Novel PET Tracers for Imaging Monoacylglycerol Lipase in Endocannabinoid Signaling

项目摘要：药物滥用和成瘾化学早期职业奖（ECHEM）的目标 (R21/R33）是帮助申请人建立一个独立的和高度竞争力的化学研究计划， 药物滥用和成瘾，主要重点是开发用于PET成像研究的放射性药物， 内源性大麻素信号系统中的单酰基甘油脂肪酶（MAGL）。 MAGL是代谢内源性大麻素配体2-花生四烯酸甘油（2-AG）的主要酶。 阻断MAGL可增加2-AG水平，导致抗伤害、抗焦虑和止吐反应， 已经成为治疗药物成瘾和物质使用障碍（SUD）的治疗策略。人类遗传 研究已经确定了MAGL突变与成瘾风险增加之间的联系。异常MAGL 在酒精中毒者的死后脑中检测到了这种表达。然而，这些结果通过 离体（破坏性）分析不能提供MAGL活性和人免疫缺陷之间的直接和实时相关性。 疾病阶段，特别是对于诸如大脑的组织。在这种情况下，PET放射性示踪剂可以填充该空隙， 提供了一种非侵入性工具，用于定量药物滥用中MAGL活性和可能的异常eCB功能， 成瘾然而，阻碍PET应用于此目的的最主要障碍是缺乏 放射性示踪剂靶向MAGL，代表了我们对这种酶的理解的重大缺陷。 PI和其他人最近开发的第一种脑渗透剂MAGL放射性示踪剂[11 C] SAR 127303显示， 但该化合物也结合第二种2-AG降解酶ABHD 6，从而破坏了 大脑中的特异性结合。为了克服这种选择性问题，我们将利用一种新的蛋白质组学技术， 基于活性的蛋白质谱分析（ABPP），以基于新型MAGL阵列进行靶选择性筛选， 内部开发的抑制剂。氮杂环丁烷氨基甲酸酯表现出对MAGL超过FAAH、CB 1和MAGL>500倍的选择性。 CB 2受体，和超过ABHD 6>30倍的MAGL。初步研究表明，11 C标记的氮杂环丁烷穿过 大鼠和非人灵长类动物（NHP）的血脑屏障，并显示出高特异性结合。虽然目前尚不清楚， 这种放射性示踪剂将是令人满意的人类使用，它显示出作为第一代选择性MAGL的希望 放射性示踪剂除了进一步评估这种示踪剂，我们将使用这种支架同时制备一系列 仔细选择的MAGL示踪剂，进一步提高选择性，并评估其定量MAGL的能力 活动使用啮齿动物和NHP。这项工作的影响不仅是开发出第一个有效的和选择性的MAGL 神经示踪剂的基础eCB研究，但也最终进展这种成像工具的翻译人类成像 研究和调查包括SUD在内的MAGL相关疾病的潜在机制。 相关性：该提案有可能改善公共卫生，帮助成瘾患者 通过使用MAGL放射性示踪剂的PET神经成像的进步。

Project Summary: The goal of the Early Career Award in Chemistry of Drug Abuse and Addiction (ECHEM) (R21/R33) is to help applicant establish an independent and highly-competitive chemistry research program applied to drug abuse and addiction, with a major focus of developing radiopharmaceuticals for PET imaging study of monoacylglycerol lipase (MAGL) in the endocannabinoid signaling system. MAGL is the principle enzyme for metabolizing endogenous cannabinoid ligand: 2-arachidonylglycerol (2-AG). Blockade of MAGL increases 2-AG levels, resulting in anti-nociceptive, anxiolytic and anti-emetic responses, and has emerged as a therapeutic strategy to treat drug addiction and substance-use disorders (SUDs). Human genetic studies have identified the link between MAGL mutations and increased risk for addiction. Abnormal MAGL expression has been detected in the post-mortem brain of alcoholic subjects. However, these results discovered via ex vivo (destructive) analysis cannot provide a direct and real-time correlation between MAGL activity and human disease stages, particularly for tissues such as the brain. In this context, a PET radiotracer can fill this void and provide a noninvasive tool for quantifying MAGL activity and possible aberrant eCB function in drug abuse and addiction. However, the foremost barrier holding back PET applications for this purpose is the scarcity of radiotracers targeting MAGL, representing a significant deficiency in our understanding of this enzyme. The first brain penetrant MAGL radiotracer, [11C]SAR127303 recently developed by the PI and others, showed saturable binding but this compound also binds a second 2-AG degrading enzyme, ABHD6, thereby undermining the specific binding in the brain. To overcome this selectivity problem, we will utilize a novel proteomic technology, activity based protein profiling (ABPP) to perform target selectivity screening based on an array of novel MAGL inhibitors developed in house. An azetidine carbamate exhibits >500-fold selectivity to MAGL over FAAH, CB1 and CB2 receptors, and >30-fold MAGL over ABHD6. Preliminary studies indicate the 11C-labeled azetidine crosses the blood brain barrier in rat and nonhuman primate (NHP), and shows high specific binding. Although it is not clear if this radiotracer will be satisfactory for human use, it shows promise as a first generation of selective MAGL radiotracers. In addition to further evaluation of this tracer, we will use this scaffold to concurrently prepare a series of carefully chosen MAGL tracers with further improved selectivity, and evaluate their ability to quantify MAGL activity using rodents and NHPs. The impact of this work is not only to develop the first potent and selective MAGL neurotracer for basic eCB research, but also ultimately to progress this imaging tool for translational human imaging studies and investigate underlying mechanisms of MAGL-linked diseases including SUDs. Relevance: This proposal has the potential to improve public health and help patients suffering from addiction through advancement of PET neuroimaging using MAGL radiotracers.