Photodynamic therapy of C6-implanted glioma cells in the rat brain employing second-generation photosensitizer talaporfin sodium

Abstract

The usefulness of photodynamic therapy (PDT) as a local therapy for malignant glioma was evaluated by investigating histological changes in a rat C6 glioma model treated with a combination of talaporfin sodium, a water-soluble photosensitizer derived from chlorophyll and exposure to a diode laser. Glioma cells (C6) at the confluence stage were transplanted stereotactically into the right frontal lobe of SD rats. Five days later, the rats underwent right frontal craniotomy and intravenous administration of talaporfin sodium. One hour after talaporfin sodium administration, each rat was irradiated by a 664 nm diode laser beam. The brain was removed 1, 3 or 6h after laser irradiation for histological examination of tumor-affected brain tissue and surrounding normal brain tissue. In addition to the tumor mass, tumor cells invading surrounding edematous brain tissue were seen in untreated rats, ranging from the brain surface to a depth of 2mm. One hour after PDT, coagulation necrosis as well as disappearance of indication of cell viability such as disappearance of tumor cell processes and foamy changes of cytoplasm were noted in the tumor tissue at a depth of 0.5mm, accompanied by reduction of cytoplasmic glial fibrillary acidic protein (GFAP) expression and appearance of granular M30 cytodeath positivity. Three hours later, the cytoplasm of the residual tumor cells showed disappearance of GFAP expression and increased expression of M30 cytodeath. Six hours later, the foamy cytoplasm of swollen tumor cells demonstrated strong positivity for M30 cytodeath. PDT using talaporfin sodium induced coagulation necrosis and apoptosis in rats with C6 glioma.