Pharmacokinetics of muraglitazar (BMS-298585), a dual peroxisome proliferator-activated receptors (PPAR) α and γ activator,in mice,rats, dogs,and monkeys

The pharmacokinetic parameters of muraglitazar, a novel dual-activator of the peroxisome proliferator-activated receptors (PPAR)?α?and γ, were determined in mice, rats, dogs, and monkeys after intravenous and oral administration. In the mouse, rat, and monkey the absolute oral bioavailability of muraglitazar ranged from 64 to 88%, and in the dog oral bioavailability was approximately 18%. The systemic clearance values of muraglitazar in the mouse, rat, dog, and cynomolgus monkey were 1.2, 3.0, 12.3 and 1.2?ml min^?1?kg^?1, respectively. The terminal elimination half-life was 2.4?h in dogs and 7.3?h in rats. The terminal elimination half-life could not be determined in the mouse and monkey because the sampling interval did not adequately cover the terminal elimination phase. Muraglitazar appears to be distributed outside of the vasculature, with the steady-state volume of distribution being approximately twofold that of the vascular volume in rats and dogs, and approximately twofold that of the total body water in mice. The systemic plasma clearance of muraglitazar in humans was predicted to be approximately 12–14?ml?min^?1?kg^?1 based on allometry or by scaling of in vitro clearance parameters. Overall, the pharmacokinetic parameters of muraglitazar in preclinical species were acceptable for the advancement of the compound as a clinical candidate.     

Preclinical pharmacokinetics and metabolism of a potent non-nucleoside inhibitor of the hepatitis C virus NS5B polymerase

The disposition of compound A, a potent inhibitor of the hepatitis C virus (HCV) NS5B polymerase, was characterized in animals in support of its selection for further development. Compound A exhibited marked species differences in pharmacokinetics. Plasma clearance was 44 ml min-1 kg-1 in rats, 9 ml min-1 kg-1 in dogs and 16 ml min-1 kg-1 in rhesus monkeys. Oral bioavailability was low in rats (10%) but significantly higher in dogs (52%) and monkeys (26%). Compound A was eliminated primarily by metabolism in rats, with biliary excretion accounting for 30% of its clearance. Metabolism was mainly mediated by cyclohexyl hydroxylation, with N-deethylation and acyl glucuronide formation constituting minor metabolic pathways. Qualitatively, the same metabolites were identified using in vitro systems from all species studied, including humans. The low oral bioavailability of compound A in rats was mostly due to poor intestinal absorption. This conclusion was borne out by the findings that hepatic extraction in the rat was only 30%, intraperitoneal bioavailability was good, and compound A was poorly absorbed from the rat isolated intestinal loop, with no detectable intestinal metabolism. Compound A was not an inhibitor of major human cytochrome P450 enzymes, indicating minimal potential for clinical drug-drug interactions. The metabolic clearance of compound A in rat, dog and monkey hepatocytes correlated with the systemic clearance observed in these species. Since compound A was very stable in human hepatocytes, the results suggest that it will be a low clearance drug in humans.     

Age related changes in the clearance and oral absorption of sodium cromoglycate in the developing albino rat

A dual radioisotope method was used to investigate the clearance and oral abso***rption of sodium cromoglycate. Radiolabelled sodium cromoglycate was administered orally at a dose of 100 mg kg ¹ (¹⁴ C-labelled) and simultaneously subcutaneously at a dose of 2 mg kg^?1 (³ H-labelled) to rat pups 5, 9, 14, 20, 29 and 75 days old. Blood concentrations of ¹⁴ C and ³ H were measured at intervals for 24 h after dosing. Since the compound is not metabolized the blood concentrations of ¹⁴ C were taken as a measure of the sodium cromoglycate absorbed orally and the blood concentrations of ³ H as a measure of the subcutaneously administered material. Using the area under the oral ¹⁴ C blood curve (AUC) as an index of bioavailability, the calculated bioavailability of sodium cromoglycate (692·9?945·9 min μg ml^?1) in 5, 9 and 14 day old pups was 4–8 times greater than that observed (61·0-118·8 min μg ml^?1) in 20, 29 and 75 day old pups. The blood clearance of sodium cromoglycate was increased four-fold in 75 day old animals (43·9 ml min^?1 kg^?1) and three-fold in 20 and 29 day old pups when compared to the clearance in 5, 9 and 14 day old pups. The clearance in 5, 9 and 14 day old pups was relatively constant (10·8 ? 9·9 ml min^?1 kg^?1). In rats less than 14 days old the systemic absorption of sodium cromoglycate after oral administration was 2–3 times greater (6·8-9·2%) than in rats aged 20, 29 or 75 days old (2·7-3·3%). The reduction in oral bioavailability of sodium cromoglycate as the pups grew older was, therefore, due to both an increased blood clearance and a decreased absorption of the compound.     

