Abstract 993: The relationship between autophagy, senescence, and DNA repair

Abstract

Abstract Radiotherapy is used along with other modalities such as surgery, chemotherapy, and immunotherapy to either shrink tumors before surgery or kill surviving tumor cells post surgery. Although radiation (and chemotherapy) induce different modes of cell death, recurrence of cancer may occur. It has been shown that DNA damage can induce cells to undergo both autophagy and senescence where both responses can function either as a pro-survival mechanism or in promoting loss of self-renewal capacity in the tumor cell. The relationship between autophagy, senescence, and the DNA repair system has not been well-characterized. The primary aims of this work were to understand whether autophagy and senescence might be permissive for DNA repair, thereby allowing the tumor cells to overcome the persistent DNA damage and recover using HCT116 WT and HCT116 Ligase IV (-/-) human colon carcinoma cells. Irradiation caused HCT116 Ligase IV (-/-) cells to lose their capacity to proliferate followed by delayed cell death, whereas HCT116 WT cells showed proliferative recovery 72 hours post-treatment, consistent with deficiencies in DNA repair in the Ligase IV (-/-) cells. Irradiation of both cell lines resulted in enlargement in cell size and accumulation of acidic vacuoles, indicative of the induction of autophagy. Inhibition of autophagy by Bafilomycin and Choroquine resulted in radio-sensitization in HCT116 WT cells but not in HCT116 Ligase IV (-/-) cells, indicating that radiation-induced autophagy in HCT116 WT cells is likely to be cytoprotective. Both repair competent HCT116 colon carcinoma cells and Ligase IV deficient cells demonstrated significant increases in senescent populations upon irradiation based on β-galactosidase staining and enlargement of treated cells. The PARP inhibitor, Olaparib, enhanced the efficacy of radiation through interference with DNA repair and the promotion of both autophagy and senescence but not apoptosis. Taken together, it appears that both autophagy and senescence may facilitate DNA repair during exposure to genotoxic stress, and that autophagy and senescence are closely linked responses in irradiated tumor cells. Citation Format: Moureq R. Alotaibi, Lawrence Povirk, Daivd Gewirtz. The relationship between autophagy, senescence, and DNA repair. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 993. doi:10.1158/1538-7445.AM2015-993