Formation of 1,4-dioxo-2-butene-derived adducts of 2′-deoxyadenosine and 2′-deoxycytidine in oxidized DNA

Oxidation of deoxyribose in DNA produces a variety of electrophilic residues that are capable of reacting with nucleobases to form adducts such as M₁dG, the pyrimidopurinone adduct of dG. We now report that deoxyribose oxidation in DNA leads to the formation of oxadiazabicyclo(3.3.0) octaimine adducts of dC and dA. We previously demonstrated that these adducts arise in reactions of nucleosides and DNA with trans-1,4-dioxo-2-butene, the β-elimination product of the 2-phosphoryl-1,4-dioxobutane residue arising from 5′-oxidation of deoxyribose in DNA, and with cis-1,4-dioxo-2-butene, a metabolite of furan. Treatment of DNA with enediyne antibiotics capable of oxidizing the 5′-position of deoxyribose (calicheamicin and neocarzinostatin) led to a concentration-dependent formation of oxadiazabicyclo(3.3.0)octaimine adducts of dC and dA, while the antibiotic bleomycin, which is capable of performing only 4-oxidation of deoxyribose, did not give rise to the adducts. The nonspecific DNA oxidant, γ-radiation, also produced the adducts that represented ∼0.1% of the 2-phosphoryl-1,4- dioxobutane residues formed during the irradiation. These results suggest that the oxadiazabicyclo(3.3.0)octaimine adducts of dC and dA could represent endogenous DNA lesions arising from oxidative stresses that also give rise to other DNA adducts.