Chromatin Condensation Mediated by EGFR and Aurora B Protects KRAS-Mutant Lung Cancer Cells Against Ionizing Radiation

Abstract

embryo fibroblasts (MEFs). The stress response to ionizing radiation YTR107 was assessed in wild-type and NPM-null MEFs and 6 NSCLC cell lines by quantifying pNPM1, gamma-H2AX, and Rad51 foci, neutral comet tail moment, and colony formation. In vivo efficacy of YTR107 radiosensitization was tested in a syngeneic xenograft model of tumor growth delay. NPM1 levels in a human-derived NSCLC tissue microarray (TMA) were determined by immunohistochemistry. Results: We observed that proliferating NPM1-null MEFs, but not wildtype MEFs, have high levels of gamma-H2AX foci, a characteristic of replication stress. In addition, NPM1-null MEFs exhibit increased radiation sensitivity via a defect in Rad51-mediated repair of DNA DSBs. We further determined that YTR107-mediated radiosensitization requires NPM1. The DNA damage response pathway is continuously activated in NSCLC due to constant replication stress. Because NPM1 expression minimizes replication stress, we further hypothesized that NSCLC tumors may have significant expression of NPM1. This was validated by analyzing a NSCLC TMA that demonstrated very low NPM1 expression in matched normal lung parenchyma but significantly increased NPM1 expression in Stage III NSCLC cores. We then observed that YTR107-mediated targeting of NPM1 resulted in radiosensitization in 6 NSCLC cell lines in vitro and in a syngeneic tumor model in vivo. Conclusions: These data demonstrate genetic evidence of NPM1 contribution to repair of radiation-induced DNA damage and suggest that NPM1 represents a potential therapeutic target for radiosensitization of NSCLC. Author Disclosure: C.A. Smith: None. K.R. Sekhar: Q. Patent/License Fee/Copyright; Co-inventor on the patent covering YTR107. M. Benamar: None. A. Venkateswaran: None. S. Sasi: None. N.R. Penthala: Q. Patent/License Fee/Copyright; Co-inventor on the patent covering YTR107. P.A. Crooks: Q. Patent/License Fee/Copyright; Co-inventor on the patent covering YTR107. S.R. Hann: None. L. Geng: None. T. Abbas: None. M.L. Freeman: Q. Patent/License Fee/Copyright; Co-inventor on the patent covering YTR107.