OV-A-3GENETIC DETERMINANTS OF THE HEPATIC EXPRES-

SION OF THE PHASE II CONJUGATING UGT1A3 ENZYME. B.Caillier, BSc, L. Villeneuve, MSc, O. Barbier, PhD, C. Guillemette,PhD, Laval University and CHUQ Research Center, Quebec, PQ,Canada.

BACKGROUND/AIMS: UDP-glucuronosyltransferase UGT1A3 issignificant for the glucuronic acid conjugation of a diversity of endo- andxenobiotics in the liver. Considering the variability in UGT1A3-mediated hepatic glucuronidation activity, this study was designed toidentify common UGT1A3 genetic variants and determine their potentialfor contributing to interindividual differences.

METHODS: Single nucleotide polymorphism (SNP) discoverywas accomplished by resequencing DNA samples from healthy Cau-casians. Haplotypes were inferred and population frequencies esti-mated using PHASE version 2.1. For functional analysis, we usedHepG2 cells in transfection studies with UGT1A3/luciferase con-structs and electromobility shift assays.

RESULTS: Sequence analysis revealed six UGT1A3 upstreamSNPs and 4 common (3-26%) promoter region haplotypes wereinferred. One of the promoter variants fell within a putative bindingfactor site for the hepatocyte nuclear factor (HNF)-1� at -148 and isassociated with a significant decrease in luciferase activity. The �148T C variant significantly decreased by 50% the binding of theprotein complex while the HNF1�-specific antibody was able tosupershift entirely the DNA-protein complex.

CONCLUSION: UGT1A3 common promoter haplotype variantsmodulate gene function, namely through a reduction of the HNF1�-mediated promoter activation, and might contribute to interindividualdifferences in UGT1A3-mediated glucuronidation.

OV-A-4INDUCTION OF CYTOCHROME P450 3A4 (CYP3A4) BY

VINBLASTINE: ROLE OF THE NUCLEAR RECEPTOR NR1I2.N. F. Smith, S. Mani, H. Huang, S. E. Bates, W. D. Figg, A.Sparreboom, National Cancer Institute, Albert Einstein College ofMedicine, Bethesda, MD.

BACKGROUND: Metabolism of the anticancer agent vinblastineis mediated by CYP3A4. It has been demonstrated that other micro-tubule stabilizing agents such as paclitaxel are capable of inducingthis enzyme via activation of NR1I2 (hPXR). Therefore, we evalu-ated the CYP3A4 induction potential of vinblastine both clinicallyand in vitro.

METHODS: The pharmacokinetics of the CYP3A4 phenotypingprobe midazolam (i.v. bolus, 0.0145 mg/kg) were determined in 6patients with renal cell cancer undergoing treatment with vinblastine(72-h i.v. q4w) at baseline and in cycle 3. Midazolam plasma con-centrations were measured by LC/MS and clearance (CL) was de-rived using non-compartmental analysis. Protein expression ofCYP3A4 and activation of hPXR by vinblastine were measured byWestern blotting and a transactivation assay using transiently trans-fected HepG2 cells, respectively (Mani et al, Clin Cancer Res 11:6359, 2005).

RESULTS: Vinblastine increased midazolam CL on average by60% (range, 2-317%; P�0.0156, Wilcoxon test). In vitro, vinblastineat clinically-relevant concentrations induced CYP3A4 and the hPXR-ligand binding domain, but had only weak to no effect on full lengthhPXR, suggesting it is only a weak activator of hPXR.

CONCLUSIONS: Vinblastine is able to induce CYP3A4 in vivoand thus has the potential to facilitate its own elimination and causeinteractions with other CYP3A4 substrates. The mechanism of pro-tein induction is likely to be at the level of RNA stabilization ordecreased protein turnover.

PII-1EFFECTS OF �2 GENETIC POLYMORPHISMS ON GLU-

COSE DYNAMICS DURING BETA-BLOCKER TITRATION INHEART FAILURE. K. I. Cheang, O. Vardeny, J. S. Zebrack, M. A.Munger, E. M. Gilbert, Virginia Commonwealth University, Univer-sity of Wisconsin, University of Utah, Richmond, VA.

