Proapoptotic and antiproliferative potential of selective cyclooxygenase-2 inhibitors in human liver tumor cells

Abstract

Recent studies have shown increased levels of cyclooxygenase‐2 (COX‐2) in a variety of human malignancies, including hepatocellular carcinoma (HCC), but so far it is unknown whether COX‐2 contributes to the malignant growth and whether inhibition of COX‐2 function modifies the malignant potential of liver tumors. COX‐1 and COX‐2 expression was determined in 4 liver tumor cell lines (Hep 3B, HuH‐7, Hep G2, Sk‐hep1) by Northern hybridization and Western immunoblot. The functional effects of the nonselective inhibitor sulindac sulfide and the COX‐2 selective inhibitors SC‐58635 and meloxicam were examined by 3(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazoliumbromide (MTT)‐assays and BrdU uptake, morphology, and TUNEL analysis of apoptosis. Apoptosis regulating proteins were analyzed by Western immunoblot. COX‐1 and COX‐2 expression was demonstrable in all tested liver tumor cell lines. Sulindac sulfide (50 to 400 μmol/L), SC‐58635 (6,25 to 400 μmol/L), and meloxicam (6.25 to 400 μmol/L) led to a significant time‐ and dose‐dependent reduction of cell numbers of up to 80% (P < .05). At equimolar concentrations the effect was more pronounced when COX‐2 was selectively blocked. COX‐2 inhibition induced apoptosis and reduced tumor cell proliferation. Apoptosis after COX‐2 inhibition with SC‐58635 (50 μmol/L) was independent of BCL‐2, BAX, and the phosphorylation status of AKT/PKB and BAD, but correlated with activation of caspase‐9, caspase‐3, and caspase‐6. In conclusion, selective inhibition of COX‐2 leads to a marked growth inhibition of human liver tumor cells, based on the induction of apoptosis and inhibition of proliferation and, thus, may offer therapeutic and preventive potential in human hepatocarcinogenesis.