In vitro and in vivo characterization of 3-[2-[6-(2-tert-butoxyethoxy)pyridin-3-yl]-1H-imidazol-4-yl]benzonitrile hydrochloride salt, a potent and selective NPY5 receptor antagonist

Neuropeptide Y Signaling in the Lateral Hypothalamus Modulates Diet Component Selection and is Dysregulated in a Model of Diet-Induced Obesity

The preclinical multicomponent free-choice high-fat high-sucrose (fcHFHS) diet has strong validity to model diet-induced obesity (DIO) and associated maladaptive molecular changes in the central nervous system. fcHFHS-induced obese rats demonstrate increased sensitivity to intracerebroventricular infusion of the orexigenic Neuropeptide Y (NPY). The brain region-specific effects of NPY signaling on fcHFHS diet component selection are not completely understood. For example, fcHFHS-fed rats have increased intake of chow and fat following intracerebroventricular NPY infusion, whereas NPY administration in the nucleus accumbens, a key hub of the reward circuitry, specifically increases fat intake. Here, we investigated whether NPY infusion in the lateral hypothalamic area (LHA), which is crucially involved in the regulation of intake, regulates fcHFHS component selection, and if LHA NPY receptor subtypes 1 or 5 (NPYR1/5) are involved. Male Wistar rats were fed a chow or fcHFHS diet for at least seven days, and received intra-LHA vehicle or NPY infusions in a cross-over design. Diet component intake was measured two hours later. Separate experimental designs were used to test the efficacy of NPY1R- or NPY5R antagonism to prevent the orexigenic effects of intra-LHA NPY. Intra-LHA NPY increased caloric intake in chow- and fcHFHS-fed rats. This effect was mediated specifically by chow intake in fcHFHS-fed rats. The orexigenic effects of intra-LHA NPY were prevented by NPY1R and NPY5R antagonism in chow-fed rats, but only by NPY5R antagonism in fcHFHS-fed rats. Thus, NPY signaling has brain region-specific effects on fcHFHS component selection and LHA NPYR sensitivity is dysregulated during consumption of a fcHFHS diet.

The importance of plasma protein binding in drug discovery

Plasma protein binding of drugs is a well-recognised phenomena, but it is only recently that the implications for drug action in vivo have been fully appreciated. Plasma proteins, by virtue of their high concentration, control the free drug concentration in plasma and in compartments in equilibrium with plasma, thereby, effectively attenuating drug potency in vivo. The historical background and thermodynamic basis for the 'Free Drug Principle' is presented, along with special considerations for intracellular targets, deep compartments and α1-acid glycoprotein binding. Real and apparent exceptions to the principle are discussed along with a survey of citations from the recent medicinal chemistry literature.

Identification of novel and orally active spiroindoline NPY Y5 receptor antagonists

A series of spiroindoline-3,4'-piperidine derivatives were synthesized and evaluated for their binding affinities and antagonistic activities at Y5 receptors. Potent Y5 antagonists were tested for their oral bioavailabilities and brain penetration in rats. Some of the antagonists showed good oral bioavailability and/or good brain penetration. In particular, compound 6e was orally bioavailable and brain penetrant, and oral administration of 6e inhibited bPP-induced food intake in rats with a minimum effective dose of 10mg/kg.

Synthesis and evaluation of 5,5-diphenylimidazolones as potent human neuropeptide Y5 receptor antagonists

A series of novel 5,5-diphenylimidazolones was synthesized and evaluated for activity against the human neuropeptide Y5 receptor. The 3-pyridyl analog 46 demonstrated an IC(50) of 8.3 nM with a favorable pharmacokinetic profile in rats, but was ineffective in reducing food intake.

A neuropeptide Y Y5 antagonist selectively ameliorates body weight gain and associated parameters in diet-induced obese mice

Neuropeptide Y (NPY) is thought to have a major role in the physiological control of energy homeostasis. Among five NPY receptors described, the NPY Y5 receptor (Y5R) is a prime candidate to mediate some of the effects of NPY on energy homeostasis, although its role in physiologically relevant rodent obesity models remains poorly defined. We examined the effect of a potent and highly selective Y5R antagonist in rodent obesity and dietary models. The Y5R antagonist selectively ameliorated diet-induced obesity (DIO) in rodents by suppressing body weight gain and adiposity while improving the DIO-associated hyperinsulinemia. The compound did not affect the body weight of lean mice fed a regular diet or genetically obese leptin receptor-deficient mice or rats, despite similarly high brain Y5R receptor occupancy. The Y5R antagonist acts in a mechanism-based manner, as the compound did not affect DIO of Y5R-deficient mice. These results indicate that Y5R is involved in the regulation and development of DIO and suggest utility for Y5R antagonists in the treatment of obesity.

