Abstract 1832: CHK1 inhibitor prexasertib induces NOXA-dependent apoptosis in ovarian cancer
Authors: Venkatachalam Annapoorna , Peterson Kevin L. , Correia Cristina , Flatten Karen S. , Hou Xianon , Schneider Paula A. , Balczewski Emily , McGehee Cordelia , Hurley Rachel M. , Meng Xue W. , Sine Chance , Shah Rameen , Vincelettte Nicole , Ding Husheng , Li Hu , Weroha Saravut (John) , Kaufmann Scott H. 
Published: June 2022

Abstract
Background: The kinases ataxia-telangiectasia-mutated-and-Rad3-related (ATR), checkpoint kinase 1 (CHK1) and WEE1 participate in the response to replication stress. Inhibitors of ATR, WEE1 and CHK1 are being tested for antineoplastic activity as monotherapies and in combination with chemotherapy. Although these agents impair cell cycle checkpoints, fork stabilization, origin firing and homologous recombination (HR), little is known about the apoptotic pathways that are engaged and the critical mediators activating cell death mechanisms. The present study utilizes high grade serous ovarian cancer (HGSOC) cell lines and patient derived xenografts (PDXs) to identify the primary mechanism of cell death in ovarian cancer and assess changes involved in the resistance setting after treatment with these inhibitors.
Methods: A panel of HGSOC cell lines was examined for responses to ceralasertib (ATRi), prexasertib (CHK1i) or adavosertib (WEE1i) using colony forming assays, immunoblotting and assays for apoptosis. Mechanisms involved in acquired resistance and downstream changes in cell fate were evaluated by generating prexasertib-resistant HGSOC cell lines. Subsequent NGS analysis was performed in the sensitive and resistant pairs.
Results: Irrespective of the homologous recombination (HR) status, ovarian cell lines and PDXs underwent cell death during prolonged exposure at clinically achievable concentrations. Treatment of ovarian cancer cell lines with ATRi, CHK1i or WEE1i activated the replication checkpoint, consistent with previously published reports. The subsequent apoptotic response involved PMAIP1 and BCL2L11 upregulation rather than the TNFa-induced death receptor-mediated apoptosis we recently described in acute leukemia (Cancer Res. PMID: 33414171). Additionally, ovarian lines selected for CHK1i resistance failed to die in response to either ATRi or WEE1i.
Conclusions: Prexasertib, ceralasertib, and adavosertib exhibit monotherapy activity in both HR deficient and proficient HGSOC cell lines and PDX models. Unlike AML, death receptor mediated apoptosis was not observed; instead, the primary mechanism of cell killing in HGSOC lines involves activation of the mitochondrial apoptotic pathway. Cross-resistance of these DNA damage repair modulators is likely multifactorial and mainly involves diminished replication stress response.
Citation Format: Annapoorna Venkatachalam, Kevin L. Peterson, Cristina Correia, Karen S. Flatten, Xianon Hou, Paula A. Schneider, Emily Balczewski, Cordelia McGehee, Rachel M. Hurley, Xue W. Meng, Chance Sine, Rameen Shah, Nicole Vincelettte, Husheng Ding, Hu Li, Saravut (John) Weroha, Scott H. Kaufmann. CHK1 inhibitor prexasertib induces NOXA-dependent apoptosis in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1832.