Zinc protoporphyrin IX enhances chemotherapeutic response of hepatoma cells to cisplatin

Figure 3 Targeted inhibition of heme oxygenase-1 activity by zinc protoporphyrin IX in liver cancer cell lines. Heme oxygenase (HO)-1 activity was measured by determining the level of bilirubin generated in isolated microsomes in cells treated with 10 μmol/L zinc protoporphyrin (ZnPP) IX, 10 μmol/L hemin, and/or 10 μg/mL cis-diaminedichloroplatinum (cisplatin; CDDP) for 24 h. ZnPP IX significantly inhibited HO-1 activity and decreased cis-diaminedichloroplatinum (cisplatin; CDDP)-induced HO-1 activity in all liver cancer cell lines compared with controls or cells treated with cisplatin alone (P < 0.05). In contrast, hemin increased CDDP-induced HO-1 activity in all liver cancer cell lines (P < 0.05).