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.     

Identification of 2-aminobenzimidazoles as potent melanin-concentrating hormone 1-receptor (MCH1R) antagonists

A series of 2-aminobenzimidazole-based MCH1R antagonists was identified by core replacement of the aminoquinoline lead 1. Subsequent modification of the 2- and 5-positions led to improvement in potency and intrinsic clearance. Compound 25 exhibited good plasma and brain exposure, and attenuated MCH induced food intake at 30 mg/kg PO in rats.     

4-Acylamino-and 4-ureidobenzamides as melanin-concentrating hormone (MCH) receptor 1 antagonists

Synthesis, in vitro biological evaluation and structure-activity relationships of 4-acylamino-and 4-ureidobenzamides as novel hMCH1R-antagonists are disclosed. The nature of the amine side chains could be varied considerably in contrast to the central benzamide scaffold and aromatic substituents.     

Structure-activity relationships of a novel series of melanin-concentrating hormone (MCH) receptor antagonists

A new series of 2-aminoquinolines has been identified as antagonists of the melanin concentrating hormone receptor (MCH-1R). Syntheses and structure-activity relationships are described leading to a compound having low nanomolar activity against the receptor and demonstrating functional antagonism. Studies also showed that some of the compounds were selective against a range of other G protein-coupled receptors.     

Identification and characterization of a selective radioligand for melanin-concentrating hormone 1-receptor (MCH1R)

We have developed and characterized [³⁵S]4a as a potent and selective radioligand for melanin-concentrating hormone 1-receptor (MCH1R). Compound [³⁵S]4a showed appreciable specific signals in brain slices prepared from wild-type mice but not from MCH1R deficient mice, confirming the specificity and utility of [³⁵S]4a as a selective MCH1R radioligand for ex vivo receptor occupancy assays.     

Discovery of melanin-concentrating hormone receptor R1 antagonists using high-throughput synthesis

A structure-activity study on benzylpiperidine 1 was accomplished by utilizing high-throughput synthesis. Three focused libraries were designed and synthesized to quickly develop SAR. Further optimization led to the discovery of compound 2, an MCH receptor R1 antagonist with over 400-fold improvement in biological activity over the original lead.     

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.     

Structure-activity relationship studies of melanin-concentrating hormone (MCH)-related peptide ligands at SLC-1, the human MCH receptor

Melanin-concentrating hormone (MCH) is a cyclic nonadecapeptide involved in the regulation of feeding behavior, which acts through a G protein-coupled receptor (SLC-1) inhibiting adenylcyclase activity. In this study, 57 analogues of MCH were investigated on the recently cloned human MCH receptor stably expressed in HEK293 cells, on both the inhibition of forskolin-stimulated cAMP production and guanosine-5'-O-(3-[(35)S]thiotriphosphate ([(35)S]- GTPgammaS) binding. The dodecapeptide MCH-(6-17) (MCH ring between Cys(7) and Cys(16), with a single extra amino acid at the N terminus (Arg(6)) and at the C terminus (Trp(17))) was found to be the minimal sequence required for a full and potent agonistic response on cAMP formation and [(35)S]- GTPgammaS binding. We Ala-scanned this dodecapeptide and found that only 3 of 8 amino acids of the ring, namely Met(8), Arg(11), and Tyr(13), were essential to elicit full and potent responses in both tests. Deletions inside the ring led either to inactivity or to poor antagonists with potencies in the micromolar range. Cys(7) and Cys(16) were substituted by Asp and Lys or one of their analogues, in an attempt to replace the disulfide bridge by an amide bond. However, those modifications were deleterious for agonistic activity. In [(35)S]- GTPgammaS binding, these compounds behaved as weak antagonists (K(B) 1-4 microm). Finally, substitution in MCH-(6-17) of 6 out of 12 amino acids by non-natural residues and concomitant replacement of the disulfide bond by an amide bond led to three compounds with potent antagonistic properties (K(B) = 0.1-0.2 microm). Exploitation of these structure-activity relationships should open the way to the design of short and stable MCH peptide antagonists.     

