DNA photocleavage and melanoma cells cytotoxicity induced by a meso-tetra-ruthenated porphyrin under visible light irradiation.

Porphyrins are used as photosensitizing agents in photodynamic therapy (PDT) for several pathologies. Here we demonstrate the DNA photocleavage and cytotoxicity properties of a free-base meso-tetra-ruthenated porphyrin (H2RuTPyP) in purified DNA samples and in a melanoma cell line, respectively. Cytotoxicity of H2RuTPyP was investigated by the tetrazolium dye (MTT) colorimetric assay and its genotoxic potential by direct plasmid DNA photocleavage after incubation with specific DNA repair enzymes. H2RuTPyP porphyrin efficiently induced DNA damage at the lower concentration of 5.0 µM, whereas it induced complete DNA degradation at 15 µM. The addition of different scavengers for reactive oxygen species (ROS) during the visible light exposures did not decrease the DNA damage formation, suggesting a hydrolytic mechanism for the induction of DNA breaks. Also, H2RuTPyP exhibited a much higher cytotoxicity in melanoma cells in comparison to a keratinocyte cell line. The detection of intracellular reactive oxygen species (ROS) produced by H2RuTPyP through the DCF-DA assay also suggests that ROS have a minor role in the induction of cytotoxicity. Therefore, H2RuTPyP seems to be a very effective photosensitizer, representing a promising alternative for the development of new skin cancer treatments using PDT process.