PET Center, Department of Radiology and Biomedical Imaging , Yale University School of Medicine , New Haven , Connecticut 06520 , United States.
Mol Pharm. 2019 Apr 1;16(4):1523-1531. doi: 10.1021/acs.molpharmaceut.8b01209. Epub 2019 Feb 28.
The kappa opioid receptor (KOR) is involved in depression, alcoholism, and drug abuse. The current agonist radiotracer C-GR103545 is not ideal for imaging KOR due to its slow tissue kinetics in human. The aim of our project was to develop novel KOR agonist radiotracers with improved imaging properties. A novel compound FEKAP ((( R))-4-(2-(3,4-dichlorophenyl)acetyl)-3-((ethyl(2-fluoroethyl)amino)methyl) piperazine-1-carboxylate) was designed, synthesized, and assayed for in vitro binding affinities. It was then radiolabeled and evaluated in rhesus monkeys. Baseline and blocking scans were conducted on a Focus-220 scanner to assess binding specificity and selectivity. Metabolite-corrected arterial activities over time were measured and used as input functions to analyze the brain regional time-activity curves and derive kinetic and binding parameters with kinetic modeling. FEKAP displayed high KOR binding affinity ( K = 0.43 nM) and selectivity (17-fold over mu opioid receptor and 323-fold over delta opioid receptor) in vitro. C-FEKAP was prepared in high molar activity (mean of 718 GBq/μmol, n = 19) and >99% radiochemical purity. In monkeys, C-FEKAP metabolized fairly fast, with ∼31% of intact parent fraction at 30 min post-injection. In the brain, it exhibited fast and reversible kinetics with good uptake. Pretreatment with the nonselective opioid receptor antagonist naloxone (1 mg/kg) decreased uptake in high binding regions to the level in the cerebellum, and the selective KOR antagonist LY2456302 (0.02 and 0.1 mg/kg) reduced C-FEKAP specific binding in a dose-dependent manner. As a measure of specific binding signals, the mean binding potential ( BP) values of C-FEKAP derived from the multilinear analysis-1 (MA1) method were greater than 0.5 for all regions, except for the thalamus. The novel KOR agonist tracer C-FEKAP demonstrated binding specificity and selectivity in vivo and exhibited attractive properties of fast tissue kinetics and high specific binding.
κ 阿片受体（KOR）参与抑郁、酗酒和药物滥用。目前的激动剂放射性示踪剂 C-GR103545 由于其在人体中的组织动力学较慢，并不适合用于 KOR 成像。我们项目的目的是开发具有改善成像特性的新型 KOR 激动剂放射性示踪剂。设计、合成了一种新型化合物 FEKAP（（（R）-4-（2-（3,4-二氯苯基）乙酰基）-3-（乙基（2-氟乙基）氨基）甲基）哌嗪-1-羧酸盐），并对其体外结合亲和力进行了检测。然后对其进行放射性标记，并在恒河猴中进行评估。在 Focus-220 扫描仪上进行基线和阻断扫描，以评估结合特异性和选择性。测量随时间变化的代谢校正动脉活性，并将其作为输入函数，通过动力学建模分析脑区时间-活性曲线，并得出动力学和结合参数。FEKAP 在体外表现出高 KOR 结合亲和力（K = 0.43 nM）和选择性（与 μ 阿片受体相比为 17 倍，与 δ 阿片受体相比为 323 倍）。C-FEKAP 以高摩尔活性（平均值为 718GBq/μmol，n = 19）和 >99%的放射化学纯度制备。在猴子中，C-FEKAP 代谢相当快，注射后 30 分钟时，完整母体分数约为 31%。在大脑中，它表现出快速和可逆的动力学，摄取良好。用非选择性阿片受体拮抗剂纳洛酮（1mg/kg）预处理可使高结合区的摄取减少到小脑水平，而选择性 KOR 拮抗剂 LY2456302（0.02 和 0.1mg/kg）则以剂量依赖性方式降低 C-FEKAP 的特异性结合。作为特异性结合信号的测量，多线性分析-1（MA1）方法得出的 C-FEKAP 的平均结合势（BP）值均大于 0.5，除丘脑外。新型 KOR 激动剂示踪剂 C-FEKAP 体内显示出结合特异性和选择性，并表现出快速组织动力学和高特异性结合的诱人特性。
