ENHANCED PHOTODYNAMIC EFFECTS USING FRACTIONATED LASER-LIGHT

Photodynamic eradication of tumour cells depends on the presence of a photosensitizer and light delivery to the cells. The present study inv estigated the influence of fractionated light (on-off mode) on cell ki lling as documented by a colony-forming assay. Photosensitizers were m -THPC (ethanol soluble, Foscan(R)) and m-THPC-MD (water soluble, both from Scotia Pharmaceuticals, Guildford, UK). Fractionated laser light at a wavelength of 652 nm with a light duration of 0.05 s was more eff ective than continuous illumination at the same power density for both photosensitizers. We propose that fractionated laser light is more to xic due to short phases of recovery during the dark intervals, probabl y resulting in more singlet oxygen under these conditions. By use of F oscan(R), for example, and fractionated laser light, a similar effect is expected for the treatment of solid tumours. In this case we expect improvements in photodynamic therapy (PDT) for patients by lowering t he concentrations of photosensitizer and/or by reducing the applied li ght dose. (C) 1998 Elsevier Science S.A.