents and in combination with PARP inhibitors, and for measuring Schlafen 11 (SLFN11) as a clinical response determinant. Citation Format: Laetitia Marzi, Ludmila Szabova, Zoe Weaver Ohler, Shyam Sharan, Mike Beshiri, Junko Murai, Kathy Kelly, Yves Pommier. Indotecan (LMP400), indimitecan (LMP776) and LMP744, a new class of non-camptothecin topoisomerase I inhibitors selective for schlafen11-positive and BRCA-deficient cells that synergize with olaparib [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 365.