Abstract 1329: Sensitization of non-small cell lung cancer cells (NSCLC) to radiation by Vitamin D (EB 1089) (2014)

Abstract Lung cancer is one of the leading causes of cancer related deaths in the United States and other industrialized countries, accounting for 40% of all cancer deaths. Although smoking cessation programs have led to a decline in death rates, the need for improved therapies remains, as the mortality rates for lung cancer patients have not significantly changed over the years. Patients with non-small cell lung cancer (NSCL) have a poor prognosis and the median survival rate is less than 12 months. Previously, vitamin D (1,25-D3) and its analogue, EB 1089, have been shown to enhance anti-proliferative and anti -tumorigenic effects in breast tumor cells exposed to radiation (IR). Our current research efforts were designed to study the effects of vitamin D on the response to radiation in models of non-small cell lung cancer. Autophagy, a catabolic process, has been shown to be the primary mode of radio-sensitization by vitamin D in breast tumor cells. H460 non-small cell lung tumor cells (wild type in p53, expressing the vitamin D receptor, mutant in ras), demonstrate transient growth inhibition followed by proliferative recovery when treated with radiation alone; growth arrest becomes prolonged with minimal recovery and reduced clonogenic survival is observed for the combination treatment of (the vitamin D analog) EB 1089 + radiation. Induction of autophagy was detected based on acridine orange staining and flow cytometric quantification of autophagic vesicles. Induction of autophagic flux was evident based on degradation of p62. In contrast, the combination treatment failed to increase the extent of apoptosis and senescence over that induced by radiation alone. Similar data were generated using the A549 NSCLC cell line which also expresses the vitamin D receptor, is wild type in p53 and mutant in ras. The autophagy induced by radiation alone is cytoprotective in nature as a blockade to autophagy increases sensitization to radiation. However, pharmacological inhibition of autophagy reversed the radio-sensitization effects of EB 1089, indicating that a novel form of autophagy, which we have termed “cytostatic”, appears to be the primary mode of radio-sensitization in H460 lung tumor cells. Our studies with autophagy inhibitors further demonstrate a switch between the cytoprotective and cytostatic roles of autophagy in response to radiation alone and the combination of IR+EB 1089. AMPK, an energy sensor, has been shown to be involved in regulating autophagy. An increase in phosphorylated AMPK levels was observed with the combination treatment. Compound C, an AMPK inhibitor, when used in combination with IR+ EB 1089, reverted the radio-sensitization effects, implicating AMPK in radio-sensitization. Ongoing studies are also focused on the potential role of ULK1 in cytostatic autophagy. These studies suggest that vitamin D could be utilized to increase sensitivity to radiation treatment for lung cancer. Citation Format: Khushboo Sharma, David Gewirtz. Sensitization of non-small cell lung cancer cells (NSCLC) to radiation by Vitamin D (EB 1089). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1329. doi:10.1158/1538-7445.AM2014-1329