Toxicological consequences may occur when drug interactions involve drugs with narrow therapeutic indices such as the cytocbrome P450 2C9 (CYP2C9) substrates warfarin and phenytoin. To minimize risk to humans, accurate predictions of in vivo drug metabolism, pharmacokinetics and drug interactions from in vitro data are needed. Recently, careful examination of drug metabolism kinetic data has demonstrated that atypical kinetics of cytochrome P450 mediated reactions may occur with greater frequency than previously believed. Atypical kinetic profiles such as autoactivation, activation and substrate inhibition have been observed for several P450 isoforms including CYP2C9. These atypical kinetic processes may be either homotropic (involving only one substrate) or heterotropic (involving a substrate and another effector/substrate). Since these kinetic patterns are observed in vitro and investigators use these in vitro data to predict in vivo pharmacokinetics, it is imperative that the mechanisms for these interactions be studied to form a better foundation for in vitro-in vivo predictions of human drug metabolism and drug interactions. We hypothesize that critical amino acid changes in the CYP2C9 enzyme can alter the degree of cooperativity observed, that key molecule structural characteristics are required for heterotropic cooperativity, that these cooperativity interactions can be modeled and cooperativity can be observed in vivo. Using expressed CYP2C9 allelic variants and site-directed mutagenesis, metabolism of CYP2C9 substrates, which exhibit various kinetic profiles, and their interactions with a known effector (and a series of structural analogs) will be studied and modeled. Additionally, in vivo studies of a CYP2C9 substrate and a known (in vitro) effector will be conducted. Taken together, these results will improve CYP2C9 in vitro-in vivo predictive capabilities.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
Project #
Application #
Study Section
Alcohol and Toxicology Subcommittee 4 (ALTX)
Program Officer
Okita, Richard T
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Minnesota Twin Cities
Schools of Pharmacy
United States
Zip Code
Zhou, Jin; Tracy, Timothy S; Remmel, Rory P (2011) Correlation between bilirubin glucuronidation and estradiol-3-gluronidation in the presence of model UDP-glucuronosyltransferase 1A1 substrates/inhibitors. Drug Metab Dispos 39:322-9
Subramanian, Murali; Tam, Harrison; Zheng, Helen et al. (2010) CYP2C9-CYP3A4 protein-protein interactions: role of the hydrophobic N terminus. Drug Metab Dispos 38:1003-9
Zhou, Jin; Tracy, Timothy S; Remmel, Rory P (2010) Glucuronidation of dihydrotestosterone and trans-androsterone by recombinant UDP-glucuronosyltransferase (UGT) 1A4: evidence for multiple UGT1A4 aglycone binding sites. Drug Metab Dispos 38:431-40
Zhou, Jin; Tracy, Timothy S; Remmel, Rory P (2010) Bilirubin glucuronidation revisited: proper assay conditions to estimate enzyme kinetics with recombinant UGT1A1. Drug Metab Dispos 38:1907-11
Subramanian, Murali; Low, Michael; Locuson, Charles W et al. (2009) CYP2D6-CYP2C9 protein-protein interactions and isoform-selective effects on substrate binding and catalysis. Drug Metab Dispos 37:1682-9
Yang, Mingli; Kabulski, Jarod L; Wollenberg, Lance et al. (2009) Electrocatalytic drug metabolism by CYP2C9 bonded to a self-assembled monolayer-modified electrode. Drug Metab Dispos 37:892-9
Kramer, Melissa A; Tracy, Timothy S (2008) Studying cytochrome P450 kinetics in drug metabolism. Expert Opin Drug Metab Toxicol 4:591-603
Hummel, Matthew A; Gannett, Peter M; Aguilar, Jarrett et al. (2008) Substrate proton to heme distances in CYP2C9 allelic variants and alterations by the heterotropic activator, dapsone. Arch Biochem Biophys 475:175-83
Mosher, Carrie M; Hummel, Matthew A; Tracy, Timothy S et al. (2008) Functional analysis of phenylalanine residues in the active site of cytochrome P450 2C9. Biochemistry 47:11725-34
Locuson, Charles W; Gannett, Peter M; Ayscue, Robyn et al. (2007) Use of simple docking methods to screen a virtual library for heteroactivators of cytochrome P450 2C9. J Med Chem 50:1158-65

Showing the most recent 10 out of 30 publications