Formation of modified cleavage termini from the reaction of chromium(V) with DNA

摘要

Reaction of a 25 bp oligonucleotide with the high valent chromium complex, bis(2-ethyl-2-hydroxybutyrato) oxochromate(V) (Cr(V)-EHBA) produced both Frank- and alkali-labile strand breaks that were sequence-neutral. Frank strand break formation was found to be O_2-dependent while formation of alkali-labile strand breaks were O_2-independent. Reaction of Cr(V)-EHBA with the 5'-~(32)P-labeled oligomer under oxygenated conditions formed the modified 3' -terminus, 3' -phosphoglycolate, as well as the 3' -phosphate terminus. Formation of the 3' -phosphoglycolate termini, and the O_2 dependence of the reactions were consistent with a mechanism involving abstraction of the C4' hydrogen atom from the deoxyribose moiety of DNA. Identical reactions using the 3'-~(32)P-labeled oligomer yielded only 5' -phosphate termini as assigned by co-migration with Maxam-Gilbert markers. Analogous cleavage profiles and modified termini were observed for the reaction of Cr(V)-EHBA and DNA in the presence of hydrogen peroxide. With the addition of hydrogen peroxide, the DNA cleavage reactions were O_2-independent and the level of DNA cleavage was enhanced over that observed with Cr(V)-EHBA alone. These findings suggest an oxidation mechanism whereby a reductive intermediate of the carcinogen chromate, Cr(V), can cause DNA damage that mimics oxygen radical DNA damaging pathways.