Abstract
Humanized mice that express the human UDP-glucuronosyltransferase (UGT) 1 locus have been developed in a Ugt1-null background as a model to improve predictions of human UGT1A-dependent drug clearance. Enzyme kinetic parameters (Km and Vmax) and pharmacokinetic properties of three probe drugs were compared using wild-type and humanized UGT1 mice that express the Gilbert’s UGT1A1*28 allele [Tg(UGT1A1*28) Ugt1(−/−) mice]. The well characterized substrate for UGT1A1, 7-ethyl-10-hydroxy-camptothecin (SN-38), showed the greatest difference in parent drug exposure (∼3-fold increase) and clearance (∼3-fold decrease) in Tg(UGT1A1*28) Ugt1(−/−) mice after intravenous administration compared with wild-type and phenobarbital-treated animals. In contrast, the clearance of the UGT2B7 substrate (−)-17-allyl-4, 5α-epoxy-3, 14-dihydroxymorphinan-6-one (naloxone) was not altered in Tg(UGT1A1*28) Ugt1(−/−) mice. In addition, pharmacokinetic parameters with 1-(4-fluorophenyl)3(R)-[3-(4-fluorophenyl)-3(S)-hydroxypropyl]-4(S)-(4-hydroxyphenyl)-2-azetidinone (ezetimibe, Zetia; Merck & Co., Whitehouse Station, NJ), considered to be a major substrate for UGT1A1, showed small to no dependence on UGT1A1-directed glucuronidation. Enzyme kinetic parameters assessed for SN-38, ezetimibe, and naloxone using liver microsomes prepared from wild-type and Tg(UGT1A1*28) Ugt1(−/−) mice showed patterns consistent with the in vivo pharmacokinetic data. For SN-38 glucuronidation, Vmax decreased 5-fold in Tg(UGT1A1*28) Ugt1(−/−) mouse liver microsomes compared with microsomes prepared from wild-type mice, and decreased 10-fold compared with phenobarbital-treated Tg(UGT1A1*28) Ugt1(−/−) mice. These differences are consistent with SN-38 glucuronidation activities using HLMs isolated from individuals genotyped as UGT1A1*1 or UGT1A1*28. For ezetimibe and naloxone the differences in Vmax were minimal. Thus, Tg(UGT1A1*28) Ugt1(−/−) mice can serve as a pharmacokinetic model to further investigate the effects of UGT1A1 expression on drug metabolism.
Footnotes
This work was supported in part by the National Institutes of Health National Institute of Environmental Health Sciences [Grant ES10337]; Pfizer; and the Tobacco-Related Disease Research Program from the State of California [Grant 15RT-0251].
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.109.030130.
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- UGT
- UDP-glucuronosyltransferase
- P450
- cytochrome P450
- SN-38
- 7-ethyl-10-hydroxy-camptothecin
- CPT-11
- irinotecan
- HLM
- human liver microsome
- MLM
- mouse liver microsome
- LC/MS/MS
- liquid chromatography/tandem mass spectrometry
- AUC
- area under the curve.
- Received September 2, 2009.
- Accepted February 2, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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