Shining a Light on Brain Cancer: Utilising Photodynamic Therapy in the Treatment of Glioblastoma

Photo diagnosis is used intraoperatively to identify glioblastoma (GBM) tumour and achieve a greater extent of resection. Patients are given a ‘pink drink’ of 5-aminolevulinic acid (5ALA), a photosensitiser, which is preferentially taken up by cancer cells and fluoresces under certain light frequencies. It has been shown that the use of photosensitisers and light in this process may cause cell death, encouraging the investigation of photodynamic therapy as a potential treatment for GBM. While the potential of photodynamic therapy (PDT) as a diagnostic option is evolving, PDT’s progress in neuro-oncology remains in its infancy. Although reactive oxygen species (ROS) generation has been proposed to be an important factor contributing to cell death in PDT treatment, limited evidence is available to confirm this. We aim to establish the mechanism of cell death observed in primary GBM 2D and 3D cells upon exposure to light and photosensitiser and confirm the efficacy of PDT therapy using an in vitro cell culture system. Primary patient derived glioma cell lines and 3D stem neurospheres were exposed to 630nm LED laser irradiation with the use of 5-ALA photosensitiser. Cell kill was assessed using microscopy and an MTS cell viability assay quantified by a 96-well Tecan plate reader. N- acetyl-L-Cysteine (NAC), L-Buthionine-sulfoximine (BSO) and assays using CellROX photosensitiser were used to investigate ROS as a mechanism of cell kill. Results show that cell death was not caused by 5ALA and irradiation alone, however, the combined effect of the two incurred cell death in cell lines tested with evidence of ROS playing a role in the mechanism of cell death.