Celecoxib suppresses the HCC development via the cell cycle arrest

Abstract

Liver cancer is the second leading cause of death in males in Hong Kong and the incidence rate of 36 per 100,000 is the second highest in the world. Previous studies have shown increased levels of cyclooxygenase-2 (COX-2) in a variety of human malignancies including hepatocellular carcinoma (HCC), suggesting that abnormal COX-2 expression plays an important role in carcinogenesis. In addition, some evidence suggests that selective COX-2 inhibitors suppress the formation of tumors in experimental models. However, there is no data in the literature on using COX-2 as an inhibitor in HCC. Hence, we performed in vivo studies to investigate the chemopreventive and therapeutic effects of Celecoxib, a selective COX-2 inhibitor, on the development and growth of HCC xenograft in nude mice. To investigate the chemopreventive effect of Celecoxib, the drug was administered at day 0 by post tumor cell injection, while the control group was given vehicle only. To investigate the therapeutic effect of celecoxib on established tumor, the drug was administered at the 100 mm3 while in the control group only vehicle was given. Celecoxib was administered orally at a dose of 250-mg/kg body weight/day. Our results showed that Celecoxib could prolong the latent period (p<0.001) of HCC xenograft development in nude mice and decreased the growth of established HCC xenograft in nude mice significantly (p=0.03). However, there was no significant decrease in MVD and apoptotic index in treatment groups compared with the control groups. In in vitro studies, we have confirmed that the Celecoxib cannot induce apoptosis significantly in PLC and Hep3B HCC cell lines in the concentration of IC50. But Celecoxib at IC50 can significantly induce apoptosis in HUVEC cell line. Interestingly, the Celecoxib can induce G1 arrest in both HCC cell lines but not induce cell cycle arrest in HUVEC cell line. We have found that the cyclin D1 decreased as the concentration of Celecoxib increased. With these evidences, it suggests that the Celecoxib drug is acting on the cell cycle pathway rather than on the apoptotic pathway in HCC cells. Furthermore, our cDNA microarray data suggests that the Celecoxib is also acting on a coagulation pathway beside the cell cycle pathway. We have found that the fibrinogen fragments A & B, kininogen, etc are downregulated as treated with Celecoxib. In conclusion, our data suggest that the selective COX-2 inhibitor, Celecoxib, can delay the development of HCC and suppress the growth of established HCC in experimental animals most likely via the growth arrest pathway. COX-2 inhibition appears to be a promising strategy for chemoprevention and treatment of HCC which deserves further investigation and clinical trial.