Disposition of GDC-0879, a B-RAF kinase inhibitor in preclinical species

1. The pharmacokinetics and disposition of GDC-0879, a small molecule B-RAF kinase inhibitor, was characterized in mouse, rat, dog, and monkey.

2. In mouse and monkey, clearance (CL) of GDC-0879 was moderate (18.7–24.3 and 14.5?±?2.1?ml min^?1 kg^?1, respectively), low in dog (5.84?±?1.06?ml min^?1 kg^?1) and high in rat (86.9?±?14.2?ml min^?1 kg^?1). The volume of distribution across species ranged from 0.49 to 1.9?l kg^?1. Mean terminal half-life values ranged from 0.28?h in rats to 2.97?h in dogs. Absolute oral bioavailability ranged from 18% in dog to 65% in mouse.

3. Plasma protein binding of GDC-0879 in mouse, rat, dog, monkey, and humans ranged from 68.8% to 81.9%.

4. In dog, the major ketone metabolite (G-030748) of GDC-0879 appeared to be formation rate-limited.

5. Based on assessment in dogs, the absorption of GDC-0879 appeared to be sensitive to changes in gut pH, food and salt form (solubililty), with approximately three- to four-fold change in areas under the curve (AUCs) observed.

     

Pharmacokinetics of gefitinib,an epidermal growth factor receptor tyrosine kinase inhibitor,in rat and dog

1.?The pharmacokinetics of gefitinib and its metabolites in rat and dog were investigated in preclinical studies conducted to support the safety evaluation and clinical development of gefitinib, the first EGFR tyrosine kinase inhibitor approved for the treatment of non-small-cell lung cancer.

2.?Following intravenous dosing (5?mg?kg^?1), gefitinib plasma half-life was 3–6?h in rats and dogs, although studies using a more sensitive HPLC-MS assay produced longer estimates of half-life (7–14?h).

3.?In these studies, plasma clearance was high (male rat: 25?ml?min^?1?kg^?1; female rat: 16?ml?min^?1?kg^?1; male dog: 16?ml?min^?1?kg^?1), as was the volume of distribution (8.0–10.4?l?kg^?1 in rat; 6.3?l?kg^?1 in dog), and exposure in female rats was double that in males.

4.?Following administration of [¹⁴C]-gefitinib, concentrations of radioactivity in plasma exceeded gefitinib throughout the profile, indicating the presence of circulating metabolites in both rat and dog.

5.?An HPLC-MS assay was developed to measure concentrations of gefitinib and five potential metabolites in plasma. All five metabolites were detected in the rat, but at levels much lower than gefitinib. In the dog, exposure to gefitinib and M523595 was similar, with much lower concentrations of M537194 and only trace levels of the other metabolites. This profile of metabolites is similar to that observed in man.     

Preclinical assessment of the ADME,efficacy and drug-drug interaction potential of a novel NAMPT inhibitor

1. GNE-617 (N-(4-((3,5-difluorophenyl)sulfonyl)benzyl)imidazo[1,2-a]pyridine-6-carboxamide) is a potent, selective nicotinamide phosphoribosyltransferase (NAMPT) inhibitor being explored as a potential treatment for human cancers.

2. Plasma clearance was low in monkeys and dogs (9.14?mL min^?1?kg^?1 and 4.62?mL min^?1?kg^?1, respectively) and moderate in mice and rats (36.4?mL min^?1?kg^?1 and 19.3?mL min^?1?kg^?1, respectively). Oral bioavailability in mice, rats, monkeys and dogs was 29.7, 33.9, 29.4 and 65.2%, respectively.

3. Allometric scaling predicted a low clearance of 3.3?mL min^?1?kg^?1 and a volume of distribution of 1.3?L kg^?1 in human.

4. Efficacy (57% tumor growth inhibition) in Colo-205 CRC tumor xenograft mice was observed at an oral dose of 15?mg/kg BID (AUC?=?10.4?µM h).

5. Plasma protein binding was moderately high. GNE-617 was stable to moderately stable in vitro. Main human metabolites identified in human hepatocytes were formed primarily by CYP3A4/5. Transporter studies suggested that GNE-617 is likely a substrate for MDR1 but not for BCRP.

