Abstract B181: The Chk1 inhibitor, SRA737, demonstrates chemical synthetic lethality with replication stress-inducing agents, including low-dose gemcitabine, in preclinical models of cancer

Abstract

Abstract Depending on genetic and other factors, tumor cells exhibit replication stress (RS) to various extents. Low levels of RS contribute to genomic instability, an enabling hallmark of cancer, whereas high levels may be cytotoxic. The DNA damage response (DDR) checkpoint kinase 1, Chk1, is essential for managing RS by stabilizing replication forks, abrogating origin firing, pausing the cell cycle, and fostering homologous recombination DNA repair. Consequently, tumor cells become highly reliant on Chk1 to manage RS and maintain proliferation and survival. Certain chemotherapeutic drugs, including nucleoside analogs, DNA cross-linkers, and topoisomerase inhibitors, are effective extrinsic inducers of RS. Here we demonstrate that the potent, selective oral Chk1 inhibitor, SRA737, strongly synergizes with a range of extrinsic inducers of RS to kill tumor cells in vitro and in vivo. We find that clinically used drugs including the DNA crosslinking agents mitomycin C and cisplatin, as well as the nucleoside analog gemcitabine, exacerbate cellular RS markers (e.g. γ-H2A.X and p-RPA) and synergize with SRA737 to increase tumor cell death in vitro. Combination indices (CI) at various doses across a cell line panel were 0.46, 0.54, and 0.25 for mitomycin C, cisplatin, and gemcitabine, respectively. Similar results were observed with both type I and type II topoisomerase inhibitors (SN-38 and etoposide). Notably, gemcitabine potentiates SRA737 in several bladder cancer cell lines including 5637, TCCSUP, and J82 cells, as well as in human primary bladder cancer patient 3D organoids. Consistent with the observed cytotoxicity, the combination of SRA737 and gemcitabine induces γ-H2A.X and p-RPA 3- to 5-fold over gemcitabine alone in tumor xenografts. Moreover, the combination inhibits tumor growth by 64% following administration of both agents at 100 mg/kg in a gemcitabine-insensitive patient-derived xenograft (PDX) model of bladder cancer. Importantly, SRA737 also synergizes with subtherapeutic doses of gemcitabine (40 mg/kg) in xenograft models of colorectal adenocarcinoma and osteosarcoma, indications where gemcitabine is not standard of care. These findings support the clinical development of SRA737 in combination with gemcitabine in bladder cancer, as well as the broader application of SRA737 in combination with extrinsic inducers of RS. Citation Format: Ryan J. Hansen, Bryan Strouse, Kenna Anderes, Gregg Smith, Christian Hassig. The Chk1 inhibitor, SRA737, demonstrates chemical synthetic lethality with replication stress-inducing agents, including low-dose gemcitabine, in preclinical models of cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B181.