UVA radiation augments cytotoxic activity of psoralens in melanoma cells

Abstract 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 μM) 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 μM (UVA dose: 1.3 J/cm2) and 105.3 μM (UVA dose: 2.6 J/cm2). 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 μM (UVA dose: 1.3 J/cm2) and 24.2 or 7.0 μM (UVA dose: 2.6 J/cm2), 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.