The MC4 receptor and control of appetite

Mutations in the human melanocortin (MC)4 receptor have been associated with obesity, which underscores the relevance of this receptor as a drug target to treat obesity. Infusion of MC4R agonists decreases food intake, whereas inhibition of MC receptor activity by infusion of an MC receptor antagonist or with the inverse agonist AgRP results in increased food intake. This review addresses the role of the MC system in different aspects of feeding behaviour. MC4R activity affects meal size and meal choice, but not meal frequency, and the type of diet affects the efficacy of MC4R agonists to reduce food intake. The central sites involved in the different aspects of feeding behaviour that are affected by MC4R signalling are being unravelled. The paraventricular nucleus plays an important role in food intake per se, whereas MC signalling in the lateral hypothalamus is associated with the response to a high fat diet. MC4R signalling in the brainstem has been shown to affect meal size. Further genetic, behavioural and brain-region specific studies need to clarify how the MC4R agonists affect feeding behaviour in order to determine which obese individuals would benefit most from treatment with these drugs. Application of MCR agonists in humans has already revealed side effects, such as penile erections, which may complicate introduction of these drugs in the treatment of obesity.     

Inverse agonism gains weight

Inverse agonism is emerging as a new endogenous principle for receptor regulation. Agouti-related protein (AgRP), following its release in the brain, stimulates food intake. AgRP binds to brain melanocortin receptors, which are involved in the regulation of body weight. In addition to antagonizing the effects of the melanocortin receptor agonist alpha-melanocyte-stimulating hormone (alpha-MSH), AgRP suppresses the constitutive activity of melanocortin MC(3) and MC(4) receptors, which characterizes AgRP as an inverse agonist rather than a neutral antagonist. The balance between the activity of AgRP-containing neurons and alpha-MSH-containing neurons determines the extent of activation of melanocortin receptors in neurons onto which they project. The identification of AgRP as an endogenous inverse agonist provides physiological relevance to inverse agonism in the control of body weight.     

Melanocortin activity in the amygdala influences alcohol intake

Melanocortins have been reported to affect alcohol intake through actions in the hypothalamus thought to be mediated by melanocortin MC4 receptors. Since these receptors are expressed in a number of amygdala regions, we have explored their role in the regulation of alcohol intake in both alcohol-preferring (P) and non-preferring (NP) rats. Injections were made at the border of the central amygdala nucleus and the basolateral amygdala. The MC3/MC4R agonist MTII reduced alcohol and food intake but increased water intake while the selective MC4R antagonist HS014 only increased food and water intake. The MC3/MC4R antagonist SHU9119 increased food and water but had little effect on alcohol intake. However, when the SHU9119 stimulation of food intake was prevented by pair-feeding, SHU9119 induced a large and prolonged decline in alcohol intake that was paralleled by an increase in water intake. These effects were only observed in P rats. We conclude that melanocortin activity in the amygdala can alter the selective preference for water and alcohol independent of effects on food intake.     

The neuroendocrine circuitry controlled by POMC, MSH, and AGRP

Obesity is one of the most challenging health problems worldwide. Over the past few decades, our knowledge concerning mechanisms of weight regulation has increased tremendously leading to the identification of the leptin-melanocortin pathway. The filling level of energy stores is signaled to the brain, and the information is integrated by hypothalamic nuclei, resulting in a well-orchestrated response to food intake and energy expenditure to ensure constant body weight. One of the key players in this system is proopiomelanocortin (POMC), a precursor of a variety of neuropeptides. POMC-derived alpha- and beta-MSH play an important role in energy homeostasis by activating melanocortin receptors expressed in the arcuate nucleus (MC3R) and in the nucleus paraventricularis (MC4R). Activation of these two G protein-coupled receptors is antagonized by agouti-related peptide (AgRP). Naturally occurring mutations in this system were identified in patients suffering from common obesity as well as in patients demonstrating a phenotype of severe early-onset obesity, adrenal insufficiency, red hair, and pale skin. Detailed understanding of the complex system of POMC-AgRP-MC3R-MC4R and their interaction with other hypothalamic as well as peripheral signals is a prerequisite to combat the obesity epidemic.     

