Abstract 4063: Effects of electronic cigarettes (E-cigs) and hookah on the metabolic activation of the tobacco carcinogen, benzo(a)pyrene (BaP), and cellular proliferation in human oral leukoplakia cells

The possible carcinogenic effects of E-cigs on the oral cavity are uncertain because their recent availability and usage precludes long-term epidemiological studies. Also of concern is the use of hookah, which has recently increased in popularity. In addition, many, E-cig and hookah users are tobacco smokers or individuals trying to quit or cut down on smoking. Such individuals likely have precancerous cells and/or lesions in the oral cavity, as do former smokers or oral cancer survivors. The use of E-cigs and hookah then, may affect the initiation and promotion/progression stages of carcinogenesis, and be of particular concern to dual users. Here we have investigated the effects of E-cigs and to a lesser extent, hookah on the metabolism of BaP to its ultimate carcinogenic metabolite, BaP diol-epoxide (BPDE), and also the effects of E-cigs on proliferation, and expression of proliferation-related genes in leukoplakia cells. Tobacco-flavored E-cigs, and hookah were prepared from local products using a mechanical smoking device to simulated smoking, and the resulting vapor collected in a liquid N2-cooled trap to generate E-cig or hookah vapor condensates (VC). To determine the effects of E-cigs and hookah on BaP metabolism, cells from a leukoplakia-derived cell line, MSKLeuk1, were pretreated for 16 hr with E-cig or hookah VC at levels yielding nicotine concentrations of 0.5 - 8 uM (similar to plasma nicotine levels in smokers) and then treated with one uM BaP. After 8 hr the concentrations of BaP-tetrols released into the medium were measured using HPLC. BPDE hydrolyzes into BP tetrols, and their concentration serves as a surrogate for BPDE concentration. Cells pretreated with a tobacco smoke extract (TSE) from the reference cigarette, 2R4F, were included, as were untreated cells. Pretreatment with E-cig or hookah VC increased the concentration of BaP tetrols in the cell medium from 22 to 165 and 64 pM, resp. at the highest dose of each. For comparison, pretreatment with TSE at a nicotine level of 4uM increased the concentration BaP tetrols to 252 pM. The effects E-cigs on cell proliferation were assayed using an MTT assay. The cells were plated with and without E-cig VC and 24 hr later cell proliferation was assayed. Exposure to E-cigs significantly increased the rate of cell proliferation by 61%. The increase maximized at one uM nicotine. We also monitored the effects of 2 different E-cigs on the expression of the certain proteins related to cell proliferation-related genes (PCNA and pAKT) by immunoblotting. Both E-cigs increased the levels of these proteins to various extents. Our results demonstrate, for the first time, that E-cig or hookah VC enhanced metabolism of BaP to its ultimate carcinogen, and E-cig VC stimulated cellular proliferation. These results suggest that “vaping”, or hookah usage may contribute to oral cancer risk. (Support: CA173465). Citation Format: Joseph B. Guttenplan, Yuan-Wan Sun, Kun-Ming Chen, Wieslawa Kosinska, Karam El-Bayoumy. Effects of electronic cigarettes (E-cigs) and hookah on the metabolic activation of the tobacco carcinogen, benzo(a)pyrene (BaP), and cellular proliferation in human oral leukoplakia cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4063.