Rapamycin inhibits cell growth by induction of apoptosis on hepatocellular carcinoma cells in vitro

Background: Rapamycin, isolated from Streptomyces hygroscopicus, is recently reported to have immunosuppressant and anti-tumor effects on a large variety of cancers. To date, no detailed data are available about the effects of rapamycin on hepatocellular carcinoma cells. Objective: In this study, the anti-proliferation effects of rapamycin on hepatocellular carcinoma cells BEL-7402 and HepG-2 in vitro were studied. Methods: Cell viability was assessed by MTT assay and [H-3]-thymidine uptake, cell apoptosis was observed by Hoechst 33258 staining and flow cytometry (FCM). The variation of caspase-3 and apoptotic related genes was assayed by Western blotting, cell mitochondrial membrane potential was also investigated by using standard methods. Results: Rapamycin could inhibit the growth of hepatocellular carcinoma cells and cause apoptosis significantly; the suppression was both in time- and dose-dependent manner, marked morphological changes of cell apoptosis were observed very clearly by Hoechst 33258 staining. Rapamycin exhibits induction apoptosis by activation of caspase-3 and disruption of the mitochondrial membrane potential on hepatocellular carcinoma cells in vitro. Western blotting analysis demonstrated that anti-apoptotic protein Bcl-2 was down-regulated while pro-apoptotic protein Bcl-x1 up-regulated remarkably in a time-dependent manner when apoptosis occurred. Conclusion: Rapamycin has significant anti-proliferation effect by induction of apoptosis via activation of caspase-3 and disruption of mitochondrial membrane potential, as well as by down-regulation of anti-apoptotic protein Bcl-2 and up-regulation of pro-apoptotic protein Bcl-x1 on hepatocellular carcinoma cells. The data provide a potential mechanism for rapamycin-induced apoptosis in hepatocellular carcinoma cells, suggesting that rapamycin may serve as both an effective adjunctive reagent for the treatment of residual cancer cells and immunosuppressant after liver transplantation of hepatocellular carcinoma, and that in vivo anti-cancer effects as well as its potential clinical effectiveness need further investigation. (C) 2007 Elsevier B.V. All rights reserved.