METABOLISM, MUTAGEN AND DNA ADDUCTION OF IQ

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2-Amino-3-methyl-imidazole (4,5-f)quinoline (IQ) is among a number of heterocyclic arylamines found in cooked foods that have been shown lo be potent carcinogens in rodent bioassays. We have initiated work involving (1) synthesis of N-OH-IQ, and N-acetoxy- IQ and IQ-N-sulfate, the reactive metabolites of IQ; (2) synthesis and characterization of the major DNA-IQ adduct; (3) examination of DNA-IQ adducts in monkeys by the 32P-postlabeling method; (4) IQ metabolism in monkeys; and (5) the role of specific cytochromes P-450 in the metabolic activation of IQ. N-OH-IQ was a direct mutagen in Salmonella TA98 and capable of covalently binding to DNA without further activation. N-OH-IQ is also metabolized by mammalian O-acetyl-transferase and sulfotransferase to N-acetoxy- IQ and IQ-N-sulfate, respectively. The C8-guanine-IQ adduct was synthesized and shown to be formed in vitro from either N-OH-IQ or N-acetoxy-IQ reacting with DNA. Using the 32P-postlabeling assay, eight DNA-IQ adducts including C8-guanine-IQ, were found in the liver of Cynomolgus monkeys fed IQ that were identical to those found in the liver of rats fed IQ. Analysis of DNA modified in vitro with N-OH-IQ showed seven adducts, including the C8-guanine- IQ adduct, that were identical to those found in vivo. Thus, N- OH-IQ appears to be responsible for all adducts found in vivo except one. DNA-IQ adducts were also detected in kidney, colon, stomach and bladder, and these adducts were identical in all organs examined. We examined the specificity of metabolic activation of IQ and a number of other mutagenic/carcinogenic heterocyclic arylamines from cooked foods by employing a novel test system combining human cells individually expressing either recombinant cytochrome P1-450 or P3-450 as the bioactivation system with Salmonella typhimurium to score mutations. Our results show that cytochrome P3-450, a single isoform of the cytochrome P.450 super- gene family, is responsible for the bioactivation of the heterocyclic arylamine food mutagens to N-hydroxylamines.