Therapeutic potential of melanin-concentrating hormone-1 receptor antagonists for the treatment of obesity

Hypothalamus-hippocampus circuitry regulates impulsivity via melanin-concentrating hormone

Behavioral impulsivity is common in various psychiatric and metabolic disorders. Here we identify a hypothalamus to telencephalon neural pathway for regulating impulsivity involving communication from melanin-concentrating hormone (MCH)-expressing lateral hypothalamic neurons to the ventral hippocampus subregion (vHP). Results show that both site-specific upregulation (pharmacological or chemogenetic) and chronic downregulation (RNA interference) of MCH communication to the vHP increases impulsive responding in rats, indicating that perturbing this system in either direction elevates impulsivity. Furthermore, these effects are not secondary to either impaired timing accuracy, altered activity, or increased food motivation, consistent with a specific role for vHP MCH signaling in the regulation of impulse control. Results from additional functional connectivity and neural pathway tracing analyses implicate the nucleus accumbens as a putative downstream target of vHP MCH1 receptor-expressing neurons. Collectively, these data reveal a specific neural circuit that regulates impulsivity and provide evidence of a novel function for MCH on behavior.

Development of Human Target Validation Classification that Predicts Future Clinical Efficacy

Fewer new medicines have become available to patients during the last decades. Clinical efficacy failures in late-phase development have been identified as a common cause of this decline. Improved ways to ensure early selection of the right drug targets when it comes to efficacy is therefore a highly desirable goal. The aim of this work was to develop a strategy to facilitate selection of novel targets already in the discovery phase that later on in clinical development would demonstrate efficacy. A cross-functional team at AstraZeneca with extensive experience in drug discovery and development participated in several workshops to identify the critical elements that contribute to building human target validation [(HTV); the relevance of the target from a human perspective]. The elements were consolidated into a 10-point HTV classification system that was ranked from lowest to highest in terms of perceived impact on future clinical efficacy. Using 50 years of legacy research and development data, the ability of the 10-point HTV classification to predict future clinical efficacy was evaluated. Drug targets were classified as having low, medium, or high HTV at the time of candidate drug selection. Comparing this HTV classification with later clinical development efficacy data showed that HTV classification was highly predictive of future clinical efficacy success. This new strategy for HTV assessment provides a novel approach to early prediction of clinical efficacy and a better understanding of portfolio risk.

Consequences of constitutive deletion of melanin-concentrating hormone-1 receptors for feeding and foraging behaviors of mice

In order to decipher the functional involvement of melanin-concentrating hormone 1 (MCH1) receptors in the control of feeding and foraging behaviors, mice with constitutive deletion of MCH1 receptors MCH1R -/- or knockout (KO) were studied and compared to age-matched littermate control mice (MCH1R +/+ or wildtype (WT)). Several challenges to food-motivated behaviors of food-restricted WT and KO mice were implemented. There were no differences between genotypes in the acquisition of a nose-poke response that produced food or in a discrimination between a response that produced food and one that did not. There were also no genotype differences in the rate of extinction of a food-motivated response. However, during the first day of extinction, foraging behaviors were increased significantly more in KO than in WT mice. Likewise, when the response requirement to obtain food was progressively increased, KO mice made significantly more food-directed responses than WT mice. Although adulteration of food with quinine did not suppress food-directed behavior in either genotype when the mice were food-restricted, manipulation of the degree of food-deprivation resulted in suppression of behavior of WT mice without suppressing the behavior of KO mice. Although response-produced foot shock suppressed food-maintained responding of both WT and KO mice, equipotent levels of shock (based upon psychophysical thresholds) suppressed behavior of WT mice without suppressing behavior of the KO mice. Finally, under a Vogel conflict procedure, KO mice had significantly higher levels of both punished and non-punished food maintained responding. Thus, the data from challenges with both appetitive and noxious stimulus challenges support the conclusion that mice with constitutive deletion of MCH1Rs have increased food seeking motivation that is coincident with their higher metabolism. The data also highlight important differences in the biological impact of MCH1 receptor KO and MCH1 receptor antagonism.

