Mechanism of growth inhibitory effects of cyclooxygenase-2 inhibitor-NS398 on cancer cells

Cyclooxygenase (COX)-2 appears to play an important role in gastrointestinal carcinogenesis, and COX-2 overexpression has been demonstrated both in esophageal adenocarcinomas and lymph nodes metastasis. The aim of our study was to investigate the mechanism of growth inhibitory effect of selective inhibition of COX-2 by NS-398 on human cancer cells. The esophageal cancer cell lines (EC9706) that express COX-2 permanently and hepatocellular carcinoma cell lines (SMMC7721) while no expression of COX-2 were studied. Two kinds of cell lines were treated with various concentrations of NS-398 (selective for COX-2 inhibition) at 0.01-0.1 mM for 24 h, 48 h and 72 h. Antiproliferation effect was measured by H-3-TdR incorporation. The cell apoptosis were determined by flow cytometry (FCM) and DNA fragmentation analysis. Survivin was detected by immunocytochemical technique. The growth inhibition could be induced by NS398 in a dose- and time-dependent manner in two kinds of cell lines. FCM analysis revealed a high sub-G(1) cell peak in EC9706 group. Agarose electrophroesis showed marked apoptosis ladder pattern, but no apoptosis by NS-398 in SMMC7721. The difference of apoptosis percentage in EC9706 and SMMC7721 was (45.23 +/- 1.08)% and (3.05 +/- 0.15)% (p < 0.001). After 24 h incubation with NS-398 at concentration of 0.1 dmM, the expression of survivin was markedly reduced in EC9706, but not in SMMC7721. We conclude that the administration of a selective inhibitor of COX-2 significantly decreases cell growth in cancer cell lines by different mechanism. NS-398 could inhibit cell proliferation in cancer cells whether or no COX-2 expression. Nevertheless, apoptosis in the cancer cells expressing COX-2 protein increase more than those lacking COX-2.