Koppara Samuel

Extrapolation of Diclofenac Clearance from in Vitro Microsomal Metabolism Data: Role of Acyl Glucuronidation and Sequential Oxidative Metabolism of the Acyl Glucuronide

Diclofenac is eliminated predominantly (∼50%) as its 4′-hydroxylated metabolite in humans, whereas the acyl glucuronide (AG) pathway appears more important in rats (∼50%) and dogs (>80–90%). However, previous studies of diclofenac oxidative metabolism in human liver microsomes (HLMs) have yielded pronounced underprediction of human in vivo clearance. We determined the relative quantitative importance of 4′-hydroxy and AG pathways of diclofenac metabolism in rat, dog, and human liver microsomes. Microsomal intrinsic clearance values (CLint =V max/K m) were determined and used to extrapolate the in vivo blood clearance of diclofenac in these species. Clearance of diclofenac was accurately predicted from microsomal data only when both the AG and the 4′-hydroxy pathways were considered. However, the fact that the AG pathway in HLMs accounted for ∼75% of the estimated hepatic CLint of diclofenac is apparently inconsistent with the 4′-hydroxy diclofenac excretion data in humans. Interestingly, upon incubation with HLMs, significant oxidative metabolism of diclofenac AG, directly to 4′-hydroxy diclofenac AG, was observed. The estimated hepatic CLint of this pathway suggested that a significant fraction of the intrahepatically formed diclofenac AG may be converted to its 4′-hydroxy derivative in vivo. Further experiments indicated that this novel oxidative reaction was catalyzed by CYP2C8, as opposed to CYP2C9-catalyzed 4′-hydroxylation of diclofenac. These findings may have general implications in the use of total (free + conjugated) oxidative metabolite excretion for determining primary routes of drug clearance and may question the utility of diclofenac as a probe for phenotyping human CYP2C9 activity in vivo via measurement of its pharmacokinetics and total 4′-hydroxy diclofenac urinary excretion.

Discovery of N-[(1S,2S)-3-(4-Chlorophenyl)-2- (3-cyanophenyl)-1-methylpropyl]-2-methyl-2- {[5-(trifluoromethyl)pyridin-2-yl]oxy}propanamide (MK-0364), a novel, acyclic cannabinoid-1 receptor inverse agonist for the treatment of obesity.

The discovery of novel acyclic amide cannabinoid-1 receptor inverse agonists is described. They are potent, selective, orally bioavailable, and active in rodent models of food intake and body weight reduction. A major focus of the optimization process was to increase in vivo efficacy and to reduce the potential for formation of reactive metabolites. These efforts led to the identification of compound 48 for development as a clinical candidate for the treatment of obesity.

Potent, Brain-Penetrant, Hydroisoindoline-Based Human Neurokinin-1 Receptor Antagonists

3-[(3aR,4R,5S,7aS)-5-{(1R)-1-[3,5-bis(trifluoromethyl)phenyl]ethoxy}-4-(4-fluorophenyl)octahydro-2H-isoindol-2-yl]cyclopent-2-en-1-one (17) is a high affinity, brain-penetrant, hydroisoindoline-based neurokinin-1 (NK(1)) receptor antagonist with a long central duration of action in preclinical species and a minimal drug-drug interaction profile. Positron emission tomography (PET) studies in rhesus showed that this compound provides 90% NK(1) receptor blockade in rhesus brain at a plasma level of 67 nM, which is about 10-fold more potent than aprepitant, an NK(1) antagonist marketed for the prevention of chemotherapy-induced and postoperative nausea and vomiting (CINV and PONV). The synthesis of this enantiomerically pure compound containing five stereocenters includes a Diels-Alder condensation, one chiral separation of the cyclohexanol intermediate, an ether formation using a trichloroacetimidate intermediate, and bis-alkylation to form the cyclic amine.

Discovery of MK-1421, a Potent, Selective sstr3 Antagonist, as a Development Candidate for Type 2 Diabetes

The imidazolyl-tetrahydro-β-carboline class of sstr3 antagonists have demonstrated efficacy in a murine model of glucose excursion and may have potential as a treatment for type 2 diabetes. The first candidate in this class caused unacceptable QTc interval prolongation in oral, telemetrized cardiovascular (CV) dogs. Herein, we describe our efforts to identify an acceptable candidate without CV effects. These efforts resulted in the identification of (1R,3R)-3-(4-(5-fluoropyridin-2-yl)-1H-imidazol-2-yl)-1-(1-ethyl-pyrazol-4-yl)-1-(3-methyl-1,3,4-oxadiazol-3H-2-one-5-yl)-2,3,4,9-tetrahydro-1H-β-carboline (17e, MK-1421).

The Discovery of MK-4256, a Potent SSTR3 Antagonist as a Potential Treatment of Type 2 Diabetes

A structure-activity relationship study of the imidazolyl-β-tetrahydrocarboline series identified MK-4256 as a potent, selective SSTR3 antagonist, which demonstrated superior efficacy in a mouse oGTT model. MK-4256 reduced glucose excursion in a dose-dependent fashion with maximal efficacy achieved at doses as low as 0.03 mg/kg po. As compared with glipizide, MK-4256 showed a minimal hypoglycemia risk in mice.

