Development Of New Pet And Spect Radiotracers And New Ap

新型宠物和光谱放射性示踪剂和新应用程序的开发

• 批准号: 6680365
• 负责人: ALANE S KIMES
• 金额: --
• 依托单位: NATIONAL INSTITUTE ON DRUG ABUSE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6680365
• 关键词: analog; cannabinoid receptor; cannabinoids; clinical research; drug design /synthesis /production; human subject; nicotine; nicotinic receptors; positron emission tomography; radiotracer; single photon emission computed tomography

Analogs of A-85380 and A-84543 have been evaluated as imaging agents for nicotinic acetylcholine receptors (nAChRs) with positron emission tomography (PET) and single photon emission computed tomography (SPECT). Radiation dosimetry and toxicological studies in animals demonstrated the safety of 5-[I-125]iodo-A-85380 (5IA). In collaboration with Yale University, the first human SPECT studies with 5IA revealed that cerebral nAChRs can be visualized in non-smokers and dosimetry data from these studies indicate that multiple studies can be performed on a single volunteer without exceeding radiation dosimetry limits. Similarly, the first human PET studies with 2-[F-18]fluoro-A-85380 (2FA) demonstrate the feasibility of quantitatively imaging nAChRs in the thalamus and visualizing these receptors in brain regions containing low to moderate receptor densities. Mice studies showed that the administration of the non-selective inhibitor of cytochrome P450, cimetidine, substantially slowed the rapid in vivo metabolism of 5IA, suggesting that the use of this or similar compounds could reduce the dose of radioactivity needed to successfully image nAChRs in human volunteers. Graphical analysis of PET data from Rhesus monkeys provided binding potential values for 2FA in the thalamus, cortex, striatum and cerebellum that were consistent with the distribution pattern of alpha4beta2 nAChRs. Methodology was developed and data were collected for estimating the density of nAChRs in the thalamus of non-human primates (NHPs).In collaboration with researchers from the University of Michigan, the loss of nAChRs in the striatum of unilaterally MPTP-lesioned NHPs with 2FA and PET was demonstrated. Kinetic studies with 2FA and PET in NHPs revealed that 2FA accumulates relatively slowly in brain, partially because its low lipophilicity slows its blood-brain-barrier penetration. Efforts were directed at developing radioligands with faster kinetics for imaging nAChRs in vivo. To that end, six novel analogs of A-85380 and A-84543 with calculated log P (Clog P) values in the range of 1.2 to 3 were synthesized, radiolabeled and evaluated in vitro and in vivo. Molecular modeling of the structures of these compounds revealed differences in their conformational profiles and the electronic properties, providing insight into structure-activity relationships with nAChRs. The molecular modeling was performed in collaboration with staff in the Medicinal Chemistry Section of the Medications Discovery Research Branch. Increasing the lipophilicity from Clog P = 0.6 (2FA) yielded ligands with faster blood brain barrier penetration and increased nonspecific binding. Although [11C]methyl-PVC, the best radioligand from the series, exhibits specific in vivo receptor binding that is half that of 2FA, [11C]methyl-PVC may be useful for studying the in vivo occupancy of nAChRs by endogenous or exogenous ligands. From in vitro and in vivo studies with these radioligands (Kd values at 37 degrees C: 9 to 600 pM, Clog P values: 0.6 to 3), an algorithm was developed for predicting binding potential (BP). BP is the one of the most important characteristic of a radioligand as it characterizes the specificity of radioligand receptor binding and reflects its suitability for qualitative and quantitative in vivo imaging. BP values for six radioligands calculated from their Kds at 37 oC, their Clog Ps, and the density of alpha4beta2 nAChRs in each brain region of interest and this algorithm were in good agreement with those observed in vivo in Rhesus monkeys, suggesting that this algorithm might be useful for screening potential compounds for a new radioligand for alpha4beta2 nAChRs with improved characteristics. As part of our effort to develop radioligands for in vivo imaging of cannabinoid receptors, we synthesized and evaluated a series of 1,5-diarylpyrazoles by modifying the substituents on positions 1,3,4 and 5 of the pyrazole core. As part of this project, we developed a practical method for preparing C-4 fluoro pyrazoles using electrophilic fluorination. One compound in the series exhibited lower lipophilicity than and comparable binding affinity to SR141716, a selective CB1 antagonist, for the CB1 cannabinoid receptor. Greater accumulation of radioactivity after administration of this compound to mice was observed in CB1-rich regions (e.g., hippocampus, striatum and cerebellum) than in receptor poor brain regions, suggesting specific binding to these receptors. Similar findings were obtained in PET studies of Rhesus monkeys with this compound.

