Abstract 332: The BET bromodomain inhibitor JQ1 synergizes with WEE1 inhibitor AZD1775 by impairing non-homologous end joining and enhancing DNA damages in non-small cell lung cancer

Abstract

Abstract Background: The bromodomain and extraterminal domain (BET) inhibitors are broadly active in different cancer types, including non-small cell lung cancer (NSCLC). Although their activity on oncogene expression such as c-Myc has been addressed in many studies, the mechanism of BET inhibition on the cytotoxicity remain unknown. BET proteins have been also reported to interact with some DNA damage repair-related genes. AZD1775, a selective WEE1 G2 checkpoint kinase inhibitor, induces DNA damage and consequent apoptosis by abrogating G2 cell cycle arrest and inducing premature mitotic entry. We hypothesized that repression of BET activity would increase WEE1 inhibitor-induced cytotoxicity by impairing DNA damage repair. Here, we evaluate the efficacy and mechanistic rationale for combining AZD1775 and JQ1 as a potential therapy for NSCLC. Methods: NSCLC cell lines (A549, H1299, H1975) and human embryonic kidney cells line (293T) were used in the present study. Anti-tumor activities of JQ1, AZD1775, or the combination were analyzed using MTT survival assay. Changes in protein expression were analyzed by Western Blot analysis. mRNA expressions were evaluated by quantitative rt-PCR. Cell cycle was analyzed by flow cytometry using PI staining. Activity of non-homologous end joining (NHEJ) was evaluated using NHEJ reporter plasmid. Results: The combination of AZD1775 and JQ1 showed synergistic effects for NSCLC cell lines in vitro with combination indices of 0.1-0.5. The JQ1 monotherapy did not induce gamma-H2AX expression, but JQ1 increased and prolonged AZD1775-induced gamma-H2AX expression. The mRNA analysis showed that JQ1 significantly repressed NHEJ-related genes, such as XRCC4 and LIG4. Moreover, NHEJ reporter assay revealed JQ1 diminished NHEJ activity. Conclusions: Our data demonstrate that the combination of JQ1 and AZD1775 has a synergistic effect against NSCLC cell lines via a mechanism of compromised DNA damage repair by JQ1. This combination therapy can be a novel therapeutic strategy for NSCLC. Citation Format: Yuta Takashima, Eiki Kikuchi, Junko Kikuchi, Tetsuaki Shoji, Megumi Furuta, Hajime Kikuchi, Jun Sakakibara-Konishi, Ichiro Kinoshita, Hirotoshi Dosaka-Akita, Masaharu Nishimura. The BET bromodomain inhibitor JQ1 synergizes with WEE1 inhibitor AZD1775 by impairing non-homologous end joining and enhancing DNA damages in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 332.