Determination of enzymatic kinetics of metabolism of dimethoate and omethoate in rats and humans.

1. Dimethoate is an organophosphate insecticide. The objective of this work was to determine the enzymatic kinetics of metabolism of dimethoate and its active metabolite omethoate in rats and humans and obtain key input parameters for physiologically based pharmacokinetic (PBPK) model.2. First, the intrinsic clearance of dimethoate expressed as formation rate of omethoate was determined to be ∼42-fold lower in human liver microsomes (HLM) (0.39 µL/min/mg) than in rat liver microsomes (RLM) (16.6 µL/min/mg) by an LC/MS/MS method. Next, dimethoate clearance in liver microsomes was determined using parent depletion and total [14C]-metabolite formation methods. Results from both approaches showed slower clearance of dimethoate in HLM (1.1-3.3 µL/min/mg) than in RLM (12.7-17.4 µL/min/mg).3. Investigation of in vitro enzymatic kinetics of omethoate demonstrated that the intrinsic clearance rates for omethoate in adult and juvenile RLM and HLM were similar. No significant turnover of dimethoate was apparent in rat cytosol or plasma. In contrast, degradation of omethoate in human plasma was slightly higher than in rat plasma.4. Finally, toxicokinetics of dimethoate were determined in adult and juvenile rats. In both age groups, following oral dosing, absorption of dimethoate was rapid with formation of significant amounts of omethoate.

In Vitro and In Vivo Metabolism of a Novel Antimitochondrial Cancer Metabolism Agent, CPI-613, in Rat and Human.

CPI-613, an inhibitor of pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (KGDH) enzymes, is currently in development for the treatment of pancreatic cancer, acute myeloid leukemia, and other cancers. CPI-613 is an analog of lipoic acid, an essential cofactor for both PDH and KGDH. Metabolism and mass balance studies were conducted in rats after intravenous administration of [14C]-CPI-613. CPI-613 was eliminated via oxidative metabolism followed by excretion of the metabolites in feces (59%) and urine (22%). ß-Oxidation was the major pathway of elimination for CPI-613. The most abundant circulating components in rat plasma were those derived from ß-oxidation. In human hepatocytes, CPI-613 mainly underwent ß-oxidation (M1), sulfur oxidation (M2), and glucuronidation (M3). The Michaelis-Menten kinetics (Vmax and Km) of the metabolism of CPI-613 to these three metabolites predicted the fraction metabolized leading to the formation of M1, M2, and M3 to be 38%, 6%, and 56%, respectively. In humans, after intravenous administration of CPI-613, major circulating species in plasma were the parent and the ß-oxidation derived products. Thus, CPI-613 metabolites profiles in rat and human plasma were qualitatively similar. ß-Oxidation characteristics and excretion patterns of CPI-613 are discussed in comparison with those reported for its endogenous counterpart, lipoic acid. SIGNIFICANCE STATEMENT: This work highlights the clearance mechanism of CPI-613 via ß-oxidation, species differences in their ability to carry out ß-oxidation, and subsequent elimination routes. Structural limitations for completion of terminal cycle of ß-oxidation is discussed against the backdrop of its endogenous counterpart lipoic acid.

Age dependent in vitro metabolism of bifenthrin in rat and human hepatic microsomes.

