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

Abstract

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′- 32P-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′- 32P-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.