Development of Novel PET Probes for Central 2‑Amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic Acid Receptors

We
document the development of PET probes for central AMPA receptors
and their application to in vivo animal imaging. An initial screening
of perampanel derivatives was performed to identify probe candidates.
Despite the high autoradiographic contrast yielded by several radioligands,
rat PET scans did not support their in vivo suitability. Further focused
derivatization and a second screening by ex vivo LC-MS measurements
led to the selection of 2-[1-(3-methylaminophenyl)-2-oxo-5-(pyrimidin-2-yl)-1,2-dihydropyridin-3-yl]­benzonitrile, 21a, and its analogues as candidates. [11C]21a was shown by autoradiography to specifically bind to the
neocortex and hippocampus, consistent with AMPA receptor localization.
PET imaging with [11C]21a demonstrated moderate
uptake of radioactivity in rat and monkey brains, with the retention
of radiosignals being consistent with that from the autoradiogram
data, and the uptake was blocked by pretreatment with unlabeled 21a in a dose-dependent manner. The current approach has facilitated
the discovery of a PET probe potentially suitable for translational
research and development focused on AMPA receptors.

本研究记录了针对中枢AMPA受体（AMPA receptor）的正电子发射断层显像（Positron Emission Tomography，PET）探针的开发流程，及其在活体（in vivo）动物成像中的应用。我们首先对吡仑帕奈（perampanel）衍生物开展初步筛选，以鉴定潜在的探针候选物。尽管多款放射性配体（radioligand）展现出优异的放射自显影（autoradiography）对比度，但大鼠PET成像结果无法支持其体内应用的可行性。随后我们进行了针对性的结构衍生化改造，并通过离体（ex vivo）液相色谱-质谱联用（Liquid Chromatography-Mass Spectrometry，LC-MS）检测完成第二轮筛选，最终选定2-[1-(3-甲氨基苯基)-2-氧代-5-(嘧啶-2-基)-1,2-二氢吡啶-3-基]苯甲腈（21a）及其类似物作为候选探针。放射自显影实验证实，[11C]21a可特异性结合新皮层与海马体，这与AMPA受体的组织分布特征相符。采用[11C]21a的PET成像结果显示，大鼠与猴脑内的放射性摄取水平适中，放射性信号的滞留情况与放射自显影图（autoradiogram）数据一致，且未标记的21a预处理可呈剂量依赖性（dose-dependent）地阻断该摄取过程。本研究的方法助力发现了一款有望用于针对AMPA受体的转化研究（translational research）与开发的PET探针。