title: Characterization of T-5 N-oxide formation as the first highly selective measure of CYP3A5 activity.
abstract: Almost half of prescription medications are metabolized by cytochrome P450 3A4 and 3A5. CYP3A4 and 3A5 have significant substrate overlap, and there is currently no way to selectively monitor the activity of these two enzymes, which has led to the erroneous habit of attributing the cumulative activity to CYP3A4. While CYP3A4 expression is ubiquitous, CYP3A5 expression is polymorphic, with large individual differences in CYP3A5 expression level. The CYP3A5 genotype has been shown to alter the pharmacokinetics of drugs in clinical trials. We report the first tool compound capable of determining CYP3A5 activity in biologic samples containing both enzymes. Oxidation of T-5 by CYP3A5 yields an N-oxide metabolite that is over 100-fold selective over CYP3A4. Formation of T-5 N-oxide highly correlates with the CYP3A5 genotype and CYP3A5 expression levels in human liver microsomes and human hepatocytes.
authors: Department of Molecular Therapeutics, Scripps Research Institute, Jupiter, Florida (M.D.C., X.L.); Celsis In Vitro Technologies, Baltimore Maryland (S.H.); Department of Chemistry, Dartmouth College, Hanover, New Hampshire (V.J., G.C.M.), Pharmacokinetics, Dynamics, and Metabolism Department, Pfizer Global Research and Development, Groton, Connecticut (G.S.W., R.S.).
authors: Xiaohai
authors: X
authors: Li
authors: Valer
authors: V
authors: Jeso
authors: Scott
authors: S
authors: Heyward
authors: Gregory S
authors: GS
authors: Walker
authors: Raman
authors: R
authors: Sharma
authors: Glenn C
authors: GC
authors: Micalizio
authors: Michael D
authors: MD
authors: Cameron
mesh_terms: D001711:Biotransformation; D002384:Catalysis; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003497:Cyclic N-Oxides / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A / Q000235:genetics / Q000378:metabolism*; D065692:Cytochrome P-450 CYP3A Inhibitors; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005838:Genotype; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D007546:Isoquinolines / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D010084:Oxidation-Reduction; D011725:Pyridines / Q000378:metabolism / Q000494:pharmacology*; D011994:Recombinant Proteins; D013379:Substrate Specificity; D053719:Tandem Mass Spectrometry
chemical_list: D003497:Cyclic N-Oxides; D065692:Cytochrome P-450 CYP3A Inhibitors; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D011725:Pyridines; D011994:Recombinant Proteins; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; C412889:T 1032