Resveratrol,purified from the stem of <Emphasis Type="Italic">Vitis coignetiae</Emphasis> Pulliat,inhibits food intake in C57BL/6J Mice

Neuropeptide Y (NPY) and agouti-related protein (AgRP) have powerful stimulatory effects on food intake, which suggests that the downregulation of brain NPY or AgRP may help reduce obesity and diabetes by inhibiting food intake. To search for active compounds that inhibit NPY and AgRP expression, we made two luciferase reporter assay systems consisting of NPY and AgRP promoter-driven luciferase genes, together with the puromycin resistance gene, in a plasmid vector. Each plasmid was permanently transfected into N29-4 neuronal cells. Using the systems, resveratrol was purified from the stem of Vitis coignetiae Pulliat by activityguided fractionation. Resveratrol downregulated NPY and AgRP promoter-driven luciferase activity in a dose-dependent manner. The inhibitory concentrations (IC₅₀, 50% inhibition) of resveratrol against pNPY-luc and pAgRP-luc activities were 8.9 μM and 8.0 μM, respectively. Furthermore, one-time intraperitoneal injection of resveratrol (100 mg/kg) suppressed 20.0% and 17.2% of food intake during 24 and 48 h, respectively. These results indicated that resveratrol inhibited food intake, which may be related to the downregulation of NPY and AgRP gene expression.     

Alcohol-preferring AA rats show a derangement in their central melanocortin signalling system

The AA (Alko, Alcohol) rats are selectively bred for their preference of alcohol to water, contrasting to ANA rats that avoid alcohol. They also exhibit a lower growth rate compared to ANA rats, as well as differences in their response to substances affecting food intake. The melanocortin (MC) system is involved in the regulation of feeding behaviour and in mechanisms underlying drug addiction and tolerance. Recently, administration of an MC receptor agonist proved to reduce alcohol intake in AA rats. We predicted that the ratio of endogenous MC receptor agonists (proopiomelanocortin, POMC) and antagonists (agouti-related protein, AgRP) would differ from ANA rats, and that subsequent differences in MC receptor levels would be detectable. We used in situ hybridization to detect an increased ratio of POMC/AgRP mRNA in the arcuate nucleus (Arc) of AA rats. Receptor autoradiography indicated that MC3 receptor binding differed in the nucleus accumbens and several hypothalamic nuclei, possibly reflecting differences in MC peptide transmission in the AA rats. Our results support the claim that AA rats have a high ratio of POMC/AgRP expression, and that this observation is accompanied by differences in MC3 receptor levels.     

Roles of threonine 192 and asparagine 382 in agonist and antagonist interactions with M1 muscarinic receptors

Conserved amino acids, such as Thr in transmembrane domains (TM) V and Asn in TM VI of muscarinic receptors, may be important in agonist binding and/or receptor activation. In order to determine the functional roles of Thr192 and Asn382 in human M1 receptors in ligand binding and receptor activation processes, we created and characterized mutant receptors with Thr192 or Asn382 substituted by Ala. HM1 wild-type (WT) and mutant receptors [HM1(Thr192Ala) and HM1(Asn382Ala)] were stably expressed in A9 L cells. The Kd values for 3H-(R)-QNB and Ki values for other classical muscarinic antagonists were similar at HM1(WT) and HM1(Thr192Ala) mutant receptors, yet higher at HM1(Asn382Ala) mutant receptors. Carbachol exhibited lower potency and efficacy in stimulating PI hydrolysis via HM1(Thr192Ala) mutant receptors, and intermediate agonist activity at the HM1(Asn382Ala) mutant receptors. The Asn382 residue in TM VI but not the Thr192 residue in TM V of the human M1 receptor appears to participate directly in antagonist binding. Both Thr192 and Asn382 residues are involved differentially in agonist binding and/or receptor activation processes, yet the Asn382 residue is less important than Thr192 in agonist activation of M1 receptors. Molecular modelling studies indicate that substitution of Thr192 or Asn382 results in the loss of hydrogen-bond interactions and changes in the agonist binding mode associated with an increase in hydrophobic interactions between ligand and receptor.     