6. Simcyp^® simulations suggested a low (CYP2C9 and CYP2C8) or moderate (CYP3A4/5) potential for drug-drug interactions. The potential for autoinhibition was low.

7. Overall, GNE-617 exhibited acceptable preclinical properties and projected human PK and dose estimates.

     

Species differences in hydrolase activities toward OT-7100 responsible for different bioavailability in rats,dogs, monkeys and humans

OT-7100 (5-n-butyl-7-(3,4,5-trimethoxybenzoylamino)pyrazolo[1,5-a] pyrimidine) is an amide moiety-bearing pyrazolopyrimidine derivative with a potential analgesic effect. To determine the factors responsible for observed species differences in the bioavailability of this drug, human and experimental animal samples were used to investigate in vitro microsomal and cytosolic hydrolase activities in the liver and small intestine vis-à-vis the pharmacokinetics of OT-7100. The AUC_0–t values of OT-7100 after oral administration in rats, dogs and monkeys were 0.163, 0.0383 and 0.00147?µg?h?ml^?1 divided by mg?kg^?1, respectively. The bioavailabilities of OT-7100 after oral administration in rats, dogs and monkeys were 36, 17 and 0.3%, respectively. The plasma concentration–time profiles of intravenously administrated OT-7100 in rats, dogs and monkeys were similar. The hydrolase activities toward OT-7100 in liver microsomes or cytosol were approximately similar in rats, dogs, monkeys and humans. In contrast, hydrolase activities of small intestinal microsomes from monkeys were higher (36.1?ng?mg?protein^?1?min^?1) than those of rats, dogs and humans (5.4, 1.4 and 4.3?ng?mg?protein^?1?min^?1, respectively). These results suggest that the primary factor influencing first-pass metabolism for the OT-7100 is enzymatic hydrolysis in the small intestine. This information provides an important index for extrapolating the pharmacokinetics of drugs in humans using studies on monkeys.     

Pharmacokinetics,disposition and lipid-modulating activity of 5-{2-[4-(3,4-difluorophenoxy)-phenyl]-ethylsulfamoyl}-2-methyl-benzoic acid,a potent and subtype-selective peroxisome proliferator-activated receptor α agonist in preclinical species and human

1. 5-{2-[4-(3,4-Difluorophenoxy)-phenyl]-ethylsulfamoyl}-2-methyl-benzoic acid (1) is a novel, potent, and selective agonist of the peroxisome proliferator-activated receptor alpha (PPAR-α).

2. In preclinical species, compound 1 demonstrated generally favourable pharmacokinetic properties. Systemic plasma clearance (CL_p) after intravenous administration was low in Sprague–Dawley rats (3.2?±?1.4?ml min^?1 kg^?1) and cynomolgus monkeys (6.1?±?1.6?ml min^?1 kg^?1) resulting in plasma half-lives of 7.1?±?0.7?h and 9.4?±?0.8?h, respectively. Moderate bioavailability in rats (64%) and monkeys (55%) was observed after oral dosing. In rats, oral pharmacokinetics were dose-dependent over the dose range examined (10 and 50?mg kg^?1).

3. In vitro metabolism studies on 1 in cryopreserved rat, monkey, and human hepatocytes revealed that 1 was metabolized via oxidation and phase II glucuronidation pathways. In rats, a percentage of the dose (approximately 19%) was eliminated via biliary excretion in the unchanged form.

4. Studies using recombinant human CYP isozymes established that the rate-limiting step in the oxidative metabolism of 1 to the major primary alcohol metabolite M1 was catalysed by CYP3A4.

5. Compound 1 was greater than 99% bound to plasma proteins in rat, monkey, mouse, and human.

6. No competitive inhibition of the five major cytochrome P450 enzymes, namely CYP1A2, P4502C9, P4502C19, P4502D6 and P4503A4 (IC₅₀’s?>?30 μM) was discerned with 1.

7. Because of insignificant turnover of 1 in human liver microsomes and hepatocytes, human clearance was predicted using rat single-species allometric scaling from in vivo data. The steady-state volume was also scaled from rat volume after normalization for protein-binding differences. As such, these estimates were used to predict an efficacious human dose required for 30% lowering of triglycerides.

8. In order to aid human dose projections, pharmacokinetic/pharmacodynamic relationships for triglyceride lowering by 1 were first established in mice, which allowed an insight into the efficacious concentrations required for maximal triglyceride lowering. Assuming that the pharmacology translated in a quantitative fashion from mouse to human, dose projections were made for humans using mouse pharmacodynamic parameters and the predicted human pharmacokinetic estimates.

