Subtype-selective NMDA ligands for Alzheimer's Disease

项目摘要：N-甲基-D-天冬氨酸受体(NMDAR)中GluN2B亚单位的功能障碍 在神经退行性疾病的生理病理学方面，如阿尔茨海默病(AD)和相关痴呆症。 GluN2B亚基的药理调节调节突触的可塑性和兴奋性，代表着一种诱人的 治疗方法。PET能够量化体内的生化过程，并且是一个合适的GluN2B配体 将极大地提高我们对基于GluN2B的亲离子谷氨酸信号的理解 生理病理条件，否则无法通过体外(破坏性)分析获得。GluN2B在体内的定量测定 利用正电子发射计算机断层扫描(PET)技术对活脑组织的分布、靶点摄取和剂量分布进行评估。 GluN2B-靶向神经疗法。到目前为止，还没有成功的例子展示GluN2B的映像 人类使用，代表着我们在体内研究这一靶点的能力的一个重大缺陷。因此，我们建议 开发一种新型的PET配体，可以克服以前尝试的主要缺点(低脑渗透性/有限 靶标特异性/高亲脂性)，作为药物发现的第一个翻译成像工具。 我们的第一代GluN2B靶向配体[18F]N2B-0518表现出优异的效力、靶向选择性和高 特异性结合，但由于脑渗透率低和体内代谢快而终止。在我们的下一代， 我们成功地鉴定出一种先导分子N2B-94，它对GluN2B具有很高的活性和选择性。 所有其他NMDAR亚基。合成了N2B-94的~(11)C同位素，并对其进行了初步的PET成像研究 确认我们已经克服了GluN2B配体开发的主要障碍，实现了：1)大脑高度发达 摄取；2)高靶点特异性，以及良好的体内稳定性。尽管N2B-94是一条很有希望的线索 分子，PET配体具有更高的脑渗透率，提高了效力和选择性，并具有适当的脑动力学 寻求跨物种的翻译成像研究，以实现活着大脑中GluN2B的最佳量化。 在N2B-94为药物化学优化提供了经过验证的成功的基础上，作为具体目标，我们将 设计和制备一系列可用11C或18F标记的GluN2B调节器，并评估它们的能力 量化GluN2B活性和在药物挑战期间在啮齿动物和非人灵长类动物中的变化 高等物种死后脑组织的放射自显影和生物学验证。这项工作的影响是 不仅开发了第一个用于研究神经退行性疾病的有效和选择性的GluN2B PET配体- 相关的生物学过程，但最终也通过在高等物种中进行PET成像验证来促进这种配体 用于潜在的临床翻译和监测神经退行性变的新神经疗法的靶向反应 疾病，包括阿尔茨海默病。 相关性：这项提议有可能改善公共健康，并帮助患有 通过使用GluN2B选择性神经疗法的发现，包括阿尔茨海默病在内的神经退行性疾病 NMDAR PET配体。

Project Summary: Dysfunction of GluN2B subunit in the N-Methyl-D-aspartic acid receptor (NMDAR) is implicated in the physiopathology of neurodegenerative diseases such as Alzheimer’s disease (AD) and related dementia. Pharmacological modulation of GluN2B subunit regulates synaptic plasticity and excitation, representing an attractive therapeutic approach. PET is capable of quantifying biochemical processes in vivo, and a suitable GluN2B ligand would substantially improve our understanding of GluN2B-based ionotropic glutamate signaling under physiopathological conditions otherwise inaccessible by ex vivo (destructive) analysis. Quantification of GluN2B in living brain by PET would provide the assessment of distribution, target engagement and dose occupancy of new GluN2B-targeted neurotherapeutics. To date, no successful examples have been demonstrated to image GluN2B for human use, representing a significant deficiency of our ability to study this target in vivo. Therefore, we propose to develop a novel PET ligand that can overcome major drawbacks of previous attempts (low brain permeability / limited target specificity / high lipophilicity), as the first translational imaging tool for drug discovery. Our first generation GluN2B-targeted ligand, [18F]N2B-0518 showed excellent potency, target selectivity and high specific binding, but was discontinued due to low brain penetration and fast metabolism in vivo. In our next generation, we successfully identified a lead molecule, N2B-94, which showed high potency and selectivity towards GluN2B over all other NMDAR subunits. An 11C-isotopologue of N2B-94 was synthesized and preliminary PET imaging studies confirmed that we have overcome the major obstacles for GluN2B ligand development by achieving: 1) high brain uptake; 2) high target specificity, as well as well-improved in vivo stability. Though N2B-94 is a promising lead molecule, PET ligands with higher brain penetration, improved potency and selectivity with proper brain kinetics are sought for translational cross-species imaging studies to achieve optimal quantification of GluN2B in the living brain. On the basis that N2B-94 serves a validated hit for medicinal chemistry optimization, as specific goals, we will design and prepare a series of GluN2B modulators amenable for labeling with 11C or 18F, and evaluate their ability to quantify GluN2B activity and changes during drug challenge in rodents and nonhuman primates, as well as autoradiography and biological validation in postmortem brain tissues from higher species. The impact of this work is not only to develop the first potent and selective GluN2B PET ligand for the study of neurodegenerative disease- related biological processes, but also ultimately, via PET imaging validation in higher species, to advance this ligand for potential clinical translation and monitor target response of novel neurotherapeutics for neurodegenerative diseases, including AD. Relevance: This proposal has the potential to improve public health and help patients suffering from neurodegenerative diseases, including AD, through the discovery of neurotherapeutics using GluN2B-selective NMDAR PET ligands.