Indanes--Properties, Preparation, and Presence in Ligands for G Protein Coupled Receptors

The indane (2,3-dihydro-1H-indene) ring system is an attractive scaffold for biologically active compounds due to the combination of aromatic and aliphatic properties fused together in one rigid system. This bicyclic structure provides a wide range of possibilities to incorporate specific substituents in different directionalities, thus being an attractive scaffold for medicinal chemists. Notably, many indane-based compounds are being used in the clinic to treat various diseases, such as indinavir, an HIV-1 protease inhibitor; indantadol, a potent Monoamine Oxidase (MAO)-inhibitor; the amine uptake inhibitor indatraline; and the ultra-long-acting β-adrenoceptor agonist indacaterol. Given the diversity of targets these drugs act on, one could argue that the indane ring system is a privileged substructure. In the present review, the synthetic and medicinal chemistry of the indane ring system is described. In more detail, it contains a comprehensive overview of compounds bearing the indane substructure with G protein coupled receptor (GPCR) activity, with particular emphasis on their structure-activity relationships (SAR).

The central question of type 2 diabetes

Type 2 diabetes (T2D) represents a significant global epidemic with more than 285 million people affected worldwide. Regulating glycemia in T2D patients can be partially achieved with currently available treatment, but intensive research during the last decades have led to the discovery of modified compounds or new targets that could represent great hope for safe and effective treatment in the future. Among them, targets in the CNS that are known to control feeding and body weight have been also shown to exert glucoregulatory actions, and could be a key in the development of a new generation of drugs in the field of T2D. Such drugs would be of great interest since they can be used both in the treatment of diabetes and obesity. This patent review aims to establish an overview of recent patents disclosing new therapeutic opportunities targeting peripheral, as well as central targets for the treatment of T2D.

Fighting obesity with a sugar-based library: discovery of novel MCH-1R antagonists by a new computational-VAST approach for exploration of GPCR binding sites

Obesity is an increasingly common disease. While antagonism of the melanin-concentrating hormone-1 receptor (MCH-1R) has been widely reported as a promising therapeutic avenue for obesity treatment, no MCH-1R antagonists have reached the market. Discovery and optimization of new chemical matter targeting MCH-1R is hindered by reduced HTS success rates and a lack of structural information about the MCH-1R binding site. X-ray crystallography and NMR, the major experimental sources of structural information, are very slow processes for membrane proteins and are not currently feasible for every GPCR or GPCR-ligand complex. This situation significantly limits the ability of these methods to impact the drug discovery process for GPCR targets in "real-time", and hence, there is an urgent need for other practical and cost-efficient alternatives. We present here a conceptually pioneering approach that integrates GPCR modeling with design, synthesis, and screening of a diverse library of sugar-based compounds from the VAST technology (versatile assembly on stable templates) to provide structural insights on the MCH-1R binding site. This approach creates a cost-efficient new avenue for structure-based drug discovery (SBDD) against GPCR targets. In our work, a primary VAST hit was used to construct a high-quality MCH-1R model. Following model validation, a structure-based virtual screen yielded a 14% hit rate and 10 novel chemotypes of potent MCH-1R antagonists, including EOAI3367472 (IC50 = 131 nM) and EOAI3367474 (IC50 = 213 nM).

Design and optimization of quinazoline derivatives as melanin concentrating hormone receptor 1 (MCHR1) antagonists

Melanin concentrating hormone (MCH) is an important mediator of energy homeostasis and plays a role in metabolic and CNS disorders. The modeling-supported design, synthesis and multi-parameter optimization (biological activity, solubility, metabolic stability, hERG) of novel quinazoline derivatives as MCHR1 antagonists are described. The in vivo proof of principle for weight loss with a lead compound from this series is exemplified. Clusters of refined hMCHR1 homology models derived from the X-ray structure of the β2-adrenergic receptor, including extracellular loops, were developed and used to guide the design.