9. First-in-human clinical studies on 1 following oral administration suggested that the human pharmacokinetics/dose predictions were in the range that yielded a favourable pharmacodynamic response.

     

Preclinical assessment of the absorption,distribution, metabolism and excretion of GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide), an orally bioavailable systemic Hedgehog signalling pathway inhibitor

1. GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide) is a potent, selective Hedgehog (Hh) signalling pathway inhibitor being developed for the treatment of various cancers.

2. The in vivo clearance of GDC-0449 was estimated to be 23.0, 4.65, 0.338, and 19.3?ml min^?1 kg^?1 in mouse, rat, dog and monkeys, respectively. The volume of distribution ranged from 0.490 in rats to 1.68 l kg^?1 in mice. Oral bioavailability ranged from 13% in monkeys to 53% in dogs. Predicted human clearance using allometry was 0.096–0.649?ml min^?1 kg^?1 and the predicted volume of distribution was 0.766 l kg^?1.

3. Protein binding was extensive with an unbound fraction less than or equal to 6%, and the blood-to-plasma partition ratio ranged from 0.6 to 0.8 in all species tested. GDC-0449 was metabolically stable in mouse, rat, dog and human hepatocytes and had a more rapid turnover in monkey hepatocytes.

4. Proposed metabolites from exploratory metabolite identification in vitro (rat, dog and human liver microsomes) and in vivo (dog and rat urine) include three primary oxidative metabolites (M1–M3) and three sequential glucuronides (M4–M6). Oxidative metabolites identified in microsomes M1 and M3 were formed primarily by P4503A4/5 (M1) and P4502C9 (M3).

5. GDC-0449 was not a potent inhibitor of P4501A2, P4502B6, P4502D6, and P4503A4/5 with IC₅₀ estimates greater than 20?μM. K_i’s estimated for P4502C8, P4502C9 and P4502C19 and were 6.0, 5.4 and 24?μM, respectively. An evaluation with Simcyp® suggests that GDC-0449 has a low potential of inhibiting P4502C8 and P4502C9. Furthermore, GDC-0449 (15?μM) was not a potent P-glycoprotein/ABCB1 inhibitor in MDR1-MDCK cells.

6. Overall, GDC-0449 has an attractive preclinical profile and is currently in Phase II clinical trials.

     

Metabolism,pharmacokinetics and excretion of the GABAA receptor partial agonist [14C]CP-409,092 in rats

1. The metabolism and excretion of a GABA_A partial agonist developed for the treatment of anxiety, CP-409,092; 4-oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethyl-phenyl)-amide, were studied in rats following intravenous and oral administration of a single doses of [¹⁴C]CP-409,092.

2. The pharmacokinetics of CP-409,092 following single intravenous and oral doses of 4 and 15?mg kg^?1, respectively, were characterized by high clearance of 169?±?18?ml min^?1 kg^?1, a volume of distribution of 8.99?±?1.46 l kg^?1, and an oral bioavailability of 2.9% ± 3%.

3. Following oral administration of 100?mg kg^?1 [¹⁴C]CP-409,092, the total recovery was 89.1% ± 3.2% for male rats and 89.3% ± 0.58% for female rats. Approximately 87% of the radioactivity recovered in urine and faeces were excreted in the first 48?h. A substantial portion of the radioactivity was measured in the faeces as unchanged drug, suggesting poor absorption and/or biliary excretion. There were no significant gender-related quantitative/qualitative differences in the excretion of metabolites in urine or faeces.

4. The major metabolic pathways of CP-409,092 were hydroxylation(s) at the oxo-tetrahydro-indole moiety and oxidative deamination to form an aldehyde intermediate and subsequent oxidation to form the benzoic acid. The minor metabolic pathways included N-demethylation and subsequent N-acetylation and oxidation.

5. The present work demonstrates that oxidative deamination at the benzylic amine of CP-409,092 and subsequent oxidation to form the acid metabolite seem to play an important role in the metabolism of the drug, and they contribute to its oral clearance and low exposure.

