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 ip 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 detoxicification pathway. Copyright © 2009 John Wiley & Sons, Ltd.