mTOR inhibitor sensitizes chemo-cytotoxicity for hepatocellular carcinoma

Objective: Chemo-resistance is a major concern in the treatment of hepatocellular carcinoma (HCC). Several studies have demonstrated that inhibition of mammalian target of rapamycin (mTOR), a downstream target of Akt, sensitizes cancer cells to chemotherapeutic agents. As the mechanism of this sensitization, especially its relationship with p53 expression remains largely unclear; we design the present study to investigate if RAD001, a mTOR inhibitor, could enhance the chemo-cytotoxicity for HCC in cell lines with different characteristics of p53. Methods: HCC cell lines with wild type (wt) p53 (HEPG2) and mutant/null p53 (PLC/HEP3B) expression were treated with RAD001 (mTOR inhibitor) alone, cisplatin alone or combination of RAD001 and cisplatin. Cell proliferation and viability were determined by MTT assay. Apoptosis was determined by Annexin V/propidium iodide staining and analyzed by flow cytometry. Results: RAD001 suppressed tumor cell proliferation in both wt and mutant/null p53 HCC cell lines. The effect of mTOR inhibition was confirmed by the dephosphorylation of 4E-BP1 and S6K1. RAD001 enhanced cisplatin induced apoptosis in both HCC cell lines with wt and mutant/null p53 expression. mTOR inhibition in combined with cisplatin up-regulated pro-apoptotic molecules and down-regulated survival molecules. Conclusion: We have shown that inhibition of mTOR enhances cisplatin induced chemo-cytotoxicity for HCC in a p53 independent manner. These results suggest that the use of mTOR inhibitors in combination with conventional chemo-therapeutic agents may offer broad clinical benefits to HCC patients