Zinc protoporphyrin IX enhances chemotherapeutic response of hepatoma cells to cisplatin

AIM:To investigate the effect of zinc protoporphyrin IX on the response of hepatoma cells to cisplatin and the possible mechanism involved.METHODS:Cytotoxicity was determined using the3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.Apoptosis was determined by a flow cytometric assay.Western blotting was used to measure protein expression.Heme oxygenase(HO)-1 activity was measured by determining the level of bilirubin generated in isolated microsomes.Reactive oxygen species(ROS)production was monitored by flow cytometry.Caspase-3 activity was measured with a colorimetric assay kit.Mice were inoculated with 1×107 tumor cells subcutaneously into the right flanks.All mice were sacrificed 6 wk after the first treatment and tumors were weighed and measured.RESULTS:Overexpression of HO-1 in HepG2 cell line was associated with increased chemoresistance to cisdiaminedichloroplatinum(cisplatin;CDDP)compared to other cell lines in vitro.Inhibition of HO-1 expression or activity by zinc protoporphyrin IX(ZnPP IX)markedly augmented CDDP-mediated cytotoxicity towards all liver cancer cell lines in vitro and in vivo.In contrast,induction of HO-1 with hemin increased resistance of tumor cells to CDDP-mediated cytotoxicity in vitro and in vivo.Furthermore,cells treated with ZnPP IX plus CDDP exhibited marked production of intracellular ROS and caspase-3 activity,which paralleled the incidence of cell apoptosis,whereas hemin decreased cellular ROS and caspase-3 activity induced by CDDP.CONCLUSION:ZnPP IX increases cellular sensitivity and susceptibility of liver cancer cell lines to CDDP and this may represent a mechanism of increasing ROS.