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 melano ma and SK-Mel 28 human melanoma) were investigated in culture. The derivati ves were all more effective photosensitizers than methylene blue in both ce ll lines over a range of light doses (3.6-17.6 J cm(-2)). The increased act ivity correlated with increased cellular uptake and inherent photosensitizi ng efficacy. The photosensitizers also showed varying level of interaction with the biopolymer melanin and although this appeared to affect uptake and activity, there was no direct correlation with toxicity.