     

Importance of mechanistic drug metabolism studies in support of drug discovery: A case study with an N -sulfonylated dipeptide VLA-4 antagonist in rats

N-(1-(3,5-dichlorobenzenesulfonyl)-2S-methyl-azetidine-2-carbonyl)-L-4-(2′,6′-dimethoxyphenyl)phenylalanine (1) is a potent antagonist of the very late activating (VLA) antigen-4. During initial screening, 1 exhibited an apparent plasma clearance (CL) of 227 ml min^?1 kg^?1 in Sprague–Dawley rats following an intravenous bolus dose formulated in an aqueous solution containing 40% polyethylene glycol. Such a high CL value led to speculation that the elimination of compound 1 involved extra-hepatic tissues. However, the apparent plasma CL was reduced to 97 ml in^?1 kg^?1 when a 2-min time point was added to sample collections, and further decreased to 48 ml min^?1 kg^?1 after the dose was formulated in rat plasma. The lung extraction of 1 in rats was negligible whereas the hepatic extraction was ≥90%, based on comparison of area under the curve (AUC) values derived from intra-artery, intravenous, and portal vein administration. In rats dosed intravenously with [¹⁴C]-1, approximately 91% of the radioactivity was recovered in bile over 48 h, with 85% accounted for in the first 4-h samples. The biliary radioactivity profile consisted of approximately 30% intact parent compound, 20% 1-glucuronide, and 50% oxidation products resulting from O-demethylation or hydroxylation reactions. When incubated with rat liver microsomes, oxidative metabolism of 1 was inhibited completely by 1-aminobenzotriazole (ABT), whereas the oxidation and glucuronidation reactions were little affected in the presence of cyclosporin A (CsA). In contrast, the hepatic extraction of 1 in rats was unperturbed in animals pre-dosed with ABT, but was reduced approximately 60% following treatment with CsA. In vitro, 1 was a substrate of the rat organic anion transporter Oatp1b2, and its cellular uptake was inhibited by CsA. In addition, the hepatic extraction of 1 was approximately 30% lower in Eisai hyperbilirubinaemic rats which lack functional multidrug resistant protein-2 (MRP2). Collectively, these data suggest that the clearance of 1 in rats likely is a result of the combined processes of hepatic oxidation, glucuronidation and biliary excretion, all of which are facilitated by active hepatic uptake of parent compound and subsequent active efflux of both unchanged parent and its metabolites into bile. It was concluded, therefore, that multiple mechanisms contribute to the clearance of 1 in rats, and suggest that appropriate pharmacokinetic properties might be difficult to achieve for this class of compounds. This case study demonstrates that an integrated strategy, incorporating both rapid screening and mechanistic investigations, is of particular value in supporting drug discovery efforts and decision-making processes.     

EXTRAHEPATIC FIRST-PASS METABOLISM OF NIFEDIPINE IN THE RAT

The peroral (po) bioavailability of nifedipine is reported to range from about 45 to 58% in the rat; this compares favourably to human beings. The metabolism of nifedipine is similar in rats and humans (oxidation of the dihydropyridine ring), with the liver believed to be solely responsible for the systemic clearance of the drug and the observed first-pass effect after po dosing. The purpose of this study was to determine whether intestinal metabolism also contributes to the first-pass elimination of nifedipine in the rat. The systemic availabilities of nifedipine doses given by po, intracolonic (ic), and intraperitoneal (ip) routes of administration were compared to that for an intravenous (iv) dose (in each case a dose of 6 mg kg⁻¹ was given) using adult male Sprague–Dawley rats (249–311 g, n =6 or 7/group). The geometric mean of systemic nifedipine plasma clearance after iv dosing was 10·3 mL min⁻¹ kg⁻¹. The nifedipine blood-to-plasma ratio was found to be about 0·59. Therefore, the systemic blood clearance of nifedipine was about 17·5 mL min⁻¹ kg⁻¹; which, compared to the hepatic blood flow of rats (55 to 80 mL min⁻¹ kg⁻¹) showed that nifedipine is poorly extracted by the liver (0·22≤E_H≤0·32). The mean absolute bioavailabilities of the po, ip, and ic doses were 61, 90, and 100%, respectively. Assuming complete absorption of the extravascular nifedipine doses these results indicate that, in addition to hepatic extraction, substantial first-pass elimination of nifedipine occurs within the wall of the small intestine but not the colon of the rat. © 1997 John Wiley & Sons, Ltd.     

Evaluation of antidiabetic properties of cactus pear seed oil in rats

Context: Cactus pear (Opuntia ficus-indica (L.) Mill. (Cactaceae)) is a medicinal plant widely used to treat diabetes.

Objective: This work investigates the hypoglycemic and antihyperglycemic effect of cactus pear seed oil (CPSO), its mechanism of action, and any toxic effects.

