Photodynamic therapy using talaporfin sodium induces concentration-dependent programmed necroptosis in human glioblastoma T98G cells

Photodynamic therapy (PDT) using photosensitizer induces several types of cell death, such as apoptosis, necrosis, and autophagy, depending on the PDT procedure, photosensitizer type, and cell type. We previously demonstrated that PDT using the photosensitizer talaporfin sodium (mono-l-aspartyl chlorine e6, NPe6; NPe6-PDT) induces both mitochondrial apoptotic and necrotic cell death in human glioblastoma T98G cells. However, details regarding the mechanism of necrosis caused by NPe6-PDT are unclear. Here, we investigated whether or not necroptosis, a recently suggested form of programmed necrosis, is involved in the necrotic cell death of NPe6-PDT-treated T98G cells. Leakage of lactate dehydrogenase (LDH) from the cell layer into conditioned medium was significantly increased by NPe6 (25 and 50 μg/ml)-PDT, indicating that NPe6-PDT induces necrosis in these cells. NPe6 (25 μg/ml)-PDT treatment also induced conversion of microtubule-associated protein 1 light-chain 3 (LC3)-I into phosphatidylethanolamine-conjugated LC3-II accompanying autophagosome formation, indicators of autophagy; however, of note, NPe6 (50 μg/ml)-PDT did not induce such autophagic changes. In addition, both necrostatin-1 (a necroptosis inhibitor) and knockdown of necroptotic pathway-related proteins [e.g., receptor interacting serine-threonine kinase (RIP)-1, RIP-3, and mixed lineage kinase domain-like protein (MLKL)] inhibited leakage of LDH caused by NPe6 (25 μg/ml)-PDT. Taken together, the present findings revealed that NPe6-PDT-induced necrotic cell death is mediated in part by the necroptosis pathway in glioblastoma T98G cells.