Melanocortin-4 receptor agonists for the treatment of obesity

The melanocortin family of receptors (MC 1-5R) and their endogenous peptide ligands (alpha, beta, gamma- MSH and ACTH) have been implicated in the control of a wide variety of behavioral and physiological functions including the homeostatic control of food intake and body weight. In rodent models, melanocortin agonists including the nonselective peptide MTII have been shown to decrease food intake and body weight while antagonists such as SHU9119 and AGRP have been shown to stimulate food intake and increase body weight. Deletion of either the MC3R or MC4R in mice was found to be associated with obesity although hyperphagia was only observed in the MC4R deficient mice. Similarly in humans, inactivating mutations of the MC4R have been found in as many as six percent of obese individuals. The suggestion from these findings that activation of MC4Rs would have an anorectic effect in humans has resulted in efforts to produce selective agonists for the treatment of obesity. Over the past decade, efforts to develop MC4R selective small molecule and peptide agonists have been met with fractional success. Many small molecule agonists have been identified; however, few have been shown to have activity in vivo. While their use as therapeutics may have limitations, selective and potent peptide agonists have been shown by several investigators to decrease food intake and body weight in rodent models. The subject of the current review is to examine the progress made to date on producing both small molecule and peptide MC4R agonists as potential therapeutics for obesity.     

The melanocortin antagonist AgRP (83-132) increases appetitive responding for a fat, but not a carbohydrate, reinforcer

Consumption of a diet high in fat is a risk factor for a number of health problems, including obesity, type 2 diabetes and cardiovascular disease. Considerable pharmacological, genetic, and molecular evidence suggests that the hypothalamic melanocortin system plays a critical role in the control of food intake and body weight and, specifically, in fat ingestion. Administration of a melanocortin antagonist, agouti-related peptide (AgRP) (83-132) selectively increases intake of pure fat and high-fat mixed diets. Here, we examined possible mechanisms for this fat-specific effect of AgRP (83-132). In Experiment 1, we determined that intracerebroventricular administration of AgRP (83-132) selectively increased operant responding for a peanut oil, but not a sucrose, reinforcer when tested under a progressive ratio schedule. Experiment 2 employed a Pavlovian conditioning paradigm, in which icv AgRP enhanced appetitive responding toward stimuli that had previously been paired with peanut oil and reduced responding toward stimuli previously paired with sucrose, in the absence of consumption of either macronutrient. Finally, in Experiment 3, we tested the hypothesis that the MC system acts in anticipation of a fat consumption and found that hypothalamic AgRP mRNA was slightly, though not significantly, elevated in an environment predicting fat availability relative to one predicting carbohydrate availability. Collectively, these data indicate that, in addition to increasing free intake of dietary fats, AgRP (83-132) promotes responding for the opportunity to consume a fat reinforcer, as well as appetitive responding to fat-paired stimuli in the absence of ingestive stimulation. These results suggest a possible role for AgRP in the increased fat intake associated with obesity.     

Structure-activity relationships of beta-MSH derived melanocortin-4 receptor peptide agonists

The recent emergence of obesity as a major health threat in the industrialized world has intensified the search for novel and effective pharmacologic treatment. The proopiomelanocortin (POMC)-melanocortin 4 receptor (MC4R) axis has been shown to regulate food intake and energy homeostasis and is considered among the most promising antiobesity targets. Our initial efforts in this area have focused on affinity and selectivity directed optimization of the native beta-MSH(5-22) sequence and resulted in the discovery of a potent MC4R agonist: Ac-Tyr-Arg-[Cys-Glu-His-D-Phe-Arg-Trp-Cys]-NH(2) (10). Subcutaneous administration of this peptide produced an excellent in vivo efficacy in reducing food intake and increasing fat metabolism. Additionally, suppression of food intake was observed in wild type but not in MC4R deficient mice, suggesting that the effects observed in the wild type mice were mediated through MC4R signaling. Subsequent optimization efforts led to the identification of a novel series of disulfide constrained hexapeptides as exemplified by Ac-[hCys-His-D-Phe-Arg-Trp-Cys]-NH(2) (100). These cyclic hexapeptides showed a further improved potency in binding MC4R and an enhanced selectivity over MC1R. At a dose of 0.07 mg/kg analog 102 reduced food intake by 38% and increased fat utilization by 58% in rats. These cyclic peptides provide novel and enhanced reagents for the elucidation of melanocortin receptors biology and may find applications in the treatment of obesity and related metabolic disorders.     