Materials and methods: The hypoglycemic effect of CPSO was evaluated in groups of six healthy Wistar rats given 1 or 2?ml?kg^?1 orally and compared with groups receiving glibenclamide (2?mg?kg^?1) or water. Glycemia was determined after 30, 60, 120, 240, and 360?min. The antihyperglycemic effect of CPSO was determined in healthy rats and in streptozotocin-induced diabetic rats (STZ); normal rats received 0.8?ml?kg^?1 CPSO, while diabetic rats received 1?ml?kg^?1 CPSO, their controls received water or 2?mg?kg^?1 glibenclamide. For the antihyperglycemic effect evaluation, all the animals were fasted for 16?h before treatment and received glucose orally at 1?g?kg^?1 30?min after treatment; blood was taken after 30, 90, 150, and 210?min. Intestinal glucose absorption was estimated in rat jejunum perfused with a solution containing 5.55?mmol?l^?1 glucose. Acute toxicity was determined in albino mice that received oral or intraperitoneal doses of 1, 3, or 5?ml?kg^?1 CPSO.

Results: CPSO (p.o.) decreased postprandial hyperglycemia (60?min after glucose loading), 40.33% and 16.01%, in healthy and STZ-diabetic glucose-loaded rats, respectively. CPSO, also, significantly decreased intestinal glucose absorption by 25.42%. No adverse effects were seen in mice administered CPSO at up to 5?ml?kg^?1.

Conclusion: CPSO is antihyperglycemic. The effect can be explained partly by inhibition of intestinal glucose absorption.     

Biotransformation and pharmacokinetics of the antiplasmodial naphthylisoquinoline alkaloid dioncophylline A

The biotransformation of the antiplasmodial naphthylisoquinoline alkaloid dioncophylline A by rat liver microsomes and its pharmacokinetics in male rats were studied. Incubation of dioncophylline A with rat liver microsomes resulted in the formation of the major metabolite 5′-O-demethyldioncophylline A, and a second minor metabolite, corresponding to the mass of an as yet unknown 4-hydroxydioncophylline A. Kinetic constants of the formation of 5′-O-demethyldioncophylline A were K_m?=?32?nmol and V_max?=?20?pmol?min^?1?mg^?1). Administration of dioncophylline A at a dose of 6.67?mg?kg^?1 body weight to rats intravenously and orally (n?=?4 per group) resulted in peak plasma levels of 0.84 and 0.11?µg?ml^?1, respectively. Levels of metabolites were below the limit of quantitation (LOQ). The following pharmacokinetic parameters of dioncophylline A were determined: oral bioavailability of 25%, plasma half-life of 2.5?h and partition volume of 8?l?kg^?1 body weight. Concentrations of dioncophylline A metabolites in all plasma and urine samples were below the limit of detection (LOD) and recovery of dioncophylline A in urine was very low, suggesting distribution into lipid rich tissues.     

Metabolism of roquinimex in mouse and rat: an in vitro/in vivo comparison

1.1. In vitro studies with roquinimex, animmuno-modulator, in liver microsomes from mouse and rat were conducted to evaluate the primary metabolism and compare the metabolite pattern as well as the rate of metabolismwith the in vivo pharmacokinetics of the compound in these two species. 2. In the presence ofNADPH, roquinimex wasmetabolized to six primary metabolites (R1-6) by liver microsomes from mouse and rat. The formation of these metabolites was qualitatively similar in both species, and was greatly enhanced by pretreatment with PCN, an inducer of cytochrome P4503A. 3. The identification of the R1-6 demonstratedthat roquinimex had been hydroxylated and demethylated. Hydroxylation at different sites of the quinoline moiety was the dominating reaction in both species. 4. Comparison of the resulting microsomal intrinsic clearance of 0.3 μmol mg^?1 protein min^?1 in mouse liver microsomes, versus 0.03 μmol mg^?1 protein min^?1 in rat liver microsomes demonstrated that the mouse possesses about a 10-fold greater metabolic capacity for roquinimex than the rat. 5. The in vivo pharmacokinetics of roquinimex demonstrated a 7-fold higher clearance in mouse than in the rat (82 ml h^?1 kg^?1 in mouse, 10.6 ml h^?1 kg^?1 in rat), which is in concordance with the in vitro findings.     

Preclinical absorption,distribution, metabolism and excretion (ADME) characterization of ICAM1988, an LFA-1/ICAM antagonist,and its prodrug

1. Intercellular adhesion molecule (ICAM)-1988 is a small molecule lymphocyte function-associated antigen-1 (LFA-1) antagonist being considered for its anti-inflammatory properties. Following intravenous administration of ICAM1988, clearances in mice, rats, dogs, and monkeys were 17.8, 3.31, 15.4, and 6.85 ml min^?1 kg^?1, respectively.

