Inhibition of specific cellular antioxidant pathways increases the sensitivity of neurons to meta-tetrahydroxyphenyl chlorin-mediated photodynamic therapy in a 3D co-culture model.

The effect of photodynamic therapy (PDT) on neurons is of critical importance when treating cancers within or adjacent to the nervous system. Neurons show reduced sensitivity to meta-tetrahydroxyphenyl chlorin (mTHPC) mediated PDT, so the aim of this study was to investigate whether neuron sparing is due to endogenous cellular antioxidant activity. Dorsal root ganglion (DRG) neurons and their associated satellite glia were subjected to mTHPC-PDT in a 3D co-culture system following incubation with antioxidant inhibitors: diethyl dithiocarbamate (DDC, SOD-1 inhibitor), 2-methoxyestradiol (2-MeOH(2), SOD-2 inhibitor) and L-buthionine sulfoximine (L-BSO, glutathione synthase inhibitor). Sensitivity of each cell type was assessed using a combination of live/dead staining and immunofluorescence. Pretreatment with DDC and with L-BSO significantly increased the sensitivity of neurons to mTHPC-PDT and also affected satellite glial cell viability, whereas 2-MeOE(2) caused only a small increase in neuron sensitivity (not significant). Pretreatment using a combination of DDC and L-BSO caused a near total loss of neuron and glial cell viability in treatment and control conditions. These findings suggest that the SOD-1 and glutathione pathways are likely to be involved in the neuronal sparing associated with mTHPC-PDT.