NS398, a selective COX-2 inhibitor, is known to inhibit the growth of COX-2 expressing hepatocellular carcinoma cells. The present study investigated whether the cytotoxic effect of NS398 was COX-2 dependent and whether caspases were involved in NS398-induced apoptosis in hepatocellular carcinoma cells.

The expressions of COX-2 in SNU 423 and SNU 449 hepatocellular carcinoma cell lines were examined using RT-PCR and Western blot. The cytotoxic effect of NS398 was measured using MTT in the presence or absence of caspase inhibitors. The distribution of the cell cycle and extent of apoptosis were analyzed using flow cytometry and a Cell Death Elisa kit, respectively.

The expression of COX-2 was observed in SNU423 cells, but not in SNU 449 cells. NS398 treatment resulted in both dose-and time-dependent growth inhibitions, with increases in apoptotic cells in both cell lines. Treatment with the pan-caspase inhibitor, z-VAD- fmk, or the caspase-3 inhibitor, Ac-DMQD-CHO, showed no attenuation of the cytotoxic effect of NS398 in either cell line.

This study demonstrated that the cytotoxic effect of NS398 was independent of COX-2 expression. Caspases were also shown not to be involved in NS398-induced apoptosis in either SNU 423 or SNU 449 Korean HCC cell lines. Our data suggests the feasibility of preventing hepatocellular carcinoma with the use of COX-2 inhibitors needs to be carefully evaluated.