Formation of DNA adducts by the food mutagen 2-amino-3,4,8-trimethyl-3H-imidazo [4,8-f]quinoxaline (4,8-DiMeIQx) in vitro and in vivo. Identification of a N-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx adduct

The covalent binding of the mutagenic N²-hydroxy metaboilteof the food mutagen 2-amino-3,4,8-trimethyl-3H-lmldazo4,5-f]quinoxaline(4,8-DiMeIQx) to 2'-deoxy-nudeosides and DNA was investigatedin vitro and in vivo. N²-Hydroxy-4,8-DiMeIQx reacted to a smallextent spontaneously with 2-deoxyguanosine. However, acetylatlonof N²-hydroxy-4,8-DiMeIqx with acetic anhydride to form theN²-acetoxy derivative prior to reaction with 2-deoxyguanosineresulted in much higher yield of adduct. N²-Acetoxy-4,8-DiMeIQxdid not form adducts with 2'-deoxy- adenosine, 2'-deoxycytldlneor 2'-deoxythymldlne. The adduct formed between the N metaboliteof 4,8- DiMeIQx and 2-deoxyguanosine was analysed by mass spectrometryand NMR spectroscopy and the structure of the adduct was shownto be N²-Acetoxy-4,8-DiMeIQx. N²-Acetoxy-4,8-DiMeIQx. reactedwith calf thymus DNA and formed a covalently bound 4,8-DiMeIQxresidue, which could not be removed by repeated precipita tionsor solvent extractions. The 4,8-DiMeIQx-DNA was hydrolysed enzymaticallywith nuclease P1/acid phosphat ase and HPLC analysis showedthat 70% of the bound mutagen was recovered as N²-Acetoxy-4,8-DiMeIQx.An additional minor adduct accounting for