Pyrrolic photosensitizers

There are three major classes of photosensitizers which can initiate a phototoxic effect to tissues upon irradiation. These are the cationic dyes (Type I Photosensitizer), the psoralens (Type I and II Photosensitizer), and cyclic polypyrrolic compounds (Type II Photosensitizer). The polypyrrolic compounds such as porphyrins have been investigated since the late 1800’s for their ability to destroy tissue. In the last ten years, compounds such as chlorins and expanded porphyrins have begun to dominate the preclinical field because they can be activated with light at wavelengths tissue does not effectively absorb. The results of these investigation have been reported in more than 10,000 papers in the field covering aspects from mechanisms of action, photophysics, structure activity relationships, new compound development and clinical investigations. With the approval of PHOTOFRIN(R), (porfimer sodium), the first of the pyrrolic compounds to win acceptance by international regulatory bodies and with nearly 10 other second generation compounds undergoing early clinical trials for diseases ranging from esophageal and skin cancers to age related macular degeneration, the field of photodynamic therapy would seem to have a bright future.