Antiobesity effects of melanin-concentrating hormone receptor 1 (MCH-R1) antagonists

Despite remarkable progress in the elucidation of energy balance and regulation, the development of new antiobesity drugs is still at the stage of infancy. This review describes the MCH and MCH receptor system with regard to its involvement in energy homeostasis and summarizes the pharmacological profiles of selected small molecule MCH-R1 antagonists that are relevant for their development as antiobesity drugs. Although their clinical value still has to be demonstrated, and challenges with regard to unwanted side effects remain to be resolved, MCH-R1 antagonists may provide an effective pharmacotherapy for the treatment of obesity in the near future.

Synthesis, structure-activity relationship, and pharmacological studies of novel melanin-concentrating hormone receptor 1 antagonists 3-aminomethylquinolines: reducing human ether-a-go-go-related gene (hERG) associated liabilities

Recently, we discovered 3-aminomethylquinoline derivative 1, a selective, highly potent, centrally acting, and orally bioavailable human MCH receptor 1 (hMCHR1) antagonist, that inhibited food intake in F344 rats with diet-induced obesity (DIO). Subsequent investigation of 1 was discontinued because 1 showed potent hERG K(+) channel inhibition in a patch-clamp study. To decrease hERG K(+) channel inhibition, experiments with ligand-based drug designs based on 1 and a docking study were conducted. Replacement of the terminal p-fluorophenyl group with a cyclopropylmethoxy group, methyl group introduction on the benzylic carbon at the 3-position of the quinoline core, and employment of a [2-(acetylamino)ethyl]amino group as the amine portion eliminated hERG K(+) channel inhibitory activity in a patch-clamp study, leading to the discovery of N-{3-[(1R)-1-{[2-(acetylamino)ethyl]amino}ethyl]-8-methylquinolin-7-yl}-4-(cyclopropylmethoxy)benzamide (R)-10h. The compound (R)-10h showed potent inhibitory activity against hMCHR1 and dose-dependently suppressed food intake in a 2-day study on DIO-F344 rats. Furthermore, practical chiral synthesis of (R)-10h was performed to determine the molecule's absolute configuration.

Melanin-concentrating hormone receptor 1 antagonists: synthesis, structure-activity relationship, docking studies, and biological evaluation of 2,3,4,5-tetrahydro-1H-3-benzazepine derivatives

Melanin-concentrating hormone receptor 1 (MCHR1) antagonists have been studied as potential agents for the treatment of obesity. Initial structure-activity relationship studies of in-house hit compound 1a and subsequent optimization studies resulted in the identification of tetrahydroisoquinoline derivative 23, 1-(2-acetyl-1,2,3,4-tetrahydroisoquinolin-7-yl)-4-[4-(4-chlorophenyl)piperidin-1-yl]butan-1-one, as a potent hMCHR1 antagonist. A homology model of hMCHR1 suggests that these compounds interact with Asn 294 and Asp 123 in the binding site of hMCHR1 to enhance binding affinity. Oral administration of compound 23 dose-dependently reduced food intake in diet-induced obesity (DIO)-F344 rats.

High-throughput screening of novel antagonists on melanin-concentrating hormone receptor-1

AIM

To find new antagonists on human melanin-concentrating hormone receptor-1 (MCHR-1) through high-throughput screening (HTS) of a diverse compound library.

METHODS

MCHR-1, [3H]SNAP7941, and FlashBlue G-protein-coupled receptor beads were used to measure the receptor-binding activities of various compounds based on scintillation proximity assay (SPA) technology. The guanosine 5'(gamma-[35S]thio) triphosphate ([35S]GTPgammaS) binding assay was subsequently applied to functionally characterize the "hits" identified by the HTS campaign.

RESULTS

Of the 48,240 compounds screened with the SPA method, 12 hits were confirmed to possess MCHR-1 binding activities, 8 were functionally studied subsequently with the [35S]GTPgammaS binding assay, and only 1 compound (NC127816) displayed moderate human MCHR-1 binding affinity (Ki=115.7 nmol/L) and relatively potent antagonism (KB=23.8 nmol/L). This compound shares a novel scaffold (1-ethoxy-2H-2-aza-1-phospha-naphthalene 1-oxide) with 3 other analogs in the group.