Bifenthrin, a pyrethroid insecticide, undergoes oxidative metabolism leading to the formation of 4'-hydroxy-bifenthrin (4'-OH-BIF) and hydrolysis leading to the formation of TFP acid in rat and human hepatic microsomes. In this study, age-dependent metabolism of bifenthrin in rats and humans were determined via the rates of formation of 4'-OH-BIF and TFP acid following incubation of bifenthrin in juvenile and adult rat (PND 15 and PND 90) and human (<5years and >18years) liver microsomes. Furthermore, in vitro hepatic intrinsic clearance (CLint) of bifenthrin was determined by substrate consumption method in a separate experiment. The mean Vmax(±SD) for the formation of 4'-OH-BIF in juvenile rat hepatic microsomes was 25.0±1.5pmol/min/mg which was significantly lower (p<0.01) compared to that of adult rats (86.0±17.7pmol/min/mg). However, the mean Km values for juvenile (19.9±6.6µM) and adult (23.9±0.4µM) rat liver microsomes were similar. On the other hand, in juvenile human hepatic microsomes, Vmax for the formation of 4'-OH-BIF (73.9±7.5pmol/min/mg) was significantly higher (p<0.05) than that of adults (21.6±0.6pmol/min/mg) albeit similar Km values (10.5±2.8µM and 8.9±0.6µM) between the two age groups. The trends in the formation kinetics of TFP acid were similar to those of 4'-OH-BIF between the species and age groups, although the differences between juveniles and adults were less pronounced. The data also show that metabolism of bifenthrin occurs primarily via oxidative pathway with relatively lesser contribution (~30%) from hydrolytic pathway in both rat and human liver microsomes. The CLint values for bifenthrin, determined by monitoring the consumption of substrate, in juvenile and adult rat liver microsomes fortified with NADPH were 42.0±7.2 and 166.7±20.5µl/min/mg, respectively, and the corresponding values for human liver microsomes were 76.0±4.0 and 21.3±1.2µl/min/mg, respectively. The data suggest a major species difference in the age dependent metabolism of bifenthrin. In human liver microsomes, bifenthrin is metabolized at a much higher rate in juveniles than in adults, while the opposite appears to be true in rat liver microsomes.

Coadministration of Rifampin Significantly Reduces Odanacatib Concentrations in Healthy Subjects.

This open-label 2-period study assessed the effect of multiple-dose administration of rifampin, a strong cytochrome P450 3A (CYP3A) and P-glycoprotein inducer, on the pharmacokinetics of odanacatib, a cathepsin K inhibitor. In period 1, 12 healthy male subjects (mean age, 30 years) received a single dose of odanacatib 50 mg on day 1, followed by a 28-day washout. In period 2, subjects received rifampin 600 mg/day for 28 days; odanacatib 50 mg was coadministered on day 14. Blood samples for odanacatib pharmacokinetics were collected at predose and on day 1 of period 1 and day 14 of period 2. Coadministration of odanacatib and rifampin significantly reduced odanacatib exposure. The odanacatib AUC0-∞ geometric mean ratio (90% confidence interval) of odanacatib + rifampin/odanacatib alone was 0.13 (0.11-0.16). The harmonic mean ± jackknife standard deviation apparent terminal half-life (t½ ) was 71.6 ± 10.2 hours for odanacatib alone and 16.0 ± 3.4 hours for odanacatib + rifampin, indicating greater odanacatib clearance following coadministration with rifampin. Samples were collected in period 2 during rifampin dosing (days 1, 14, and 28) and after rifampin discontinuation (days 35, 42, and 56) to evaluate the ratio of plasma 4ß-hydroxycholesterol to total serum cholesterol as a CYP3A4 induction biomarker; the ratio increased ∼5-fold over 28 days of daily dosing with 600 mg rifampin, demonstrating sensitivity to CYP3A4 induction.

Prednisone has no effect on the pharmacokinetics of CYP3A4 metabolized drugs - midazolam and odanacatib.

