Anticatabolic properties of melanocortin-4 receptor antagonists

Treatment of cachexia: melanocortin and ghrelin interventions

Cachexia is a condition typified by wasting of fat and LBM caused by anorexia and further endocrinological modulation of energy stores. Diseases known to cause cachectic symptoms include cancer, chronic kidney disease, and chronic heart failure; these conditions are associated with increased levels of proinflammatory cytokines and increased resting energy expenditure. Early studies have suggested the central melanocortin system as one of the main mediators of the symptoms of cachexia. Pharmacological and genetic antagonism of these pathways attenuates cachectic symptoms in laboratory models; effects have yet to be studied in humans. In addition, ghrelin, an endogenous orexigenic hormone with receptors on melanocortinergic neurons, has been shown to ameliorate symptoms of cachexia, at least in part, by an increase in appetite via melanocortin modulation, in addition to its anticatabolic and anti-inflammatory effects. These effects of ghrelin have been confirmed in multiple types of cachexia in both laboratory and human studies, suggesting a positive future for cachexia treatments.

Targeting melanocortin receptors: an approach to treat weight disorders and sexual dysfunction

The melanocortin system has multifaceted roles in the control of body weight homeostasis, sexual behaviour and autonomic functions, and so targeting this pathway has immense promise for drug discovery across multiple therapeutic areas. In this Review, we first outline the physiological roles of the melanocortin system, then discuss the potential of targeting melanocortin receptors by using MC3 and MC4 agonists for treating weight disorders and sexual dysfunction, and MC4 antagonists to treat anorectic and cachectic conditions. Given the complexity of the melanocortin system, we also highlight the challenges and opportunities for future drug discovery in this area.

Melanocortin interventions in cachexia: how soon from bench to bedside?

PURPOSE OF REVIEW

Cachexia is a condition of anorexia and wasting that accompanies many diseases including cancer, heart failure, and renal failure. One key center that is probably involved in the propagation of symptoms of cachexia is the melanocortin system in the hypothalamus and brainstem. This review focuses on cachexia treatment interventions that act via melanocortin antagonism, by direct or indirect means.

RECENT FINDINGS

Recent reports include a description of the physiology of the melanocortin system and its responsiveness to inflammatory cytokines. Regarding treatment potential, multiple reports describe the effectiveness of small molecule antagonists of the melanocortin-4 receptor in animal models of cachexia. These melanocortin antagonists, given by peripheral injection, improve food intake and lean body mass retention in the setting of cancer and renal failure. Additional reports provide evidence of melanocortin antagonism following treatment of cachexia using ghrelin and eicosonoic acid.

SUMMARY

Cachexia is a serious condition that accompanies various disease states and currently does not have effective treatments. The melanocortin system may play a direct role in producing symptoms of cachexia, making antagonism of this system a logical objective for ameliorating these symptoms. Thus far, however, no data on human application have been published.

Emerging therapeutic strategies for obesity

The rising tide of obesity is one of the most pressing health issues of our time, yet existing medicines to combat the problem are disappointingly limited in number and effectiveness. Fortunately, a recent burgeoning of mechanistic insights into the neuroendocrine regulation of body weight provides an expanding list of molecular targets for novel, rationally designed antiobesity pharmaceuticals. In this review, we articulate a set of conceptual principles that we feel could help prioritize among these molecules in the development of obesity therapeutics, based on an understanding of energy homeostasis. We focus primarily on central targets, highlighting selected strategies to stimulate endogenous catabolic signals or inhibit anabolic signals. Examples of the former approach include methods to enhance central leptin signaling through intranasal leptin delivery, use of superpotent leptin-receptor agonists, and mechanisms to increase leptin sensitivity by manipulating SOCS-3, PTP-1B, ciliary neurotrophic factor, or simply by first losing weight with traditional interventions. Techniques to augment signaling by neurochemical mediators of leptin action that lie downstream of at least some levels of obesity-associated leptin resistance include activation of melanocortin receptors or 5-HT2C and 5-HT1B receptors. We also describe strategies to inhibit anabolic molecules, such as neuropeptide Y, melanin-concentrating hormone, ghrelin, and endocannabinoids. Modulation of gastrointestinal satiation and hunger signals is discussed as well. As scientists continue to provide fundamental insights into the mechanisms governing body weight, the future looks bright for development of new and better antiobesity medications to be used with diet and exercise to facilitate substantial weight loss.