Abstract B39: Estrogen and cytochrome P450 1B1 contribute to early-stage head and neck carcinogenesis

Squamous cell carcinoma of the head and neck (HNSCC) is the sixth most common type of cancer in the U.S. Major risk factors for HNSCC include tobacco and alcohol use. Data from this group and others suggest that estrogens may also contribute to the development of HNSCCs. We demonstrated previously that various cell lines derived from both premalignant (MSK-Leuk1) and HNSCCs express estrogen metabolism genes, including cytochrome P450 1B1 (CYP1B1) and estrogen receptor β (ERβ). CYP1B1 is the major enzyme that catalyzes the formation of carcinogenic metabolites of both 17β-estradiol (E₂) and constituents of tobacco smoke. The goal of the present study was to assess the impact of E₂ exposure on CYP1B1 expression and evaluate the role of E₂ and CYP1B1 in regulating motility, apoptosis and proliferation of epithelial cells of the head and neck. Cell lines established from a dysplastic leukoplakia of the oral cavity (MSK-Leuk1) and five human tongue SCCs were exposed to either vehicle (0.01% ethanol) or E₂ (1 nM) for 24 hours and the level of CYP1B1 transcripts was analyzed by quantitative real-time PCR. Exposure to E₂ induced CYP1B1 expression in MSK-Leuk1 cells (2.3-fold relative to vehicle-treated controls, P=0.0004) but not in HNSCC cells.

To further evaluate the contribution of CYP1B1 to early head and neck carcinogenesis, CYP1B1 was knocked down in MSK-Leuk1 cells by lentivirus encoded shRNA, and the effect of CYP1B1 depletion on cell motility, proliferation and apoptosis was analyzed. Cell motility was evaluated by monitoring the ability of vector and shRNA-expressing cells to close an evenly distributed gap in the cell monolayer over a 16-hour period. CYP1B1 knockdown inhibited the migration of MSK-Leuk1 cells by 57%. Proliferation and apoptosis were assessed in MSK-Leuk1 cells (expressing either vector or CYP1B1 shRNA) exposed to either vehicle or E₂ (1 nM) for 3 days. CYP1B1 knockdown inhibited the proliferation of MSK-Leuk1 cells by 45%, relative to vector expressing cells, as measured by total DNA content. E₂ inhibited apoptosis by 26%, as compared to vehicle-treated cells, as measured using a Nexin kit.

These data provide novel insight into the mechanisms underlying head and neck carcinogenesis and may facilitate the identification new targets for chemopreventive intervention.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):B39.