Evidence for the existence of an additional class of neuropeptide Y receptor sites in rat brain

Five distinct neuropeptide Y (NPY) receptors have been cloned thus far. Selective agonists and antagonists have recently been developed allowing for detailed functional studies as to the pathophysiological role of a given subtype as well as receptor binding characteristics and distribution. To precisely investigate the discrete localization and ligand selectivity profile of Y4 and Y5 receptors, a series of selective molecules were used as radioligands and competitors in rat brain tissues. Binding data revealed that Y4 and Y5 receptor-related agonists and antagonists competed with high affinity for specific 125I-[Leu31,Pro34]human peptide YY (hPYY) binding in the presence of BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]-methyl]-N2-(diphenylacetyl)-argininamide trifluoroacetate] to mask Y1 sites as well as specific 125I-labeled human pancreatic polypeptide (hPP) binding. Competition binding profiles were best fitted to a two-site model for both radioligands, suggesting the likely recognition of the Y4 and Y5 subtypes. We were surprised to find that the visualization of these specific binding sites by receptor autoradiography clearly revealed the distinct distribution of specific 125I-[Leu31,Pro34]hPYY (in presence of Y1 and Y5 blockers) and 125I-hPP (in presence of Y5 blocker) binding sites. Moreover, significant amounts of specific 125I-hPP binding were observed in the medial preoptic area, paraventricular nucleus of the hypothalamus, interpeduncular nucleus, and various brainstem nuclei, even after masking Y4 and Y5 receptors. Similar results were obtained using 125I-hPYY(3-36) in presence of Y2 and Y5 blockers. These results suggest the possible existence of at least one additional subtype of NPY receptor sites in the rat brain, with enrichment seen in midbrain and brainstem areas involved in the regulation of food intake and cardiorespiratory parameters.

Isosteric N-arylpiperazine replacements in a series of dihydropyridine NPY1 receptor antagonists

4-Amino-N-arylpiperidines serve as effective bioisosteres for N-arylpiperazines in the series of dihydropyridine NPY1 receptor antagonists. These were prepared by a ZnCl2-mediated reductive amination reaction between elaborated primary amines, 2 or 5, and 4-arylpiperidones.

Design, synthesis, and biological evaluation of substituted 2-cyclohexyl-4-phenyl-1H-imidazoles: potent and selective neuropeptide Y Y5-receptor antagonists

Antagonizing the robust stimulation of food intake by neuropeptide Y represents a new potential therapeutic approach for the treatment of obesity. Earlier pharmacological studies have pointed to the Y1 and Y5 receptors as the most likely mediators of the NPY orexigenic response. In this paper, we describe a new series of small molecule Y5 antagonists derived from a 2,4-diaryl-1H-imidazole lead. The main objectives of our structural optimization efforts were to produce novel and potent Y5 antagonists with an improved oral pharmacokinetic profile and less affinity for the hERG potassium channel compared to the lead 2,4-diarylimidazole structures. These goals were accomplished by replacement of the 2-aryl ring with a cyclohexyl ring and subsequent elaboration of the 4-position of the cyclohexyl ring with a variety of hydrophilic functionalities. The resulting compound, N-(2-hydroxy-tert-butyl)(4-[4-[3-(trifluoromethyl)phenyl]imidazol-2-yl]cyclohexyl)carboxamide (20), displayed good potency at the Y5 receptor (K(i) = 3 nM), while interactions at the hERG channel were essentially eliminated (6% inhibition at a concentration of 3 microM). Importantly, the pharmacokinetic properties of 20 (F = 36%) represented a marked improvement over that of the initial 2,4-diarylimidazole structures.

Discovery and SAR of potent, orally available and brain-penetrable 5,6-dihydro-4H-3-thia-1-aza-benzo[e]azulen- and 4,5-dihydro-6-oxa-3-thia-1-aza-benzo[e]azulen derivatives as neuropeptide Y Y5 receptor antagonists

Combination of structural elements from a potent Y5 antagonist (2) with thiazole fragments that exhibit weak Y5 affinities followed by lead optimisation led to the discovery of (5,6-dihydro-4H-3-thia-1-aza-benzo[e]azulen-2-yl)-piperidin-4-ylmethyl-amino and (4,5-dihydro-6-oxa-3-thia-1-aza-benzo[e]azulen-2-yl)-piperidin-4-ylmethyl-amino derivatives. Both classes of compounds are capable of delivering potent and selective orally and centrally bioavailable NPY Y5 receptor antagonists.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.

Structure–activity relationship studies on 2-heteroaryl-4-arylimidazoles NPY5 receptor antagonists

A series of 2-heteroaryl-4-arylimidazoles with potent in vitro activity at the NPY5 receptor was developed. Introduction of electron-withdrawing groups on the 4-aryl ring led to a significant improvement of in vitro potency. Several analogues from this series had anorectic activity in rodent feeding models, but were also found to have undesired behavioral effects in spontaneous locomotor activity.

Structure-activity relationships in a series of NPY Y5 antagonists: 3-amido-9-ethylcarbazoles, core-modified analogues and amide isosteres

Beginning with carbazole 1a, the amide and alkyl substituents were optimized to maintain potency while adding solubilizing groups. Efforts to replace the 3-amino-9-ethylcarbazole core, a known carcinogen, used the SAR generated in the carbazole series for guidance and led to the synthesis of a number of core-modified analogues. In addition, an isosteric series, in which the amide was replaced with an imidazole, was prepared. Two potent new series lacking the putative toxicophore were identified from these endeavors.