THYMIDINE FREE-RADICALS GENERATED DURING METALLO-PHTHALOCYANINE PHOTOSENSITIZATION - A COMPARISON WITH GAMMA-RADIATION

In order to obtain information concerning the mechanism(s) of metallo- phthalocyanine (MePcS(4)) photosensitized damage of DNA constituents, the EPR-spin trapping method in conjunction with liquid chromatography was used to study thymidine (dThd) free radicals formed during photos ensitization or exposure to gamma-radiation in solution. Under specifi ed conditions two dThd free radical species, 5-hydroxy-5,6-dihydrothym idine-6-yl and 6-hydroxy-5,6-dihydrothymidine-5-yl, were formed both d uring exposure to ionizing radiation and photosensitization. These res ults imply that identical reactive intermediates ((OH)-O-. radicals) a re involved in the radiolytic and photosensitized oxidation of dThd. A light-dependent, Fenton-type mechanism is proposed to explain the gen eration of hydroxyl radicals during MePcS(4) photosensitization.