PHOTOCHEMICAL AND PHOTOBIOLOGICAL STUDIES WITH ACRIDINE AND PHENANTHRIDINE HYDROPEROXIDES IN CELL-FREE DNA

The acridine and phenanthridine hydroperoxides 3 and 7 were synthesize d as photochemical hydroxyl radical sources for oxidative DNA damage s tudies, The generation of hydroxyl radicals upon WA irradiation (lambd a = 350 nm) was verified by trapping experiments with 5,5-dimethyl-1-p yrroline N-oxide and benzene, The enzymatic assays of the damage in ce ll-free DNA from bacteriophage PM2 caused by the acridine and phenanth ridine hydroperoxides 3 and 7 under near-UVA irradiation revealed a wi de range of DNA modifications. Particularly, extensive single-strand b reak formation and DNA base modifications sensitive to formamidopyrimi dine DNA glycosylase (Fpg protein) were observed, In the photooxidatio n of calf thymus DNA, up to 0.69 +/- 0.03% 8-oxo-7,8-dihydroguanine wa s formed by the hydroperoxides 3 and 7 on irradiation, whose yield was reduced up to 40% in the presence of the hydroxyl radical scavengers mannitol and tert-butanol, The acridine and phenanthridine hydroperoxi des 3 and 7 also induce DNA damage through the type I photooxidation p rocess, for which photoinduced electron transfer from 2'-deoxyguanosin e to the singlet states of 3 and 7 was estimated by the Rehm-Weller eq uation to possess a negative Gibb's free energy of ca -5 kcal/mol. Con trol experiments with the sensitizers acridine 1 and the acridine alco hol 4 in calf thymus and PM2 DNA confirmed the photosensitizing propen sity of the WA-absorbing chromophores, The present study emphasizes th at for the development of selective and efficient photochemical hydrox yl radical sources, chromophores with law photosensitizing ability mus t be chosen to avoid type I and type II photooxidation processes.