CONICET | Buscador de Institutos y Recursos Humanos

Malignant melanoma is the most aggressive form of skin carcinoma, which possesses fast proliferation rate and highly invasive characteristics. Phthalocyanines (Pcs) are synthetic photosensitizers with potential application in photodynamic therapy. In order to find an efficient photosensitizer to be used in melanoma treatment, we study the effect of a sulfur-linked cationic zinc(II) phthalocyanine named Pc13 on murine melanoma B16F0 cells. While no citotoxicity was observed by MTT assay when cells were incubated with Pc13 in the dark, cell viability diminished in a concentration-dependent manner upon exposure to a light dose of 9.2 Jcm-2, being the IC50 value of 0.19 ± 0.09 µM. The production of ROS in Pc13-loaded cells was demonstrated immediately after irradiation with the probe DCFH-DA. When cells were pretreated with 5 mM of the antioxidant trolox, cell viability was completely recovered. A cytosolic localization of Pc13, that emits a red fluorescence after exciting at 633 nm, was revealed by confocal microscopy. The presence of picnotic nuclei in Pc13-treated cells was also detected after Hoechst staining. In order to elucidate the induction of the mitochondrial pathway, Pc13-treated cells were irradiated and incubated with DiOC6 probe. Mitochondrial depolarization was observed 1 h post irradiation by fluorescence microscopy and flow cytometry. We also detected lower levels of poly-ADPribose-polymerase (PARP), a caspase-3 substrate involved in DNA repair. In addition, a rapid phosphorylation of p38, JNK and Erk1/2 MAPK, and a decrease of p-Akt levels were observed after irradiation of Pc13-loaded cells. Taken together, these results indicate that the phototoxic effect exerted by Pc13 on melanoma B16F0 cells is mediated by the formation of ROS and the induction of an apoptotic response characterized by mitochondrial depolarization, PARP cleavage and nuclear shrinkage. The role of kinases in the phototoxic action will be further investigated.