A variety of alkylated base adducts are repaired by 3-methyladenine DNA 
glycosylases, one of the base excision repair enzymes. In this study, we 
examined the DNA adducts induced by hepsulfam and determined whether alkylated 
base adducts can be substrates for bacterial and mammalian 3-methyladenine DNA 
glycosylases by electrophoresis methods. Hepsulfam, a synthetic analogue of 
busulfan, is known to alkylate DNA and form interstrand cross-links. The extent 
of DNA interstrand cross-links induced by hepsulfam and busulfan was found to be 
similar but significantly lower than that induced by chlorambucil, as measured 
by an agarose gel assay. The major monofunctional alkylation site of hepsulfam 
was observed at the N7 position of guanine, and not at the N3 position of 
adenine. Both compounds did not exhibit any sequence selective DNA alkylation 
patterns. The excision of hepsulfam-induced DNA adducts has been determined by 
treatment with homogeneous recombinant bacterial, rat and human 3-methyladenine 
DNA glycosylases and successive treatments by formamidopyrimidine-DNA 
glycosylase. The Escherichia coli alkA protein was shown to completely excise N7 
guanine adducts, whereas mammalian 3-methyladenine DNA glycosylase failed to 
excise them. In addition, the cytotoxicity assay showed that E. coli mutant 
strains defective in the alkA gene or the uvrA gene were more sensitive to 
killing by hepsulfam than the wild type.