Department of Radiology & Nuclear Medicine, Neuroscience Campus Amsterdam, VU University Medical Center, Amsterdam, the Netherlands.
Pharmacol Res Perspect. 2019 Feb;7(1):e00458. doi: 10.1002/prp2.458.
Labeled with carbon-11, N-(2-chloro-5-thiomethylphenyl)-N'-(3-methoxyphenyl)-N'-methylguanidine ([ C]GMOM) is currently the only positron emission tomography (PET) tracer that has shown selectivity for the ion-channel site of N-methyl-D-aspartate (NMDA) receptors in human imaging studies. The present study reports on the selectivity profile and in vitro binding properties of GMOM. The compound was screened on a panel of 80 targets, and labeled with tritium ([ H]GMOM). The binding properties of [ H]GMOM were compared to those of the reference ion-channel ligand H-dizocilpine maleate ([ H]MK-801), in a set of concentration-response, homologous and heterologous inhibition, and association kinetics assays, performed with repeatedly washed rat forebrain preparations. GMOM was at least 70-fold more selective for NMDA receptors compared to all other targets examined. In homologous inhibition and concentration-response assays, the binding of [ H]GMOM was regulated by NMDA receptor agonists, albeit in a less prominent manner compared to [ H]MK-801. Scatchard transformation of homologous inhibition data produced concave upward curves for [ H]GMOM and [ H]MK-801. The radioligands showed bi-exponential association kinetics in the presence of 100 μmol L l-glutamate/30 μmol L glycine. [ H]GMOM (3 nmol L and 10 nmol L ) was inhibited with dual affinity by (+)-MK-801, (R,S)-ketamine and memantine, in both presence and absence of agonists. [ H]MK-801 (2 nmol L ) was inhibited in a monophasic manner by GMOM under baseline and combined agonist conditions, with an IC value of ~19 nmol L . The non-linear Scatchard plots, biphasic inhibition by open channel blockers, and bi-exponential kinetics of [ H]GMOM indicate a complex mechanism of interaction with the NMDA receptor ionophore. The implications for quantifying the PET signal of [ C]GMOM are discussed.
用碳-11 标记的 N-(2-氯-5-硫甲基苯基）-N'-(3-甲氧基苯基）-N'-甲基胍（[C]GMOM）是目前唯一一种在人类成像研究中显示出对 N-甲基-D-天冬氨酸（NMDA）受体离子通道部位选择性的正电子发射断层扫描（PET）示踪剂。本研究报告了 GMOM 的选择性特征和体外结合特性。该化合物在 80 个靶点的筛选中进行了筛选，并与氚（[H]GMOM）标记。在一组浓度反应、同源和异源抑制以及结合动力学测定中，比较了[H]GMOM 的结合特性与参考离子通道配体[H]（+）-二噻唑啉马来酸（[H]MK-801）的结合特性，该测定是在反复洗涤的大鼠前脑制剂中进行的。GMOM 对 NMDA 受体的选择性至少是其他所有检测靶点的 70 倍。在同源抑制和浓度反应测定中，NMDA 受体激动剂调节了[H]GMOM 的结合，尽管与[H]MK-801 相比，调节作用不那么明显。同源抑制数据的 Scatchard 转化为[H]GMOM 和[H]MK-801 产生向上凹的曲线。放射性配体在 100μmol L l-谷氨酸/30μmol L 甘氨酸存在下表现出双指数结合动力学。[H]GMOM（3nmol L 和 10nmol L ）在存在和不存在激动剂的情况下，均被（+）-MK-801、（R，S）-氯胺酮和美金刚以双重亲和力抑制。[H]MK-801（2nmol L ）在基线和联合激动剂条件下以单相位方式被 GMOM 抑制，IC 值约为 19nmol L 。非线性格拉查德图、开放通道阻滞剂的双相抑制以及[H]GMOM 的双指数动力学表明，它与 NMDA 受体离子通道的相互作用机制复杂。讨论了定量[C]GMOM 的 PET 信号的影响。