CONCLUSION

Considering the marked difference in molecular shape and electrostatic status between NC127816 and the structures reported elsewhere, we anticipate that its derivatives may represent a new class of potent MCHR-1 modulators.

Synthesis and SAR Investigations for Novel Melanin-Concentrating Hormone 1 Receptor (MCH1) Antagonists Part 2: A Hybrid Strategy Combining Key Fragments of HTS Hits

A novel series of melanin-concentrating hormone (MCH1) receptor antagonists based on combining key fragments from the high-throughput screening (HTS) hits compound 2 (SNAP 7941) and compound 5 (chlorohaloperidol) are described. The resultant analogs, exemplified by compounds 11a-11h, 15a-15h, and 16a-16g, were evaluated in in vitro and in vivo assays for their potential in treatment of mood disorders. From further SAR investigations, N-(3-{1-[4-(3,4-difluorophenoxy)benzyl]-4-piperidinyl}-4-methylphenyl)-2-methylpropanamide (16g, SNAP 94847) was identified to be a high affinity and selective ligand for the MCH1 receptor. Compound 16g also shows good oral bioavailability (59%) and exhibits a brain/plasma ratio of 2.3 in rats. Compound 16g showed in vivo inhibition of a centrally induced MCH-induced drinking effect and exhibited a dose-dependent anxiolytic effect in the rat social interaction model.

Anti-obesity effects of small molecule melanin-concentrating hormone receptor 1 (MCHR1) antagonists

Over the past ten years, tremendous advances in our understanding of the role of the hypothalamic neurohormone, melanin-concentrating hormone (MCH), and its involvement in the regulation of food intake and body weight have been achieved. The MCHR1 receptor has been actively targeted as a much-needed, novel treatment for obesity, a disease of epidemic proportion in the United States. Numerous companies have joined the competition to be the first to produce a small molecule antagonist targeting MCHR1 receptors in the race for therapeutics for this disease. This review details the rising need for new treatments for obesity; the rationale and target validation of MCHR1 receptor antagonists as potential treatments for this disease; and the current status of the numerous small molecule MCHR1 antagonists in development by different companies. MCHR1 antagonists might find an additional usage in the treatment of anxiety and depression disorders. The rationale and current status of this effort by several companies is also reviewed.

Identification of diamino chromone-2-carboxamides as MCHr1 antagonists with minimal hERG channel activity

A series of potent 2-carboxychromone-based melanin-concentrating hormone receptor 1 (MCHr1) antagonists were synthesized and evaluated for hERG (human Ether-a-go-go Related Gene) channel affinity and functional blockade. Basic dialkylamine-terminated analogs were found to weakly bind the hERG channel and provided marked improvement in a functional patch-clamp assay versus previously reported antagonists of the series.

Quinazoline and benzimidazole MCH-1R antagonists

We have modified the previously reported 2-aminoquinoline 1 to provide two novel series of MCH-1R antagonists. Representative compounds from the quinazoline and benzimidazole series have been shown to be potent and selective, with promising in vitro eADME profiles.

Cardiovascular effects of melanin-concentrating hormone

Melanin-concentrating hormone (MCH) is a cyclic 19-amino acid neuropeptide exclusively synthesized in the lateral hypothalamic area (LHA) and the zona incerta (ZI) that has been implicated in the regulation of energy balance. Despite what is known about the orexigenic effect of MCH, whether MCH has distinct cardiovascular and metabolic effects has yet to be determined. Thus, our goal here was to characterize the concurrent cardiovascular, metabolic, and behavioral responses of male rats to chronic intracerebroventricular (icv) infusion of MCH. Male Long-Evans rats were instrumented with telemetry transmitters for measurement of heart rate (HR) and housed in room calorimeters for assessment of food intake and oxygen consumption (VO(2)) at standard lab ambient temperature (23 degrees C) in order to examine physiological responses to chronic infusion of MCH (8 microg/d and 16 microg/d). Our findings provide the first evidence that chronic administration of MCH induces bradycardia and reduced mean arterial pressure, while it did not affect VO(2). A second experiment was performed in which the physiological responses to an acute icv infusion of MCH were observed. The results of experiment 2 indicate that MCH leads to a low HR that is maintained during the first 2 h post-infusion, the time period during which MCH acutely stimulated feeding. Collectively, these findings confirm that MCH may be an important modulator of sympathetic nervous system activity and thus may play a critical role in coordinating normal responses to negative energy balance.

Aminomethyl tetrahydronaphthalene biphenyl carboxamide MCH-R1 antagonists—Increasing selectivity over hERG

Aminomethyl tetrahydronaphthalene biphenyl carboxamide MCH-R1 antagonists with greater selectivity over hERG were identified. SAR studies addressing two distinct alternatives for structural modifications leading to improve hERG selectivity are described.

Aminomethyl tetrahydronaphthalene ketopiperazine MCH-R1 antagonists—Increasing selectivity over hERG

A direct correlation between hERG binding and QTc prolongation was established for a series of aminomethyl tetrahydronaphthalene ketopiperazine MCH-R1 antagonists. Compounds within this class with greater selectivity over hERG were developed. Compound 4h proved to have the best profile, with MCH-R1 Ki = 16 nm and hERG IC50 = 25 microM.

MCH-R1 antagonists based on an arginine scaffold: SAR studies on the amino-terminus

We have identified a novel series of potent MCH-R1 antagonists based on l-arginine. As predicted by computational methods, there was an activity dependence on the pi-electronic character of the aromatic systems corresponding to the amino-terminus of these molecules. These results have enhanced our understanding of the MCH-R1 receptor and the potential for a predictive homology model.

An evaluation of 3,4-methylenedioxy phenyl replacements in the aminopiperidine chromone class of MCHr1 antagonists

The optimization of potent MCHr1 antagonist 1 with respect to improving its in vitro profile by replacement of the 3,4-methylenedioxy phenyl (piperonyl) moiety led to the discovery of 19, a compound that showed excellent MCHr1 binding and functional potencies in addition to possessing superior hERG separation, CYP3A4 profile, and receptor cross-reactivity profiles.

Novel pyrazolopiperazinone- and pyrrolopiperazinone-based MCH-R1 antagonists

The synthesis and biological testing of novel classes of potent melanin-concentrating hormone (MCH-R1) antagonists based on pyrazolopiperazinone and pyrrolopiperazinone scaffolds are described.

Melanin-Concentrating Hormone Receptor-1 Antagonists as Antiobesity Therapeutics

There is compelling genetic and pharmacologic evidence to indicate that melanin-concentrating hormone receptor-1 (MCHR1) signaling is involved in the regulation of food intake and energy expenditure. The medical need for novel therapies to treat obesity and related metabolic disorders has led to a great deal of interest by pharmaceutical companies in the discovery of MCHR1 antagonists. Recent publications describing preclinical studies have demonstrated that small-molecule MCHR1 antagonists decrease food intake, bodyweight, and adiposity in rodent models of obesity. Results from ongoing early-stage clinical trials with MCHR1 antagonists are eagerly awaited, as is the movement of other MCHR1 antagonists into the clinic.

The efficacy and cardiac evaluation of aminomethyl tetrahydronaphthalene ketopiperazines: a novel class of potent MCH-R1 antagonists

The design, synthesis, and biological studies of a novel class of MCH-R1 antagonists based on an aminotetrahydronaphthalene ketopiperazine scaffold is described. Compounds within this class promoted significant body weight reduction in mouse diet induced obesity studies. The potential for hERG blockage activity and QT interval studies in anesthetized dogs are discussed.

2-Aminoquinoline melanin-concentrating hormone (MCH)1R antagonists

A series of 2-aminoquinoline compounds was prepared and evaluated in MCH1R binding and functional antagonist assays. Small dialkyl, methylalkyl, methylcycloalkyl, and cyclic amines were tolerated at the quinoline 2-position. The in vivo efficacy of compound 12 was explored and compared to that of a related inactive analog to determine their effects on food intake and body weight in rodents.

Identification of substituted 4-aminopiperidines and 3-aminopyrrolidines as potent MCH-R1 antagonists for the treatment of obesity

A substituted 4-aminopiperidine was identified as showing activity in an MCH assay from an HTS effort. Subsequent structural modification of the scaffold led to the identification of a number of active MCH antagonists. 3,5-Dimethoxy-N-(1-(naphthalen-2-ylmethyl)piperidin-4-yl)benzamide (5c) was among those with the highest binding affinity to the MCH receptor (K(i)=27nM), when variations were made at benzoyl and naphthylmethyl substitution sites from the initial HTS hit. Further optimization via piperidine ring contraction resulted in enhanced MCH activity in a 3-aminopyrrolidine series, where (R)-3,5-dimethoxy-N-(1-(naphthalen-2-ylmethyl)-pyrrolidin-3-yl)benzamide (10i) was found to be an excellent MCH antagonist (K(i)=7nM).

Novel benzimidazole-based MCH R1 antagonists

The identification of an MCH R1 antagonist screening hit led to the optimization of a class of benzimidazole-based MCH R1 antagonists. Structure-activity relationships and efforts to optimize pharmacokinetic properties are detailed along with the demonstration of the effectiveness of an MCH R1 antagonist in an animal model of obesity.

4-Aminoquinoline melanin-concentrating hormone 1-receptor (MCH1R) antagonists

Structure-activity relationships of a 4-aminoquinoline MCH1R antagonist lead series were explored by synthesis of analogs with modifications at the 2-, 4-, and 6-positions of the original HTS hit. Improvements to the original screening lead included lipophilic groups at the 2-position and biphenyl, cyclohexyl phenyl, and hydrocinnamyl carboxamides at the 6-position. Modifications of the 4-amino group were not well tolerated.

The discovery and optimization of pyrimidinone-containing MCH R1 antagonists

Optimization of a series of constrained melanin-concentrating hormone receptor 1 (MCH R1) antagonists has provided compounds with potent and selective MCH R1 activity. Details of the optimization process are provided and the use of one of the compounds in an animal model of diet-induced obesity is presented.

The melanocortins and melanin-concentrating hormone in the central regulation of feeding behavior and energy homeostasis

A number of different neuropeptides exert powerful concerted controls on feeding behavior and energy balance, most of them being produced in hypothalamic neuronal networks under stimulation by anabolic and catabolic peripheral hormones such as ghrelin and leptin, respectively. These peptide-expressing neurons interconnect extensively to integrate the multiple opposing signals that mediate changes in energy expenditure. In the present review I have summarized our current knowledge about two key peptidic systems involved in regulating appetite and energy homeostasis, the melanocortin system (alpha-MSH, agouti and Agouti-related peptides, MC receptors and mahogany protein) and the melanin-concentrating hormone system (proMCH-derived peptides and MCH receptors) that contribute to satiety and feeding-initiation, respectively, with concurrent effects on energy expenditure. I have focused particularly on recent data concerning transgenic mice and the ongoing development of MC/MCH receptor antagonists/agonists that may represent promising drugs to treat human eating disorders on both sides of the energy balance (anorexia, obesity).

Design and synthesis of orally efficacious benzimidazoles as melanin-concentrating hormone receptor 1 antagonists

Biaryl urea lead compound 1 was discovered earlier in our MCH antagonist program. Novel benzimidazole analogues with increased chemical stability, devoid of the potential carcinogenic liability associated with a biarylamine moiety, were synthesized and evaluated to be potent MCH R1 antagonists. Two compounds in this series have demonstrated in vivo efficacy in a rodent obesity model.

Synthesis and structure–activity relationships of piperidine-based melanin-concentrating hormone receptor 1 antagonists

Isosteric replacement of the urea group of lead compound 1 led to novel substituted piperidine phenylamide analogues. SAR on the electron-induced effects of various linkers as well as substituents on the phenyl rings and the piperidine nitrogen has been investigated. Many single-digit nanomolar MCH R1 antagonists have been identified from this series.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Development of a time-resolved fluorometric assay for the high throughput screening of melanin concentrating hormone receptor antagonists

INTRODUCTION

Melanin concentrating hormone is an orexigenic hypothalamic neuropeptide, which plays an important role in the complex regulation of energy balance and body weight mediated by the melanin concentrating hormone receptor subtype 1 (MCH1). Compelling pharmacological evidence implicating MCH1 signaling in the regulation of food intake and energy expenditure has generated a great deal of interest by pharmaceutical companies as MCH1 antagonists may have potential therapeutic benefit in the treatment of obesity and metabolic syndrome.

