DIRECT ORTHO-ACETYLATION OF NORMAL-HYDROXY ARYLAMINES BY ACETYLSALICYLIC-ACID TO FORM CARCINOGEN DNA ADDUCTS

Acetylsalicylic acid (aspirin) has been shown to acetylate a number of drugs and biological macromolecules. Since enzymatic O-acetylation of N-hydroxy arylamines is regarded as an important activation step for DNA adduct formation, we initially examined the ability of aspirin to serve as an acetyl donor for this reaction, using rabbit liver cytosol. Instead, a direct non-enzymatic reaction was observed. Arylamine-DNA binding was enhanced from 3- to 25-fold at pH 7 by addition of aspirin to reactions containing the N-hydroxy derivatives of 2-aminofluorene (AF), 4-aminobiphenyl, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, but not for 2-amino-3-methylimidazo[4,5-f]quinoline or 2-amino-6-methyldipyrido [1,2-a:3',2'-d]imidazole. Further studies with N-hydroxy-AF showed that reaction rates were first order with respect to both aspirin (0.1 - 10 mM) and N-hydroxy-AF (0.01 - 0.1 mM) concentrations. In contrast, aspirin had no effect on reactions conducted at pH 5 where N-hydroxy-AF is known to undergo protonation and react with DNA to form high levels of N-(deoxyguanosin-8-yl)-AF. N-Acetylation of AF by aspirin under these conditions was also negligible. However, the formation of the adduct from N-hydroxy-AF occurred at high yield (64-82%) at pH 7 with either DNA or 2'-deoxyguanosine. HPLC analyses showed only an aspirin-dependent loss of N-hydroxy-AF and concomitant adduct formation, with no detectable formation of solvolysis products. This indicated that the reaction proceeds to a significant extent only upon addition of the nucleophile, and suggests the formation of an O-tetrahedral intermediate that is in equilibrium with both the N-hydroxy derivative and the reactive N-acetoxy arylamine. Thus, the apparent O-acetylation of certain N-hydroxy arylamines selectively by aspirin offers a convenient route for the synthesis of arylamine - DNA adducts. The potential biological significance of this reaction in vivo is also discussed.