BackgroundElectronic cigarette (EC) aerosols contain unique compounds in addition to toxicants and carcinogens traditionally found in tobacco smoke. Studies are warranted to understand the public health risks of ECs.ObjectiveThe aim of this study was to determine the genotoxicity and the mechanisms induced by EC aerosol extracts on human oral and lung epithelial cells.MethodsCells were exposed to EC aerosol or mainstream smoke extracts and DNA damage was measured using the primer anchored DNA damage detection assay (q-PADDA) and 8-oxo-dG ELISA assay. Cell viability, reactive oxygen species (ROS) and total antioxidant capacity (TAC) were measured using standard methods. mRNA and protein expression were evaluated by RT-PCR and western blot, respectively.ResultsEC aerosol extracts induced DNA damage in a dose-dependent manner, but independently of nicotine concentration. Overall, EC aerosol extracts induced significantly less DNA damage than mainstream smoke extracts, as measured by q-PADDA. However, the levels of oxidative DNA damage, as indicated by the presence of 8-oxo-dG, a highly mutagenic DNA lesion, were similar or slightly higher after exposure to EC aerosol compared to mainstream smoke extracts. Mechanistically, while exposure to EC extracts significantly increased ROS, it decreased TAC as well as the expression of 8-oxoguanine DNA glycosylase (OGG1), an enzyme essential for the removal of oxidative DNA damage.ConclusionsExposure to EC aerosol extracts suppressed the cellular antioxidant defenses and led to significant DNA damage. These findings emphasize the urgent need to investigate the potential long-term cancer risk of exposure to EC aerosol for vapers and the general public.

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Tobacco smoking is the leading preventable cause of cancer. Moreover, continued smoking during cancer therapy reduces overall survival. Aware of the negative consequences of tobacco smoking and the challenges of smoking cessation, cancer patients are inquiring whether they should switch to electronic cigarettes (e-cigarettes). To obtain evidence-based data to inform this decision, we examined the effects of e-cigarette aerosol exposure on cisplatin resistance in head and neck cancer cells. Our results show that cancer cells exposed to e-cigarette aerosol extracts and treated with cisplatin have a significant decrease in cell death, increase in viability, and increase in clonogenic survival when compared to non-exposed cells. Moreover, exposure to e-cigarette aerosol extracts increased the concentration of cisplatin needed to induce a 50% reduction in cell growth (IC50) in a nicotine-independent manner. Tobacco smoke extracts induced similar increases in cisplatin resistance. Changes in the expression of drug influx and efflux transporters, rather than activation of cell growth-promoting pathways or DNA damage repair, contribute to e-cigarette induced cisplatin resistance. These results suggest that like combustible tobacco, e-cigarette use might increase chemotherapy resistance, and emphasize the urgent need for rigorous evaluation of e-cigarettes health effects to ensure evidence-based public health policies.

Background and Aim: The use of conventional cigarettes is a major and preventable health problem and the leading cause of preventable morbidity and mortality. Electronic cigarettes have been shown to yield plasma nicotine levels similar to that seen in traditional cigarette users. E-cigarettes have been touted as a healthier alternative to traditional cigarettes and as a smoking cessation tool with mixed results. The increasing use of e-cigarettes by youth is concerning with 27.5% of high school students and 10.5% of middle school students reporting using e-cigarettes in 2019. Use among young adults (18-24) is increasing with 7.6% reporting use in 2018. Toll-like receptors (TLRs) are key sensors in the activation of innate immunity. In addition to activating antiviral and pro-inflammatory responses, TLR3 in particular has been shown to behave as a death receptor, causing apoptosis in cancer cells. TLR3 expression is reduced in the airway epithelial cells of smokers, leading to a reduction in the downstream expression of type I interferons following viral infection. Methods: E-cigarette aerosol extracts were prepared from two brands of e-cigarettes, as previously described. Mainstream tobacco smoke extract was used as a positive control. Normal lung epithelial cells were exposed for 2 weeks to e-cigarette aerosol extracts at nicotine doses comparable to those observed in e-cigarette users. Whole-cell RNA was isolated. Gene expression was assessed by RNA-sequencing and validated by western blot. Results: Exposure of lung epithelial cells to e-cigarette aerosol extracts significantly decreased the mRNA expression levels of TLR3 (p<0.0001). A significant reduction (p<0.0001) in the mRNA expression of downstream innate immune system molecules including RIG1, IRF7 and interferons was also observed. The reduction in gene expression was similar to that observed from traditional cigarette smoke extracts. Conclusions: Our study suggests that exposure to e-cigarette aerosol can decrease the expression of key genes involved in innate immune response. TLR3 expression has been associated with good prognosis in early stage lung cancer. A decrease in TLR3 expression could allow tumors to evade immune surveillance and apoptosis Citation Format: Daniel Brobst, Jimmy Manyanga, Constantin Georgescu, Jonathan Wren, Lurdes Queimado. Exposure to E-cigarette aerosol reduces the expression of Toll-like receptor 3 in lung epithelial cells [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO033.

