ORIGINAL ARTICLESStudy of the genetic determinants of UGT1A1 inducibility by phenobarbital in cultured human hepatocytesRamírez, Jacquelinea *; Komoroski, Bernard J.e *; Mirkov, Snezanaa; Graber, Andrea Yodera; Fackenthal, Donna Leeb; Schuetz, Erin G.f; Das, Somab; Ratain, Mark J.a c d; Innocenti, Federicoa c d; Strom, Stephen C.eAuthor Information Departments of aMedicine bHuman Genetics cCommittee on Clinical Pharmacology and Pharmacogenomics dCancer Research Center, University of Chicago, Chicago, Illinois eDepartment of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, Pennsylvania fDepartment of Pharmaceutical Sciences, St Jude Children's Research Hospital, Memphis, Tennessee, USA Correspondence and requests for reprints to Federico Innocenti, University of Chicago, Department of Medicine, 5841 South Maryland Avenue, MC2115, Chicago, IL 60637, USA Tel: +1 773 834 2452; fax: +1 773 702 9698; e-mail: [email protected] Sponsorship: This work was supported by the Pharmacogenetics of Anticancer Agents Research (PAAR) Group (http://pharmacogenetics.org) (NIH/NIGMS grant U01 GM61393). Data will be deposited into PharmGKB (supported by NIH/NIGMS U01 GM61374, http://pharmgkb.org/). Received 21 April 2005 Accepted 6 September 2005 *Both authors contributed equally to the work. Pharmacogenetics and Genomics: February 2006 - Volume 16 - Issue 2 - p 79-86 doi: 10.1097/01.fpc.0000182784.77630.48 Buy Metrics Abstract UGT1A1 is induced by phenobarbital. We investigated whether three common UGT1A1 variants are associated with the variability in UGT1A1 inducibility. Human hepatocytes were incubated with 2 mM phenobarbital for 2 and 6 days followed by 5 μM SN-38 (1 h), a UGT1A1 probe. SN-38 glucuronidation in the cell media was measured by high-performance liquid chromatography. Three UGT1A1 promoter variants [−53(TA)6>7, −3156G>A and −3279T>G] were genotyped. Significant induction of UGT1A1 catalytic activity was observed in 82% and 100% of the cultures treated with phenobarbital for 2 days (median fold-induction=1.6, range 1.3–2.8; n=28) and 6 days (median fold-induction=2.8, range 1.6–6.4; n=16), respectively. After 2 days of treatment, a negative correlation was observed between the UGT1A1 basal activities and the fold-induction (Spearman r=−0.52, P<0.005). By contrast, the UGT1A1 activities in the basal and induced states were highly correlated (Spearman r=0.95, P<0.0001). Similar results were observed after 6 days of treatment. The allele frequencies were not significantly different between induced (n=22) and non-induced preparations (n=6) (P>0.05). The fold-induction was not associated with any variants (P>0.05). The basal and induced activities were correlated with −53(TA)6>7 (and with −3156G>A due to almost complete linkage with the −53 indel) (P=0.001). No association was found with the −3279T>G single nucleotide polymorphism (P>0.05). The indel at −53 affects the basal phenotype and appears to limit the hepatocyte capability of maximal induction after phenobarbital. However, variants at −53, −3156 and −3279 are not associated with variability in UGT1A1 inducibility. © 2006 Lippincott Williams & Wilkins, Inc.