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.     

Thienopyrimidinone bis-aminopyrrolidine ureas as potent melanin-concentrating hormone receptor-1 (MCH-R1) antagonists

A series of thienopyrimidinone bis-aminopyrrolidine ureas were designed, synthesized, and evaluated for their ability to bind melanin-concentrating hormone receptor-1. These compounds exhibit potent binding affinity (K(i)=3 nM) and good in vitro metabolic stability.     

Feeding-induced changes of melanin-concentrating hormone (MCH)-like immunoreactivity in goldfish brain

Intracerebroventricular (ICV) injection of melanin-concentrating hormone (MCH) influences feeding behavior in the goldfish and exerts an anorexigenic action in goldfish brain, unlike its orexigenic action in mammals. Despite a growing body of knowledge concerning MCH function in mammals, the role of MCH in appetite has not yet been well studied in fish. The aim of the present study was to investigate the involvement of endogenous MCH in the feeding behavior of the goldfish. We examined the distribution of MCH-like immunoreactivity (MCH-LI) in the goldfish brain and the effect of feeding status upon this distribution. Neuronal cell bodies containing MCH-LI were localized specifically to four areas of the hypothalamus. Nerve fibers with MCH-LI were found mainly in the neurohypophysis, with a few in the telencephalon, mesencephalon, and diencephalon. The number of neuronal cell bodies containing MCH-LI in the dorsal area adjoining the lateral recess of the third ventricle in the posterior and inferior lobes of the hypothalamus showed a significant decrease in fasted fish compared with that in normally fed fish, although other areas showed no evident differences. We also administered an antiserum against fish MCH (anti-MCH serum) by ICV injection and examined its immunoneutralizing effect on food intake by using an automatic monitoring system. Cumulative food intake was significantly increased by ICV injection of the anti-MCH serum. These results indicate that MCH potentially functions as an anorexigenic neuropeptide in the goldfish brain, and that the further study of the evolutionary background of the MCH system and its role in appetite is warranted. This work was supported by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (K.M. and A.T.) and by a research grant from the Toyama Marine Biotechnology Association (K.M.).     

SAR of biphenyl carboxamide ligands of the human melanin-concentrating hormone receptor 1 (MCH R1): discovery of antagonist SB-568849

We report here the discovery of a class of MCH R1 ligands based on a biphenyl carboxamide template. A docked-in model is presented indicating key interactions in the putative binding site of the receptor. Parallel high throughput synthetic techniques were utilised to allow rapid exploration of the structure-activity relationship around this template, leading to compound SB-568849 which possessed good receptor affinity and selectivity. This compound proved to be an antagonist with stability in vivo, an acceptable brain-blood ratio and oral bioavailability.     

The melanin-concentrating hormone (MCH) system modulates behaviors associated with psychiatric disorders

Deficits in sensorimotor gating measured by prepulse inhibition (PPI) of the startle have been known as characteristics of patients with schizophrenia and related neuropsychiatric disorders. PPI disruption is thought to rely on the activity of the mesocorticolimbic dopaminergic system and is inhibited by most antipsychotic drugs. These drugs however act also at the nigrostriatal dopaminergic pathway and exert adverse locomotor responses. Finding a way to inhibit the mesocorticolimbic- without affecting the nigrostriatal-dopaminergic pathway may thus be beneficial to antipsychotic therapies. The melanin-concentrating hormone (MCH) system has been shown to modulate dopamine-related responses. Its receptor (MCH1R) is expressed at high levels in the mesocorticolimbic and not in the nigrostriatal dopaminergic pathways. Interestingly a genomic linkage study revealed significant associations between schizophrenia and markers located in the MCH1R gene locus. We hypothesize that the MCH system can selectively modulate the behavior associated with the mesocorticolimbic dopamine pathway. Using mice, we found that central administration of MCH potentiates apomorphine-induced PPI deficits. Using congenic rat lines that differ in their responses to PPI, we found that the rats that are susceptible to apomorphine (APO-SUS rats) and exhibit PPI deficits display higher MCH mRNA expression in the lateral hypothalamic region and that blocking the MCH system reverses their PPI deficits. On the other hand, in mice and rats, activation or inactivation of the MCH system does not affect stereotyped behaviors, dopamine-related responses that depend on the activity of the nigrostriatal pathway. Furthermore MCH does not affect dizocilpine-induced PPI deficit, a glutamate related response. Thus, our data present the MCH system as a regulator of sensorimotor gating, and provide a new rationale to understand the etiologies of schizophrenia and related psychiatric disorders.     

