In vitro toxicity testing of zinc tetrasulfophthalocyanines in fibroblast and keratinocyte cells for the treatment of melanoma cancer by photodynamic therapy

A series of water-soluble tetrasulfonated metallophthalocyanines (MPcs) dyes have been studied to be used as a drug or photosensitizer (PS) in photodynamic therapy (PDT) for the treatment of cancers. During PDT the PS is administrated intravenously or topically to the patient before laser light at an appropriate wavelength is applied to the cancerous area to activate the PS. The activated PS will react with oxygen typically present in the cancerous tissue to generate reactive oxygen species for the destruction of the cancerous tissue. This in vitro study aimed at investigating the cytotoxic effects of different concentrations of zinc tetrasulfophthalocyanines (ZnTSPc) activated with a diode laser (λ=672nm) on melanoma, keratinocyte and fibroblast cells. To perform this study 3×10⁴cells/ml were seeded in 24-well plates and allowed to attach overnight, after which cells were treated with different concentrations of ZnTSPc. After 2h, cells were irradiated with a constant light dose of 4.5J/cm². Post-irradiated cells were incubated for 24h before cell viability was measured using the CellTiter-Blue Viability Assay. Data indicated high concentrations of ZnTSPc (60–100μg/ml) in its inactive state are cytotoxic to the melanoma cancer cells. Also, results showed that photoactivated ZnTSPc (50μg/ml) was able to reduce the cell viability of melanoma, fibroblast and keratinocyte cells to 61%, 81% and 83% respectively. At this photosensitizing concentration the efficacy the treatment light dose of 4.5J/cm² against other light doses of 2.5J/cm², 7.5J/cm² and 10J/cm² on the different cell lines were analyzed. ZnTSPc at a concentration of 50μg/ml activated with a light dose of 4.5J/cm² was the most efficient for the killing of melanoma cancer cells with reduced killing effects on healthy normal skin cells in comparison to the other treatment light doses. Melanoma cancer cells after PDT with a photosensitizing concentration of 50μg/ml and a treatment light dose of 4.5J/cm² showed certain apoptosis characteristics such as chromatin condensation and fragmentation of the nucleus. This concludes that low concentrations of ZnTSPc activated with the appropriate light dose can be used to induce cell death in melanoma cells with the occurrence of minimal damage to surrounding healthy tissue.