Preparation and characterization of radioligands for the orphan receptor GPR88

项目摘要 本申请是对旨在支持共同基金试点项目的RFA-RM-19-011号文件的响应 “照亮可药物基因组”(IDG)计划研究符合IDG条件的未研究的GPCRs、蛋白激酶、 和离子通道。孤儿受体GPR88是一种符合IDG条件的GPCRs，在纹状体有很强的表达 整个背部和腹侧区域。多条证据表明GPR88在其中起着重要作用 参与纹状体功能的调节，并与帕金森氏症等一系列疾病有关， 精神分裂症、焦虑症和毒瘾。到目前为止，还没有发现GPR88的内源性配体。 为了研究GPR88的信号机制和生物学功能，我们小组开展了一项 药物化学活动开发GPR88小分子激动剂探针。我们最近开发了 第一种高效、选择性和脑穿透的GPR88激动剂RTI-33，它在体内具有GPR88靶点 对大鼠和小鼠减少饮酒和寻找行为的作用。然而，该药的药理作用 受体及其作用机制在很大程度上仍不清楚，因此限制了对其潜在作用的探索 治疗应用。在这方面，一个目前无法获得的合适的放射性配基将是一个强有力的工具 对于配体-受体相互作用的研究和用于绘制大脑中的受体结合位置的放射自显影， 它可以用来预测受体的潜在功能，并指导体内研究。在目标1中，我们将 优化合成具有合适放化纯度和特异性的氚标记放射性配体RTI-33 受体结合研究的放射性。在目标2中，我们将使用以下方法表征受体结合特性 饱和度、动力学和竞争结合实验。总体而言，完成这笔赠款将提供GPR88 放射性配基为IDG和研究界服务，努力进一步确定GPR88系统的特征。

Project Summary This application is in response to RFA-RM-19-011, which aims to support pilot projects for the Common Fund Program "Illuminating the Druggable Genome" (IDG) to study IDG-eligible understudied GPCRs, protein kinases, and ion channels. The orphan receptor GPR88 is an IDG-eligible GPCR with robust expression in the striatum throughout the dorsal and ventral areas. Multiple lines of evidence suggest that GPR88 plays an important role in the regulation of striatal functions and is implicated in a number of disorders such as Parkinson’s disease, schizophrenia, anxiety, and drug addiction. To date, the endogenous ligand for GPR88 has not been discovered. In order to characterize GPR88 signaling mechanisms and biological functions, our group has carried out a medicinal chemistry campaign to develop GPR88 small-molecule agonist probes. We have recently developed the first highly potent, selective, and brain-penetrant GPR88 agonist RTI-33 that has GPR88 on-target in vivo activity in reducing alcohol drinking and seeking behaviors in rats and mice. However, the pharmacology of the receptor and its mechanism of action are still largely unknown, thus limiting exploration of its potential for therapeutic applications. In this regard, a suitable radioligand, that is currently unavailable, will be a powerful tool for ligand-receptor interactions studies and for autoradiography to map the receptor binding sites in the brain, which can be used to predict the potential functions of the receptor and guide in vivo studies. In Aim 1, we will optimize and synthesize tritium-labeled RTI-33 radioligands with suitable radiochemical purity and specific radioactivity for receptor binding studies. In Aim 2, we will characterize the receptor binding properties using saturation, kinetic, and competition binding experiments. Overall, completion of this grant will provide GPR88 radioligands to serve IDG and the research community in an effort to further characterize the GPR88 system.