Abstract 3299: Radiation induced p53-dependent cytoprotective autophagy fails to reduce radiation sensitivity in H460 non-small cell lung cancer cells

Abstract

Abstract Our previous studies showed that radiation-induced autophagy could be either cytoprotective or nonprotective in A549 non-small cell lung cancer cells, HN30 and HN6 head and neck cancer cells and 4T1 breast tumor cells, and that this functional difference was related to the status of p53 in the cells (i.e. cytoprotective autophagy in p53 wild type (wt) cells and nonprotective autophagy in cells with mutant or null p53) [1]. Despite the fact that inhibition of autophagy has been proposed as a strategy to overcome resistance to radiation and chemotherapy, there is little direct information in support of the premise that the induction of autophagy confers resistance. As an example, studies in HCT-116 cells that are either wt or null in p53 demonstrate essentially identical radiation sensitivity [2], although the nature of radiation induced autophagy was not determined in these cell lines. To address this question, p53 wt and p53 null H460 cell lines were utilized to evaluate whether cytoprotective autophagy actually suppressed radiation sensitivity. Acridine orange staining, flow cytometric analysis and western blotting (LC3B, p62, Atg5) showed that following exposure to 6 Gy of radiation wtp53 and p53-null H460 cells exhibited a significant induction of autophagy. p53 wt H460 cells showed sensitization to radiation upon pharmacological autophagy inhibition and Atg5 knock down. However, pharmacological inhibition of autophagy and knock down of Atg5 genes failed to influence sensitivity to radiation in p53-null H460 cells. Furthermore, clonogenic survival assays showed that while exposure to radiation induced a dose-dependent (2, 4, 6, 8 Gy) decrease in clonogenicity in both p53wt and p53-null H460 cells, radiation sensitivity was not decreased in the p53 wt cells. Taken together, these findings indicate that cytoprotective autophagy may not actually alter the nature of radiation (and possibly chemotherapeutic) sensitivity in tumor cells. [1] Chakradeo, S, et al. Mol Pharm (2015): [2] Lindgren, T, et al. Int J Rad Biol (2015). Acknowledgments We would like to thank Dr. Santiago Lima (Virginia Commonwealth University) for the H460 p53-null cells. Citation Format: Jingwen Xu, Tareq Saleh, Liliya Tyutynuk-Massey, Yingliang Wu, David A. Gewirtz. Radiation induced p53-dependent cytoprotective autophagy fails to reduce radiation sensitivity in H460 non-small cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3299. doi:10.1158/1538-7445.AM2017-3299