Photodynamic Therapy Mediated by a Novel Chlorin Derivative, TONS 501-Na, in EMT6 cells

BACKGROUND: The lipophilic photosensitizer, TONS 501, is a novel porphyrin-derived methyl ester that was developed for photodynamic antimicrobial chemotherapy. This study developed a hydrophilic and anionic porphyrin salt of this compound (TONS 501-Na) for use in photodynamic therapy (PDT). This chlorin derivative is synthesized from the protoporphyrin IX dimethyl ester. MATERIALS AND METHODS: We investigated the in vitro cytotoxic effects of TONS 501-Na-mediated PDT on EMT6 mouse breast cancer cells. EMT6 cells were incubated with 0-100 μg/ml TONS 501-Na for 24 h prior to replacing the culture medium and exposing the cells to 6 mW/cm2 diode laser irradiation at 0-13 J/cm2 to induce PDT. Morphological changes and cell viability were evaluated 24 h after PDT. The percentages of apoptotic cells were evaluated 4 h and 24 h after PDT. RESULTS: The concentrations of TONS 501-Na that killed 50% of EMT6 cells after exposure to light doses of 0, 0.4, 3, 6, or 13 J/cm2 were 84.6, 33.2, 18, 8.2, and 2.2 μg/ml, respectively. Tumor cells exposed to PDT showed chromatin condensation and fragmentation. The percentages of apoptotic cells increased in a TONS 501-Na concentration-dependent manner in the PDT group, and were significantly higher than those in the control group or in cells treated with TONS 501-Na or laser irradiation alone. CONCLUSION: TONS 501-Na-mediated PDT induced mouse breast cancer cell death in a concentration-dependent manner. Future studies should evaluate the in vivo pharmacokinetics, tissue distribution, and photodynamic effects of TONS 501-Na.