Mukhin A G, Gündisch D, Horti A G, Koren A O, Tamagnan G, Kimes A S, Chambers J, Vaupel D B, King S L, Picciotto M R, Innis R B, London E D
Brain Imaging Center, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland, USA.
Mol Pharmacol. 2000 Mar;57(3):642-9. doi: 10.1124/mol.57.3.642.
In an effort to develop selective radioligands for in vivo imaging of neuronal nicotinic acetylcholine receptors (nAChRs), we synthesized 5-iodo-3-(2(S)-azetidinylmethoxy)pyridine (5-iodo-A-85380) and labeled it with (125)I and (123)I. Here we present the results of experiments characterizing this radioiodinated ligand in vitro. The affinity of 5-[(125)I]iodo-A-85380 for alpha4beta2 nAChRs in rat and human brain is defined by K(d) values of 10 and 12 pM, respectively, similar to that of epibatidine (8 pM). In contrast to epibatidine, however, 5-iodo-A-85380 is more selective in binding to the alpha4beta2 subtype than to other nAChR subtypes. In rat adrenal glands, 5-iodo-A-85380 binds to nAChRs containing alpha3 and beta4 subunits with 1/1000th the affinity of epibatidine, and exhibits 1/60th and 1/190th the affinity of epibatidine at alpha7 and muscle-type nAChRs, respectively. Moreover, unlike epibatidine and cytisine, 5-[(125)I]iodo-A-85380 shows no binding in any brain regions in mice homozygous for a mutation in the beta2 subunit of nAChRs. Binding of 5-[(125)I]iodo-A-85380 in rat brain is reversible, and is characterized by high specificity and a slow rate of dissociation of the receptor-ligand complex (t(1/2) for dissociation approximately 2 h). These properties, along with other features observed previously in in vivo experiments (low toxicity, rapid penetration of the blood-brain barrier, and a high ratio of specific to nonspecific binding), suggest that this compound, labeled with (125)I or (123)I, is superior to other radioligands available for in vitro and in vivo studies of alpha4beta2 nAChRs, respectively.
为了开发用于神经元烟碱型乙酰胆碱受体（nAChRs）体内成像的选择性放射性配体，我们合成了5-碘-3-(2(S)-氮杂环丁烷甲氧基)吡啶（5-碘-A-85380），并用(125)I和(123)I对其进行标记。在此，我们展示了在体外对这种放射性碘化配体进行表征的实验结果。5-[(125)I]碘-A-85380对大鼠和人脑中α4β2 nAChRs的亲和力分别由K(d)值10和12 pM定义，与埃博霉素（8 pM）相似。然而，与埃博霉素不同的是，5-碘-A-85380与α4β2亚型结合时比与其他nAChR亚型更具选择性。在大鼠肾上腺中，5-碘-A-85380与含有α3和β4亚基的nAChRs结合的亲和力是埃博霉素的1/1000，在α7和肌肉型nAChRs上分别表现出埃博霉素1/60和1/190的亲和力。此外，与埃博霉素和金雀花碱不同，5-[(125)I]碘-A-85380在nAChRsβ2亚基发生突变的纯合小鼠的任何脑区中均未显示出结合。5-[(125)I]碘-A-85380在大鼠脑中的结合是可逆的，其特点是具有高特异性以及受体-配体复合物的解离速率较慢（解离的t(1/2)约为2小时）。这些特性，连同先前在体内实验中观察到的其他特征（低毒性、快速穿透血脑屏障以及高特异性与非特异性结合比）表明，这种用(125)I或(123)I标记的化合物分别优于可用于α4β2 nAChRs体外和体内研究的其他放射性配体。