Investigation of Cardiovascular Effects of Tetrahydro-β-carboline sstr3 antagonists

Antagonism of somatostatin subtype receptor 3 (sstr3) has emerged as a potential treatment of Type 2 diabetes. Unfortunately, the development of our first preclinical candidate, MK-4256, was discontinued due to a dose-dependent QTc (QT interval corrected for heart rate) prolongation observed in a conscious cardiovascular (CV) dog model. As the fate of the entire program rested on resolving this issue, it was imperative to determine whether the observed QTc prolongation was associated with hERG channel (the protein encoded by the human Ether-à-go-go-Related Gene) binding or was mechanism-based as a result of antagonizing sstr3. We investigated a structural series containing carboxylic acids to reduce the putative hERG off-target activity. A key tool compound, 3A, was identified from this SAR effort. As a potent sstr3 antagonist, 3A was shown to reduce glucose excursion in a mouse oGTT assay. Consistent with its minimal hERG activity from in vitro assays, 3A elicited little to no effect in an anesthetized, vagus-intact CV dog model at high plasma drug levels. These results afforded the critical conclusion that sstr3 antagonism is not responsible for the QTc effects and therefore cleared a path for the program to progress.

2-[(3aR,4R,5S,7aS)-5-{(1S)-1-[3,5-Bis(trifluoromethyl)phenyl]-2-hydroxyethoxy}-4-(2-methylphenyl)octahydro-2H-isoindol-2-yl]-1,3-oxazol-4(5H)-one: A Potent Human NK1 Receptor Antagonist with Multiple Clearance Pathways

Hydroisoindoline 2 has been previously identified as a potent, brain-penetrant NK1 receptor antagonist with a long duration of action and improved profile of CYP3A4 inhibition and induction compared to aprepitant. However, compound 2 is predicted, based on data in preclinical species, to have a human half-life longer than 40 h and likely to have drug-drug-interactions (DDI), as 2 is a victim of CYP3A4 inhibition caused by its exclusive clearance pathway via CYP3A4 oxidation in humans. We now report 2-[(3aR,4R,5S,7aS)-5-{(1S)-1-[3,5-bis(trifluoromethyl)phenyl]-2-hydroxyethoxy}-4-(2-methylphenyl)octahydro-2H-isoindol-2-yl]-1,3-oxazol-4(5H)-one (3) as a next generation NK1 antagonist that possesses an additional clearance pathway through glucuronidation in addition to that via CYP3A4 oxidation. Compound 3 has a much lower propensity for drug-drug interactions and a reduced estimated human half-life consistent with once daily dosing. In preclinical species, compound 3 has demonstrated potency, brain penetration, and a safety profile similar to 2, as well as excellent pharmacokinetics.

SAR exploration at the C-3 position of tetrahydro-β-carboline sstr3 antagonists

MK-4256, a tetrahydro-β-carboline sstr3 antagonist, was discontinued due to a cardiovascular (CV) adverse effect observed in dogs. Additional investigations revealed that the CV liability (QTc prolongation) was caused by the hERG off-target activity of MK-4256 and was not due to sstr3 antagonism. In this Letter, we describe our extensive SAR effort at the C3 position of the tetrahydro-β-carboline structure. This effort resulted in identification of 5-fluoro-pyridin-2-yl as the optimal substituent on the imidazole ring to balance sstr3 activity and the hERG off-target liability.

In vitro and in vivo metabolism of a novel cannabinoid-1 receptor inverse agonist, taranabant, in rats and monkeys

The metabolism and excretion of taranabant (MK-0364, N-[(1S,2S)-3-(4-chlorophenyl)-2-(3-cyanophenyl)-1-methylpropyl]-2-methyl-2{[5-(trifluoromethyl)pyridine-2-yl]oxy}propanamide), a potent cannabinoid-1 receptor inverse agonist, were evaluated in rats and rhesus monkeys. Following administration of [14C]taranabant, the majority of the radioactivity was excreted within 72 h. In both rats and rhesus monkeys, taranabant was eliminated primarily via oxidative metabolism, followed by excretion of metabolites into bile. Major pathways of metabolism that were common to rats and rhesus monkeys included hydroxylation at the benzylic carbon adjacent to the cyanophenyl ring to form a biologically active circulating metabolite M1, and oxidation of one of the two geminal methyl groups of taranabant or M1 to the corresponding diastereomeric carboxylic acids. Oxidation of the cyanophenyl ring, followed by conjugation with glutathione or glucuronic acid, was a major pathway of metabolism only in the rat and was not detected in the rhesus monkey. Metabolism profiles of taranabant in liver microsomes in vitro were qualitatively similar in rats, rhesus monkeys and humans and included formation of M1 and oxidation of taranabant or M1 to the corresponding carboxylic acids via oxidation of a geminal methyl group. In human liver microsomes, metabolism of taranabant was mediated primarily by CYP3A4.

Absorption, metabolism and excretion of [14C]omarigliptin, a once-weekly DPP-4 inhibitor, in humans

Abstract 1. Omarigliptin (MARIZEV®) is a once-weekly DPP-4 inhibitor approved in Japan for the treatment of type 2 diabetes. The objective of this study was to investigate the absorption, metabolism and excretion of omarigliptin in humans. 2. Six healthy subjects received a single oral dose of 25 mg (2.1 μCi) [14 C]omarigliptin. Blood, plasma, urine and fecal samples were collected at various intervals for up to 20 days post-dose. Radioactivity levels in excreta and plasma/blood samples were determined by accelerator mass spectrometry (AMS). 3. [14 C]Omarigliptin was rapidly absorbed, with peak plasma concentrations observed at 0.5–2 h post-dose. The majority of the radioactivity was recovered in urine (∼74.4% of the dose), with less recovered in feces (∼3.4%), suggesting the compound was well absorbed. 4. Omarigliptin was the major component in urine (∼89% of the urinary radioactivity), indicating renal excretion of the unchanged drug as the primary clearance mechanism. Omarigliptin accounted for almost all the circulating radioactivity in plasma, with no major metabolites detected. 5. The predominantly renal elimination pathway, combined with the fact that omarigliptin is not a substrate of key drug transporters, suggest omarigliptin is unlikely to be subject to pharmacokinetic drug-drug interactions with other commonly prescribed agents.