DNA ADDUCT FORMATION OF THE FOOD-DERIVED MUTAGEN 2-AMINO-3-METHYLIMIDAZO[4,5-F]QUINOLINE IN NONHUMAN-PRIMATES UNDERGOING CARCINOGEN BIOASSAY

DNA adduct formation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) w as investigated in cynomolgus monkeys. The pattern and distribution of DNA adducts examined by P-32-postlabeling were similar in all tissues 24 h after a single oral dose of IQ (20 mg/kg). The highest DNA adduc t levels were found in the liver (3.67-11.19 adducts per 10(7) bases), followed by kidney (0.53-1.16 adducts per 10(7) bases), with comparab le adduct levels detected in colon, heart, and pancreas (0.15-0.40 add ucts per 10(7) leases). Two 2'-deoxyguanosine (dG) adducts accounted f or approximately 90% of the observed lesions in all tissues. N-(Deoxyg uanosin-8- yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-C8-IQ) was the major adduct and accounted for approximately 50-80% of the adducts , followed by osin-N-2-yl)-amino-3-methylimidazo[4,5-f]quinoline (dG-N -2-IQ) which accounted for 20-40% of the adducts. DNA adduct formation was also investigated in animals undergoing carcinogen bioassay with IQ administered at 10 or 20 mg/kg, 5 days per week for up to 9.2 years . In chronically treated animals, the DNA adduct levels in pancreas, k idney, and heart increased on average by 40- to 90-fold over those obs erved in animals given a single dose, while only 3- to 10-fold increas es in adducts were observed in colon and liver. A sharp increase in th e contribution of dG-N-2-IQ to total DNA adducts occurred in all slowl y dividing tissues during chronic treatment, and dG-N-2-IQ became the predominant lesion. There was no preferential accumulation of dG-N-2-I Q in the colon, a tissue with a high rate of cell division, and dG-C8- IQ remained the predominant lesion. These findings point to a preferen tial removal of the dG-C8-IQ adduct by enzyme repair system(s) in slow ly dividing tissues. The respective roles of dG-N-2-IQ and dG-C8-IQ, a nd the involvement of adduct repair in the potent hepatocarcinogenicit y of IQ, merit further investigation.