Abstract 3305: The role of mTOR in mediating nicotine induced alpha-7 nicotinic acetylcholine receptor activation and the regulation of radiotherapeutic response

Abstract

Abstract Tobacco use is the single largest preventable risk factor for developing cancer. Furthermore, tobacco is associated with poor therapeutic outcomes in part because its continued use has been shown to decrease the efficacy of conventional chemotherapy and/or radiotherapy (RT). Preclinical data suggests that nicotine administration decreases RT efficacy by activating the alpha-7-nicotinic acetylcholine receptor (a7-nAChR). Our study evaluated the effects of nicotine and selective a7-nAChR agonists (LY 2087101, PHA 543613, PNU 282987, and TC 1698) administration on radiotherapeutic efficacy. H460 and A549 human lung cancer cell lines were dose escalated with nicotine and the a7-nAChR agonists alone or in combination with single fraction X-ray radiation (2, 6 Gy) and cell survival was assessed by clonogenic assay. Nicotine administration and activation of a7-nAChR by LY 2087101 or PHA 543613 was found to have a radioprotective effect in both cell lines by increasing cell survival following RT. Conversely, activation of a7-nAChR by PNU 282987 or TC 1698 did not modulate radiotherapeutic response. Western blot analysis demonstrated that although all four tested a7-nAChR agonists increased phosphorylation of AKT (S473), only PHA 543613 and LY 2087101 were found to also activate mTOR (S2448). Additional clonogenic studies were performed to further examine the role of mTORC1 in governing response to RT. Inhibition of mTORC1 by rapamycin alone sensitized both A549 and H460 cells to the effect of RT. Interestingly, rapamycin treatment was sufficient to block the radioprotective effects of nicotine, PHA 543613, and LY 2087101 in A549 cells, however, in H460 cells rapamycin did not restore radiotherapeutic efficacy. Moreover, examination of Deptor, a key component of mTOR complexes shown to be associated with RT response, demonstrated that a7-nAChR activation by nicotine, PHA 543613, or LY 2087101 increased Deptor degradation in A549 cells, while a7-nAChR activation decreased Deptor degradation in H460 cells. These observations suggest that differences in the regulation of Deptor level may contribute to the variation in both rapamycin sensitivity and restoration of therapeutic efficacy to RT between H460 and A549 cell lines. Additional studies will be necessary to further elucidate the role of the mTOR complexes in mediating a7-nAChR induced modulation of response to RT. Citation Format: Samantha L. Sobus, Sundaravadivel Balasubramanian, Michelle A. Romano, Graham W. Warren. The role of mTOR in mediating nicotine induced alpha-7 nicotinic acetylcholine receptor activation and the regulation of radiotherapeutic response. [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 3305. doi:10.1158/1538-7445.AM2015-3305