Effect of talaporfin sodium-mediated photodynamic therapy on cell death modalities in human glioblastoma T98G cells

While photodynamic therapy (PDT) is an effective treatment for glioma, induction of apoptotic cell death of glioma cells is important for ensuring efficacy and safety of PDT treatment in glioma patients, as necrotic cell death can induce late appearance of obstacles in treatment. Here, we investigated the relationship between type of cell death and PDT treatment conditions involved in laser and photosensitizer dosage in human glioblastoma T98G cells. Photosensitizer talaporfin sodium-mediated PDT (NPe6-PDT) treatment induced laser and NPe6 dose-dependent cell death in T98G cells, whereas almost all cells pretreated with NPe6 at ≥ 30 µg/mL were killed by laser irradiation, regardless of laser dose. Morphological analysis showed that combination of high doses of NPe6 and laser irradiation changes the dominant cell death process from apoptosis to necrosis. Biochemical analysis (detection of caspase-3 activity and staining of cell surface-exposed phosphatidylserine) also showed that increasing laser dose changes the type of cell death from apoptotic to necrotic cell death after high-dose treatment with NPe6. Lactate dehydrogenase leakage assay demonstrated that a laser dose of 5 J/cm2 induced less leakage than 30 J/cm2. Our results suggested that type of glioma cell death in NPe6-PDT changed with fluctuations in laser and NPe6 dose, and that combination of 30 µg/mL NPe6 with 5 J/cm2 laser is the best treatment condition for inducing an increase in apoptotic cells while keeping rate of necrotic cell death low in this in vitro study.