S. Muller et al., ENHANCED PHOTODYNAMIC EFFECTS USING FRACTIONATED LASER-LIGHT, Journal of photochemistry and photobiology.B, Biology, 42(1), 1998, pp. 67-70
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.