Rapamycin and CCI-779 suppress the growth of hepatocellular carcinoma cells

Abstract

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide and in Hong Kong, with a high mortality rate. The mammalian target of rapamycin (mTOR), which is upregulated in a number of cancers, phosphorylates p70S6K and 4EBP1 and activates the protein translation process. Since mTOR activation is suggested to be involved in cancer development, the use of mTOR inhibitors rapamycin and its new analog CCI-779 to block the pathway would be a promising way to suppress HCC cell growth.

In this study, we investigated the tumor suppressive effects of rapamycin and CCI-779 on HCC. To examine the mRNA expression level of mTOR in HCC, we performed real-time RT-PCR. Significant overexpression of mTOR transcripts (68%, 37/55) was observed in our human HCC clinical samples. Furthermore, Western blot analysis demonstrated that the level of phospho-p70S6K in HCC cell lines was reduced upon rapamycin and CCI-779 treatment, suggesting that both drugs can suppress mTOR activity in HCC cells. To find out the effects of the drugs on the proliferation of HCC cell lines, colony formation assay with drug treatment was performed. The HCC cell line, PLC, showed the most obvious reduction in cell proliferation when compared with the other hepatoma cell lines HepG2, Hep3B, HLE and MHCC97H. In all these cell lines, rapamycin was a more potent anti-proliferative agent than CCI-779, except BEL7402 and SMMC-7721, both of which showed no significant difference in the cell proliferation rate upon treatment with these two drugs. Proliferation assays by cell counting revealed that the IC50 of rapamycin was lower than that of CCI-779 in PLC cells, and flow cytometric analysis showed that both drugs did not induce apoptosis of these cells. In addition, our preliminary results on animal models suggested that both drugs could inhibit the growth of xenografts of PLC cells in vivo. Taken together, our findings indicate that rapamycin and its clinical analog possess tumor suppressive functions towards HCC.