Abstract 2747: Pharmacological inhibition of the DNA damage response kinases, ATR (Ataxia telangiectasia and Rad3 related) and ATM (Ataxia telangiectasia mutated), broadly sensitizes diverse subtypes of gynecological cancer cells to ionizing radiation

Abstract

Abstract Objectives: The management of gynecological malignancies includes exposure of tumor cells to genotoxic insults, such as ionizing radiation (IR), and focuses on damaging cellular DNA and inducing subsequent cell death. As cells possess innate mechanisms to repair DNA damage, this study focused on combining IR with pharmacological inhibition of key mediators of DNA repair, ATR (Ataxia telangiectasia and Rad3 related) and ATM (Ataxia telangiectasia mutated), to further sensitize gynecological cancer cells to this mode of genotoxic stress. Methods: Clonogenic survival assays: A panel of human cell line models of ovarian, endometrial and cervical cancer were treated with drug vehicle, 5.0 µM ATR inhibitor (ETP-46464), 10.0 µM ATM inhibitor (KU55933) or a combination of ATRi and ATMi, prior to exposure to IR doses up to 6.0 Gy. Drug was removed four hours later and resulting colonies were counted when mean colony size was ≥ 50 cells. Western blot: ATM, ATR and downstream canonical signaling effectors were assessed in cell lysates harvested from representative cell line models of ovarian (A2780), endometrial (HEC1B) and cervical (HELA) cancers, one hour following treatment with inhibitors and IR exposure (2.0 Gy only) as described above. Results: Clonogenic survival assays revealed that inhibition of ATR and ATM increased sensitization to IR across all cell line models of gynecological cancer assessed. This effect was further increased with combined ATR and ATM inhibitor treatments. Western blot analyses revealed activation of ATM and ATR signaling in response to IR via increases in phospho-ATM (Ser1981), p-Chk1 (Ser345) and p-Chk2 (T68) levels. Activation of Chk1, a downstream effector of ATR, was attenuated in ATRi-treated conditions and activation of Chk2, a downstream effector of ATM, were reduced in ATMi-treated conditions. Conclusions: These studies revealed that inhibition of the DNA damage response kinases, ATR and ATM, markedly sensitizes diverse gynecological cancer subtypes to IR. They provide evidence to support further consideration of therapies pairing modulation of DNA damage signaling with IR in the treatment of gynecological malignancies. Citation Format: Nicholas Bateman, Pang-ing Teng, Kelly Conrads, Chad Hamilton, George Maxwell, Christopher Bakkenist, Thomas Conrads. Pharmacological inhibition of the DNA damage response kinases, ATR (Ataxia telangiectasia and Rad3 related) and ATM (Ataxia telangiectasia mutated), broadly sensitizes diverse subtypes of gynecological cancer cells to ionizing radiation. [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 2747. doi:10.1158/1538-7445.AM2014-2747