Abstract 6044: BR101801: A potent and selective inhibitor of DNA-PK, potentiates the activity of topoisomerase II inhibitor in vitro and causes tumor inhibition in cancer models

Introduction: The DNA-dependent protein kinase (DNA-PK) plays an instrumental role in the overall survival and proliferation of cells. As a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, DNA-PK is best known as a mediator of the cellular response to DNA damage. DNA-PK plays a key role in the repair of DNA double-strand breaks (DSBs) that are probably the most deleterious form of DNA damage. Inhibition of DNA-PK has been considered as an attractive approach to decrease resistance to therapeutically induced DNA DSBs. In this context, DNA-PK has emerged as an intriguing therapeutic target in the treatment of a variety of cancers, especially when used in conjunction with genotoxic chemotherapy. We have developed a high potent and selective inhibitor of DNA-PK, BR101801, which inhibits topoisomerase II inhibitor-induced γ-H2AX with an IC50. In this study, BR101801, a first-in class inhibitor of DNA-PK, will be introduced as a novel candidate of human cancer therapy. Methods: The enzyme selectivity of BR101801 was determined by Eurofins kinase profiling services. To assess the effect of BR101801 on DNA-PK in LoVo cell, cells were pre-incubated with etoposide for 2 hours and then exchanged into new media containing BR101801 or other compounds without etoposide. Activity of BR101801 was evaluated based on prolongation of γ-H2AX using western blot. In vitro GI50 was tested by WST-based viability assay in various cancer cell lines. Synergy of the combination with cytotoxic agents was analyzed using CT-26 mouse model, respectively. Results: In the enzymatic analysis, BR101801 showed selectivity on DNA-PK. (IC50 DNA-PK = 6 nM, respectively). The combined inhibitory effect of DNA-PK was comparable to the effect of BR101801. The several cytotoxic agents that are known as a booster of γ-H2AX, including doxorubicin and etoposide were selected and all combination treatments of BR101801 with the cytotoxic agents showed significant result by having less than a combination index value of 0.5. The in vivo efficacy of the combination with doxorubicin and oxaliplatin was assessed in a CT-26 colon cancer model Conclusions: These data confirm that DNA-PK inhibition of BR101801 enhanced the efficacy of rage of DSB inducing agent in vitro and in vivo, providing a clear rationale for its clinical use. Citation Format: Mi Kwon Son, Seungho Wang, Bo Ram Lee, Byeongwook Jeon, Soo jung Kim, Enhui Yang, Min Park, Joo han Lee, Jayhyuk Myung. BR101801: A potent and selective inhibitor of DNA-PK, potentiates the activity of topoisomerase II inhibitor in vitro and causes tumor inhibition in cancer models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6044.