Zinc protoporphyrin IX enhances chemotherapeutic response of hepatoma cells to cisplatin

Figure 4 Inhibition of heme oxygenase-1 activity led to increased susceptibility to chemotherapy in vitro. Cell viability was assessed via MTT assay. zinc protoporphyrin (ZnPP) IX (10 μmol/L) significantly increased apoptosis in cis-diaminedichloroplatinum (cisplatin; CDDP)-treated cells, compared with those treated with CDDP alone (A) (P < 0.05). In contrast, hemin decreased apoptosis induced by CDDP in all liver cancer cell lines. FACS analysis with propidium iodide staining also showed that downregulation of heme oxygenase (HO)-1 by ZnPP IX increased apoptosis after exposure to CDDP in comparison with the control group (P < 0.05), whereas increased expression of HO-1 by hemin resulted in decreased sensitivity to CDDP (B).