Abstract
Summary Fractionated treatment is often used in chemo- and radiotherapy of tumors. Such an approach is likely to improve the therapeutic success also in photodynamic tumor therapy (PDT): discontinuous irradiation with dark intervals of seconds or even milliseconds seems indeed to increase the photodynamic efficiency. Therefore in vitro experiments with a laser light source, which can be programmed for irradiation pulses of different duration and shape, were performed to compare the delivery of regular rectangle pulses of 100 ms to continuous irradiation with respect to the efficiency of PDT. Mammary carcinoma cells (MCF-7) were incubated with the photosensitizers meta-tetrahydroxyphenyl-chlorine (mTHPC)®, Photofrin II® and with 5-aminolevulinic acid (ALA), and exposed to continuous and pulsed laser light. The results obtained from two different cytotoxicity tests (tests for mitochondrial function and membrane integrity) demonstrate that at the same given total light fluence, irradiation with regular on-off light pulses and therefore 50% reduction of the power density causes double cytotoxicity of the tumor cells. This could be explained by diffusion processes of the molecular oxygen, of targets and/ or of oxidised products around the intracellular reactions sites. This method of efficiency increase could be used in clinical application.
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