2. In mass balance studies using [¹⁴C]-ICAM1988 in rats dosed intravenously, unchanged ICAM1988 contributed to 25.1% of the dose.

3. In rats, the systemic bioavailability of ICAM1988 was improved to 0.28 when the drug was administered orally as its isobutyl ester, ICAM2660. In rats, this was consistent with the complete in vitro conversion of ICAM2660 to ICAM1988 in plasma, and liver and intestinal S9.

4. In dogs and monkeys, ICAM2660 did not improve the bioavailability of ICAM1988. This is consistent with limited in vitro conversion of ICAM2660 to ICAM1988 in plasma and liver S9.

5. In human in vitro studies, ICAM2660 conversion to ICAM1988 in liver was similar to rats while no conversion in plasma and intestinal S9 fractions were observed. Based on the in vitro metabolism similarities of human and rat, it would be anticipated that in human oral administration of ICAM2660 would improve the systemic exposure of ICAM1988.

     

Disposition of SK&F L-190144 in rats and monkeys after oral,intravenous or ocular administration

The objective of the study was to investigate the systemic disposition of ¹⁴C-SK&F L-190144 after single intravenous (10mg kg^?1) and oral (200 mg kg^?1) doses to rats and after single intravenous and ocular doses (0.33 mg kg^?1) to monkeys. After the intravenous dose, the blood concentration-time profile of ¹⁴C-SK&F L-190144 followed a rapid triexponential decline with half-lives of 2.5, 15, and 246 min in rats and 3, 19, and 2520 min in monkeys. The ¹⁴C-label in blood was mainly the parent compound. The terminal elimination half-life detected in rats using the urinary excretion rate-time data was 700 min. The total body clearance values were 17.6 ± 2.1 (mean ± SD, n = 6) and 1.11 ± 0.41 (n=4) mlmin^?1 kg^?1 for rats and monkeys, respectively. Both species had similar values of volume of distribution at the terminal phase, 4 to 6 l kg^?1, and similar excretion patterns, approximately 60 per cent and 30 per cent of the dose were excreted in the urine and feces, respectively. ¹⁴C-SK&F L-190144 was not absorbed orally in rats with the majority of the dose recovered in the feces. Following ocular administration to monkeys, the plasma drug concentrations peaked at 8 h post-dosing but did not reach a biexponential elimination phase until 18 h post-dosing, suggesting slow systemic absorption of drug from the ocular site. The monkeys excreted 42 per cent of the dose in urine and 50 per cent in feces after ocular administration. This increase in fecal excretion compared to the intravenous route of administration may have been due to the slow absorption by the ocular and nasal tissues altering the relative proportions of drug elimination via the renal and hepatic routes, or to a proportion of the dose passing into the gastrointestinal tract and exiting unabsorbed. Study results demonstrate similar excretion patterns and volume of distribution after intravenous administration in both species. The slow terminal elimination phase in monkeys was attributed to the low body clearance. The low oral bioavailability was possibly due to the poor partitioning behavior of the drug (logarithm of partition coefficient - 2.6). A significant fraction of the dose was absorbed in the body via the ocular route.     

Pharmacokinetics and metabolism of NO-1886, a lipoprotein lipase-promoting agent,in cynomolgus monkey

1. The study was conducted to investigate the pharmacokinetics and metabolism of NO-1886 (diethyl 4-[(4-bromo-2-cyanophenyl) carbamoyl] benzylphosphonate) in cynomolgus monkeys.

2. After single intravenous administration of NO-1886 at a dose of 3?mg?kg^?1, the total clearance (CL_tot), area under the plasma concentration–time curve (AUC_0–t), half-life (t_1/2), and volume of distribution (V_d) in cynomolgus monkeys were 531?ml?h^?1?kg^?1, 5.63?µg?h?ml^?1, 0.96?h and 679?ml?kg^?1, respectively. The AUC_0–t for oral administration of NO-1886 (3?mg?kg^?1) was 4.23?µg?h?ml^?1 and the bioavailability was 75%.

3. M-2 (ethyl 4-[(4-bromo-2-cyanophenyl) carbamoyl] benzylphosphonate) and M-3 (4-[(diethoxy-phosphoryl) methyl)] benzoic acid) were present as metabolites in plasma and urine. In faeces, M-2 was present but M-3 was not.

