Photochemical and photobiological studies with acridine and phenanthridine hydroperoxides in cell-free DNA.
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.
Adam
W
W
Institute of Organic Chemistry, University of Würzburg, Germany. adam@chemie.uni-wuerzburg.de
Groer
P
P
Mielke
K
K
Saha-Möller
C R
CR
Hutterer
R
R
Kiefer
W
W
Nagel
V
V
Schneider
F W
FW
Ballmaier
D
D
Schleger
Y
Y
Epe
B
B
D002474:Cell-Free System; D003497:Cyclic N-Oxides; D004249:DNA Damage; D004278:DNA, Superhelical / Q000737:chemistry* / Q000187:drug effects / Q000528:radiation effects*; D017665:Hydroxyl Radical; D010084:Oxidation-Reduction; D010545:Peroxides / Q000138:chemical synthesis / Q000494:pharmacology*; D010777:Photochemistry; D013113:Spin Labels; D014466:Ultraviolet Rays
D003497:Cyclic N-Oxides; D004278:DNA, Superhelical; D010545:Peroxides; D013113:Spin Labels; D017665:Hydroxyl Radical; C017245:5,5-dimethyl-1-pyrroline-1-oxide