Ibrexafungerp: An orally active ß-1,3-glucan synthesis inhibitor.

We previously reported medicinal chemistry efforts that identified MK-5204, an orally efficacious ß-1,3-glucan synthesis inhibitor derived from the natural product enfumafungin. Further extensive optimization of the C2 triazole substituent identified 4-pyridyl as the preferred replacement for the carboxamide of MK-5204, leading to improvements in antifungal activity in the presence of serum, and increased oral exposure. Reoptimizing the aminoether at C3 in the presence of this newly discovered C2 substituent, confirmed that the (R) t-butyl, methyl aminoether of MK-5204 provided the best balance of these two key parameters, culminating in the discovery of ibrexafungerp, which is currently in phase III clinical trials. Ibrexafungerp displayed significantly improved oral efficacy in murine infection models, making it a superior candidate for clinical development as an oral treatment for Candida and Aspergillus infections.

MK-5204: An orally active ß-1,3-glucan synthesis inhibitor.

Our previously reported efforts to produce an orally active ß-1,3-glucan synthesis inhibitor through the semi-synthetic modification of enfumafungin focused on replacing the C2 acetoxy moiety with an aminotetrazole and the C3 glycoside with a N,N-dimethylaminoether moiety. This work details further optimization of the C2 heterocyclic substituent, which identified 3-carboxamide-1,2,4-triazole as a replacement for the aminotetrazole with comparable antifungal activity. Alkylation of either the carboxamidetriazole at C2 or the aminoether at C3 failed to significantly improve oral efficacy. However, replacement of the isopropyl alpha amino substituent with a t-butyl, improved oral exposure while maintaining antifungal activity. These two structural modifications produced MK-5204, which demonstrated broad spectrum activity against Candida species and robust oral efficacy in a murine model of disseminated Candidiasis without the N-dealkylation liability observed for the previous lead.

Novel orally active inhibitors of ß-1,3-glucan synthesis derived from enfumafungin.

The clinical success of the echinocandins, which can only be administered parentally, has validated ß-1,3-glucan synthase (GS) as an antifungal target. Semi-synthetic modification of enfumafungin, a triterpene glycoside natural product, was performed with the aim of producing a new class of orally active GS inhibitors. Replacement of the C2 acetoxy moiety with various heterocycles did not improve GS or antifungal potency. However, replacement of the C3 glycoside with an aminoether moiety dramatically improved oral pharmacokinetic (PK) properties while maintaining GS and antifungal potency. Installing an aminotetrazole at C2 in conjunction with an N-alkylated aminoether at C3 produced derivatives with significantly improved GS and antifungal potency that exhibited robust oral efficacy in a murine model of disseminated candidiasis.

The design and synthesis of potent, selective benzodiazepine sulfonamide bombesin receptor subtype 3 (BRS-3) agonists with an increased barrier of atropisomerization.

Bombesin receptor subtype 3 (BRS-3) is an orphan G-protein coupled receptor expressed primarily in the hypothalamus which plays a role in the onset of both diabetes and obesity. We report herein our progress made towards identifying a potent, selective bombesin receptor subtype-3 (BRS-3) agonist related to the previously described MK-7725(1) Chobanian et al. (2012) that would prevent atropisomerization through the increase of steric bulk at the C-2 position. This would thereby make clinical development of this class of compounds more cost effective by inhibiting racemization which can occur over long periods of time at room/elevated temperature.

Discovery of MK-7725, A Potent, Selective Bombesin Receptor Subtype-3 Agonist for the Treatment of Obesity.

Extensive structure-activity relationship studies of a series derived from atropisomer 1, a previously described chiral benzodiazepine sulfonamide series, led to a potent, brain penetrant and selective compound with excellent preclinical pharmacokinetic across species. We also describe the utilization of a high throughput mouse pharmacodynamic assay which allowed for expedient assessment of pharmacokinetic and brain distribution.

Characterization of multidrug resistance 1a/P-glycoprotein knockout rats generated by zinc finger nucleases.