We evaluated the effect of prednisone on midazolam and odanacatib pharmacokinetics. In this open-label, 2-period crossover study in healthy male subjects, midazolam 2 mg was administered (Day -1) followed by odanacatib 50 mg (Day 1) during Part 1. In Period 2, prednisone 10 mg once daily (qd) was administered on Days 1-28; odanacatib was co-administered on Day 14 and midazolam 2 mg was co-administered on Days 1 and 28. Subjects were administered midazolam 2 mg on Days 42 and 56. Safety and tolerability were assessed throughout the study. A physiologically-based pharmacokinetic (PBPK) model was also built. There were 15 subjects enrolled; mean age was 31 years. The odanacatib AUC(0- ∞) GMR (90% CI) [odanacatib + prednisone (Day 14, Period 2)/odanacatib alone (Day 1, Period 1] was 1.06 (0.96, 1.17). AUC(0-∞) GMR (90%CI) [midazolam + prednisone (Day 28, Period 2)/midazolam alone (Day -1, Period 1] was 1.08 (0.93,1.26). There were no serious AEs or AEs leading to discontinuation. PBPK modeling showed that prednisone does not cause significant effects on the exposure of sensitive CYP3A4 substrates in vivo at therapeutic doses. Co-administration of prednisone 10 mg qd had no effect on pharmacokinetics of either odanacatib 10 mg or midazolam 2 mg.

Disposition and metabolism of the cathepsin K inhibitor odanacatib in humans.

Odanacatib is a selective inhibitor of the cathepsin K enzyme that is expressed in osteoclasts involved in the degradation of bone organic matrix, and is being developed as a novel treatment of osteoporosis. Odanacatib has demonstrated increases in bone mineral density in postmenopausal women and is undergoing a pivotal phase III trial. The absorption, metabolism, and excretion of [(14)C]odanacatib were studied in healthy male volunteers (n = 6) after a single oral dose of 25 mg (100 µCi). Plasma, urine, and fecal samples were collected at intervals up to 34 days postdose. The pharmacokinetics of odanacatib were characterized by slow absorption (mean time to achieve maximum plasma concentration of 14.2 hours) and long apparent elimination half-life (mean t1/2 96.7 hours); 74.5% of the dose was recovered in feces and 16.9% in urine, resulting in a total recovery of 91.4%. Seven metabolites were identified in urine; the major pathway (methyl hydroxylation producing M8 and its derivatives) was largely dependent on CYP3A. Metabolites and odanacatib accounted for 77% and 23% of urinary radioactivity, respectively. In fecal extracts, the only radioactive components identified were odanacatib (60.9%) and M8 (9.5%). The fraction of odanacatib in feces derived from absorbed drug was estimated using a bioavailability value obtained from the results of a separate intravenous study. Collectively, the data indicate that odanacatib has a long t1/2 on account of its low metabolic intrinsic clearance, and that metabolism (principally mediated by CYP3A) and excretion of intact parent compound account for ∼70% and ∼30% of the clearance of odanacatib in humans.

Pharmacokinetics and metabolism in rats, dogs, and monkeys of the cathepsin k inhibitor odanacatib: demethylation of a methylsulfonyl moiety as a major metabolic pathway.

Odanacatib is a potent cathespin K inhibitor that is being developed as a novel therapy for osteoporosis. The disposition and metabolism of odanacatib were evaluated in rats, dogs, and rhesus monkeys after intravenous and oral administration of [¹4C]odanacatib. Odanacatib was characterized by low systemic clearance in all species and by a long plasma half-life in monkeys (18 h) and dogs (64 h). The oral bioavailability was dependent on the vehicle used and ranged from 18% (monkey) to ~100% (dog) at doses of 1 to 5 mg/kg, using nonaqueous vehicles. After intravenous and oral administration to intact rats and monkeys > 90% of the dose was recovered, mainly in the feces. Studies in bile duct-cannulated animals indicated that biliary secretion was the major mode of elimination of radioactivity; odanacatib also underwent some intestinal secretion. In monkeys, odanacatib was almost completely eliminated by metabolism; metabolism also played a major role in the clearance of odanacatib in rats and dogs. The major metabolic pathways were methyl hydroxylation (formation of M8 and its derivatives), methyl sulfone demethylation (formation of M4 and its derivative M5), and glutathione conjugation (formation of the cyclized cysteinylglycine adduct M6 after addition of glutathione to the nitrile group of odanacatib). The major metabolites in rats [M4 (parent-14 Da) and M5 (oxygenated derivative of M4)] were determined to arise from a novel pathway that involved oxidative demethylation of the methylsulfonyl moiety of odanacatib. Overall, odanacatib displayed species-dependent metabolism, which explains, at least in part, the divergent plasma half-life observed.