Synthesis and SAR investigations of novel 2-arylbenzimidazole derivatives as melanin-concentrating hormone receptor 1 (MCH-R1) antagonists

Compounds containing 2-arybenzimidazole ring systems linked to arylpiperidines were synthesized and evaluated as MCH-R1 antagonists. The results of structure-activity relationship studies led to the identification of compound 4c as a potent MCH-R1 antagonist (IC₅₀ = 1 nM). This compound also has good metabolic stability, and favorable pharmacokinetic and brain penetration properties. However 4c was found to be potent inhibitor of the hERG potassium channel.     

Synthesis and characterization of new radioligands for the mammalian melanin-concentrating hormone (MCH) receptor

Melanin-concentrating hormone (MCH) is a neuropeptide present in the brain of all vertebrates. For the characterization of MCH receptors, a monoiodinated [Phe13, Tyr19]-MCH radioligand analogue was developed. The high susceptibility of [125I]-[Phe13, Tyr19]-MCH to oxidative damage and its very lipophilic nature made it necessary to develop new MCH radioligands. To increase the stability, native methionines were replaced by non-sulphur containing amino acid residues. In one analogue, the L-enantiomer of the phenylalanine residue at position 13 was substituted by the D-enantiomer, which increased the relative affinity of the ensuing [125I]-[D-Phe13, Tyr19]-MCH about 7-fold. The different analogues were iodinated by an enzymatic reaction and used for binding studies with mouse melanoma cells. [125I]-[Met(O)4,8, Phe13, Tyr19]-MCH and [125I]-[Hse4,8, Phe13, Tyr19]-MCH showed only about 19% of total binding and [125I]-[Ser4,8, Phe13, Tyr19]-MCH displayed about 44% of total binding when compared with [125I]-[Phe13, Tyr19]-MCH. Non-specific binding for all tracers was below 11% of total binding of [125I]-[Phe13, Tyr19]-MCH binding. [125I]-[D-Phe13, Tyr19]-MCH was used for saturation binding studies and revealed a KD of 122.7 +/- 15.3 pmol/l. This radioligand was further characterized by association and dissociation binding studies.     

Expression of receptors for melanin-concentrating hormone (MCH) in different tissues and cell lines

Melanin-concentrating hormone (MCH) is a potent orexigenic neuropeptide and a physiological antagonist of alpha-melanocyte-stimulating hormone (alpha-MSH) in the brain as well as at peripheral sites, including the pigmentary systems of specific vertebrates. Two receptor subtypes for MCH, MCH-R1 and MCH-R2, have been cloned, but other receptor subtypes are likely to exist. Based on our own data and the current literature, we have compared the expression of different receptors for MCH in various mammalian cell lines and tissues. Summarizing all data currently available, we conclude that the two cloned MCH receptors, MCH-R1 and MCH-R2, exhibit differences in their expression pattern, although MCH-R1 is generally colocalized in all tissues where MCH-R2 expression is found. It appears that MCH-R1 is more abundant and has a wider distribution pattern than MCH-R2. Other hypothetical MCH-R subtypes may be expressed in specific tissues, e.g., in the pigment cell system.     

Discovery of 1,3-disubstituted-1H-pyrrole derivatives as potent melanin-concentrating hormone receptor 1 (MCH-R1) antagonists

A series of 1,3-disubstituted-1H-pyrrole-based antagonists of the human Melanin-Concentrating Hormone Receptor 1 (h-MCH-R1) are reported. High-throughput screening of the AstraZeneca compound collection yielded 1, a hit with moderate affinity towards MCH-R1. Subsequent structural manipulations and SAR analysis served to rationalize potency requirements, and 12 was identified as a novel, functional MCH-R1 antagonist with favorable pharmacokinetic properties.     

