DNA methylation by tert-butyl hydroperoxide-iron (II) - A role for the transition metal ion in the production of DNA base adducts

Metabolic degradation of both endogenous and exogenous peroxides is associa ted with the etiology of several diseases including cancer. Tert-butyl hydr operoxide (TBHP) has been widely employed as a model compound to study the cytotoxicity and promoting effects of organic peroxides. Recently, we repor ted that incubations of TBHP with iron (II) and calf thymus DNA led to gene ration of high yields of methyl radicals and to DNA methylation. Interestin gly, DNA was methylated to products expected from both free radical and ion ic mechanisms such as 8-methylguanine (C-8-MeGua) and 7-methylguanine (N-7- MeGua), respectively. To elucidate the mechanisms by which methyl radicals can produce different types of DNA adducts, we examined the effects of tran sition metal ions (iron (II), iron (III) and copper (I)) and metal ion chel ators (ethylenediamine-N,N, N ",N "-tetraacetate (EDTA) and desferal) on th e nature and the yields of the DNA adducts produced during TBHP decompositi on. The results led us to propose that a direct methyl radical attack on DN A guanine residues produces C-8-MeGua whereas N-7-MeGua and 3-methyladenine (N-3-MeAde) are likely to be produced by attack of nucleophilic DNA center s on methyl radical generated in situ by the assistance of transition metal ions bound to DNA. (C) 1999 Elsevier Science Ireland Ltd. All rights reser ved.