OBJECTIVETo determine the sensitivity of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induced apoptosis in Hep-2 cells by means of systematically evaluating the cytotoxicity of TRAIL alone and TRAIL in combination with chemotherapeutic agents (cisplatin, paclitaxel) or radiation in Hep-2 cells in vitro, and whether the synergistic killing effects correlated with the expression level of TRAIL receptors and the activity of caspase-8 or caspase-9.

METHODSThe cytotoxicities of TRAIL, cisplatin and paclitaxel were investigated by cell counting kit-8 (CCK-8) assay. The expression levels of four TRAIL receptors in Hep-2 cells after treated by TRAIL, chemotherapeutic agents or radiation alone and by combined treatments were measured by flow cytometry and Western blotting respectively. The growth inhibition effects of caspase-8 or caspase-9 inhibitor on Hep-2 cells were determined by CCK-8 assay, and the activities of caspase-8, caspase-9 and caspase-3 were measured by Western blotting.

RESULTSThe half maximal inhibitory concentration (IC50) of TRAIL to Hep-2 cells on 24 h was 596.92 microg/L. Cisplatin, paclitaxel and radiation had synergistic inhibitory effects with TRAIL on the growth of Hep-2 cell line. After the activity of caspase-9 was inhibited by Z-LETD-FMK, the inhibition effects of TRAIL, cisplatin and paclitaxel on Hep-2 cells decreased significantly (all P<0.05). The expressions of caspase-8, caspase-9 and the death receptors (DR4 and DR5) increased significantly (all P<0.05) after combined administration.

CONCLUSIONSHep-2 cells are resistant to the apoptosis induced by TRAIL and TRAIL can induce the apoptosis of Hep-2 cells through the endogenous apoptotic pathway. The increase of death receptors expression by chemotherapeutic agents or radiation could enhance the sensitivity of Hep-2 cells to TRAIL and the synergistic killing effects.