The development of zinc finger nuclease (ZFN) technology has enabled the genetic engineering of the rat genome. The ability to manipulate the rat genome has great promise to augment the utility of rats for biological and pharmacological studies. A Wistar Hannover rat model lacking the multidrug resistance protein Mdr1a P-glycoprotein (P-gp) was generated using a rat Mdr1a-specific ZFN. Mdr1a was completely absent in tissues, including brain and small intestine, of the knockout rat. Pharmacokinetic studies with the Mdr1a P-gp substrates loperamide, indinavir, and talinolol indicated that Mdr1a was functionally inactive in the blood-brain barrier and intestine in Mdr1a(-/-) rats. To identify possible compensatory mechanisms in Mdr1a(-/-) rats, the expression levels of drug-metabolizing enzyme and transporter-related genes were compared in brain, liver, kidney, and intestine of male and female Mdr1a(-/-) and control rats. In general, alterations in gene expression of these genes in Mdr1a(-/-) rats seemed to be modest, with more changes in female than in male rats. Taken together, our studies demonstrate that the ZFN-generated Mdr1a(-/-) rat will be a valuable tool for central nervous system drug target validation and determining the role of P-gp in drug absorption and disposition.

Pyridinesulfonylureas and pyridinesulfonamides as selective bombesin receptor subtype-3 (BRS-3) agonists.

Bombesin receptor subtype-3 (BRS-3) is an orphan G-protein coupled receptor belonging to the subfamily of bombesin-like receptors. BRS-3 is implicated in the development of obesity and diabetes. We report here small-molecule agonists that are based on a 4-(alkylamino)pyridine-3-sulfonamide core. We describe the discovery of 2a, which has mid-nanomolar potency, selectivity for human BRS-3 versus the other bombesin-like receptors, and good bioavailability.

Bicyclo[2.2.2]octyltriazole inhibitors of 11ß-hydoxysteroid dehydrogenase type 1. Pharmacological agents for the treatment of metabolic syndrome.

Following the discovery of a metabolic 'soft-spot' on a bicyclo[2.2.2]octyltriazole lead, an extensive effort was undertaken to block the oxidative metabolism and improve PK of this potent HSD1 lead. In this communication, SAR survey focusing on various alkyl chain replacements will be detailed. This effort culminated in the discovery of a potent ethyl sulfone inhibitor with an improved PK profile across species and improved physical properties.

Discovery of MK-5046, a Potent, Selective Bombesin Receptor Subtype-3 Agonist for the Treatment of Obesity.

We report the development and characterization of compound 22 (MK-5046), a potent, selective small molecule agonist of BRS-3 (bombesin receptor subtype-3). In pharmacological testing using diet-induced obese mice, compound 22 caused mechanism-based, dose-dependent reductions in food intake and body weight.

Discovery of benzodiazepine sulfonamide-based bombesin receptor subtype 3 agonists and their unusual chirality.

We report herein the discovery of benzodiazepine sulfonamide-based bombesin receptor subtype 3 (BRS-3) agonists and their unusual chirality. Starting from a high-throughput screening lead, we prepared a series of BRS-3 agonists with improved potency and pharmacokinetic properties, of which compound 8a caused mechanism-based, dose-dependent food intake reduction and body weight loss after oral dosing in diet-induced obese mice. This effort also led to the discovery of a novel family of chiral molecules originated from the conformationally constrained seven-membered diazepine ring.

Antiobesity effect of MK-5046, a novel bombesin receptor subtype-3 agonist.

Bombesin receptor subtype-3 (BRS-3) is an orphan G protein-coupled receptor implicated in the regulation of energy homeostasis. Here, we report the biologic effects of a highly optimized BRS-3 agonist, (2S)-1,1,1-trifluoro-2-[4-(1H-pyrazol-1-yl)phenyl]-3-(4-{[1-(trifluoromethyl)cyclopropyl]methyl}-1H-imidazol-2-yl)propan-2-ol (MK-5046). Single oral doses of MK-5046 inhibited 2-h and overnight food intake and increased fasting metabolic rate in wild-type but not Brs3 knockout mice. Upon dosing for 14 days, MK-5046 at 25 mg · kg(-1) · day(-1) reduced body weight of diet-induced obese mouse by 9% compared with vehicle-dosed controls. In mice, 50% brain receptor occupancy was achieved at a plasma concentration of 0.34 ± 0.23 µM. With chronic dosing, effects on metabolic rate, rather than food intake, seem to be the predominant mechanism for weight reduction by MK-5046. The compound also effectively reduced body weight in rats and caused modest increases in body temperature, heart rate, and blood pressure. These latter effects on temperature, heart rate, and blood pressure were transient in nature and desensitized with continued dosing. MK-5046 is the first BRS-3 agonist with properties suitable for use in larger mammals. In dogs, MK-5046 treatment produced statistically significant and persistent weight loss, which was initially accompanied by increases in body temperature and heart rate that abated with continued dosing. Our results demonstrate antiobesity efficacy for MK-5046 in rodents and dogs and further support BRS-3 agonism as a new approach to the treatment of obesity.

