[18F]-FE-DABP688作为代谢型谷氨酸受体5型的正电子发射断层显像（PET）放射性配体的放射性标记及体外和体内评价

Radiolabeling and in vitro and in vivo evaluation of [18F]-FE-DABP688 as a PET radioligand for the metabotropic glutamate receptor subtype 5.

作者信息

Honer Michael, Stoffel Anja, Kessler Lea J, Schubiger P August, Ametamey Simon M

机构信息

Animal Imaging Center - PET, Center for Radiopharmaceutical Science of ETH, PSI and USZ, ETH Hoenggerberg, CH-8093 Zurich, Switzerland.

出版信息

Nucl Med Biol. 2007 Nov;34(8):973-80. doi: 10.1016/j.nucmedbio.2007.07.017. Epub 2007 Sep 19.

DOI:10.1016/j.nucmedbio.2007.07.017

PMID:17998101

Abstract

INTRODUCTION

Fluoroethyl-desmethyl-ABP688 (FE-DABP688) is a novel derivative of the previously described positron emission tomography (PET) ligand 3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-O-[11C]-methyl-oxime. FE-DABP688 was radiolabeled with fluorine-18 and characterized as a PET imaging agent for the metabotropic glutamate receptor subtype 5 (mGluR5).

METHODS

FE-DABP688 was radiolabeled by reacting 2-[18F]-fluoroethyl tosylate with the sodium salt of 3-(pyridin-2-ylethynyl)-cyclohex-2-enone-oxime in dry DMF. The in vitro affinity of [18F]-FE-DABP688 for mGluR5 was determined by Scatchard analysis of saturation binding data using rat whole-brain membranes (without cerebellum). Further in vitro characterization of the tracer involved plasma stability and lipophilicity testing. In vivo evaluation of [18F]-FE-DABP688 was performed by postmortem biodistribution experiments and PET studies in rats using the dedicated small-animal PET tomograph quad-HIDAC.

RESULTS

The radiotracer was obtained in good radiochemical yields in an overall synthesis time of 150 min. The radiochemical yield after semipreparative HPLC was 25+/-8% (n>7, decay corrected), and specific activity was 30+/-5 GBq/micromol (n>7). [18F]-FE-DABP688 exhibited optimal lipophilicity with a logD value of 2.1+/-0.1 and high plasma stability. Saturation assays of [(18)F]-FE-DABP688 revealed a single high-affinity binding site with a dissociation constant (Kd) of 1.6+/-0.4 nM and a Bmax value of 119+/-24 fmol/mg protein. PET scanning indicated radioactivity uptake in mGluR5-rich regions such as the hippocampus, striatum and cortex, while radioactivity accumulation in the cerebellum, a region with negligible mGluR5 density, was significantly lower. Biodistribution studies showed a similar distribution pattern of [18F]-FE-DABP688 binding in the brain. The hippocampus-to-cerebellum and striatum-to-cerebellum ratios were 1.81+/-0.16 and 1.93+/-0.36, respectively. Blocking studies using coinjection of [18F]-FE-DABP688 and unlabeled 2-methyl-6-((3-methoxyphenyl)ethynyl)-pyridine (1 mg/kg) revealed more than 45% specific binding in the hippocampus and striatum, thus demonstrating the in vivo specificity of tracer binding.

CONCLUSIONS

[18F]-FE-DABP688 may be a useful PET tracer for imaging mGluR5 in rodents.

摘要

引言

氟乙基 - 去甲基 - ABP688（FE - DABP688）是先前所述正电子发射断层扫描（PET）配体3 - （6 - 甲基 - 吡啶 - 2 - 基乙炔基） - 环己 - 2 - 烯酮 - O - [11C] - 甲基肟的新型衍生物。FE - DABP688用氟 - 18进行放射性标记，并被表征为代谢型谷氨酸受体5（mGluR5）的PET显像剂。

方法

通过使2 - [18F] - 氟乙基甲苯磺酸酯与3 - （吡啶 - 2 - 基乙炔基） - 环己 - 2 - 烯酮肟的钠盐在干燥的N，N - 二甲基甲酰胺（DMF）中反应来对FE - DABP688进行放射性标记。使用大鼠全脑匀浆（不含小脑）对[18F] - FE - DABP688与mGluR5的体外亲和力通过对饱和结合数据进行Scatchard分析来确定。该示踪剂的进一步体外特性研究包括血浆稳定性和脂溶性测试。通过大鼠死后生物分布实验以及使用专用小动物PET断层扫描仪quad - HIDAC进行的PET研究对[18F] - FE - DABP688进行体内评估。

结果

在150分钟的总合成时间内以良好的放射化学产率获得了放射性示踪剂。半制备高效液相色谱（HPLC）后的放射化学产率为25±8％（n>7，衰变校正），比活度为30±5 GBq/μmol（n>7）。[18F] - FE - DABP688表现出最佳脂溶性，logD值为2.1±0.1，并且具有高血浆稳定性。[18F] - FE - DABP688的饱和分析显示存在一个单一的高亲和力结合位点，解离常数（Kd）为1.6±0.4 nM，Bmax值为119±24 fmol/mg蛋白质。PET扫描显示在富含mGluR5的区域如海马体、纹状体和皮质中有放射性摄取，而在mGluR5密度可忽略不计的小脑区域中的放射性积累明显较低。生物分布研究显示[18F] - FE - DABP688在脑中的结合具有相似的分布模式。海马体与小脑以及纹状体与小脑的比率分别为1.81±0.16和1.93±0.36。使用[18F] - FE - DABP688与未标记的2 - 甲基 - 6 - （（3 - 甲氧基苯基）乙炔基） - 吡啶（1 mg/kg）共同注射的阻断研究显示在海马体和纹状体中有超过45％的特异性结合，从而证明了示踪剂结合的体内特异性。