Abstract LB301: Molecular pharmacology and broad synergy of the novel ATR inhibitor M1774 with DNA damaging anticancer agents

Abstract Ataxia telangiectasia and Rad3-related (ATR) checkpoint kinase orchestrates DNA damage response and repair pathways stimulated by replicative stresses. Recent studies have established that pharmacological inhibition of ATR is clinically promising. As M1774 is an oral ATR inhibitor in clinical development, we explored the molecular basis by which M1774 induces cancer cell death. As a single agent, we found that M1774 suppresses cancer cell viability at nanomolar concentrations with a potency higher than ceralasertib and berzosertib, but lower than gartisertib (M4344) and elimusertib in the small cell lung cancer (SCLC) cell lines H146, H82, and DMS114. We found that M1774 efficiently suppresses the ATR/CHK1 checkpoints. While M1774 alone induced apoptosis and G2/M cell cycle arrest at micromolar concentrations, at a non-toxic low dose, M1774 enhanced TOP1 inhibitor-mediated cancer cell death by preventing replication arrest and inducing DNA damage detected by EdU and γH2AX staining. Tandem mass tagging (TMT) coupled with mass spectrometry revealed that M1774 combined with SN-38 increases the expression of replication-related proteins (TIPIN, CDC45, TIMELESS, and RPA1) and G2/M-related proteins (PLK1 and CCNB1). To establish the synergistic combinations of M1774 with clinical anticancer DNA damaging agents in preclinical models, we performed experiments in cancer cell lines, patient-derived organoids, and xenograft models. Low doses of M1774 significantly synergized with the clinical TOP1 inhibitor SN-38, the TOP2 inhibitor etoposide, cisplatin, and the PARP inhibitor talazoparib in SCLC cell lines. We also found that M1774 significantly reversed chemoresistance to DNA-damaging agents in cancer cells lacking SLFN11 expression, suggesting that SLFN11 expression can be utilized for combination therapy with M1774 as a biomarker. The synergistic efficacy between M1774 and DNA-damaging agents was confirmed in SCLC patient-derived organoids, colon cancer patient-derived organoids, and H82 SCLC xenografts. Together, these results provide insights into the molecular mechanism and potential combination strategies for M1774 in cancer therapy. Citation Format: Ukhyun Jo, Yasuhiro Arakawa, Astrid Zimmermann, Daiki Taniyama, Makito Mizunuma, Lisa M Jenkins, Suresh Kumar, Frank T Zenke, Yves Pommier. Molecular pharmacology and broad synergy of the novel ATR inhibitor M1774 with DNA damaging anticancer agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB301.