Activity of the mTOR inhibitor RAD001, the dual mTOR and PI3-kinase inhibitor BEZ235 and the PI3-kinase inhibitor BKM120 in hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is one of the most deadly cancers worldwide with only few therapeutic options for patients with advanced disease. There is growing evidence indicating that activation of the PI3K/Akt/mTOR pathway plays an important role in HCC and therefore represents a promising target for novel therapeutic approaches. The aim of this study was to evaluate and compare the antitumour activity of the mTOR inhibitor RAD001, the dual mTOR and PI3-kinase inhibitor BEZ235 and the PI3-kinase inhibitor BKM120 in vitro and in vivo. EXPERIMENTAL DESIGN: The antitumour effects of RAD001, BEZ235 and BKM120 were analysed in seven hepatoma cell lines as mono and combination therapy with Doxorubicin, Cisplatin, Irinotecan or 5-Flourouracil in vitro and in xenografts. Cell-cycle progression, apoptosis, and autophagy were analysed. Furthermore, effects on mitochondrial respiration and glycolysis were assessed. RESULTS: Treatment with RAD001, BEZ235 and BKM120 markedly reduced tumour cell viability. Combination of PI3K inhibitors with chemotherapy was most effective. RAD001, BEZ235 and BKM120 reduced tumour growth mainly by inhibiting cell-cycle progression rather than by inducing apoptosis. Interestingly, the antitumour effects were strongly associated with a reduction of mitochondrial respiration. BKM120, which exhibited the strongest antiproliferative effect, most strongly impaired oxidative phosphorylation compared with the other drugs. CONCLUSIONS: In this study, BKM120 showed the strongest antitumour activity. Our findings suggest impairment of mitochondrial function as a relevant mechanism of BKM120. Moreover, combination of PI3K and mTOR inhibitors with cytotoxic agents could be promising option for non-cirrhotic HCC patients.

Rapamycin delays tumor development in murine livers by inhibiting proliferation of hepatocytes with DNA damage.

UNLABELLED: In this study, everolimus (RAD001) was used to determine the role of mammalian target of rapamycin (mTOR) in hepatocarcinogenesis. We show that RAD001 effectively inhibits proliferation of hepatocytes during chronic liver injury. Remarkably, the ability of RAD001 to impair cell cycle progression requires activation of the DNA damage response; loss of p53 significantly attenuates the antiproliferative effects of mTOR inhibition. RAD001 modulates the expression of specific cell cycle-related proteins and the assembly of cyclin-cyclin-dependent kinase complexes to prevent cell cycle progression. Furthermore, RAD001 sustains the apoptosis sensitivity of hepatocytes during chronic liver injury by inhibiting p53-induced p21 expression. Long-term treatment with RAD001 markedly delays DNA damage-induced liver tumor development. CONCLUSION: We provide evidence that mTOR inhibition has a substantial effect on sequential carcinogenesis and may offer an effective strategy to delay liver tumor development in patients at risk.