用正电子发射断层扫描和单光子发射计算机断层扫描对A-85380和A-84543类似物作为烟碱型乙酰胆碱受体显像剂进行了评价。动物辐射剂量学和毒理学研究证明了5-[I-125]碘-A-85380(5IA)的安全性。与耶鲁大学合作，首次使用5IA进行的人类SPECT研究显示，脑内nAChRs可以在不吸烟的人身上可视化，这些研究的剂量学数据表明，可以在一名志愿者身上进行多项研究，而不会超过辐射剂量学限制。同样，首次使用2-[F-18]氟-A-85380(2FA)的人类正电子发射计算机断层扫描研究证明了对丘脑中的nAChRs进行定量成像并在含有低到中等受体密度的大脑区域显示这些受体的可行性。小鼠研究表明，细胞色素P450的非选择性抑制剂西咪替丁显著减缓了5IA在体内的快速代谢，这表明使用这种或类似的化合物可以减少在人类志愿者身上成功成像nAChRs所需的放射性剂量。对恒河猴PET数据的图形分析提供了丘脑、皮质、纹状体和小脑中2FA的结合电位值，这与α4β2 nAChRs的分布模式一致。建立了用于估计非人灵长类动物丘脑nAChRs密度的方法学，并收集了数据，与密歇根大学的研究人员合作，证明了2FA和PET在单侧MPTP损毁的NHP纹状体内nAChRs的丢失。2FA和PET在NHP中的动力学研究表明，2FA在大脑中的积累相对较慢，部分原因是它的低亲脂性减缓了其血脑屏障的穿透。努力开发具有更快动力学的放射性配体，以便在体内对nAChRs进行成像。为此，合成了六个新的A-85380和A-84543类似物，计算的对数P(Clog P)值在1.2到3之间，并对其进行了放射性标记和体内外评价。对这些化合物的结构进行了分子模拟，揭示了它们的构象分布和电子性质的差异，为深入了解nAChRs的结构-活性关系提供了依据。分子建模是与药物发现研究分部药物化学科的工作人员合作进行的。增加BLOG的亲脂性P=0.6(2FA)可产生更快的血脑屏障穿透速度和更多的非特异性结合。虽然该系列中最好的放射性配体[11C]甲基-聚氯乙烯在体内的特异性受体结合率是2FA的一半，但[11C]甲基-聚氯乙烯可能有助于研究内源性或外源性配体对nAChRs的体内占位。从体外和体内对这些放射性配体(37℃时的Kd值：9到600 pm，堵塞P值：0.6到3)的研究中，开发了一种预测结合势(BP)的算法。BP是放射性配基最重要的特征之一，因为它表征了放射性配基受体结合的特异性，并反映了其在体内定性和定量成像的适用性。根据6个放射性配基在37oC时的kDS、阻塞率和每个感兴趣脑区的α4β2 nAChRs密度计算的BP值与在猕猴体内观察到的结果一致，表明该算法可能有助于筛选具有改进特性的新放射性配基的潜在化合物。作为开发用于大麻素受体体内成像的放射性配体的努力的一部分，我们通过修饰吡唑核心1、3、4和5位上的取代基合成并评价了一系列1，5-二芳基吡唑。作为该项目的一部分，我们开发了一种利用亲电氟化制备C-4氟吡唑的实用方法。该系列中的一种化合物对CB1大麻受体的亲脂性低于选择性CB1受体拮抗剂SR141716，而与SR141716的结合亲和力相当。给小鼠服用该化合物后，在CB1丰富的区域(如海马体、纹状体和小脑)比在受体贫乏的脑区观察到更大的放射性积累，这表明它与这些受体具有特异性结合。在用这种化合物对恒河猴进行的正电子发射计算机断层扫描研究中也得到了类似的发现。