(A) SK-Mel-5 cells were treated with 10 μM cobalt protoporphyrin IX (CoPP) and melanosphere formation was assessed. Error bars represent the SEM of four biological replicates of each melanosphere assay. (B) Following the melanosphere assay, all cells from each well were collected independently, melanospheres were dissociated by incubating with TrypLE and the cells were counted. Error bars represent the SEM of four biological replicates. (C) SK-Mel-5 cells were grown in adherent conditions and treated with 10 μM CoPP overnight. HMOX1 protein levels were assessed by immunoblot analysis and band intensity measured and normalized to tubulin. Error bars represent the SEM of three biological replicates. (D) SK-Mel-5 cells were treated with 10 μM tin protoporphyrin IX dichloride (SnPP) every 48 hours and melanosphere formation assessed over a 10-day melanosphere assay. Error bars represent the SEM of four biological replicates. (E) HMOX1 protein levels in SK-Mel-5 cells grown in adherent conditions and treated with 10 μM SnPP overnight were assessed by immunoblot analysis and band intensity measured and normalized to tubulin. Error bars represent the SEM of three biological replicates for immunoblot analysis and all statistical significance was determined using the standard Student’s t-test. *P < 0.05, **P < 0.01, ***P < 0.001, NS is not significant.