Characterization of new metabolites from in vivo biotransformation of 2-amino-3-methylimidazo[4,5-f]quinoline in mouse by mass spectrometry.

In studying the metabolic pathways underlying the mechanism of carcinogenesis of the heterocyclic amine of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), we recently found a new metabolite which gave an M + H ion of m/z 217 when subjected to electrospray ionization (ESI) in positive-ion mode. Following i.p. injection of this metabolite of m/z 217 (designated as m/z 217) to beta-naphthoflavone-treated mice, 57% of the total radioactivity was recovered in a 24-h mouse urine sample. HPLC separation followed by MS analysis indicates that the urine sample contained m/z 217 (36 +/- 3% of total recovered radioactivity) and two other peaks that gave rise to the M + H ions of m/z 393 (31 +/- 4%, designated as m/z 393) and m/z 233 (14 +/- 1%, designated as m/z 233). Beta-glucuronidase treatment of m/z 393 resulted in a radioactive peak corresponding to m/z 217. ESI in combination with various mass spectrometry techniques, including multiple-stage mass spectrometry, exact mass measurements and H/D exchange followed by tandem mass spectrometry, was used for structural characterization. The urinary metabolites of m/z 217, 393 and 233 were identified as 1,2-dihydro-2-amino-5-hydroxy-3-methylimidazo[4,5-f]quinoline, 1,2-dihydro-2-amino-5-O-glucuronide-3-methylimidazo[4,5-f]quinoline and 1,2-dihydro-2-amino-5,7-dihydroxy-3-methylimidazo[4,5-f]quinoline, respectively. Our results demonstrated that m/z 217 is biotransformed in vivo to m/z 393 by O-glucuronidation and to m/z 233 by oxidation. The observation of these more polar metabolites relative to IQ suggests that they may arise from a previously undescribed detoxification pathway.