Coined by O. Raab in 1900, this is a form of photochemotherapy in which a photosensitizer (e.g., 5-aminolevulinic acid, porphyrin derivatives) reacts with visible light to produce cyto- or tissue-toxic products. The basic prerequisite for this reaction is the presence of oxygen. Redox processes and radical chain reactions produce reactive singlet oxygen, which reacts cytotoxically and can destroy tissue structures as well as amino acids, nucleic acids and fatty acids. The method exploits the affinity of certain porphyrin derivatives on tumor cells. Tumor cells, as well as macrophages, take up LDL-bound photosensitizers by endocytosis. Subsequent irradiation with polychromatic light sources leads to the destruction of the cells while sparing the surrounding tissue. Irradiation doses range from 25 to 300 J/cm².
see also antimicrobial photodynamic therapy, aPDT, PACT