Cytotoxic and DNA-binding properties of two ruthenium(II) porphyrin complexes

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.

In vitro evaluation of ruthenium complexes for photodynamic therapy

BACKGROUND

Photodynamic therapy (PDT) is a promising anti-tumor treatment strategy. Photosensitizer is one of the most important components of PDT. In this work, the anticancer activities of PDT mediated by six new ruthenium porphyrin complexes were screened. The mechanisms of the most efficacious candidate were investigated.

METHODS

Photocytotoxicity of the six porphyrins was tested. The most promising complex, Rup-03, was further investigated using Geimsa staining, which indirectly detects reactive oxygen species (ROS) and subcellular localization. Mitochondrial membrane potential (MMP), cell apoptosis, DNA fragmentation, c-Myc gene expression, and telomerase activities were also assayed.

RESULTS

Rup-03 and Rup-04 had the lowest IC₅₀ values. Rup-03 had an IC₅₀ value of 29.5±2.3μM in HepG2 cells and 59.0±6.1μM in RAW264.7 cells, while Rup-04 had an IC₅₀ value of 40.0±3.8μM in SGC-7901 cells. The complexes also induced cellular morphological changes and impaired cellular ability to scavenge ROS, and accumulated preferentially in mitochondria and endoplasmic reticulum. Rup-03 reduced MMP levels, induced apoptosis, and repressed both c-Myc mRNA expression and telomerase activity in HepG2 cells.

CONCLUSIONS

Among six candidates, Rup-03-mediated PDT is most effective against HepG2 and RAW264.7, with a similar efficacy as that of Rup-04-mediated PDT against SGC-7901 cells. Repression of ROS scavenging activities and c-Myc expression, which mediated DNA damage-induced cell apoptosis and repression of telomerase activity, respectively, were found to be involved in the anticancer mechanisms of Rup-03.