title: Bioreductive metabolism of the novel fluorinated 2-nitroimidazole hypoxia probe N-(2-hydroxy-3,3,3-trifluoropropyl)-2-(2-nitroimidazolyl) acetamide (SR-4554).
abstract: The aim of this work was to study the metabolic characteristics of the novel fluorinated 2-nitroimidazole hypoxia probe N-(2-hydroxy-3,3,3-trifluoropropyl)-2-(2-nitroimidazolyl) acetamide (SR-4554). HPLC and 19F NMR methods were employed to evaluate the rate of reductive metabolism of SR-4554 and the nature of the resulting metabolites, respectively. SR-4554 was enzymatically reduced by mouse liver microsomes (1.1 +/- 0.1 nmol of SR-4554 reduced/min/mg protein), purified rat and human NADPH:cytochrome P450 reductase (17.8 +/- 0.4 and 5.0 +/- 0.5 nmol of SR-4554 reduced/min/mg protein, respectively), and SCCVII tumour homogenates (2.3 +/- 0.3 nmol of SR-4554 reduced/min/g tumour) under nitrogen. NADPH:cytochrome P450 reductase was a major microsomal enzyme involved in the bioreduction of SR-4554 by liver microsomes. In a panel of murine and human tumour xenografts, cytochrome P450 reductase activities were found to be low and only varied by 3-fold between different tumour types, suggesting that enzyme activities within the tumours are unlikely to influence markedly in vivo reductive metabolism. Reduction of SR-4554 by mouse liver microsomes showed a characteristic oxygen dependence with a half-maximal inhibition of 0.48 +/- 0.06%. Thus, the reductive metabolism of SR-4554 can be employed to detect the low oxygen tensions that occur within both murine and human tumours. Soluble, low molecular weight reductive metabolites of SR-4554 were identified by 19F NMR. These metabolite peaks appeared (up to 0.12 ppm) downfield of the parent drug peak. In conclusion, SR-4554 undergoes an oxygen-dependent metabolism that involves NADPH:cytochrome P450 reductase. 19F NMR is capable of identifying reduced metabolites that are undetectable by HPLC.
authors.affiliation: Clinical Pharmacology and New Drug Development Team, CRC Department of Medical Oncology, University of Glasgow, UK.
authors.forename: E O
authors.initials: EO
authors.lastname: Aboagye
authors.forename: A D
authors.initials: AD
authors.lastname: Lewis
authors.forename: M
authors.initials: M
authors.lastname: Tracy
authors.forename: P
authors.initials: P
authors.lastname: Workman
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D015335:Molecular Probes / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000502:physiology; D009593:Nitroimidazoles / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000494:pharmacology; D051381:Rats
chemical_list: D015335:Molecular Probes; D009593:Nitroimidazoles; C095171:SR 4554; D009251:NADPH-Ferrihemoprotein Reductase; D010100:Oxygen