Fig 1: The effect of KD87 on the expression of HO-1 and HO-2 at the mRNA (A,B) and protein (C,D) level and influence of the HO-1 inhibitor SnPPIX (E,F) or its non-HO-1-inhibiting analogue CuPPIX (G,H) on the KD87-mediated decrease in metabolic activity of A375 and A431 cells. Cells were incubated with KD87 at the indicated concentrations (A–D) concentrations or at 6 µM (E–H) for 24 h (A–D,F,H) or 48 h (E,G). In the inhibitor experiments (E–H), cells were pre-treated with SnPPIX (25 µM), CuPPIX (25 µM) or vehicle for 1 h, followed by a 24 h or 48 h co-incubation with KD87 or vehicle. The values given in the bar charts are based on quantitative RT-PCR (A,B), the densitometric analyses of blots (C,D) or WST-1 assay experiments (E–H). HO mRNA levels (A,B) were normalised to PPIA mRNA levels and HO protein levels (C,D) to β-actin. All percentage values shown refer to the respective vehicle control, which was set to 100%. The blots shown are representative. The mRNA and protein data are mean values ± SEM of n = 4 (A,B), n = 8 (C (HO-1)), n = 6 (C (HO-2)), n = 6 (D (HO-1)) or n = 5 (D (HO-2)) independent experiments. Metabolic activity data are mean values ± SEM of n = 20 (E) or n = 18–20 (F) per group from 5 independent experiments each, and n = 8–9 (G) or n = 9 (H) per group from 3 independent experiments each. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, **** p ≤ 0.0001 vs. corresponding vehicle control; ## p ≤ 0.01, ### p ≤ 0.001 vs. corresponding KD87-treated group; one-way ANOVA with Dunnett’s (A–D) or Bonferroni’s (E–H) post hoc test.