Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, School of Pharmacy, Xuzhou Medical University, Xuzhou, 221004, China.
NHC Key Laboratory of Nuclear Medicine, Jiangsu Key Laboratory of Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi, 214063, China.
Mol Imaging Biol. 2021 Oct;23(5):733-744. doi: 10.1007/s11307-021-01603-2. Epub 2021 Apr 13.
The dopamine transporter (DAT) is a marker of the occurrence and development of Parkinson's disease (PD) and other diseases with nigrostriatal degeneration. 2β-Carbomethoxy-3β-(4-chlorophenyl)-8-(2-[F]-fluoroethyl)nortropane ([F]FECNT), an F-labelled tropane derivative, was reported to be a useful positron-emitting probe for DAT. However, the rapid formation of brain-penetrating radioactive metabolites is an impediment to the proper quantitation of DAT in PET studies with [F]FECNT. Deuterium-substituted analogues have presented better in vivo stability to reduce metabolites. This study aimed to synthesize a deuterium-substituted DAT radiotracer, [F]FECNT-d, and to make a preliminary investigation of its properties as a DAT tracer in vivo.
The ligand [F]FECNT-d was obtained by one-step radiolabelling reaction. The lipophilicity was measured by the shake-flask method. Binding properties of [F]FECNT-d were estimated by in vitro binding assay, biodistribution, and microPET imaging in rats. In vivo stability of [F]FECNT-d was estimated by radio-HPLC.
[F]FECNT-d was synthesized at an average activity yield of 46 ± 17 % (n = 15) and the molar activity was 67 ± 12 GBq/μmol. The deuterated tracer showed suitable lipophilicity and the ability to penetrate the blood-brain barrier (brain uptake of 1.72 % ID at 5 min). [F]FECNT-d displayed a high binding affinity for DAT comparable to that of [F]FECNT in rat striatum homogenates. Biodistribution results in normal rats showed that [F]FECNT-d exhibited a higher ratio of the target to non-target (striatum/cerebellum) at 15 min post administration (5.00 ± 0.44 vs 3.84 ± 0.24 for [F]FECNT-d vs [F]FECNT). MicroPET imaging studies of [F]FECNT-d in normal rats showed that the ligand selectively localized to DAT-rich striatal regions and the accumulation could be blocked with DAT inhibitor. Furthermore, in the unilateral PD model rat, a significant reduction of the signal was found in the lesioned side relative to the unlesioned side. Striatal standardized uptake value of [F]FECNT-d remained ~4.02 in the striatum between 5 and 20 min, whereas that of [F]FECNT fell rapidly from 4.11 to 2.95. Radio-HPLC analysis of the plasma demonstrated better in vivo stability of [F]FECNT-d than [F]FECNT.
The deuterated compound [F]FECNT-d may serve as a promising PET imaging agent to assess DAT-related disorders.
多巴胺转运体（DAT）是帕金森病（PD）和其他黑质纹状体变性疾病发生和发展的标志物。2β- carbomethoxy-3β-（4-氯苯基）-8-（2-[F]- 氟乙基）-nortropane([F]FECNT)，一种 F 标记的托烷衍生物，被报道为 DAT 的有用正电子发射探针。然而，脑穿透放射性代谢物的快速形成是在使用 [F]FECNT 进行 PET 研究中对 DAT 进行适当定量的障碍。氘代类似物已呈现出更好的体内稳定性，以减少代谢物。本研究旨在合成氘代 DAT 放射性示踪剂 [F]FECNT-d，并对其作为体内 DAT 示踪剂的特性进行初步研究。
通过一步放射性标记反应获得配体 [F]FECNT-d。通过振摇瓶法测量亲脂性。通过体外结合测定、生物分布和大鼠 microPET 成像来估计 [F]FECNT-d 的结合特性。通过放射性 HPLC 评估 [F]FECNT-d 的体内稳定性。
[F]FECNT-d 的平均产率为 46±17%（n=15），摩尔活性为 67±12GBq/μmol。氘代示踪剂表现出适宜的亲脂性和穿透血脑屏障的能力（5min 时脑摄取率为 1.72%ID）。[F]FECNT-d 在大鼠纹状体匀浆中对 DAT 表现出与 [F]FECNT 相当的高结合亲和力。在正常大鼠的生物分布研究中，与 [F]FECNT 相比，[F]FECNT-d 在给药后 15min 时具有更高的靶/非靶（纹状体/小脑）比值（[F]FECNT-d 为 5.00±0.44，[F]FECNT 为 3.84±0.24）。正常大鼠的 [F]FECNT-d microPET 成像研究表明，该配体选择性地定位于富含 DAT 的纹状体区域，并且可以用 DAT 抑制剂阻断其积累。此外，在单侧 PD 模型大鼠中，与未损伤侧相比，损伤侧的信号明显降低。[F]FECNT-d 的纹状体标准化摄取值在 5 至 20min 之间保持在纹状体约 4.02，而 [F]FECNT 迅速从 4.11 降至 2.95。血浆的放射性 HPLC 分析表明，[F]FECNT-d 的体内稳定性优于 [F]FECNT。
氘代化合物 [F]FECNT-d 可作为评估 DAT 相关疾病的有前途的 PET 成像剂。
