Phenothiazine photosensitizers. III. Activity of methylene blue derivatives against pigmented melanoma cell lines.

The cytotoxicity and photocytotoxicity of methylene blue and several of its derivatives against two pigmented melanoma cell lines (SK-23 murine melanoma and SK-Mel 28 human melanoma) were investigated in culture. The derivatives were all more effective photosensitizers than methylene blue in both cell lines over a range of light doses (3.6-17.6 J cm(-2)). The increased activity correlated with increased cellular uptake and inherent photosensitizing efficacy. The photosensitizers also showed varying levels of interaction with the biopolymer melanin and although this appeared to affect uptake and activity, there was no direct correlation with toxicity.