ALLOSTERIC MODULATORS OF MC4R SIGNALING

描述（由申请人提供）：黑素皮质素-4受体（MC4R）是一种经过充分验证的药物靶点，可用于开发治疗肥胖和疾病恶病质的疗法。最近的研究表明，MC4R化合物在糖尿病和代谢综合征、抑郁症相关的厌食症和快感缺乏以及强迫症方面有潜在的应用。然而，使用MC4R的强效矫形受体激动剂治疗常见肥胖的临床试验失败了，原因是不可接受的靶标介导的压力活性。然而，两项独立的研究已经确定了肽MSH类似物可以产生显著的体重减轻而没有加压反应。因此，我们假设MC4R的减肥和升压作用可以从药理学上进行区分，从而更深入地了解MC4R信号在减肥和心血管调节中的作用模式和部位。在之前的资助期内，我们对MC4R的阳性变构调节剂进行了高通量筛选，确定了165种多种机制类别的受体特异性化合物，并证明了其中几种的体内活性。MC4R的变构调节剂应该可以通过恢复黑素皮质素受体单倍功能不全的正常受体活性水平来应用于综合征型肥胖的治疗，这种综合征可导致高达5%的早发性肥胖，而且我们的一部分化合物目前正在GSK的药物开发中。然而，众所周知，GPCRs的变构调节剂通常表现出优异的受体亚型、配体和信号模式特异性，也是探测受体功能的杰出工具。我们在鉴定MC4R信号的体内分化模式方面也取得了重大进展。在之前的资助期内，我们确定了该受体的两种新的信号传导方式，即黑色素皮质素受体相关蛋白2 （MRAP2）介导的受体致敏，以及受体与向内纠偏的K通道Kir7.1的偶联，该通道对于下丘脑MC4R神经元通过-MSH去极化至关重要。在本应用中，我们建议使用上述独特的药理学工具和一组组织特异性敲除小鼠，这些小鼠删除MC4R神经元中的G -s、Kir7.1、MRAP2和-arrestin1信号，以验证MC4R PAMS可以纠正黑素皮质素单倍不足的假设，并确定MC4R在介导其特征明确的减肥、降压和心脏加速作用中的作用模式和部位。本研究项目的结果将：(1)促进我们对MC4R独特药理学性质的理解，(2)增强我们对能量稳态中央控制的理解，(3)为研究界提供一套独特的药理学和遗传学工具，(4)为有效利用MC4R作为药物靶点提供必要的基础知识。

DESCRIPTION (provided by applicant): The melanocortin-4 receptor (MC4R) is a well-validated drug target for the development of therapeutics for the treatment of obesity and disease cachexia. More recent studies suggest potential applications for MC4R compounds in diabetes and aspects of metabolic syndrome, depression related anorexia and anhedonia, and obsessive compulsive disorder. Clinical trials for treatment of common obesity using potent orthosteric agonists of the MC4R have failed, however, due to unacceptable target-mediated pressor activity. Two independent studies, however, have identified peptide MSH analogues that produce significant weight loss without a pressor response. Therefore, we hypothesize that the weight loss and pressor actions of MC4R can be discriminated pharmacologically, given a more thorough understanding of the mode(s) and site(s) of action of MC4R signaling in weight loss and cardiovascular regulation. During the previous funding period, we conducted a high throughput screen for positive allosteric modulators of the MC4R that identified a collection of 165 receptor-specific compounds in multiple mechanistic classes, and have demonstrated in vivo activity for several of these. Allosteric modulators of the MC4R should be applicable to treatment of syndromic obesity through restoration of normal levels of receptor activity in melanocortin receptor haploinsufficiency, a syndrome responsible for up to 5% of early onset obesity, and indeed a subset of our compounds are currently in the drug development pipeline at GSK. However, allosteric modulators of GPCRs, known to often exhibit excellent receptor subtype, ligand, and signaling mode specificity, are also outstanding tools for probing receptor function. We have also made significant progress in the identification of differentiated modes of MC4R signaling in vivo. During the previous funding period, we identified two novel signaling modalities of the receptor, melanocortin receptor associated protein 2 (MRAP2) mediated receptor-sensitization, and coupling of the receptor to an inwardly-rectifying K channel, Kir7.1 that is essential for depolarization of hypothalamic MC4R neurons by �-MSH. In this application, we propose to use the unique pharmacological tools described above, and a set of tissue-specific knockout mice that delete G�s, Kir7.1, MRAP2, and �-arrestin1 signaling in MC4R neurons to test the hypothesis that MC4R PAMS can correct melanocortin haploinsufficiency, and to identify the mode(s) and site(s) of action of MC4R in mediating its well-characterized weight loss, pressor, and cardioacceleratory effects. The results of this research program should 1) advance our understanding of the unique pharmacological properties of the MC4R, 2) enhance our understanding of the central control of energy homeostasis, 3) provide a unique set of pharmacological and genetic tools for the research community, and 4) provide the basic knowledge necessary to effectively utilize the MC4R as a drug target.