Abstract 3758: Inhibition of ATR, but not ATM, sensitizes gynecologic cancer cells to cisplatin

Abstract

Abstract Resistance to platinum-based therapies remains a major hurdle in the management of gynecologic (GYN) cancer especially in ovarian cancer. Platinum such as cisplatin damages DNA by inducing DNA crosslinks that stalls DNA replication forks where significant accumulation of single-stranded DNA from persistently stalled replication forks could ultimately lead to double strand breaks and activation of apoptosis. Ataxia telangiectasia mutated (ATM) and ATM and Rad-3-related (ATR) are two main DNA damage response (DDR) protein kinases that recognize genotoxic stress and function to initiate cell cycle arrest and DNA repair mechanisms. We hypothesized by combining genotoxic stress with inhibition of DDR kinases ATR and/or ATM, therapeutic response of GYN cancer cells to platinum-based chemotherapy could be improved. To test our hypothesis, we assessed cell survival of multiple GYN cell lines including ovarian (A2780, A2780-CP20, OVCAR3), endometrial (KLE, HEC1B), and cervical (HELA, SIHA) carcinoma cells exposed to cisplatin along with ATR inhibitor (ETP-46464) and/or ATM inhibitor (KU55933). We observed inhibition of ATR significantly enhanced cisplatin induced cell death in all seven cell lines tested, resulting in 65 - 96% increased sensitivity to cisplatin. Inhibition of ATM did not sensitize GYN cancer cells to cisplatin and cells were not further sensitized by co-inhibition of ATM and ATR beyond that observed by inhibition of ATR alone. DDR signaling was assessed by immunoblotting in cells exposed to cisplatin with or without the presence of ETP-46464 and/or KU55933 where elevated levels of phospho-ATM (Ser1981), phospho-Chk2 (Thr68) and phospho-Chk1 (Ser345) observed in cisplatin treated cells were attenuated in cells that were co-treated with cisplatin and ETP-46464. In addition, increased levels of cleaved PARP1 and caspase 3 were observed in cisplatin-treated, ATR-inhibited cells, suggesting the enhancement of cisplatin induced cell death with ATR inhibition occurs through elevated apoptosis. Further, no differential effect was observed in GYN cancer cells harboring wild type (A2780, OVCAR3, HELA, SIHA) or mutant (CP20, KLE, HEC1B) TP53. These data support further investigation of pharmacologic inhibitors of ATR in combination with existing platinum based therapeutics for treating GYN cancer. Citation Format: Pang-Ning Teng, Nicholas W. Bateman, Chad A. Hamilton, G. Larry Maxwell, Christopher J. Bakkenist, Thomas P. Conrads. Inhibition of ATR, but not ATM, sensitizes gynecologic cancer cells to cisplatin. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3758. doi:10.1158/1538-7445.AM2014-3758