Induction of heme oxygenase-1 (HO-1) mRNA expression in different colon cancer cell lines by hemin and anticancer drug pirarubicin (THP) (a-c), and the affect of HO-1 on chemosensitivity of these cells to THP (d-f). (a) C26 cells were treated with 1 μM hemin (HO-1 inducer) or 0.01 μM of THP for 24 h followed by the RT-PCR assay of HO-1; data are presented as relative HO-1 expression compared to the HO-1 expression in control cells without hemin or THP treatment. Similar experiments were performed in HT29 cells (b) and DLD cells (c). (d) C26 cells were treated with different concentrations of THP in the presence/absence of hemin (1 μM) or HO inhibitor ZnPP (0.5 μM); cell viability after treatment was determined by MTT assay, and the data was described as the percent viability of cells under different treatments. Similar experiments were performed in HT29 cells (e) and DLD cells (f). Values are means ± SD; *P < 0.05, **P < 0.01 vs control group (one-way ANOVA followed by Bonferroni t-test). See text for details.