Effect of photosensitisers on glioma cells

Abstract

The invasive nature of malignant glioma makes it extremely difficult to be treated by surgery alone. However, the preferential accumulation of photosensitisers in neoplastic tissues suggests that photodynamic therapy (PDT) may be useful as an adjunct therapy following tumour resection. The potential use of three different photosensitisers namely, Photofrin, 5-Aminolevulinic acid (5-ALA) and Calphostin C, in the treatment of glioma was investigated. The uptake, intracellular localisation, cytotoxicity of U87 and GBM6840 glioma cell lines were determined by flow cytometry, fluorescence microscopy and tetrazolium colorimetric reduction (MTT) assay respectively. Their effect on glioma cell invasiveness was evaluated by (1) measuring the levels of matrix metalloproteinase (MMP)-2 and -9 using gelatin zymography, and (2) Matrigel invasion assay. The results showed that uptake of Calphostin C reached saturation within 4 hours, while Photofrin and 5-ALA elevated steadily up to 24 hours. Calphostin C and 5-ALA predominantly localised in the perinuclear region corresponding to the endoplasmic reticulum, whereas Photofrin displayed a lysosomal pattern. The photocytotoxic effect on the two glioma cell lines was similar with LD50 at optimal uptake as follows: 1 ug/mL Photofrin at 1.5 J/cm2, ImM 5-ALA at 2 J/cm2 and l00nM calphostin C at 2 J/cm2. The inhibition of cell proliferation after Photofrin treatment was similar for both cell lines, which correlated with more cells being arrested in the G0/G1 phase of the cell cycle (P<0.001). By contrast, U87 was more sensitive to calphostin C whereas GBM6840 was more susceptible to 5-ALA treatment. The ability of both cell lines to migrate through the Matrigel artificial basement membrane was significantly reduced after PDT (P<0.001). This might be due to a decreased production in MMP-2 and MMP-9, together with the reduction of adhesion molecule expression. Photofrin was the most superior in inhibiting cell invasion and calphostin C was the least effective in reducing adhesion molecule expression. Taken together, PDT could be useful in the treatment of gliomas but the choice of photosensitisers must be taken into consideration.