Cigarette Smoke Containing Acrolein Upregulates EGFR Signaling Contributing to Oral Tumorigenesis In Vitro and In Vivo

SIMPLE SUMMARY: Oral squamous cell carcinoma (OSCC) is one of the most common smoking-related cancer types in the world. Better understanding of the pathophysiology of OSCC would lead to the development of novel therapeutic options. The epidermal growth factor receptor (EGFR) pathway plays a crucial role in the development of OSCC, and aberrant EGFR expression levels have been associated with smoking. Cigarette smoke contains large amounts of aldehydes such as acrolein, which is a highly reactive environmental toxin. In this study, our results present that acrolein is important in oncogenic transformation through activating the EGFR signaling pathway, contributing to oral carcinogenesis. To the best of our knowledge, this is the first study to provide molecular evidence, showing that cigarette smoke containing acrolein contributes to EGFR amplification and activation of downstream signaling in OSCC. Thus, acrolein might be a novel target for early detection and prevention of oral cancer in the future. ABSTRACT: Oral squamous cell carcinoma (OSCC) accounts for 80–90% of all intraoral malignant neoplasms. The single greatest risk factor for oral cancer is tobacco use, including cigarettes, cigars, chewing tobacco, and snuff. Aberrations of the epidermal growth factor receptor (EGFR) pathway features prominently in oral tumorigenesis and progression. It was shown that cigarette smoking (CS) is associated with worse prognosis in OSCC patients and overexpression of EGFR in tumor tissue. However, the mechanism by which cigarette smoking induced EGFR pathway activation remains to be fully elucidated. Acrolein, an IARC group 2A carcinogen, is a highly reactive aldehyde found in CS. Here we report that acrolein is capable of inducing tumorigenic transformation in normal human oral keratinocytes (NOK). The acrolein-transformed NOK cells showed EGFR copy number amplification, increased EGFR expression, and activation of downstream ERK and AKT signaling pathway. No p53 mutations were observed in acrolein-transformed NOK cells. Inhibiting EGFR pathway using an anti-EGFR antibody, cetuximab, inhibits tumor growth. Furthermore, by examining tissue sample from patients, we found an increased EGFR copy number was positively associated with acrolein-induced DNA damages in OSCC patients. Taken together, our results indicate that acrolein is important in tumorigenic transformation through amplification of EGFR and activating the downstream signaling pathway, contributing to oral carcinogenesis. This is the first study to provide molecular evidence showing that CS containing acrolein contributes to EGFR amplification in OSCC.