Induction of apoptosis and cell cycle arrest by NS398 in oral squamous cell carcinoma cells via downregulation of E2 promoter-binding factor-1.

Overexpression of cyclooxygenase-2 (COX-2) plays an important role in development and progression of different human cancers, but the underlying molecular mechanisms remain to be defined. Tissue specimens of normal oral epithelia (n=9), dysplasia (n=38), and oral squamous cell carcinoma (SCC, n=54) were immunohistochemically analyzed for COX-2 and E2F-1 expression. A human oral SCC cell line, Tca8113, was used to assess NS398 antitumor activity. PGE2 levels were measured by using radioimmunoassay, and COX-2, pRb, and E2F-1 proteins were determined by Western blot assay. We found expression of COX-2 and E2F-1 proteins was significantly increased in both oral dysplasia and SCC compared to the normal epithelium. Increased COX-2 expression was associated with E2F-1 expression in both oral dysplasia and SCC. NS398 treatment reduced viability of Tca8113 cells in a dose- and time-dependent manner. NS398 suppressed PGE2 levels, a product of COX-2 enzyme, in the tumor cells. The reduced cell viability is due to induction of apoptosis by NS398, which activates caspase-3, but does not inhibit bcl-2. NS398 also induced tumor cell arrest at G1 phase of the cell cycle and inhibited expression of COX-2, pRb and E2F-1 proteins. This study provides evidence that E2F-1 and COX-2 are overexpressed in oral cancer, and further supports suppression of COX-2 in control of oral cancer.