The Uracil Breath Test in theAssessment of Dihydropyrimidine Dehydrogenase Activity: Pharmacokinetic Relationship between Expired 13 CO 2 and Plasma [2- 13 C]Dihydrouracil LoriK.Mattison, 1 Jeanne Fourie, 1 YukihiroHirao, 3 ToshihisaKoga, 3 Renee A.Desmond, 2 JenniferR.King, 1 TakefumiShimizu, 3 andRobertB.Diasio 1 Abstract Purpose: Dihydropyrimidine dehydrogenase (DPD) deficiency is criticalinthe predisposition to 5-fluorouracil dose-related toxicity.We recently characterized the phenotypic [2- 13 C]uracil breathtest(UraBT)with96%specificityand100%sensitivityforidentificationofDPDdeficien- cy.Inthepresentstudy,wecharacterizetherelationshipsamongUraBT-associatedbreath 13 CO 2 metabolite formation, plasma [2- 13 C]dihydrouracil formation, [2- 13 C]uracil clearance, and DPD activity. Experimental Design: Anaqueoussolutionof[2- 13 C]uracil(6mg/kg)wasorallyadministered to 23 healthy volunteers and 8 cancer patients. Subsequently, breath 13 CO 2 concentrations and plasma[2- 13 C]dihydrouraciland[2- 13 C]uracilconcentrationsweredeterminedover180minutes usingIRspectroscopyandliquidchromatography-tandemmassspectrometry,respectively.Phar- macokinetic variables were determined using noncompartmental methods. Peripheral blood mononuclearcell(PBMC)DPDactivitywasmeasuredusingtheDPDradioassay. Results: The UraBT identified 19 subjects with normal activity, 11subjects with partial DPD deficiency, and 1subject with profound DPD deficiency with PBMC DPD activity within the corresponding previously established ranges. UraBT breath 13 CO 2 DOB 50 significantly cor- related with PBMC DPD activity ( r p = 0.78), plasma [2- 13 C]uracil area under the curve ( r p = 0.73), [2- 13 C]dihydrouracil appearance rate ( r p = 0.76), and proportion of [2- 13 C]uracil metabolized to [2- 13 C]dihydrouracil ( r p = 0.77; all Ps < 0.05). Conclusions: UraBT breath 13 CO 2 pharmacokinetics parallel plasma [2- 13 C]uracil and [2- 13 C]dihydrouracilpharmacokineticsandareanaccuratemeasureofinterindividualvariationin DPDactivity.ThesepharmacokineticdatafurthersupportthefutureuseoftheUraBTasascreen- ingtesttoidentifyDPDdeficiencybefore5-fluorouracil-basedtherapy. Dihydropyrimidine dehydrogenase (EC 1.3.1.2, DPD) is the rate-limiting enzyme in uracil and 5-fluorouracil (5-FU) catabolism, converting >80% of an administered dose of 5-FU to inactive metabolites (1, 2). The initial step of catabolism is mediated by DPD converting 5-FU to 5-dihydrofluorouracil, with subsequent catabolism by dihydropyrimidinase and h-ureidopropionase enzymes to ultimately produce fluoro- h-alanine, ammonia, and CO 2 . The latter final metabolic end- products are excreted in the urine and breath (3). The pharmacogenetic syndrome of complete and partial DPD deficiency is prevalent in f0.1% and 3% to 5% of the general population, respectively (4). DPD deficiency is a significant pharmacogenetic factor in the predisposition of cancer patients to increased risk of altered 5-FU pharmacoki- netics and associated toxicity. Specifically, 60% of patients presenting with severe 5-FU-related hematologic toxicity showed reduced DPD activity (5). Recent studies have investigated the predictive value of the ratio of plasma dihydrouracil area under the curve (AUC) to uracil AUC (DUUR) for the assessment of DPD activity and potential individualization of 5-FU therapy. Specifically, 5-FU dose optimization may be based on the plasma DUUR observed before 5-FU administration (6). Jiang et al. have also showed that the pre-5-FU treatment DUUR may be a good index of DPD activity (7, 8). Our laboratory recently reported the rapid noninvasive phenotypic [2- 13 C]uracil breath test (UraBT) for assessment of DPD activity with 96% specificity and 100% sensitivity (9). Application of the UraBT to a large population of cancer-free subjects (n = 255) showed an observed 86% sensitivity (with 12 of 14 DPD-deficient subjects identified as DPD deficient) and Cancer Therapy: Clinical Authors’Affiliations: Divisions of 1 Clinical Pharmacology andToxicology and 2 Biostatistics, Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, Alabama and 3 Otsuka Pharmaceutical Co., Ltd., Tokushima,Japan Received9/15/05;revised10/18/05;accepted11/7/05. Grant support: NIH grant CA62164 (R.B. Diasio) and National Center for Research Resources grant M01RR-00032 (General Clinical Research Center, UniversityofAlabamaatBirmingham). Thecostsofpublicationofthisarticleweredefrayedinpartbythepaymentofpage charges.Thisarticlemustthereforebeherebymarked advertisement inaccordance with18U.S.C.Section1734solelytoindicatethisfact. Requests for reprints: Robert B. Diasio, Division of Clinical Pharmacology and Toxicology, Comprehensive Cancer Center, University of Alabama at Birmingham, 1824 6th Avenue South,WallaceTumor Institute, Room 620, Birmingham, AL 35294-3300.Fax:205-975-5650;E-mail:robert.diasio@ccc.uab.edu. F 2006AmericanAssociationforCancerResearch. doi:10.1158/1078-0432.CCR-05-2020 www.aacrjournals.org Clin Cancer Res 2006;12(2) January15, 2006 549 Cancer Research. on November 27, 2021. © 2006 American Association for clincancerres.aacrjournals.org Downloaded from