| [ Summary ] |
The mode of cell death induced by photodynamic therapy (PDT) was investigated from the perspective of apoptosis. In an in vivo study using human pancreatic carcinoma, transplanted into nude mice, PDT showed significant therapeutic effects at seven days post treatment, as compared with laser irradiation alone when the mean of each overall split surface of the necrotic area was measured. The characteristic DNA ladder formation and TUNEL signals in nuclei of tumor cells were demonstrated two hours after PDT.However, no evidence of DNA ladder formation nor TUNEL signals was found in the untreated control group or in groups given laser irradiation alone. Additionally, we investigated chronological changes in intracellular Ca2+ concentrations during PDT-induced apoptosis, using human squamous cell carcinoma cells by in vitro. Extensive DNA fragmentation was recognized within two hours of PDT. The proportion of cells with DNA fragmentation on flow cytometric analysis was significantly increased to 44% and 78% one hour and two hours after PDT, respectively, compared to the control groups. Confocal laser scanning microscopy revealed a slight change in intracellular Ca2+ concentrations occurring at thirty minutes after PDT, and a subsequent marked increase in Ca2+ concentration one to two hours after PDT, but no change was observed in the cells exposed to laser irradiation only or the cells immediately after PDT. These findings suggest that an increase in intracellular Ca2+ concentrations may play an important role in the induction of PDT-induced apoptosis. Further work to clarify molecular mechanisms of PDT-induced apoptosis should be conducted. With development of new photosensitizers or laser appratus, it is expected that the therapeutic effects, the appropriate administration time or the concentrations of photo sensitizers, and treatment conditions can be decided objectively in relation to apoptosis. |