Effect of serotonergic anorectics on food intake and induction of Fos in brain of mice with disruption of melanocortin 3 and/or 4 receptors

Previous studies have indicated that type 3 or 4 melanocortin receptors (MCR) are downstream of the critical anorectic action of drugs that stimulate 5-HT_2C receptors. To characterize further the receptor types involved, we have studied the effect of serotonergic anorectics in mice with genomic disruption of either MC3R or MC4R, or their combined knockout. In a first experiment, we showed that wild type (WT) and MC4R−/− mice showed comparable inhibition of food intake following acute treatment with dexnorfenfluramine. In a second experiment using WAY-161503, a 5-HT receptor full agonist with selectivity for 2B and 2C subtypes, we found that MC4R−/− responded comparably to WT, while MC3R−/− had reduced sensitivity. Double receptor knockout (DKO) mice responded comparably to WT and MC4R−/−. Surprisingly, brain Fos-ir was not strongly induced in any brain region by WAY-16103 with the exception of the paraventricular nucleus of DKO. These data suggest that MC3Rs may be involved in the response to serotonergic anorectic agents, and more generally in control of food intake.     

Identification of 2-[2-[2-(5-bromo-2- methoxyphenyl)-ethyl]-3-fluorophenyl]-4,5-dihydro-1H-imidazole (ML00253764), a small molecule melanocortin 4 receptor antagonist that effectively reduces tumor-induced weight loss in a mouse model

The melanocortin 4 receptor (MC4R) plays an important role in body weight regulation and energy homeostasis. Administration of peptidic MC4R antagonists (usually by intracerebro ventricular injection) has been shown in the literature to increase body weight and/or food intake in several rodent models. We report here the identification of a novel nonpeptidic MC4R antagonist and its effects on tumor-induced weight loss in mice following peripheral administration.     

Stereochemical studies of the monocyclic agouti-related protein (103-122) Arg-Phe-Phe residues: conversion of a melanocortin-4 receptor antagonist into an agonist and results in the discovery of a potent and selective melanocortin-1 agonist

The agouti-related protein (AGRP) is an endogenous antagonist of the centrally expressed melanocortin receptors. The melanocortin-4 receptor (MC4R) is involved in energy homeostasis, food intake, sexual function, and obesity. The endogenous hAGRP protein is 132 amino acids in length, possesses five disulfide bridges at the C-terminus of the molecule, and is expressed in the hypothalamus of the brain. We have previously reported that a monocyclic hAGRP(103-122) peptide is an antagonist at the melanocortin receptors expressed in the brain. Stereochemical inversion from the endogenous l- to d-isomers of single or multiple amino acid modifications in this monocyclic truncated hAGRP sequence resulted in molecules that are converted from melanocortin receptor antagonists into melanocortin receptor agonists. The Asp-Pro-Ala-Ala-Thr-Ala-Tyr-cyclo[Cys-Arg-DPhe-DPhe-Asn-Ala-Phe-Cys]-Tyr-Ala-Arg-Lys-Leu peptide resulted in a 60 nM melanocortin-1 receptor agonist that is 100-fold selective versus the mMC4R, 1000-fold selective versus the mMC3R, and ca. 180-fold selective versus the mMC5R. In attempts to identify putative ligand-receptor interactions that may be participating in the agonist induced stimulation of the MC4R, selected ligands were docked into a homology molecular model of the mMC4R. These modeling studies have putatively identified hAGRP ligand DArg111-mMC4RAsn115 (TM3) and the hAGRP DPhe113-mMC4RPhe176 (TM4) interactions as important for agonist activity.     

Pharmacological Effects and Regulatory Mechanisms of Tobacco Smoking Effects on Food Intake and Weight Control

Beyond promoting smoking initiation and preventing smokers from quitting, nicotine can reduce food intake and body weight and thus is viewed as desirable by some smokers, especially many women. During the last several decades, the molecular mechanisms underlying the inverse correlation between smoking and body weight have been investigated extensively in both animals and humans. Nicotine’s weight effects appear to result especially from the drug’s stimulation of α3β4 nicotine acetylcholine receptors (nAChRs), which are located on pro-opiomelanocortin (POMC) neurons in the arcuate nucleus (ARC), leading to activation of the melanocortin circuit, which is associated with body weight. Further, α7- and α4β2-containing nAChRs have been implicated in weight control by nicotine. This review summarizes current understanding of the regulatory effects of nicotine on food intake and body weight according to the findings from pharmacological, molecular genetic, electrophysiological, and feeding studies on these appetite-regulating molecules, such as α3β4, α7, and α4β2 nAChRs; neuropeptide Y (NPY); POMC; melanocortin 4 receptor (MC4R); agouti-related peptide (AgRP); leptin, ghrelin, and protein YY (PYY).     

