Rapamycin and CCI-779 inhibit the mammalian target of rapamycin signalling in hepatocellular carcinoma.
BACKGROUND
The mammalian target of rapamycin (mTOR), which phosphorylates p70S6K and 4EBP1 and activates the protein translation process, is upregulated in cancers and its activation may be involved in cancer development.


OBJECTIVE
In this study, we investigated the tumour-suppressive effects of rapamycin and its new analogue CCI-779 on hepatocellular carcinoma (HCC).


METHODS
Rapamycin and its new analogue CCI-779 were applied to treat HCC cells. Cell proliferation, cell cycle profile and tumorigenicity were analysed.


RESULTS
In human HCCs, we observed frequent (67%, 37/55) overexpression of mTOR transcripts using real-time reverse transcriptase-polymerase chain reaction. Upon drug treatment, PLC/PRF/5 showed the greatest reduction in cell proliferation using the colony formation assay, as compared with HepG2, Hep3B and HLE. Rapamycin was a more potent antiproliferative agent than CCI-779 in HCC cell lines. Proliferation assays by cell counting showed that the IC(50) value of rapamycin was lower than that of CCI-779 in PLC/PRF/5 cells. Furthermore, flow cytometric analysis showed that both drugs could arrest HCC cells in the G(1) phase but did not induce apoptosis of these cells, suggesting that these mTOR inhibitors are cytostatic rather than cytotoxic. Upon rapamycin and CCI-779 treatment, the phosphorylation level of mTOR and p70S6K in HCC cell lines was significantly reduced, indicating that both drugs can suppress mTOR activity in HCC cells. In addition, both drugs significantly inhibited the growth of xenografts of PLC/PRF/5 cells in nude mice.


CONCLUSIONS
Our findings indicate that rapamycin and its clinical analogue CCI-779 possess tumour-suppressive functions towards HCC cells.
Liver Cancer and Hepatitis Research Laboratory, Department of Pathology, LKS Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong, China.
Ivan Chun-Fai
IC
Hui
Edmund Kwok-Kwan
EK
Tung
Karen Man-Fong
KM
Sze
Yick-Pang
YP
Ching
Irene Oi-Lin
IO
Ng
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002452:Cell Count; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D005260:Female; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000187:drug effects* / Q000378:metabolism; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000187:drug effects* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases
D000903:Antibiotics, Antineoplastic; D047908:Intracellular Signaling Peptides and Proteins; C401859:temsirolimus; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus