Laboratory of Physical Chemistry, Showa Pharmaceutical University, Tokyo, Japan.
Laboratory for Labeling Chemistry, RIKEN Center for Biosystems Dynamics Research, Hyogo, Japan.
J Nucl Med. 2022 Nov;63(11):1761-1767. doi: 10.2967/jnumed.121.263713. Epub 2022 Mar 24.
Cyclooxygenase (COX) is a rate-limiting enzyme in the synthesis of proinflammatory prostanoids from arachidonic acid. In vivo imaging of COX by PET is a potentially powerful tool for assessing the inflammatory response to injury, infection, and disease. We previously reported on a promising PET probe for COX imaging, C-labeled ketoprofen methyl ester, which can detect COX-1 activation in models of neuroinflammation and neurodegenerative disorders. In the current study, we aimed to design a fluorine-substituted benzoyl group of ketoprofen (FKTP) and to evaluate its racemate and enantiomers (F-labeled ketoprofen methyl ester, [F]FKTP-Me) as PET proradiotracers, potential radiopharmaceuticals for in vivo PET study of COX-1. We performed nucleophilic aromatic F-fluorination to obtain the desired racemic radiolabeled probe, ()-[F]FKTP-Me, at a radiochemical yield of 11%-13%. Subsequent high-performance liquid chromatography separation with a chiral column yielded the desired enantiomerically pure ()- and ()-[F]FKTP-Me. We examined the in vivo properties of ()-, ()-, and ()-[F]FKTP-Me in PET studies using rats in which hemispheric inflammation was induced by intrastriatally injecting a lipopolysaccharide. Racemic ()-[F]FKTP-Me and enantiomeric ()- or ()-[F]FKTP-Me were synthesized with radiochemical and chemical purities of more than 99%. The metabolite analysis revealed that the racemic ()-[F]FKTP-Me crossed the blood-brain barrier and entered the brain, where it was subsequently hydrolyzed to its pharmacologically active acid form. PET images revealed a high accumulation of ()-, ()-, and ()-[F]FKTP in the inflamed regions in rat brain. Moreover, the accumulated radioactivity of ()-[F]FKTP-Me was higher than that of ()-[F]FKTP-Me and ()-[F]FKTP-Me, which was correlated with the stereospecific inhibitory activity of FKTP against COX-1. From the results of this study, we conclude that racemic ()-[F]FKTP-Me and its enantiomers could act as proradiotracers of neuroinflammation in rat brain by the association of their hydrolyzed acid forms with COX-1 in inflamed regions. In particular, ()-[F]FKTP-Me demonstrated suitable properties as a COX-1-specific probe in PET imaging of neuroinflammation.
环氧化酶 (COX) 是花生四烯酸合成致炎前列腺素的限速酶。通过正电子发射断层扫描术 (PET) 对 COX 进行体内成像，是评估损伤、感染和疾病炎症反应的一种潜在强大工具。我们之前曾报道过一种有前途的 COX 成像 PET 探针，即 C 标记的酮洛芬甲酯，它可以检测神经炎症和神经退行性疾病模型中的 COX-1 激活。在当前的研究中，我们旨在设计酮洛芬的氟取代苯甲酰基 (FKTP)，并评估其外消旋体和对映异构体 (F 标记的酮洛芬甲酯，[F]FKTP-Me) 作为 PET 前导示踪剂，用于 COX-1 的体内 PET 研究的潜在放射性药物。我们进行了亲核芳香 F 氟化反应，以获得所需的外消旋放射性标记探针 ()-[F]FKTP-Me，放射化学产率为 11%-13%。随后使用手性柱进行高效液相色谱分离，得到所需的对映体纯 ()-和 ()-[F]FKTP-Me。我们使用通过纹状体注射脂多糖诱导半球性炎症的大鼠，在 PET 研究中检查了 ()-[F]FKTP-Me、()-[F]FKTP-Me 和 ()-[F]FKTP-Me 的体内特性。外消旋 ()-[F]FKTP-Me 和对映异构体 ()-或 ()-[F]FKTP-Me 的放射性化学和化学纯度均超过 99%。代谢物分析表明，外消旋 ()-[F]FKTP-Me 穿过血脑屏障进入大脑，随后被水解为其具有药理活性的酸形式。PET 图像显示，在大鼠大脑的炎症区域有大量 ()-[F]FKTP 的积累。此外，()-[F]FKTP-Me 的放射性积累高于 ()-[F]FKTP-Me 和 ()-[F]FKTP-Me，这与 FKTP 对 COX-1 的立体特异性抑制活性相关。从这项研究的结果中，我们得出结论，外消旋 ()-[F]FKTP-Me 及其对映异构体可以通过其水解酸形式与炎症区域的 COX-1 结合，作为大鼠脑中神经炎症的前导示踪剂。特别是，()-[F]FKTP-Me 作为神经炎症的 PET 成像 COX-1 特异性探针表现出合适的特性。
