One in four Americans, 40.6% of whom are children, are involuntarily exposed to secondhand smoke (SHS). Yet, the impact of SHS exposure on cancer treatment is unknown. A recent study has shown that exposure to SHS during head and neck squamous cell carcinoma (HNSCC) therapy is a significant independent predicator of HNSCC recurrence. Our study examines the effect of SHS smoke exposure on HNSCC cisplatin treatment and investigates the potential mechanisms leading to the observed effects.
METHODS: Sidestream smoke (SS), the main component of SHS, was extracted as previously described. Three different human HNSCC cell lines (UM-SCC1, WSU-HN6, and WSU-HN30) were exposed to SS extract for 48 hours at doses mimicking the nicotine levels observed in the saliva of passive smokers. Then, cancer cells were treated with cisplatin (0.1-100 µM) in the presence of SS extract. Cancer cell death and indefinite survival capacity were assessed with trypan blue staining and clonogenic survival assay, respectively. The cisplatin half-maximal inhibitory concentration (IC50) was determined for each cell line using GraphPad Prism software. The expression of ABCG2, a drug transporter associated with cisplatin resistance, was quantified using qPCR and Western blot analysis. Linear regression analysis was performed to evaluate the overall effect after adjusting data from all three cell lines.
RESULTS: Exposure to SS extract significantly decreased cell death (P<0.0001) and increased clonogenic survival capacity (P<0.017) in the cancer cells treated with cisplatin in the presence of SS extract, compared to cisplatin treated but unexposed HNSCC cells. Cisplatin sigmoidal dose-response curves indicate that cancer cells exposed to SS extract significantly increased their cisplatin resistance when compared to respective control cells: UM-SCC1 (p<0.0001), WSU-HN6 (p<0.0035), and WSU-HN30 (p<0.0001). The observed data indicate that in the presence of SS extract, cancer cells required a minimum of 1.5 to 2-fold increase in cisplatin concentration to reach IC50 in all three HNSCC cells. Compared to control, cells treated with SS extract, showed a significant increase in both mRNA and protein expression of ABCG2: UM-SCC1 (p<0.0001), WSU-HN6 (p<0.031), and WSU-HN30 (p<0.003). The linear regression analysis strengthens the observed overall increase in ABCG2 expression (p<0.0001). Our data suggest there is an active cisplatin efflux mechanism in the SS-treated cells.
CONCLUSIONS: Overall, our study documents for the first time that even short-term exposure to SHS can lead to cisplatin resistance in head and neck cancer cells by altering the expression of multidrug resistance and ability to evade cisplatin-induced cell death. Further studies in HNSCC patients-based observation are warranted. Our data stresses the urgent need for clinicians to consider the potential role of SHS exposure on treatment outcome and to advise cancer patients or caregivers of adults and children with cancer about the potential risks of SHS exposure during cancer treatment.
Funding: This work was partially supported by National Cancer Institute of the National Institutes of Health (R33CA202898, R01CA242168 and P30CA225520), the TSET Health Promotion Cancer Center, and the Oklahoma Center for Advancement of Science and Technology (HR16-007). Dr. Queimado holds a Presbyterian Health Foundation Endowed Chair in Otorhinolaryngology Position.