Photochemical and photobiological studies with acridine and phenanthridine hydroperoxides in cell-free DNA

• Published in: Photochemistry and photobiology 1997-07, Vol.66 (1), p.26-33
• Main Authors: Adam, W, Groer, P, Mielke, K, Saha-Möller, C R, Hutterer, R, Kiefer, W, Nagel, V, Schneider, F W, Ballmaier, D, Schleger, Y, Epe, B
• Format: Article
• Language: English
• Subjects: Cell-Free System; Cyclic N-Oxides; DNA Damage; DNA, Superhelical - chemistry; DNA, Superhelical - drug effects; DNA, Superhelical - radiation effects; Hydroxyl Radical; Oxidation-Reduction; Peroxides - chemical synthesis; Peroxides - pharmacology; Photochemistry; Spin Labels; Ultraviolet Rays
• ISSN: 0031-8655
• DOI: 10.1111/j.1751-1097.1997.tb03134.x

The acridine and phenanthridine hydroperoxides 3 and 7 were synthesized as photochemical hydroxyl radical sources for oxidative DNA damage studies. The generation of hydroxyl radicals upon UVA irradiation (lambda = 350 nm) was verified by trapping experiments with 5,5-dimethyl-1-pyrroline N-oxide and benzene. The enzymatic assays of the damage in cell-free DNA from bacteriophage PM2 caused by the acridine and phenanthridine hydroperoxides 3 and 7 under near-UVA irradiation revealed a wide range of DNA modifications. Particularly, extensive single-strand break formation and DNA base modifications sensitive to formamidopyrimidine DNA glycosylase (Fpg protein) were observed. In the photooxidation of calf thymus DNA, up to 0.69 +/- 0.03% 8-oxo-7,8-dihydroguanine was 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 hydroperoxides 3 and 7 also induce DNA damage through the type I photooxidation process, for which photoinduced electron transfer from 2'-deoxyguanosine to the singlet states of 3 and 7 was estimated by the Rehm-Weller equation to possess a negative Gibb's free energy of ca -5 kcal/ mol. Control experiments with the sensitizers acridine 1 and the acridine alcohol 4 in calf thymus and PM2 DNA confirmed the photosensitizing propensity of the UVA-absorbing chromophores. The present study emphasizes that for the development of selective and efficient photochemical hydroxyl radical sources, chromophores with low photosensitizing ability must be chosen to avoid type I and type II photooxidation processes.