Metabolism And Excretion of the Dipeptidyl Peptidase 4 Inhibitor [C]Sitagliptin in Humans

The metabolism and excretion of [C]sitagliptin, an orally active, potent and selective dipeptidyl peptidase 4 inhibitor, were investigated in humans after a single oral dose of 83 mg/193 Ci. Urine, feces, and plasma were collected at regular intervals for up to 7 days. The primary route of excretion of radioactivity was via the kidneys, with a mean value of 87% of the administered dose recovered in urine. Mean fecal excretion was 13% of the administered dose. Parent drug was the major radioactive component in plasma, urine, and feces, with only 16% of the dose excreted as metabolites (13% in urine and 3% in feces), indicating that sitagliptin was eliminated primarily by renal excretion. Approximately 74% of plasma AUC of total radioactivity was accounted for by parent drug. Six metabolites were detected at trace levels, each representing <1 to 7% of the radioactivity in plasma. These metabolites were the N-sulfate and N-carbamoyl glucuronic acid conjugates of parent drug, a mixture of hydroxylated derivatives, an ether glucuronide of a hydroxylated metabolite, and two metabolites formed by oxidative desaturation of the piperazine ring followed by cyclization. These metabolites were detected also in urine, at low levels. Metabolite profiles in feces were similar to those in urine and plasma, except that the glucuronides were not detected in feces. CYP3A4 was the major cytochrome P450 isozyme responsible for the limited oxidative metabolism of sitagliptin, with some minor contribution from CYP2C8. Dipeptidyl peptidase 4 (DPP-4) is a ubiquitous proline-specific serine protease responsible for the rapid inactivation of incretins, including glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (Gorrell, 2005). GLP-1, which is released upon nutrient ingestion, stimulates meal-induced insulin secretion and contributes to glucose homeostasis (Kieffer and Habener, 1999). Stabilization of GLP-1 via DPP-4 inhibition is a new therapeutic approach for type 2 diabetes (Drucker, 2003; Holst, 2004; Mest and Mentlein, 2005; Nielsen, 2005). Sitagliptin (Januvia), also known as MK-0431 (Fig. 1), is an orally active, potent and selective DPP-4 inhibitor with an IC50 value of 18 nM (Kim et al., 2005). Sitagliptin has been shown to inhibit plasma DPP-4 activity in a dose-dependent manner and to enhance active GLP-1 levels in normal volunteers (Bergman et al., 2005, 2006; Herman et al., 2005b) and patients with type 2 diabetes (Herman et al., 2004). Furthermore, in patients with type 2 diabetes, single doses of sitagliptin enhanced insulin and C-peptide release, decreased glucagon secretion, and reduced plasma glucose levels after an oral glucose tolerance test (Herman et al., 2004), whereas 12-week treatment with sitagliptin significantly reduced HbA1c and fasting plasma glucose (Herman et al., 2005a; Scott et al., 2005). The metabolism and excretion of [C]sitagliptin were studied in male human volunteers after oral administration of 83 mg/193 Ci. In preclinical species, [C]sitagliptin was shown to be eliminated by biliary and/or renal excretion of parent drug (Beconi et al., 2007). Metabolism was minimal, and it involved N-sulfation (M1), N-carbamoyl glucuronidation (M4), hydroxylation (M6) followed by ether glucuronidation (M3), and oxidative desaturation followed by cyclization (M2 and M5) (Fig. 1). Synthetic standards of metabolites M1, M2, and M5 were tested for DPP-4 inhibition and shown to be 300-, 1000-, and 1000-fold less active, respectively, than parent drug. Materials and Methods Chemicals and Dose Preparation. [C]Sitagliptin was synthesized as the phosphate salt with a specific activity of 2.36 Ci/mg free base (1.9 Ci/mg salt) by the Labeled Compound Synthesis Group [Merck Research Laboratories (MRL), Rahway, NJ]. The chemical purity was 99.7%, as determined by HPLC. The dose was prepared as a capsule formulation containing 20 mg/48.3 Ci [C]sitagliptin (25 mg of phosphate salt). The 2,5-difluoro analog of sitagliptin used to saturate nonspecific binding sites on the solid phase extraction cartridges was provided by Process Research (MRL, Rahway, NJ). The Article, publication date, and citation information can be found at http://dmd.aspetjournals.org. doi:10.1124/dmd.106.013136. ABBREVIATIONS: DPP-4, dipeptidyl peptidase 4; GLP-1, glucagon-like peptide-1; LC-MS/MS, liquid chromatography-tandem mass spectrometry; LC-MS, LC-mass spectrometry; MRL, Merck Research Laboratories; sitagliptin, (2R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine); HPLC, high-performance liquid chromatography; MRM, multiple reaction monitoring; AUC, area under the curve; ADME, absorption, distribution, metabolism, and excretion. 0090-9556/07/3504-533–538$20.00 DRUG METABOLISM AND DISPOSITION Vol. 35, No. 4 Copyright © 2007 by The American Society for Pharmacology and Experimental Therapeutics 13136/3187368 DMD 35:533–538, 2007 Printed in U.S.A. 533 at A PE T Jornals on Jne 3, 2017 dm d.aspurnals.org D ow nladed from