Necrotic and apoptotic cell death of human malignant melanoma cells following photodynamic therapy using an Amphiphilic photosensitizer, ATX-S10(Na)

Background and Objectives: To investigate the phototoxic effect on and cell death modes of human malignant melanoma cells following photodynamic therapy (PDT) using ATX-S10(Na), an amphiphilic photosensitizer. Materials and Methods: Cultured human malignant melanoma cells were incubated in a medium containing various concentrations of ATX-S10(Na) and irradiated with a 670 nm wavelength diode laser. Phototoxicity was analyzed by a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay, and cell death modes were investigated by fluorescence microscopy using a Hoechst 33342-propidium iodide double-staining method as well as by static gel electrophoresis. The subcellular localization of ATX-S10(Na) and mitochondrial destabilization following PDT were observed by fluorescence microscopy. Results: Higher phototoxicity was obtained with higher dye and/or laser doses. Most of the dead cells appeared apoptotic with dye and irradiation doses that induced less than 70% cytotoxicity. In contrast, most of them appeared necrotic with doses that induced 99% cytotoxicity. Cells receiving PDT showed disturbances of mitochondrial transmembrane potential, although the primary site of ATX-S10(Na) accumulation was in lysosomes. Conclusions: ATX-S10(Na) has a phototoxic effect on malignant melanoma cells and, therefore, potential as a photosensitizing agent for PDT designed to kill these cells. Apoptotic pathways may be activated via mitochondrial destabilization following the damage of lysosomes by PDT. Further study, including investigation of therapeutic efficacy in vivo, is warranted. Lasers Surg. Med. 33:6470, 2003. (C) 2003 Wiley-Liss, Inc.