METHODS

Although radioligand receptor binding assay has been one of the most powerful tools for receptor research and drug discovery, the limitations of radioisotopes and the problems related to safety and waste disposal limits their application in high throughput screening and has led to a growing interest in alternative, nonradioactive technologies. To develop a sensitive and reproducible assay system for MCH1, the time-resolved fluorescence (TRF) receptor binding assay with AcroWell filter plates was tested and validated.

RESULTS

Comparing to the radioligand receptor binding assay for MCH1, the TRF assay presented higher Z/Z' factors with the lower signal-to-noise ratio. The known high-affinity MCH1 receptor antagonist, SNAP-7941, exhibited an IC50 value of 1.66+/-0.10 nM that is very similar to the IC50 value of MCH in a radioligand binding assay with an excellent correlation coefficient (0.9884).

DISCUSSION

These results suggest that our TRF receptor binding assay for MCH1 can achieve the desired sensitivity and reproducibility to replace the radioligand receptor assay in a fluorometric system that can be developed for high throughput screening.

Advances in anti-obesity therapeutics

Obesity is rapidly becoming an epidemic in developed countries. Currently available anti-obesity therapeutics are only modestly effective and are accompanied by significant adverse effects. In recent years, substantial advances have been made in the basic understanding of brain control of feeding behaviour and metabolism. As a result, several compounds have progressed to Phase III development, with additional compounds at various stages of Phase II development. Most of the late-stage development candidates are CNS agents, which reflects the consensus that the brain exerts a dominant control on feeding behaviour and peripheral metabolism through the autonomic nervous system. Homeostatic mechanisms encompassing hypothalamic/brainstem pathways have long been recognised in obesity research. In addition, non-homeostatic mechanisms encompassing the reward circuit and volitional control need to be targeted to control feeding behaviour and physical activity, especially in humans. While recognising the importance of CNS control, certain peripherally acting agents can affect mitochondrial metabolism, lipolysis, nutrient absorption or the vagal feedback pathway, such that these peripherally acting agents can potentially be combined with CNS agents to achieve maximal efficacy. It is expected that newer generations of anti-obesity therapeutics will be superior to existing agents and will facilitate lifestyle modification.

Further insights into the neurobiology of melanin-concentrating hormone in energy and mood balances

Melanin-concentrating hormone (MCH) is a critical hypothalamic anabolic neuropeptide, with key central and peripheral actions on energy balance regulation. The actions of MCH are, so far, known to be transduced through two seven-transmembrane-like receptor paralogues, named MCH1R and MCH2R. MCH2R is not functional in rodents. MCH1R is an important receptor involved in mediating feeding behaviour modulation by MCH in rodents. Pharmacological antagonism at MCH1R in rodents diminishes food intake and results in significant and sustained weight loss in fat tissues, particularly in obese animals. Additionally, MCH1R antagonists have been shown to have anxiolytic and antidepressant properties. The purpose of this review is to highlight the recent numerous pieces of evidence showing that pharmacological blockade at MCH1R could be a potential treatment for obesity and its related metabolic syndrome, as well as for various psychiatric disorders.

