Radiosynthesis and <i>in Vivo</i> and <i>ex Vivo</i> Evaluation of Isomeric [<sup>11</sup>C]methoxy Analogs of Nimesulide as Brain Cyclooxygenase-2-Targeted Imaging Agents
作者:Yumi Yamamoto、Tetsuro Tago、Jun Toyohara、Yohei Saito、Fumihiko Yamamoto
DOI:10.1248/bpb.b21-00608
日期:2022.1.1
Our previous studies identified that nimesulide analogs which bear a methoxy substituent at the para-position of the phenyl ring could be potential radiotracer candidates for detecting disorders related to cyclooxygenase-2 (COX-2) expression and activity in vivo using positron emission tomography (PET) in the brain. The present study was conducted to evaluate the in vivo characteristics of 11C-labeled para-methoxy nimesulide ([11C]1d) as a brain COX-2-targeted imaging agent compared to other isomeric methoxy analogs of nimesulide ([11C]1b and [11C]1c). [11C]1b–d were synthesized with reasonable yield and purity by the methylation of the O-desmethyl precursor with [11C]methyl triflate in the presence of NaOH at room temperature. We performed in vivo biodistribution analysis, brain PET imaging, ex vivo autoradiography, and metabolite analysis in mice. The uptake of [11C]1b–d was lower in the brain than in other tissues, including in the blood, and both [11C]1c and [11C]1d were rapidly metabolized. However, [11C]1d showed a small, but significant, specific signal and heterogeneous distribution in the brain. In vivo evaluation suggested that [11C]1d might correlate with COX-2 expression in the brain. Given its instability in vivo, [11C]1d seems unsuitable as a brain-COX-2 radioimaging agent. Further structural refinement of these radiotracers is necessary to enhance their uptake in the brain and to achieve sufficient metabolic stability.
我们之前的研究发现,在苯环对位上带有甲氧基取代基的尼美舒利类似物可能是潜在的放射性示踪剂候选物,可用于使用正电子发射断层扫描(PET)检测脑内与环氧化酶-2(COX-2)表达和活性有关的疾病。本研究旨在评估 11C 标记的对甲氧基尼美舒利([11C]1d)与尼美舒利的其他异构甲氧基类似物([11C]1b 和 [11C]1c)相比,作为脑 COX-2 靶向成像剂的体内特性。[11C]1b-d是在室温下,在NaOH存在下,通过用三氯[11C]甲基将O-去甲基前体甲基化而合成的,具有合理的产率和纯度。我们对小鼠进行了体内生物分布分析、脑 PET 成像、体外自显影和代谢物分析。大脑对[11C]1b-d的摄取低于其他组织,包括血液,而且[11C]1c和[11C]1d都被迅速代谢。不过,[11C]1d 在大脑中的特异性信号很小,但很显著,而且分布不均。体内评估表明,[11C]1d 可能与 COX-2 在大脑中的表达有关。鉴于其在体内的不稳定性,[11C]1d 似乎不适合作为脑 COX-2 放射性成像剂。有必要进一步完善这些放射性racers的结构,以提高它们在大脑中的吸收率,并获得足够的代谢稳定性。