Peripheral neural cell sensitivity to mTHPC-mediated photodynamic therapy in a 3D in vitro model

The effect of photodynamic therapy (PDT) on neural cells is important when tumours are within or adjacent to the nervous system. The purpose of this study was to investigate PDT using the photosensitiser, meta-tetrahydroxyphenyl chlorin (mTHPC), on rat neurons and satellite glia, compared with human adenocarcinoma cells (MCF-7).

Fluorescence microscopy confirmed that mTHPC was incorporated into all three cell types. Sensitivity of cells exposed to mTHPC-PDT (0-10 microg ml(-1)) was determined in a novel 3-dimensional collagen gel culture system. Cell death was quantified using propidium iodide and cell types were distinguished using immunocytochemistry. In some cases, neuron survival was confirmed by measuring subsequent neurite growth in monolayer culture.

MCF-7s and satellite glia were significantly more sensitive to PDT than neurons. Importantly, 4 microg ml(-1) mTHPC-PDT caused no significant neuron death compared with untreated controls but was sufficient to elicit substantial cell death in the other cell types. Initially, treatment reduced neurite length; neurons then extended neurites equivalent to those of untreated controls. The protocol was validated using hypericin (0-3 microg ml(-1)), which caused neuron death equivalent to other cell types.

Neurons in culture can survive mTHPC-PDT under conditions sufficient to kill tumour cells and other nervous system cells.