Abstract 3948: The role of α7 nicotinic acetylcholine receptor activation and pharmacologic tobacco cessation agents on response to radiotherapy

Purpose: Tobacco use is associated with poor therapeutic outcome because it in part decreases the efficacy of conventional cancer treatments including chemotherapy and/or radiotherapy (RT). However, preclinical data suggests that nicotine replacement decreases effectiveness of cancer treatment potentially through action of the α7-nicotinic acetylcholine receptor(nAChR). The purpose of this study is to examine the role of the α7-nAChR in mediating response to RT, evaluate the effect of nAChR and non-nAChR based pharmacologic tobacco cessation agents on response to RT, and identify critical downstream signal transduction pathways associated with changes in response. Methods: α4, α7 and β2-nAChR subunit expression was verified in H460, A549 (lung cancer) and FaDu (oropharyngeal cancer) using western blot. All three cell lines were dose-escalated with nicotine, α7-nAChR selective agonists (TC 1698, PNU 282987, PHA 543613, LY 2087101), or pharmacologic tobacco cessation agents (varenicline, bupropion, hydroxybupropion, cytisine) alone or in combination with single fraction 2Gy X-ray radiation treatment. Clonogenic survival assays were used to assess cell survival and downstream activation of radioprotective pathways (Akt, ERK, mTOR, MMP2, and hypoxia inducible factor 1-alpha [HIF-1α]) were analyzed by western blot. Results: Nicotine administration and activation of the α7- nAChR by PHA 543613 or LY 2087101 were found to have a radioprotective effect in the three tested cancer cell lines as indicated by increased cell survival. Conversely, TC 1698 and PNU 282987 treatment did not modulate cell survival when in combination with radiation. Nicotine, PHA 543613, LY 2087101, TC 1698 and PNU 282987 were all shown to induce a time and dose dependent increase in p-AKT, p-ERK, and HIF-1α. However, treatment with PHA 543613 or LY 2087101 induced an increase in mTOR phosphorylation at S2448 with no change in phosphorylation with TC 1698 or PNU282987. Furthermore, other nAChR-involved agents, cytisine and varenicline, showed mixed results with varenicline inducing radioprotection while cytisine did not alter response to RT. The non-nAChR involved agents, bupropion and hydroxybupropion, did not modulate response to radiotherapy and dose escalated bupropion did not change activation of p-Akt, p-ERK, or HIF-1α. Conclusions: Collectively, these data suggests that the non-nAChR based agent bupropion and its metabolite hydroxybupropion may be the ideal tobacco cessation strategy for cancer patients in order to maintain the biologic effectiveness of radiation treatment. Data further suggests that downstream activation of mTOR may be critical to modulating α7- nAChR based changes in response to RT. Citation Format: Samantha L. Sobus, Michelle A. Romano, Graham W. Warren. The role of α7 nicotinic acetylcholine receptor activation and pharmacologic tobacco cessation agents on response to radiotherapy. [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 3948. doi:10.1158/1538-7445.AM2014-3948