Lack of a clinically meaningful pharmacokinetic effect of rifabutin on raltegravir: in vitro/in vivo correlation.

Raltegravir is an HIV-1 integrase strand transfer inhibitor with potent activity against HIV-1. A prior investigation of raltegravir coadministered with rifampin demonstrated a decrease in plasma concentrations of raltegravir likely secondary to induction of UGT1A1, the enzyme primarily responsible for the metabolism of raltegravir. Little is known regarding the induction of UGT1A1 by rifabutin, an alternate rifamycin. In vitro characterization of the induction potency of rifampin and rifabutin on UGT1A1 was performed. In vitro studies indicate that rifabutin is a less potent inducer of UGT1A1 messenger RNA expression than is rifampin. A fixed-sequence, 2-period, clinical crossover study was conducted to assess the effect of rifabutin on plasma levels of raltegravir: period 1, 400 mg of raltegravir every 12 hours for 4 days; period 2, 400 mg of raltegravir every 12 hours and 300 mg of rifabutin once daily for 14 days. Geometric mean ratio (GMR) (coadministration of rifabutin and raltegravir vs raltegravir alone) of raltegravir area under the concentration-time curve from 0 to 12 hours post dose (AUC(0-12h)) and the 90% confidence interval (CI) was 1.19 (0.86-1.63); GMR of concentration at 12 hours (C(12h)) and 90% CI was 0.80 (0.68-0.94); and GMR of time to maximal concentration (C(max)) and 90% CI was 1.39 (0.87-2.21). Overall, coadministration of rifabutin did not alter raltegravir pharmacokinetics to a clinically meaningful degree.

Approaches for minimizing metabolic activation of new drug candidates in drug discovery.

A large body of circumstantial evidence suggests that metabolic activation of drug candidates to chemically reactive electrophilic metabolites that are capable of covalently modifying cellular macromolecules may result in acute and/or immune system-mediated idiosyncratic toxicities in humans. Thus, minimizing the potential for metabolic activation of new drug candidates during the drug discovery and lead optimization stage represents a prudent strategy to help discover and develop the next generation of safe and effective therapeutic agents. In the present chapter, we discuss the scientific methodologies that currently are available to industrial pharmaceutical scientists for assessing and minimizing metabolic activation during drug discovery, their attributes and limitations, and future scientific directions that have the potential to help advance progress in this field. We also propose a roadmap that should help utilize the armamentarium of available scientific tools in a logical way and contribute to addressing metabolic activation issues in the drug discovery-setting in a rapid, scientifically appropriate, and resource-conscious manner.

Metabolism and renal elimination of gaboxadol in humans: role of UDP-glucuronosyltransferases and transporters.

PURPOSE: Gaboxadol, a selective extrasynaptic agonist of the delta-containing gamma-aminobutyric acid type A (GABAA) receptor, is excreted in humans into the urine as parent drug and glucuronide conjugate. The goal of this study was to identify the UDP-Glucuronosyltransferase (UGT) enzymes and the transporters involved in the metabolism and active renal secretion of gaboxadol and its metabolite in humans.Methods. The structure of the glucuronide conjugate of gaboxadol in human urine was identified by LC/MS/MS. Human recombinant UGT isoforms were used to identify the enzymes responsible for the glucuronidation of gaboxadol. Transport of gaboxadol and its glucuronide was evaluated using cell lines and membrane vesicles expressing human organic anion transporters hOAT1 and hOAT3, organic cation transporter hOCT2, and the multidrug resistance proteins MRP2 and MRP4.Results. Our study indicated that the gaboxadol-O-glucuronide was the major metabolite excreted in human urine. UGT1A9, and to a lesser extent UGT1A6, UGT1A7 and UGT1A8, catalyzed the O-glucuronidation of gaboxadol in vitro. Gaboxadol was transported by hOAT1, but not by hOCT2, hOAT3, MRP2, and MRP4. Gaboxadol-O-glucuronide was transported by MRP4, but not MRP2.Conlusion. Gaboxadol could be taken up into the kidney by hOAT1 followed by glucuronidation and efflux of the conjugate into urine via MRP4.

