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.

Genotoxicity induced by furocoumarin hydroperoxides in mammalian cells upon UVA irradiation.

The mutagenicity and micronucleus induction by the furocoumarin hydroperoxides 1a and 2a and, for comparison, their corresponding alcohols 1b and 2b were investigated in L5178Y tk+/- mouse lymphoma cells and AS52 Chinese hamster ovary cells. The furocoumarin hydroperoxide 1a enhanced the micronucleus frequency in L5178Y tk+/- mouse lymphoma cells significantly, while its alcohol 1b exhibited a rather moderate effect. In contrast, both the furocoumarin hydroperoxide 2a and its alcohol 2b induced high frequencies of micronuclei. Only the furocoumarin hydroperoxide 1a, but not its alcohol 1b, was mutagenic in both L5178Y tk+/- and AS52 cells. On the other hand, the furocoumarin hydroperoxide 2a and its alcohol 2b were mutagenic. For all furocoumarin derivatives 1a,b and 2a,b no mutagenicity and genotoxicity was observed in the absence of UVA light. The multifunctional furocoumarin hydroperoxides may serve as potential photochemotherapeutic agents.