Synthesis of 7-benzyl-5-(piperidin-1-yl)-6,7,8,9-tetrahydro-3H-pyrazolo[3,4-c][2,7]naphthyridin-1-ylamine and its analogs as bombesin receptor subtype-3 agonists.

The original structure of a high-throughput screening hit obtained from an external vendor was revised based on multiple NMR studies. The active compound was re-synthesized via a novel route and its structure and biological activity as a BRS-3 agonist were unambiguously confirmed. Multi-gram quantities of the hit were prepared for pharmacokinetic and efficacy studies. The synthetic strategy allowed for the preparation of multiple analogs for SAR exploration.

Discovery of potent, orally active benzimidazole glucagon receptor antagonists.

The discovery and optimization of potent and selective aminobenzimidazole glucagon receptor antagonists are described. One compound possessing moderate pharmacokinetic properties in multiple preclinical species was orally efficacious at inhibiting glucagon-mediated glucose excursion in transgenic mice expressing the human glucagon receptor, and in rhesus monkeys. The compound also significantly lowered glucose levels in a murine model of diabetes.

Phenylcyclobutyl triazoles as selective inhibitors of 11beta-hydroxysteroid dehydrogenase type I.

3-(Phenylcyclobutyl)-1,2,4-triazoles were identified as selective inhibitors of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). These were active both in vitro and in an in vivo mouse pharmacodynamic (PD) model. Fluorine substitution of the cyclobutane ring improved the pharmacokinetic profile significantly. The synthesis and structure-activity relationships are presented.

Discovery of 4-heteroarylbicyclo[2.2.2]octyltriazoles as potent and selective inhibitors of 11beta-HSD1: novel therapeutic agents for the treatment of metabolic syndrome.

Replacement of the pentyl chain on our original bicyclo[2.2.2]octyltriazole leads 1 and 2 has led to the discovery that heteroaryl substituted bicyclo[2.2.2]octyltriazoles are potent and selective 11beta-hydroxysteroid dehydrogenase type I (11beta-HSD1) inhibitors with excellent pharmacokinetic profiles.

Discovery of novel, potent, and orally active spiro-urea human glucagon receptor antagonists.

A novel class of spiro-ureas has been discovered as potent human glucagon receptor antagonists in both binding and functional assays. Preliminary studies have revealed that compound 15 is an orally active human glucagon receptor antagonist in a transgenic murine pharmacodynamic model at 10 and 30 mpk. Compound 15 is orally bioavailable in several preclinical species and shows selectivity toward cardiac ion channels and other family B receptors, such as hGIP1 and hGLP.

The role of dipeptidyl peptidase IV in the cleavage of glucagon family peptides: in vivo metabolism of pituitary adenylate cyclase activating polypeptide-(1-38).

Dipeptidyl peptidase IV (DP-IV) is a cell surface serine dipeptidase that is involved in the regulation of the incretin hormones, glucagon-like peptide (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). There is accumulating evidence that other members of the glucagon family of peptides are also endogenous substrates for this enzyme. To identify candidate substrates for DP-IV, a mass spectrometry-based protease assay was developed that measures cleavage efficiencies (kcat/Km) of polypeptides in a mixture, using only a few picomoles of each substrate and physiological amounts of enzyme in a single kinetic experiment. Oxyntomodulin and the growth hormone-(1-43) fragment were identified as new candidate in vivo substrates. Pituitary adenylate cyclase-activating polypeptide-(1-38) (PACAP38), a critical mediator of lipid and carbohydrate metabolism, was also determined to be efficiently processed by DP-IV in vitro. The catabolism of exogenously administered PACAP38 in wild type and DP-IV-deficient C57Bl/6 mice was monitored by tandem mass spectrometry. Animals lacking DP-IV exhibited a significantly slower clearance of the circulating peptide with virtually complete suppression of the inactive DP-IV metabolite, PACAP-(3-38). These in vivo results suggest that DP-IV plays a major role in the degradation of circulating PACAP38.