Minimizing metabolic activation during pharmaceutical lead optimization: progress, knowledge gaps and future directions.

Minimizing the potential for drug candidates to form chemically reactive metabolites that can covalently modify cellular macromolecules represents a rational strategy to reduce the risk of drug-induced idiosyncratic toxicity in humans. In this review, the approaches that are currently available for addressing this issue during the lead optimization phase of drug discovery, their limitations, and future scientific directions that have the potential to address these limitations are discussed.

Lack of a pharmacokinetic effect of raltegravir on midazolam: in vitro/in vivo correlation.

Raltegravir is a novel HIV-1 integrase inhibitor with potent in vitro activity (95% inhibitory concentration = 33 nM in 50% human serum). In vitro characterization of raltegravir inhibition potential was assessed against a panel of cytochrome P450 (CYP) enzymes. An open-label, 2-period study was conducted to assess the effect of raltegravir on the pharmacokinetics of midazolam, a sensitive CYP 3A4 probe substrate: period 1, 2.0 mg of midazolam; period 2, 400 mg of raltegravir every 12 hours for 14 days with 2.0 mg of midazolam on day 14. There was no meaningful in vitro effect of raltegravir on inhibition of a panel of CYP enzymes and induction of CYP 3A4. In the presence of raltegravir, midazolam area under the curve extrapolated to infinity (AUC(0-infinity)) and maximum plasma concentration (C(max)) geometric mean ratios were similar (geometric mean ratios and 90% confidence intervals: 0.92 [0.82, 1.03] (P = .208) and 1.03 [0.87, 1.22] (P = .751), respectively). No substantial differences were observed in T(max) (P = .750) or apparent half-life (P = .533) of midazolam. Plasma levels of midazolam were not substantially affected by raltegravir, which implies that raltegravir is not a clinically important inducer or inhibitor of CYP 3A4 and that raltegravir would not be expected to affect the pharmacokinetics of other drugs metabolized by CYP 3A4 to a clinically meaningful extent.

Metabolism and disposition in humans of raltegravir (MK-0518), an anti-AIDS drug targeting the human immunodeficiency virus 1 integrase enzyme.

Raltegravir is a potent human immunodeficiency virus 1 (HIV-1) integrase strand transfer inhibitor that is being developed as a novel anti-AIDS drug. The absorption, metabolism, and excretion of raltegravir were studied in healthy volunteers after a single oral dose of 200 mg (200 microCi) of [(14)C]raltegravir. Plasma, urine, and fecal samples were collected at specified intervals up to 240 h postdose, and the samples were analyzed for total radioactivity, parent compound, and metabolites. Radioactivity was eliminated in substantial amounts in both urine (32%) and feces (51%). The elimination of radioactivity was rapid, since the majority of the recovered dose was attributable to samples collected through 24 h. In extracts of urine, two components were detected and were identified as raltegravir and the glucuronide of raltegravir (M2), and each accounted for 9% and 23% of the dose recovered in urine, respectively. Only a single radioactive peak, which was identified as raltegravir, was detected in fecal extracts; raltegravir in feces is believed to be derived, at least in part, from the hydrolysis of M2 secreted in bile, as demonstrated in rats. The major entity in plasma was raltegravir, which represented 70% of the total radioactivity, with the remaining radioactivity accounted for by M2. Studies using cDNA-expressed UDP-glucuronosyltransferases (UGTs), form-selective chemical inhibitors, and correlation analysis indicated that UGT1A1 was the main UGT isoform responsible for the formation of M2. Collectively, the data indicate that the major mechanism of clearance of raltegravir in humans is UGT1A1-mediated glucuronidation.

Quantitation of geometric isomers of a phosphodiesterase inhibitor in rat and monkey plasma using liquid chromatography-tandem mass spectrometry.

Quantitation of geometric isomers of a phosphodiesterase inhibitor was required to determine the extent of interconversion following dosing of a single isomer in preclinical pharmacokinetic studies. Assays were developed for the simultaneous determination of Compound A (Fig. 1), 6-[1-methyl-1-(methylsulfonyl)ethyl-8(3-{(E)-2-(3-methyl-1,2,4-oxadiazol-5-yl)-2-[4-(methylsulfonyl)phenyl]ethenyl}phenyl)quinoline] and its geometric Z-isomer, Compound B, in plasma using liquid chromatography-tandem mass spectrometry. Sample clean-up was performed using a semi-automated liquid-liquid extraction procedure. Separation was achieved on a Phenomenex Synergi MAX-RP column. The method was validated in the linear range of 2-2000 ng/mL for Compound A and 0.5-500 ng/mL for Compound B in plasma and successfully applied to preclinical pharmacokinetic studies. Compound A was dosed in rats and Compound B in monkeys and the degree of conversion was determined by comparing the area under the curve. The relative amount of conversion was less than 1 and 10% in rats and monkeys, respectively. Because of the small amount of conversion and minor peak tailing of the dosed geometric isomer, the order of elution of the two analytes was important in order to achieve best quantitative results. The minor component needs to elute first; thus, a second assay was developed in which the order of elution was reversed. This was achieved by changing the mobile phase modifier.

Zafirlukast metabolism by cytochrome P450 3A4 produces an electrophilic alpha,beta-unsaturated iminium species that results in the selective mechanism-based inactivation of the enzyme.

Zafirlukast is a leukotriene antagonist indicated for the treatment of mild to moderate asthma, but the drug has been associated with occasional idiosyncratic hepatotoxicity. Structurally, zafirlukast is similar to 3-methylindole because it contains an N-methylindole moiety that has a 3-alkyl substituent on the indole ring. The results presented here describe the metabolic activation of zafirlukast via a similar mechanism to that described for 3-methylindole. NADP(H)-dependent biotransformation of zafirlukast by hepatic microsomes from rats and humans afforded a reactive metabolite, which was detected as its GSH adduct. Mass spectrometry and NMR data indicated that the GSH adduct was formed by the addition of GSH to the methylene carbon between the indole- and methoxy-substituted phenyl rings of zafirlukast. The formation of this reactive metabolite in human liver microsomes was shown to be exclusively catalyzed by CYP3A enzymes. Evidence for in vivo metabolic activation of zafirlukast was obtained when the same GSH adduct was detected in bile of rats given an iv or oral dose of the drug. On the basis of results with model peroxidases and of the structures of product alcohols from incubations containing H2(18)O, it appeared that zafirlukast underwent dehydrogenation by two sequential one-electron oxidations. In addition, zafirlukast proved to be a mechanism-based inhibitor of CYP3A4 activity in human liver microsomes and in microsomes containing cDNA-expressed CYP3A4. The enzyme inhibitory property of zafirlukast was selective for this enzyme among all of the P450 enzymes that were tested in human liver microsomes. The inactivation was characterized by a K(I) of 13.4 microM and k(inact) of 0.026 min(-1). In summary, zafirlukast dehydrogenation to an electrophilic alpha,beta-unsaturated iminium intermediate may be associated with idiosyncratic hepatotoxicity and/or cause drug-drug interactions through inactivation of CYP3A4.

A naphthyridine carboxamide provides evidence for discordant resistance between mechanistically identical inhibitors of HIV-1 integrase.

The increasing incidence of resistance to current HIV-1 therapy underscores the need to develop antiretroviral agents with new mechanisms of action. Integrase, one of three viral enzymes essential for HIV-1 replication, presents an important yet unexploited opportunity for drug development. We describe here the identification and characterization of L-870,810, a small-molecule inhibitor of HIV-1 integrase with potent antiviral activity in cell culture and good pharmacokinetic properties. L-870,810 is an inhibitor with an 8-hydroxy-(1,6)-naphthyridine-7-carboxamide pharmacophore. The compound inhibits HIV-1 integrase-mediated strand transfer, and its antiviral activity in vitro is a direct consequence of this ascribed effect on integration. L-870,810 is mechanistically identical to previously described inhibitors from the diketo acid series; however, viruses selected for resistance to L-870,810 contain mutations (integrase residues 72, 121, and 125) that uniquely confer resistance to the naphthyridine. Conversely, mutations associated with resistance to the diketo acid do not engender naphthyridine resistance. Importantly, the mutations associated with resistance to each of these inhibitors map to distinct regions within the integrase active site. Therefore, we propose a model of the two inhibitors that is consistent with this observation and suggests specific interactions with discrete binding sites for each ligand. These studies provide a structural basis and rationale for developing integrase inhibitors with the potential for unique and nonoverlapping resistance profiles.

3-Aminopyrrolidinone farnesyltransferase inhibitors: design of macrocyclic compounds with improved pharmacokinetics and excellent cell potency.

A series of macrocyclic 3-aminopyrrolidinone farnesyltransferase inhibitors (FTIs) has been synthesized. Compared with previously described linear 3-aminopyrrolidinone FTIs such as compound 1, macrocycles such as 49 combined improved pharmacokinetic properties with a reduced potential for side effects. In dogs, oral bioavailability was good to excellent, and increases in plasma half-life were due to attenuated clearance. It was observed that in vivo clearance correlated with the flexibility of the molecules and this concept proved useful in the design of FTIs that exhibited low clearance, such as FTI 78. X-ray crystal structures of compounds 49 and 66 complexed with farnesyltransferase (FTase)-farnesyl diphosphate (FPP) were determined, and they provide details of the key interactions in such ternary complexes. Optimization of this 3-aminopyrrolidinone series of compounds led to significant increases in potency, providing 83 and 85, the most potent inhibitors of FTase in cells described to date.

The disposition, metabolism, and pharmacokinetics of a selective metabotropic glutamate receptor agonist in rats and dogs.

Compound LY354740 [(+)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid], an analog of glutamic acid, is a selective group 2 metabotropic glutamate receptor agonist in clinical development for the treatment of anxiety. Studies have been conducted to characterize the absorption, disposition, metabolism, and excretion of LY354740 in rats and dogs after intravenous bolus or oral administration. Plasma concentrations of LY354740 were measured using a validated gas chromatography/mass spectrometry assay. In rats, LY354740 demonstrated linear pharmacokinetics after oral administration from 30 to 1000 mg/kg. The oral bioavailability of LY354740 was approximately 10% in rats and 45% in dogs. In the dog, food decreased the mean area under the plasma concentration-time curve value by approximately 34%, hence, decreasing the oral bioavailability of the compound. Excretion studies in both rats and dogs indicate that the absorbed drug is primarily eliminated via renal excretion. In addition, tissue distribution in rats showed that the highest levels of radioactivity were in the kidney and gastrointestinal tract, which is consistent with the excretion studies. Metabolism of LY354740 was evaluated in vitro using rat and dog liver microsomes and rat liver slices. In addition, urine and fecal samples from rat and dog excretion studies were profiled using HPLC with radio-detection. These evaluations indicated that neither rats nor dogs metabolized LY354740. In summary, LY354740 is poorly absorbed in rats, moderately absorbed in dogs, and rapidly excreted as unchanged drug in the urine.