Different structural requirements for melanin-concentrating hormone (MCH) interacting with rat MCH-R1 (SLC-1) and mouse B16 cell MCH-R

Melanin-concentrating hormone (MCH) is a neuropeptide occurring in all vertebrates and some invertebrates and is now known to stimulate pigment aggregation in teleost melanophores and food-intake in mammals. Whereas the two MCH receptor subtypes hitherto cloned, MCH-R1 and MCH-R2, are thought to mediate mainly the central effects of MCH, the MCH-R on pigment cells has not yet been identified, although in some studies MCH-R1 was reported to be expressed by human melanocytes and melanoma cells. Here we present data of a structure-activity study in which 12 MCH peptides were tested on rat MCH-R1 and mouse B16 melanoma cell MCH-R, by comparing receptor binding affinities and biological activities. For receptor binding analysis with HEK-293 cells expressing rat MCH-R1 (SLC-1), the radioligand was [125I]-[Tyr13]-MCH with the natural sequence. For B16 cells (F1 and G4F sublines) expressing B16 MCH-R, the analog [125I]-[D-Phe13, Tyr19]-MCH served as radioligand. The bioassay used for MCH-R1 was intracellular Ca2+ mobilization quantified with the FLIPR instrument, whereas for B16 MCH-R the signal determined was MAP kinase activation. Our data show that some of the peptides displayed a similar relative increase or decrease of potency in both cell types tested. For example, linear MCH with Ser residues at positions 7 and 16 was almost inactive whereas a slight increase in side-chain hydrophilicity at residues 4 and 8, or truncation of MCH at the N-terminus by two residues hardly changed binding affinity or bioactivity. On the other hand, salmonic MCH which also lacks the first two residues of the mammalian sequence but in addition has different residues at positions 4, 5, 9, and 18 exhibited a 5- to 10-fold lower binding activity than MCH in both cell systems. A striking difference in ligand recognition between MCH-R1 and B16 MCH-R was however observed with modifications at position 13 of MCH: whereas L-Phe13 in [Phe13, Tyr19]-MCH was well tolerated by both MCH-R1 and B16 MCH-R, change of configuration to D-Phe13 in [D-Phe13, Tyr19]-MCH or [D-Phe13]-MCH led to a complete loss of biological activity and to a 5- to 10-fold lower binding activity with MCH-R1. By contrast, the D-Phe13 residue increased the affinity of [D-Phe13, Tyr19]-MCH to B16 MCH-R about 10-fold and elicited MAP kinase activation as observed with [Phe13, Tyr19]-MCH or MCH. These data demonstrate that ligand recognition by B16 MCH-R differs from that of MCH-R1 in several respects, indicating that the B16 MCH-R represents an MCH-R subtype different from MCH-R1.     

Optimization of 2-piperidin-4-yl-acetamides as melanin-concentrating hormone receptor 1 (MCH-R1) antagonists: Designing out hERG inhibition

Herein, we disclose the discovery and optimization of 2-piperidin-4-yl-acetamide derivatives as MCH-R1 antagonists. Structural investigation of piperidin-4-yl-amide and piperidin-4-yl-ureas identified 2-piperidin-4-yl-acetamide-based MCH-R1 antagonists with outstanding in vivo efficacy but flawed with high affinity towards the hERG potassium channel. While existing hERG SAR information was employed to discover highly potent MCH-R1 antagonists with minimized hERG inhibition, additional hurdles prevented their subsequent clinical exploration.     

Synthesis and structure-activity relationships of spirohydantoin-derived small-molecule antagonists of the melanin-concentrating hormone receptor-1 (MCH-R1)

The design, synthesis, and SAR of a series of substituted spirohydantoins are described. Optimization of an in-house screening hit gave compounds that exhibited potent binding affinity and functional activity at MCH-R1.