BACKGROUND: �2-adrenergic receptor (ADRB2) polymor-phisms affect �2-mediated glucose production by terbutaline.Whether beta-blockers’ effects on �2-mediated glucose productionare affected by ADRB2 polymorphisms is unknown. This studydetermines the effect of ADRB2 Arg16Gly and Glu27Gln polymor-phisms on �2-mediated glucose dynamics during beta-blocker titra-tion in heart failure.

METHODS: From a previous heart failure cohort whose meto-prolol or carvedilol were titrated to maximally tolerated doses (up tometoprolol 200mg/d or carvedilol 25mg twice daily) in 5 visits, weanalyzed ADRB2 polymorphisms at codons 16 and 27, and glucoseAUC0-180min upon a �2-agonist (terbutaline) infusion in nondia-betic individuals.

RESULTS: Glucose AUC (mmol/Lx180 min) upon terbutalineinfusion decreases as beta-blocker dosages increase (p�0.0033, re-peated measure ANOVA). At baseline, subjects carrying a Glu alleleat codon 27 demonstrated lower glucose AUC compared to individ-uals homozygous for Gln, although this difference was not signifi-cant. After maximal beta-blocker titration, glucose AUC decreasedfrom 5.5�0.2 to 4.9�0.2 in subjects carrying a Glu allele at codon 27versus from 6.3�0.4 to 5.5�0.4 in subjects homozygous for Gln(p�0.0342, ANCOVA for comparisons between genotype groups).The ADRB2 Arg16Gly variant was not associated with differences inglucose values.

CONCLUSIONS: ADRB2 polymorphisms may play a role in�2-mediated glucose production in heart failure patients taking beta-blockers.

PII-2EFFECTS OF BUPRENORPHINE TRANSDERMAL SYSTEM

10 MG. AND 2 � 20 MG. ON QT INTERVALS IN HEALTHYSUBJECTS. S. C. Harris, MD, D. Hoelscher, MD, A. Kristensen,MS, S. A. O’Keefe, BSN, A. Schemera, BA, Purdue Pharma, LP,PPD Development, Stamford, CT.

AIM: Evaluate the effect of buprenorphine transdermal system(BTDS) 10 mg and 2 � 20 mg on QT/QTc intervals in healthysubjects, compared with placebo and oral moxifloxacin 400 mg.

METHODS: Randomized, placebo- and positive-controlled,parallel-group, thorough QTc study in 132 healthy adults (18 to 55years), BMI�30 kg/m2, normal cardiac conduction, and resting heartrate 50-85 bpm. Safety was assessed with adverse event reports,clinical laboratory results, vital signs and SpO2, physical examina-tions, ECGs, and telemetry.

RESULTS: BTDS 10 was not associated with a change in QTci.However, BTDS 2 � 20 (supratherapeutic dose) resulted in a pro-longation comparable to moxifloxacin 400 mg (Day 13). Mean (90%CI) changes from baseline in QTci over 24 hours compared withplacebo were 7.6 (5.4, 9.9) and 5.9 (3.3, 8.4) for single 400 mgmoxifloxacin doses on Days 6 and 13 respectively, and 0.4 (�1.8,2.6) and 5.9 (3.4, 8.4) for BTDS 10 and BTDS 2 � 20, respectively.No subjects had maximum QT/QTc intervals �480 msec, and nosubject had increases in QTci �30 msec.

Most common adverse events in BTDS group were nausea, head-ache, constipation, vomiting, and dizziness. No changes of potentialclinical importance were observed in vital signs, ECGs (except QTc),or laboratory tests.

CONCLUSIONS: BTDS 10 does not increase QTci in healthysubjects. BTDS 2 � 20 increases the QTci in healthy subjects by anamount comparable to 400 mg moxifloxacin. Most BTDS subjectswere successfully titrated to the supratherapeutic dose of 2 x BTDS-20.

CLINICAL PHARMACOLOGY & THERAPEUTICS2006;79(2) American Society for Clinical Pharmacology and Therapeutics P35