4. The major metabolite of NO-1886 in liver S9 or microsomes was M-2 in the presence of NADPH. On the other hand, M-3 was formed in the absence of NADPH in liver S9 or microsomes and its formation was inhibited by bis-(?p-nitrophenyl) phosphate (BNPP) in liver S9, suggesting that the formation of M-3 was catalysed by carboxylesterase.

5. The findings suggest that the main metabolic pathway of NO-1886 in cynomolgus monkeys is the O-deethylation of NO-1886 to M-2, as in rats and humans, and that the hydrolysis of the amide bond is a minor metabolic pathway.     

Species and gender differences in the formation of an active metabolite of a substituted 2,4-thiazolidinedione insulin sensitizer

1. The metabolism of a substituted 2,4-thiazolidinedione (P1) with dual PPARα/γ activity was evaluated in male and female rats, dogs and monkeys. A para-hydroxylated metabolite (M1) with potent PPARγ-selective agonist, was a major circulating drug-related component in female rats, dogs and monkeys, but not in male rats (M1-to-P1 exposure ratio of <1, 3–5, 5 and 5–11 in male rat, monkey, female rat, and dog, respectively).

2. M1 (%) formed in vitro (5, 53, 57–65, 67 and 67% in male rat, monkey, female rat, dog, and human liver microsomes, respectively), rank ordered with M1 (%) formed in vitro (24–45, 53–57, 78 and 75–85%, for male rat, monkey, female rat and dog, respectively, after oral administration of P1).

3. The plasma clearance of M1 was higher in male rats (32 ml min^-1 kg^-1 compared with 6, 7 and 2 ml min^-1 kg^-1 in female rat, male monkey and male dogs, respectively).

4. The low amounts of M1 observed in male rats, with the appearance of products of the cleavage of the propyl group between the phenyl groups was probably due to the presence of the sex-specific CYP2C11, which cleaves P1 at the propyl bridge. None of the CYPs present in female rats cleaved P1 at this site and M1 was only produced by CYP2C6. In humans, only CYP2C8 and the polymorphic CYP2C19 produced M1.     

Pharmacokinetics of the novel,high-affinity and selective dopamine D3 receptor antagonist SB-277011 in rat,dog and monkey: in vitro/in vivo correlation and the role of aldehyde oxidase

1. In vitro studies with the selective dopamine D3 receptor antagonist SB-277011 were conducted in liver microsomes and homogenates from rat, dog, cynomolgus monkey and human to correlate the rate of metabolism with the in vivo pharmacokinetics of the compound in rat, dog and cynomolgus monkey. 2. In the presence of NADPH, SB-277011 was relatively stable in the presence of liver microsomes from rat, dog, cynomolgus monkey and human with an intrinsic clearance (CL_i) of &lt;2ml min^-1 g^-1 liver for all species. In total liver homogenates, SB-277011 was metabolized at a similar rate in rat and dog (CL_i &lt;2mlmin^-1 g^-1 liver) to that in liver microsomes but in cynomolgus monkey and human (CL_i = 9.9 and 45 mlmin ^-1 g-^-1 liver, respectively) the intrinsic clearance was ~6- and 35-fold higher, respectively, than that in liver microsomes. 3. In the absence of NADPH, SB-277011 was rapidly cleared in liver homogenates from cynomolgus monkey and human (CL_i = 7.4 and 27ml min^-1 g^-1 liver, respectively) demonstrating that a significant pathway of metabolism of this compound was via an NADPH-independent non-microsomal oxidative route. This pathway was sensitive to inhibition with isovanillin suggesting that the enzyme responsible was aldehyde oxidase. 4. The in vivo pharmacokinetics showed that the plasma clearance of SB-277011 was low in rat (20 mlmin^-1 kg^-1), moderate in dog (14 mlmin^-1 kg^-1) and high in cynomolgus monkey (58 mlmin^-1 kg^-1), which is consistent with the in vitro findings and demonstrated a greater capacity for the monkey to metabolize this compound. The oral bioavailability of SB-277011 in rat, dog and cynomolgus monkey was 35, 43 and 2%, respectively. Given the high clearance of this compound in cynomolgus monkey, the low oral bioavailability is probably as a result of high first-pass elimination, specifically by aldehyde oxidase, rather than poor absorption. 5. The high in vitro clearance of SB-277011 in human liver homogenates and the involvement of aldehyde oxidase in the metabolism of SB-277011 indicates that the bioavailability of the compound is likely to be low in human.