RELATIONSHIP BETWEEN PHOTODYNAMIC THERAPY AND THE REDOX STATUS OF COMPANION ANIMAL TUMORS.

Photodynamic therapy is a relatively new modality of cancer treatment in human and veterinary medicine. It uses a photosensitizing drug called photosensitizer, which in the presence of oxygen delivers reactive species (singlet oxygen and flee radicals) upon irradiation of the tumor with visible light. In contrast to classical chemotherapy, the original compound (sensitizer or photosensitizer) has a minimal toxic effect on the whole body. Its effect is due to the activation of the accumulated sensitizer in a given tissue by visible light around 630 nm wavelength or above. Excitation by light produces activated oxygen- and nitrogen species, which are able to rapidly kill cells. No harming radiation is involved. The administered compound gets activated only in the illuminated area, mainly killing actively dividing cells. The treatment achieves its selectivity by illuminating only the area affected by the tumor. Apparently, it does not solve the problem of metastasis, but offers many advantages against chemotherapy, radiation or surgery. PDT offers an additional method in treat patients with certain kinds of cancer. Here we present some preliminary data on the application of PDT on companion animals with malignant tumors. We have applied 5-aminolevulinic acid (ALA)-based PDT on cats and dogs with different kinds of tumors, and investigated the effect of treatment on reduction-oxidation parameters of tissue samples taken from the tumors before and after PDT. Results of free radical concentrations measured using Electron Spin Resonance and of reduced glutathione in tumor tissues give a direct correlation with the outcome of PDT. [ABSTRACT FROM AUTHOR]