Background: Cigarette smoking is the leading preventable cause of mortality in the world and the main risk factor for lung and head and neck cancer. E-cigarettes (ECs) are battery-operated devices that deliver nicotine via inhaled aerosols. Although ECs are marketed as a less harmful alternative to tobacco cigarettes and a smoking cessation aid, the health risks posed by exposure to EC aerosols are unknown. Nonetheless, the use of ECs has increased exponentially since 2003, with EC users reporting inhaling on average 200 puffs a day. EC aerosols have been reported to contain variable levels of genotoxins, including carcinogenic substances and reactive oxygen species (ROS). Some toxins in EC aerosols have been reported to reach the levels of similar to those in tobacco smoke. However, the genotoxicity of EC aerosols has not been characterized. Aims: (1) To determine the cytotoxicity and genotoxicity of short and long-term exposure to EC aerosols on human epithelial normal and cancer cell lines. (2) To evaluate whether exposure of EC aerosols modifies the cellular total antioxidant capacity (TAC). Methods: EC extracts were prepared from NJOY (12 or 18 mg/ml of nicotine) and Oakley eGo-T (0, 12 or 18 mg/ml of nicotine). Standard tobacco extracts were used for comparison. To assess the effects of short-term exposure, human epithelial normal (NuLi-1) and cancer (UD-SCC1) cell lines were exposed for 1 hour to various EC extract concentrations. To assess the effects of long-term exposure, cells lines were exposed every other day for 2 weeks to EC extracts. Cytotoxicity, DNA damage and TAC were evaluated at 1 h and 2 weeks. Cell viability was determined by MTT assay. DNA damage was quantified using the primer anchored DNA damage detection assay (PADDA). TAC was determined by the Antioxidant Assay Kit (Cayman). Data were analyzed by Student's t-test. Results: At the range of EC extract concentrations used in this study and expected to occur in EC users (1 to 100 puffs/5 L of blood), no cytotoxicity was observed for either normal or cancer cells. However, significant levels of DNA damage were observed in cancer cells exposed to 10 or more puffs/5 L of EC extracts and in normal cells exposed to100 puffs/5 L. Long-term exposure to EC extracts resulted in a significant decrease in TAC, a measure of free radical scavengers. Conclusion: Even short-term exposure to low levels of EC aerosols can cause significant DNA damage. Our study emphasizes the need to further investigate the carcinogenic potential of EC aerosols and highlights the importance of regulating EC use. Grant support: This work was supported by the Oklahoma Tobacco Research Center (LQ). Dr. Queimado holds a Presbyterian Health Foundation Endowed Chair in Otorhinolaryngology. Citation Format: Vengatesh Ganapathy, Jimmy Manyanga, Lacy Brame, David Rubenstein, Theodore L. Wagener, Ilangovan Ramachandran, Lurdes Queimado. Electronic cigarettes induce significant DNA damage and reduce cellular antioxidant levels. [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 3593.