Psychiatric disorders and neural mechanisms underlying energy intake and expenditure: a review]

Anorexia is one of the common symptoms caused by various psychiatric disorders. Increasing evidence indicates that neuroleptics can induce weight gain, obesity, and diabetes mellitus. However, the mechanisms underlying these conditions have not been fully elucidated. In this review, we describe molecular neuroanatomic aspects of current biology of energy homeostasis that would help to address the psychiatric issues noted above, focusing on the central leptin/melanocortin system. An adipocyte-derived hormone, leptin acts on the arcuate hypothalamic nucleus (Arc) to inhibit feeding behavior and simultaneously to promote energy expenditure. Leptin activates Arc neurons producing alpha-melanocyte-stimulating hormone (alpha-MSH) and inhibits those producing agouti-related protein (AgRP). alpha-MSH is an endogenous agonist for the melanocortin-4 receptor (MC4-R) that is expressed exclusively in the central nervous system (CNS), whereas AgRP acts as a MC4-R antagonist. It is also established that MC4-R blockade produces an over-eating/obesity syndrome in rodents and humans. Thus, MC4-R-expressing neurons are downstream targets of leptin. Of interest, MC4-R-positive neurons densely populate in CNS sites critical for energy homeostasis and associated with psychiatric disorders, including the paraventricular hypothalamic nucleus and central amygdaloid nucleus. In addition, Arc alpha-MSH neurons receive serotonergic inputs from raphe neurons. Finally, an AgRP gene polymorphism has been associated with anorexia nervosa. These findings suggest that the central melanocortin system is a target for psychiatry.     

AgRP(83-132) and SHU9119 differently affect activity-based anorexia.

Activity-based anorexia (ABA) mimics starvation and hyperactivity of anorexia nervosa patients in rats. Activation of the melanocortin (MC) system leads to hypophagia and increased energy expenditure in ad libitum fed rats. Therefore, activation of the MC system might underlie the development and propagation of ABA. Pro-opiomelanocortin (POMC) gene expression is normally decreased during negative energy balance. Strikingly, we found a transient up-regulation of POMC mRNA levels in the arcuate nucleus during the development of ABA, indicating a hyperactive MC system. However, wheel running and food intake were not influenced by treating ABA rats with the competitive antagonist SHU9119. This suggests that agonism of MC receptors by endogenous alpha-melanocyte-stimulating hormone (alpha-MSH) levels does not underlie ABA. Instead, treatment with the inverse agonist AgRP(83-132) did ameliorate signs of ABA. This implies that modulation of constitutive MC receptor activity rather than antagonizing putative alpha-MSH release contributes to the development and propagation of ABA.     

Synthesis and biological evaluation on hMC3, hMC4 and hMC5 receptors of γ‐MSH analogs substituted with l‐alanine

Abstract: To elucidate the molecular basis of the interaction of the native dodecapeptide γ‐MSH with the melanocortin receptors, we performed a structure?activity study in which we systematically replaced l ‐Ala in each position of this peptide. Here we report the binding affinity and agonist potency on human MC3R, MC4R and MC5R. Intracellular cAMP concentration was measured on CHO cells, and binding assays were carried out using membranes prepared from these cell lines which stably express hMC3R, hMC4R and hMC5R. Our results indicate that the last four amino acids in the C‐terminal region of γ‐MSH are not important determinants of biological activity and selectivity at human melanocortin receptors. Interesting results were obtained when l ‐Ala was substituted for His⁶, Phe⁷, Arg⁸ and Trp⁹. For these peptides, the affinity and activity at all three human receptors (MC3R, MC4R and MC5R) decreased significantly, demonstrating that the His‐Phe‐Arg‐Trp sequence in γ‐MSH is important for activity at these three melanocortin receptors. Similar results were obtained when Met³ was replaced with l ‐Ala, suggesting the importance of this position in the interaction with all three receptors. This study highlights the role played by the His‐Phe‐Arg‐Trp sequence in receptor binding and in agonist activity of γ‐MSH.     

