Enhanced photocytotoxicity induced by a triphenylphosphonium-appended platinum diimine complex

Abstract

Photodynamic therapy (PDT) agents induce photodamage only where photosensitizers localize in tumor cells. Since apoptosis is a major pathway of PDT-mediated cell death in vivo, the therapeutic efficacy of PDT drugs against tumor cells may be improved by regulating intrinsic apoptosis. Mitochondria are the major intracellular organelles that regulate apoptosis, thus triphenylphosphonium, a well-known mitochondria-targeting molecule, was appended to a photoactive platinum diimine complex. The ability of the triphenylphosphonium-appended complex to generate singlet oxygen was assessed by fluorescence spectroscopy using 1,3-diphenylisobenzofuran as a probe. The photocytotoxicity towards HeLa cells (human cervical cancer cell line) or HL-7702 cells (human liver cell line) was assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assays. The platinum complex has moderate capability to generate singlet oxygen and it has more potent photocytotoxicity than its analogue Pt-CA. Both platinum diimine complexes studied are largely nontoxic to human liver cells either in the dark or after irradiation.