A new P2Y12R PET radioligand for measuring microglial function in Alzheimer's disease

总结 阿尔茨海默病（AD）是老年人中最常见的痴呆形式，也是老年痴呆症的第六大原因。 死亡在美国。不幸的是，目前没有FDA批准的疾病修饰疗法 可用于AD，并且只有通过尸检分析才有可能进行明确诊断。数量有限 敏感的生物标志物能够检测AD的早期、功能相关的神经分子变化， 这是提高诊断和验证新疗法的障碍。虽然来自全基因组的数据 相关研究和免疫组织化学表明，神经炎症和健康的先天性 免疫功能是AD的主要危险因素，研究神经免疫功能的生物标志物， 在AD期间仍然非常有限。正电子发射断层扫描（PET）是一种高灵敏度的分子 成像模式非常适合于纵向研究这种生物标志物， 生物化学过程的活体研究。神经炎症的现有PET成像生物标志物（例如，的 转运蛋白18 kDa [TSPO]）具有显著的缺点，包括功能性不清楚的功能性蛋白质， 中枢神经系统（CNS）中多种细胞类型的作用和/或表达，这使得图像复杂化。 分析.在CNS内，腺苷二磷酸受体（P2 Y12 R）的表达仅限于小胶质细胞， 大脑的先天免疫效应细胞。P2 Y12 R通常被认为是稳态小胶质细胞的生物标志物， 表达驱动趋化性和活化相关的形态学变化。重要的是，P2 Y12 R 在急性和慢性神经炎症中表达减少，如啮齿动物在脂多糖后所示。 攻击和AD转基因小鼠。此外，晚期AD患者的死后人脑组织 结果显示，P2 Y12 R表达整体减少，周围小胶质细胞几乎完全缺失。 β淀粉样斑块虽然P2 Y12 R是一种非常好表征的药理学靶点，但 目前没有用于该生物标志物的CNS可穿透的PET放射性示踪剂。我们已经鉴定了P2 Y12 R拮抗剂 AZD 1283具有高亲和力和良好的亲脂性（测量值），是一种有前途的潜在PET示踪剂 LogD 2.8），表明其CNS摄取的高可能性。氰化放射化学的优化 本文概述，我们建议评估体内动力学，生物分布，稳定性和特异性， [11 C] AZD 1283在健康小鼠中的作用，以及[11 C] AZD 1283检测P2 Y12 R表达变化的能力 在人类AD死后组织中使用放射自显影术（Aim 1）。此外，我们将询问 小胶质细胞P2 Y12 R在两种急性和慢性神经炎症小鼠模型中的表达（目的2）。完成 这些目标将导致第一个P2 Y12 R PET示踪剂的开发和表征，适用于体内 PET成像，具有很高的临床转化潜力。最终，这样一个工具可以作为一个端点， 新型AD免疫调节治疗的临床试验，除了帮助监测疾病进展外， 个别患者。

SUMMARY Alzheimer's disease (AD) is the most common form of dementia in older adults and the 6th leading cause of death in the United States. Unfortunately, there are currently no FDA approved disease-modifying therapeutics available for AD, and definitive diagnosis is only possible via postmortem analysis. The limited number of sensitive biomarkers enabling detection of early, functionally relevant, neuromolecular changes in AD is a major impediment to improving diagnosis and validating novel therapeutics. Although data from genome wide association studies and immunohistochemistry have implicated neuroinflammation and a loss of healthy innate immune function as major AD risk factors, biomarkers to investigate neuro-immune function preceding and during AD remain extremely limited. Positron Emission Tomography (PET) is an highly sensitive molecular imaging modality well suited to studying such biomarkers longitudinally, with established utility for non-invasive in vivo interrogation of biochemical processes. Existing PET imaging biomarkers of neuroinflammation (e.g., the translocator protein 18 kDa [TSPO]) suffer from significant drawbacks, including a poorly elucidated functional role and/or expression across multiple cell types in the central nervous system (CNS), which complicates image analysis. Within the CNS, adenosine diphosphate receptor (P2Y12R) expression is restricted to microglia, the innate immune effector cells of the brain. Generally considered a biomarker of homeostatic microglia, P2Y12R expression drives chemotaxis and activation-associated morphological changes. Importantly, P2Y12R expression decreases in both acute and chronic neuroinflammation, as shown in rodents after lipopolysaccharide challenge and in AD transgenic mice. Moreover, postmortem human brain tissue from advanced AD patients demonstrated global reduction in P2Y12R expression, with a near total absence on microglia surrounding amyloid-beta plaques. While P2Y12R is an extremely well characterized pharmacological target, there are currently no CNS-penetrable PET radiotracers for this biomarker. We have identified the P2Y12R antagonist AZD1283 as a promising potential PET tracer based on its high affinity and favorable lipophilicity (measured LogD 2.8) indicative of its high likelihood for CNS uptake. Upon optimization of the cyanation radiochemistry outlined herein, we propose to assess the in vivo kinetics, biodistribution, stability, and specificity of [11C]AZD1283 in healthy mice, as well as the ability of [11C]AZD1283 to detect alterations in P2Y12R expression in human AD postmortem tissue using autoradiography (Aim 1). Additionally, we will interrogate the dynamics of microglial P2Y12R expression in two murine models of acute and chronic neuroinflammation (Aim 2). Completion of these aims will result in development and characterization of the first P2Y12R PET tracer suitable for in vivo PET imaging, with high potential for clinical translation. Ultimately, such a tool could serve as an endpoint in clinical trials of novel AD immunomodulatory therapies, in addition to helping monitor disease progression in individual patients.