Photodynamic therapy using zinc phthalocyanine with low dose of diode laser combined with doxorubicin is a synergistic combination therapy for human SK-MEL-3 melanoma cells

Chemotherapy is a generally used anticancer strategy for melanoma and it may have improved outcomes in combination with other approaches. One such strategy is photodynamic therapy (PDT), where a photosensitizer (PS) generates reactive oxygen species (ROS) after illumination of target cells. Interestingly, in low doses and high doses of light sources, special cellular responses can be induced. Regarding this fact, in this study, the combination of zinc phthalocyanine (ZnPc)-PDT and Doxorubicin (DOX) was applied at low and high dose of diode laser to treat SK-MEL-3 cells. Cytotoxic effects were determined by MTT assay for assessment synergistic effects were estimated by calculation of Combination Index (CI); that synergistic effects were observed in most groups. In low dose of laser irradiation higher synergism effects were observed. Significant changes of ROS were not observed with combinations, but autophagy, subG1 and G2/M phase cell cycle arrest, decreased cell migration ability and apoptosis induction were significantly increased compared to either treatment alone. The expression of caspase-8, -9, -3 and Bcl-2 genes revealed caspase-dependent apoptosis in all groups. Moreover, ZnPc-PDT and chemo-PDT down-regulated the expression of MMP-9 and Vimentin genes that impaired cell migration. In conclusion, it can be suggested that pre-treatment with ZnPc-PDT has high effects to sensitize SK-MEL-3 cells to DOX, in particular with low dose of diode laser.