Ligand-dependent and independent modulation of aryl hydrocarbon receptor localization,degradation, and gene regulation

The aim of this study was to use pharmacological inhibition of protein kinase A and mutation of potential protein kinase A phosphorylation sites to determine the role of protein kinase A-catalyzed phosphorylation of the dopamine D(1) receptor in agonist-stimulated desensitization and internalization of the receptor. To facilitate purification and imaging of the D(1) receptor, we attached a polyhistidine tag to the amino terminus and enhanced green fluorescent protein to the carboxyl terminus of the receptor (D(1)-EGFP). D(1)-EGFP was similar to the untagged D(1) receptor in terms of affinity for agonist and antagonist ligands, coupling to G proteins, and stimulation of cyclic AMP accumulation. D(1)-EGFP and two mutants in which either Thr268 or Ser380 was replaced with Ala were stably expressed in NS20Y neuroblastoma cells. Pretreatment with the protein kinase A inhibitor H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) or substitution of Ala for Thr268 reduced agonist-stimulated phosphorylation of the receptor and resulted in diminished trafficking of the receptor to the perinuclear region of the cell. Substitution of Ala for Thr268 had no effect, however, on agonist-induced receptor sequestration or desensitization of cyclic AMP accumulation. Substitution of Ala for Ser380 had no effect on D(1) receptor phosphorylation, sequestration, desensitization, or trafficking to the perinuclear region. We conclude that protein kinase A-dependent phosphorylation of the D(1) receptor on Thr268 regulates a late step in the sorting of the receptor to the perinuclear region of the cell, but that phosphorylation of Thr268 is not required for receptor sequestration or maximal desensitization of cyclic AMP accumulation.     

GABAergic signaling by AgRP neurons prevents anorexia via a melanocortin-independent mechanism

The hypothalamic arcuate nucleus contains two anatomically and functionally distinct populations of neurons—the agouti-related peptide (AgRP)- and pro-opiomelanocortin (POMC)-expressing neurons that integrate various nutritional, hormonal, and neuronal signals to regulate food intake and energy expenditure, and thereby help achieve energy homeostasis. AgRP neurons, also co-release neuropeptide Y (NPY) and γ-aminobutyric acid (GABA) to promote feeding and inhibit metabolism through at least three possible mechanisms: (1) suppression of the melanocortin signaling system through competitive binding of AgRP with the melanocortin 4 receptors; (2) NPY-mediated inhibition of post-synaptic neurons that reside in hypothalamic nuclei; (3) GABAergic inhibition of POMC neurons in their post-synaptic targets including the parabrachial nucleus (PBN), a brainstem structure that relays gustatory and visceral sensory information. Acute ablation of AgRP neurons in adult mice by the action of diphtheria toxin (DT) results in precipitous reduction of food intake, and eventually leads to starvation within 6 days of DT treatment. Chronic delivery of bretazenil, a GABA_A receptor partial agonist, into the PBN is sufficient to restore feeding and body weight when AgRP neurons are ablated, whereas chronic blockade of melanocortin 4 receptor signaling is inadequate. This review summarizes the physiological roles of a neural circuitry regulated by AgRP neurons in control of feeding behavior with particular emphasis of the GABA output to the parabrachial nucleus. We also describe a compensatory mechanism that is gradually engaged after ablation of AgRP neurons that allows mice to continue eating without them.     

Design, synthesis, in vitro, and in vivo characterization of phenylpiperazines and pyridinylpiperazines as potent and selective antagonists of the melanocortin-4 receptor

Benzylamine and pyridinemethylamine derivatives were synthesized and characterized as potent and selective antagonists of the melanocortin-4 receptor (MC4R). These compounds were also profiled in rodents for their pharmacokinetic properties. Two compounds with diversified profiles in chemical structure, pharmacological activities, and pharmacokinetics, 10 and 12b, showed efficacy in an established murine cachexia model. For example, 12b had a K(i) value of 3.4 nM at MC4R, was more than 200-fold selective over MC3R, and had a good pharmacokinetic profile in mice, including high brain penetration. Moreover, 12b was able to stimulate food intake in the tumor-bearing mice and reverse their lean body mass loss. Our results provided further evidence that a potent and selective MC4R antagonist with appropriate pharmacokinetic properties might potentially be useful for the treatment of cancer cachexia.