PET Probes for Imaging the Vesicular Acetylcholine Transporter

描述（由申请人提供）：本研究项目的目标是开发PET放射性示踪剂，以定量囊泡乙酰胆碱转运蛋白（VAChT）。VAChT是在突触前胆碱能神经末梢表达的一种新蛋白。这种蛋白质是研究胆碱能神经元和突触丧失的关键生物标志物，胆碱能神经元和突触在痴呆的认知功能障碍中起主要作用，并与许多神经退行性疾病相关。PET示踪剂VAChT将提供一个独特的工具来测量胆碱能神经元的损失，并评估与神经退行性疾病相关的痴呆症的认知功能障碍的严重程度。此外，已经发现大脑中VAChT的水平在药物滥用和精神病的治疗期间发生改变。因此，VAChT的PET示踪剂也将提供一种新的工具来监测药物滥用和精神病的治疗。目前，由于缺乏合适的PET示踪剂，PET测量脑中的脑VAChT受到阻碍。因此，开发VAChT的体内PET显像剂是非常重要的。为了开发用于VAChT成像的PET放射性示踪剂，我们建议探索一系列新的含羰基的VAChT抑制剂，并通过体外生物活性测定来鉴定具有纳摩尔亲和力（Ki < 10 nM）和对VAChT的高选择性的先导化合物的更有效的异构体。将用C-11或F-18对已鉴别的异构体进行放射合成，然后在大鼠和非人灵长类动物体内进行验证。此外，将进一步评价属于这类新VAChT抑制剂的主要放射性药物（-）-[18 F]FBBV，以确定其是否是VAChT临床成像研究的合适PET示踪剂。（-）-[18 F]FBBV的初始体内验证证明了在脑的富含VAChT的纹状体中的高特异性结合亲和力。在本项目中，我们建议进一步评估（-）[18F]FBBV和几种结构同系物。在这个补助金申请中有五个具体目标：具体目标1，合成和放射合成。我们将首先解析5种新先导化合物的外消旋混合物，以确定哪种对映异构体更有效，使用体外结合亲和力筛选试验更具选择性;然后将更有效的对映异构体与C-11或F-18进行放射合成。具体目标2，大鼠生物学评价。将进行大鼠生物分布和放射自显影研究，以确定放射性示踪剂是否与大脑富含VAChT的纹状体结合。具体目标3，非人灵长类动物的MicroPET成像和血液代谢物分析。将在猕猴中进行18 F或11 C标记放射性示踪剂的基线研究、重测变异性研究、特异性研究和可逆性/不可逆性研究，包括动脉血样的代谢物分析。具体目标4，剂量测定研究。将在猕猴中进行全身microPET成像研究，以估计人体不同器官吸收的辐射剂量。具体目标5，毒性研究。将对最有前途的PET放射性示踪剂的未标记形式进行毒性研究。具体目标4和5是未来人体PET成像研究的先决条件。 公共卫生相关性：据最近估计，美国的痴呆症患病率为530万人，其中510万人年龄在65岁以上，20万人年龄在65岁以下。在美国，阿尔茨海默病（AD）占所有痴呆症的60 - 80%。据报道，在美国，AD和其他痴呆症的社会成本为1720亿美元。一种新的PET示踪剂VAChT可用于临床，以测量胆碱能神经元和突触的损失将是巨大的有用的临床评估的认知功能障碍的严重程度和监测胆碱能治疗的神经退行性疾病的疗效。它也可能为药物滥用和精神病的机制研究或疗效监测提供一种新的工具。

DESCRIPTION (provided by applicant): The goal of this research project is to develop a PET radiotracer to quantify the vesicular acetylcholine transporter (VAChT). VAChT is a novel protein expressed in presynaptic cholinergic nerve terminals. This protein is a key biomarker for studying the loss of cholinergic neurons and synapses, which plays a major role in the cognitive dysfunction of dementia and is associated with a number of neurodegenerative diseases. A PET tracer for VAChT will provide a unique tool to measure the loss of cholinergic neurons and assess the severity of cognitive dysfunction of dementia associated with neurodegenerative diseases. In addition, it has been found that the level of VAChT in the brain is altered during treatment of drug abuse and psychosis. Therefore, a PET tracer for VAChT also will provide a new tool to monitor treatment of drug abuse and psychosis. Currently, PET measurement of brain VAChT in the brain has been hampered due to the lack of a suitable PET tracer. Therefore, it is extremely important to develop in vivo PET imaging agents for VAChT. To develop a PET radiotracer for imaging VAChT, we propose to explore a series of new novel carbonyl containing VAChT inhibitors and identify the more potent isomers of the lead compounds with nanomolar affinity (Ki < 10 nM) and high selectivity for VAChT by in vitro bioactivity determination. The identified isomers will be radiosynthesized with C-11 or F-18 and then will be validated in vivo rats and non-human primates. In addition, (-)-[18F]FBBV, a lead radio agent that belongs in this new class of VAChT inhibitors will be further evaluated to determine if it will be a suitable PET tracer for clinical imaging studies of VAChT. The initial in vivo validation of (-)-[18F]FBBV demonstrated high specific binding affinity in the VAChT enriched striatum of the brain. In the current project, we propose to further evaluate (-)[18F]FBBV and several structural congeners. There are five specific aims in this grant application: Specific Aim 1, Synthesis and Radiosynthesis. We will first resolve the racemic mixtures of 5 new lead compounds to determine which enantiomeric isomers are more potent and more selective using in vitro binding affinity screening assays; the more potent enantiomers will then be radiosynthesized with C-11 or F-18. Specific Aim 2, Biological evaluation in rats. Rat biodistribution and autoradiography studies will be conducted to determine if the radiotracers bind to VAChT-enriched striatum of the brain. Specific Aim 3, MicroPET imaging and blood metabolite analysis in nonhuman primates. Baseline studies, test-retest variability studies, specificity studies and reversibility/irreversibility studies of the 18F or 11C-labeled radiotracers will be conducted in macaques including metabolite analysis of arterial blood samples. Specific Aim 4, Dosimetry Studies. Whole body microPET imaging studies will be conducted in macaques to estimate the dose of radiation absorbed by different organs in human. Specific Aim 5, Toxicity Studies. Toxicity studies of the unlabeled form of the most promising PET radiotracer will be conducted. Specific Aims 4 and 5 are prerequisite steps for future PET imaging studies in humans. PUBLIC HEALTH RELEVANCE: Dementia prevalence in the United States has been recently estimated at 5.3 million individuals 5.1 million over the age of 65 and old and 200,000 under 65. In America, Alzheimer's Disease (AD) alone accounts for 60 - 80% of all dementia. In the United States, the social cost for AD and other dementias is reported to be $172 billion. A novel PET tracer of VAChT that could be used on clinic to measure the loss of cholinergic neurons and synapses will be tremendous useful on clinic assessing the severity of cognitive dysfunction of dementia and monitoring the efficacy of cholinergic therapies of neurodegenerative diseases. It also could provide a new tool to investigating the mechanism or monitoring the efficacy of therapy for drug abuse and psychosis.