UVA radiation augments cytotoxic activity of psoralens in melanoma cells

Purpose: Melanoma is an aggressive form of skin cancer. The aim of the study was to evaluate the influence of UVA radiation and psoralens: 5-methoxypsoralen (5-MOP) or 8-methoxypsoralen (8-MOP) on melanoma cells viability.Materials and methods: The amelanotic C32 and melanotic COLO829 human melanoma cell lines were exposed to increasing concentrations of psoralens (0.1-100 M) in the presence or absence of UVA radiation. Cell viability was evaluated by the WST-1 assay.Results: We demonstrated that 8-MOP, in contrast to 5-MOP, has no cytotoxic effect on both melanoma cell lines. Simultaneous exposure of cells to 8-MOP and UVA radiation caused significant cytotoxic response in C32 cells where the EC50 value was estimated to be 131.0 M (UVA dose: 1.3 J/cm(2)) and 105.3 M (UVA dose: 2.6 J/cm(2)). The cytotoxicity of 5-MOP on both C32 and COLO829 cells was significantly augmented by UVA radiation - the EC50 was estimated to be 22.7 or 7.9 M (UVA dose: 1.3 J/cm(2)) and 24.2 or 7.0 M (UVA dose: 2.6 J/cm(2)), respectively.Conclusions: The demonstrated high cytotoxic response after simultaneous exposure of melanoma cells to psoralens and UVA radiation in vitro suggests the usefulness of PUVA therapy to treat melanoma in vivo.