NOVEL DOPAMINE D3 RECEPTOR LIGANDS

对可卡因增强作用的神经化学机制的阐明导致了针对可卡因滥用和成瘾的药物治疗发展战略的有针对性的研究。可卡因抑制单胺类神经递质多巴胺、5-羟色胺和去甲肾上腺素在各自神经元中的重新摄取，导致这些物质在各自突触中的基础水平增加。到目前为止，内源性神经递质对多巴胺受体的过度刺激被认为是古柯碱增强作用的最可能的神经化学机制。由于在两个多巴胺受体家族中有5个受体亚型，即D1(D1和D5)和D2(D2，D3，D4)，因此，如果有的话，每个多巴胺受体亚型在可卡因的药理作用中可能发挥的作用是有意义的。为了实现这些目标，必须开发针对每个受体亚型的高度选择性和有效的配体。最近，在可卡因滥用动物模型中的行为和神经解剖学证据表明，多巴胺D3受体可能影响可卡因的行为效应。此外，最近已经证明，据称的D3受体拮抗剂可能能够阻断可卡因的一些药理作用。然而，有人担心这些作用可能是通过D2受体介导的，而不是完全通过D3，因为所用化合物缺乏选择性，而且在这些动物模型中需要高剂量才能影响行为行为。作为这些研究的结果，我们开始了一项新的研究，以设计和制备新型的D3多巴胺受体配体。基于文献报道的构效关系和从我们实验室筛选的26个化合物的结果，这些化合物的结构成分与报道的与多巴胺D3受体结合重要的那些相似，我们开发了一个新的D3配体的设计策略。我们合成了10个新的化合物，它们的结构特征如下：1)末端的三环芳香族部分，2)带有3-5个碳链连接物的酰胺，3)芳基取代的哌嗪。所有化合物在灵长类D3受体转染的CHO细胞系中进行结合实验。此外，对所有化合物在D2和D4转基因细胞系中的结合以及与去甲肾上腺素能α1受体的结合进行了评估。这些初步研究的结果表明，在这一系列化合物中，D3受体具有以下SAR。D3受体对三环芳基末端有很好的耐受性。酰胺基团似乎是必需的，并且至少4个碳链连接体在D3处比较短的链节具有更高的亲和力结合。2，3-二氯芳基取代的哌嗪环在D3处具有最佳的结合亲和力。在这个最初的系列中，最有效和最有选择性的D3配体在D3时的Ki=24 nm，D3/D4的选择性比为50，D3/D2的选择性比为20。这一系列化合物的进一步优化正在进行中，特别是芳基末端之间的碳链。对最具选择性和最有效的D3配体的功能评估将允许确定激动剂或拮抗剂的轮廓。这些研究有望提供一种高选择性的多巴胺D3受体亚型配体，可用于可卡因滥用动物模型的行为评估。此外，从这些研究和其他研究中得出的合成孔径雷达将提供有用的结构信息，可用于开发不可逆配体和/或放射性标记配体等分子工具。这些配体将使进一步表征D3多巴胺受体亚型的结构和功能成为可能。-多巴胺D3受体亚型，可卡因，D3灵长类克隆CHO细胞

The elucidation of the neurochemical mechanisms underlying the reinforcing effects of cocaine has lead to targetted research on strategies for the development of pharmacological treatments for cocaine abuse and addiction. Cocaine inhibits the reuptake of the monoamine neurotransmitters dopamine, serotonin and norepinephrine into their respective neurons resulting in an increase in basal levels of these substances in their respective synapses. To date, it is the overstimulation of dopamine receptors by the endogenous neurotransmitter that has been identified as the most likely neurochemical mechanism underlying cocaines reinforcing effects. Since there are five receptor subtypes in two families of dopamine receptors namely D1 (D1 and D5) and D2 (D2, D3, D4), it is of interest to characterize the role, if any, each dopamine receptor subtype may play in the pharmacological effects of cocaine. In order to achieve these goals, highly selective and potent ligands for each receptor subtype must be developed. Recently, behavioral and neuroanatomical evidence in animal models of cocaine abuse has suggested that dopamine D3 receptors may influence the behavioral effects of cocaine. Furthermore, it has recently been demonstrated that purported D3 receptor antagonists may be able to block some of the pharmacological effects of cocaine. However, there is concern that these actions may be mediated through D2 receptors and not exclusively through D3, due to the lack of selectivity of the compounds used and the high doses need to effect behavioral actions in these animal models. As a result of these investigations we have embarked on a new study to design and prepare novel D3 dopamine receptor ligands. Based on structure-activity relationships (SAR) reported in the literature and results of screening 26 compounds from our laboratory that had structural components that were similar to those reported to be important for dopamine D3 receptor binding, we developed a design strategy for novel D3 ligands. We have synthesized 10 novel compounds that incorporated the following structural features: 1)terminal tricyclic aromatic moiety, 2)amide with 3-5 carbon chain linker, 3)aryl-substituted piperazine. All compounds were evaluated for binding in a primate D3 receptor transfected CHO cell line. In addition, all compounds were evaluated for binding in D2 and D4 transfected cell lines and for binding at noradrenergic alpha 1 receptors. The results of these initial studies demonstrated the following SAR for D3 receptors in this series of compounds. A tricyclic aryl terminus is well tolerated at D3 receptors. An amide function appears to be required and at least a 4 carbon linker gives higher affinity binding at D3 than the shorter chain links. The 2,3-dichloro- aryl substituted piperazine ring provided optimal binding affinity at D3. The most potent and selective D3 ligand in this initial series demonstrated a Ki=24 nM at D3 with a D3/D4 selectivity ratio of 50 and a D3/D2 selectivity ratio of 20. Further optimization of this series of compounds is underway with a particular focus on the carbon linking chain between the aryl termini. Functional evaluation of the most selective and potent D3 ligand will allow the determination of agonist or antagonist profile. These studies are anticipated to provide a highly selective dopamine D3 receptor subtype ligand that can be used for behavioral evaluation in animal models of cocaine abuse. Furthermore, the SAR deduced from these and other studies will provide useful structural information that can be applied to the development of molecular tools such as irreversible and/or radiolabeled ligands. These ligands will enable further characterization of the structure and function of the D3 dopamine receptor subtype. - dopamine D3 receptor subtype, cocaine, D3 primate clone CHO cells