Effect of single strand breaks on the formation of DNA interstrand crosslinks induced by the major oxidative adenine lesion 7,8-dihydro-8-oxoadenine

The major oxidative adenine lesion, 7,8-dihydro-8-oxoadenine (oxoA), can readily undergo further oxidation to generate the highly genotoxic DNA interstrand cross-links (ICLs). Herein we report that the presence of single-strand breaks (SSBs), the major lesion formed at sites of oxidative stress, in the form of a nick or single-nucleotide gap in the phosphodiester backbone of duplex DNA significantly increases the cross-linking yield of oxoA with all canonical nucleotides (up to 67.5%) upon oxidation. The cross-linking reaction occurs between the purine/pyrimidine moiety of a nucleotide on the complementary strand of the duplex and the oxoA modification on the template strand, which was confirmed by the experiment involving the use of 2',3'-dideoxycytosine. Interestingly, the minor cross-linking products in intact DNA saw a more significant increase in reactivity relative to the major oxoA-G ICL. SSBs in the form of a gap or nick between the reacting nucleotide and thymine residue base paired to oxoA produced the most significant increase in yield.