Rapamycin and CCI-779 inhibit the mammalian target of rapamycin signalling in hepatocellular carcinoma

Authors

  • Ivan Chun-Fai Hui,

    1. Liver Cancer and Hepatitis Research Laboratory and S. H. Ho Foundation Research Laboratories, Department of Pathology, LKS Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong, China
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  • Edmund Kwok-Kwan Tung,

    1. Liver Cancer and Hepatitis Research Laboratory and S. H. Ho Foundation Research Laboratories, Department of Pathology, LKS Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong, China
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  • Karen Man-Fong Sze,

    1. Liver Cancer and Hepatitis Research Laboratory and S. H. Ho Foundation Research Laboratories, Department of Pathology, LKS Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong, China
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  • Yick-Pang Ching,

    1. Liver Cancer and Hepatitis Research Laboratory and S. H. Ho Foundation Research Laboratories, Department of Pathology, LKS Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong, China
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  • Irene Oi-Lin Ng

    1. Liver Cancer and Hepatitis Research Laboratory and S. H. Ho Foundation Research Laboratories, Department of Pathology, LKS Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong, China
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Correspondence
Prof. Irene O. L. Ng, Room 127B, University Pathology Building, Department of Pathology, The University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong, China
Tel: +852 2855 3967
Fax: +852 2872 5197
e-mail: iolng@hkucc.hku.hk

Abstract

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.

Aims: 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 IC50 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 G1 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.

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