Abstract 1326: Nonprotective autophagy fails to confer resistance to radiation

Abstract

Abstract Radiation remains a predominant treatment option for advanced, inoperable lung cancer, however, resistance represents a major barrier against effective therapy. The exact mechanisms through which cancer cells exhibit resistance to radiotherapy still remains unresolved. Traditionally, radiation-induced autophagy is considered as a mechanism of resistance which attenuates the antitumor effects of radiotherapy i.e., autophagy plays a cytoprotective role on cell survival. To examine this concept further, we employed H460 non-small cell lung cancer (NSCLC) cells that were either p53 wild-type (p53 +/+) or p53 null (p53 -/-) to study the contribution of autophagy to radiation sensitivity. While autophagy was markedly higher in p53 +/+ cells (determined by p62 degradation, LC3B conversion, and acidic vesicle formation) the p53 +/+ cells were actually more radiosensitive than their counterpart H460 p53 -/- cells, which showed lower levels of radiation-induced autophagy. Despite modest radiosensitization by chloroquine, alternative pharmacological (3-methly adenine) and genetic (ATG5 silencing) inhibition of autophagy failed to radiosensitize either p53 +/+ or p53 -/- cells, indicating that radiation induced autophagy is not cytoprotective in function in these experimental models. Furthermore, secretome analysis (nLC-MS/MS) of p53 +/+ H460 cells showed no significant association with radioresistance-related proteins in comparison with p53 -/- H460 cells. The rate and extent of apoptosis was quite low and similar in the two cells lines, essentially ruling out apoptotic cell death as the basis for differential radiation sensitivity. Finally, Senescence was more pronounced in the p53 +/+ cells compared to the p53 -/- cells, which may contribute to the greater radiation sensitivity in the p53 +/+ cells. However, the most relevant finding in this work was that when autophagy is the nonprotective form, it does not confer inherent radiation resistance in tumor cells. Citation Format: Jingwen Xu, Emmanuel Kenneth Cudjoe, Tareq Saleh, Nipa Patel, Moureq Alotaibi, Yingliang Wu, Santiago Lima, David Gewirtz. Nonprotective autophagy fails to confer resistance to radiation [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 1326.