Discovery of Orally Efficacious Melanin-Concentrating Hormone Receptor-1 Antagonists as Antiobesity Agents. Synthesis, SAR, and Biological Evaluation of Bicyclo[3.1.0]hexyl Ureas

Melanin-concentrating hormone (MCH) is a cyclic, nonadecapeptide expressed in the CNS of all vertebrates that regulates feeding behavior and energy homeostasis via interaction with the central melanocortin system. Regulation of this interaction results in modulation of food intake and body weight gain, demonstrating significant therapeutic potential for the treatment of obesity. The MCH-1 receptor (MCH-R1) has been identified as a key target in MCH regulation, as small molecule antagonists of MCH-R1 have demonstrated activity in vivo. Herein, we document our research in a bicyclo[3.1.0]hexyl urea series with particular emphasis on structure-activity relationships and optimization of receptor occupancy, measured both in vitro and via an ex vivo binding assay following an oral dosing regimen. Several compounds have been tested in vivo and exhibit oral efficacy in relevant acute rodent feeding models. In particular, 24u has proven efficacious in chronic rodent models of obesity, showing a statistically significant reduction in food intake and body weight over a 28 day study.

The Use of Three-Dimensional Shape and Electrostatic Similarity Searching in the Identification of a Melanin-Concentrating Hormone Receptor 1 Antagonist

To aid in the identification of novel melanin-concentrating hormone receptor 1 (MCHr1) antagonists, a unique virtual library of readily synthesized molecules was designed and assembled based on 323 monomer compounds containing reactive moieties in combination with 30 core molecules having diamine functionality. The resulting library of 3,129,870 molecules was searched using three-dimensional shape similarity measures that were complimented with a novel electrostatic distribution similarity-matching algorithm. One of the top scoring hits in this library was synthesized and characterized for MCHr1 antagonism, where it exhibited at least a threefold improvement in binding affinity and cellular potency relative to the parent MCHr1 ligand. This work demonstrates that the use of shape and electrostatic similarity matching in combination with a well-designed virtual library can be used to augment standard medicinal chemistry techniques.

6-Acylamino-2-amino-4-methylquinolines as potent melanin-concentrating hormone 1 receptor antagonists: Structure–activity exploration of eastern and western parts

SAR explorations of the eastern and western parts of recently disclosed 2-aminoquinoline MCH1R-antagonists are reported. Eastern part investigations confirmed a high degree of structural freedom, and a number of additional single digit nanomolar antagonists were identified. Investigations of the western part also confirmed the initial SAR analysis, requiring a para-substituted phenyl ring spaced from the 6-amide by two connecting atoms. The exploration led to the discovery of a novel sub-series with a 4-biphenylcarboxamide western part, also exhibiting single digit nanomolar affinity.

Melanin concentrating hormone innervation of caudal brainstem areas involved in gastrointestinal functions and energy balance

Neural signaling by melanin-concentrating hormone and its receptor (SLC-1) has been implicated in the control of energy balance, but due to the wide distribution of melanin-concentrating hormone-containing fibers throughout the neuraxis, its critical sites of action for a particular effect have not been identified. The present study aimed to anatomically and functionally characterize melanin-concentrating hormone innervation of the rat caudal brainstem, as this brain area plays an important role in the neural control of ingestive behavior and autonomic outflow. Using retrograde tracing we demonstrate that a significant proportion (5-15%) of primarily perifornical and far-lateral hypothalamic melanin-concentrating hormone neurons projects to the dorsal vagal complex. In the caudal brainstem, melanin-concentrating hormone-ir axon profiles are distributed densely in most areas including the nucleus of the solitary tract, dorsal motor nucleus of the vagus, and sympathetic premotor areas in the ventral medulla. Close anatomical appositions can be demonstrated between melanin-concentrating hormone-ir axon profiles and tyrosine hydroxylase, GABA, GLP-1, NOS-expressing, and nucleus of the solitary tract neurons activated by gastric nutrient infusion. In medulla slice preparations, bath application of melanin-concentrating hormone inhibited in a concentration-dependent manner the amplitude of excitatory postsynaptic currents evoked by solitary tract stimulation via a pre-synaptic mechanism. Fourth ventricular administration of melanin-concentrating hormone (10 microg) in freely moving rats decreased core body temperature but did not change locomotor activity and food and water intake. We conclude that the rich hypothalamo-medullary melanin-concentrating hormone projections in the rat are mainly inhibitory to nucleus of the solitary tract neurons, but are not involved in the control of food intake. Projections to ventral medullary sites may play a role in the inhibitory effect of melanin-concentrating hormone on energy expenditure.