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

Discovery of (3-(4-(2-Oxa-6-azaspiro[3.3]heptan-6-ylmethyl)phenoxy)azetidin-1-yl)(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl)methanone (AZD1979), a Melanin Concentrating Hormone Receptor 1 (MCHr1) Antagonist with Favorable Physicochemical Properties

A novel series of melanin concentrating hormone receptor 1 (MCHr1) antagonists were the starting point for a drug discovery program that culminated in the discovery of 103 (AZD1979). The lead optimization program was conducted with a focus on reducing lipophilicity and understanding the physicochemical properties governing CNS exposure and undesired off-target pharmacology such as hERG interactions. An integrated approach was taken where the key assay was ex vivo receptor occupancy in mice. The candidate compound 103 displayed appropriate lipophilicity for a CNS indication and showed excellent permeability with no efflux. Preclinical GLP toxicology and safety pharmacology studies were without major findings and 103 was taken into clinical trials.

Recent progress in the discovery of melanin-concentrating hormone 1-receptor antagonists

INTRODUCTION

The appetite stimulating effects of melanin-concentrating hormone (MCH) continues to be of high interest, and there is substantial support to investigate the use of MCH 1-receptor antagonists for the treatment of obesity. Other areas of potential use for MCH 1-receptor antagonists include depression and anxiety. There are, to date, no clinical proof of concept data, and efforts are ongoing for the discovery of novel MCH 1-receptor antagonists, as evidenced by the number of patent applications published over the last 5 years.

AREAS COVERED

This review covers the patent literature on MCH 1-receptor antagonists from January 2006 to November 2010. The emphasis is on disclosed biological data, especially in vivo data, of exemplified compounds. Wherever possible, selectivity towards undesired pharmacology is analysed.

EXPERT OPINION

Over the years, different approaches have been taken to overcome the undesired effects of MCH 1-receptor antagonists, such as interactions with the hERG channel. Many programmes have faced difficulties and, to date, only a few compounds have progressed into humans. From this point of view, the MCH 1-receptor is regarded as a difficult target, and whether newer programmes will be successful depends, to a large extent, on their selectivity.

Cellular models for the study of the pharmacology and signaling of melanin-concentrating hormone receptors

Cellular models for the study of the neuropeptide melanin-concentrating hormone (MCH) have become indispensable tools for pharmacological profiling and signaling analysis of MCH and its synthetic analogues. Although expression of MCH receptors is most abundant in the brain, MCH-R(1) is also found in different peripheral tissues. Therefore, not only cell lines derived from nervous tissue but also from peripheral tissues that naturally express MCH receptors have been used to study receptor signaling and regulation. For screening of novel compounds, however, heterologous expression of MCH-R(1) or MCH-R(2) genes in HEK293, Chinese hamster ovary, COS-7, or 3T3-L1 cells, or amplified MCH-R(1) expression/signaling in IRM23 cells transfected with the G(q) protein gene are the preferred tools because of more distinct pharmacological effects induced by MCH, which include inhibition of cAMP formation, stimulation of inositol triphosphate production, increase in intracellular free Ca(2+) and/or activation of mitogen-activated protein kinases. Most of the published data originate from this type of model system, whereas data based on studies with cell lines endogenously expressing MCH receptors are more limited. This review presents an update on the different cellular models currently used for the analysis of MCH receptor interaction and signaling.

Melanin-concentrating hormone 1-receptor antagonist suppresses body weight gain correlated with high receptor occupancy levels in diet-induced obesity mice

Melanin-concentrating hormone (MCH), which is a neuropeptide expressed in the hypothalamus of the brain, is involved in regulating feeding behavior and energy homeostasis via the MCH(1) receptor in rodents. It is widely considered that MCH(1) receptor antagonists are worthy of development for medical treatment of obesity. Here we report on the development of an ex vivo receptor occupancy assay using a new radiolabeled MCH(1) receptor antagonist, [(35)S]-compound D. An MCH(1) receptor antagonist inhibited the binding of [(35)S]-compound D to brain slices in a dose-dependent manner. The result showed a good correlation between the receptor occupancy levels and plasma or brain levels of the MCH(1) receptor antagonist, suggesting that the ex vivo receptor binding assay using this radioligand is practical. Quantitative analysis in diet-induced obese mice showed that the efficacy of body weight reduction correlated with the receptor occupancy levels at 24h. Furthermore, more than 90% occupancy levels of MCH(1) receptor antagonists during 24h post-dosing are required for potent efficacy on body weight reduction. The present occupancy assay could be a useful pharmacodynamic marker to quantitatively estimate anti-obese efficacy, and would accelerate the development of MCH(1) receptor antagonists for treatment of obesity.

Discovery of novel diarylketoxime derivatives as selective and orally active melanin-concentrating hormone 1 receptor antagonists

Optimization of the lead 2a led to the identification of a novel diarylketoxime class of melanin-concentrating hormone 1 receptor (MCH-1R) antagonists. Our focus was directed toward improvement of hERG activity and metabolic stability. The representative derivative 4b showed potent and dose-dependent body weight reduction in diet-induced obese (DIO) C57BL/6J mice after oral administration. The synthesis and structure-activity relationships of the novel diarylketoxime MCH-1R antagonists are described.