SPECTRAL CHARACTERIZATION OF THE BENZOPORPHYRIN DERIVATIVE MONOACID RING-A PHOTOPRODUCT FORMED IN FETAL CALF SOLUTIONS DURING IRRADIATION WITH 694-NM CONTINUOUS-WAVE RADIATION

Benzoporphyrin derivative monoacid ring A (BPD-MA) is a second-generat ion photosensitizer for photodynamic therapy (PDT) that has shown good results in phase I clinical trials. Similar to other porphyrin deriva tives, BPD-MA readily photobleaches during in-vivo PDT treatment. This study investigated the photodegradation of BPD-MA in fetal calf serum (FCS) solutions in vitro. Absorption and fluorescence spectra from di lute solutions of BPD-MA in 10% FCS were recorded before and immediate ly after irradiation with light at 694 nm. After irradiation, the appe arance of a new fluorescence emission band at 650 nm and changes in th e fluorescence excitation spectra indicate the formation of a photopro duct. Photoproduct formation was observed only when BPD-MA was bound t o FCS and in oxygenated solutions. The spectroscopy of the photoproduc t is consistent with the reaction of an oxygen species with the ring B vinyl group, forming a hydroxyaldehyde photoproduct. Monitoring the i ncrease in photoproduct fluorescence during treatment may provide an i n-vivo dosimeter to measure PDT efficacy.