11C-Labeled Analogs of Indomethacin Esters and Amides for Brain Cyclooxygenase-2 Imaging: Radiosynthesis, in Vitro Evaluation and in Vivo Characteristics in Mice
作者:Yumi Yamamoto、Jun Toyohara、Kiichi Ishiwata、Kohei Sano、Fumihiko Yamamoto、Takahiro Mukai、Minoru Maeda
DOI:10.1248/cpb.59.938
日期:——
There is great potential in the use of positron emission tomography (PET) and suitable radiotracers for the study of cyclooxygenase type 2 (COX-2) enzyme in living subjects. In the present study, we prepared and evaluated five 11C-labeled ester and amide analogs derived from indomethacin as potential PET imaging agents for the in vivo visualization of the brain COX-2 enzyme. Five 11C-labeled COX-2 inhibitors, with different lipophilicities and moderate COX-2 inhibitory activity, were prepared by treatment of the corresponding O-desmethyl precursors with [11C]methyl triflate and purified by HPLC (radiochemical yields of 55—71%, radiochemical purity of >93%, and the specific activities of 22—331 GBq/μmol). In mice, radioactivity in the brain for all radiotracers was low, with very low brain-to-blood ratios. A clear inverse relationship was observed between brain uptake at 1 min postinjection and the lipophilicity (experimental log P7.4) of the studied 11C-radiotracers. Pretreatment of mice with cyclosporine A to block P-glycoproteins caused a significant increase in brain uptake of radioactivity following injection of the 11C-radiotracer compared to control. HPLC analysis showed that each radiotracer was rapidly metabolized, and a few metabolites, which were more polar than the original radiotracers, were found in both plasma and brain. No specific binding of the tracers towards the COX-2 enzyme in the brain was clearly revealed by in vivo blocking study. Further structural refinement of the tracer agent is necessary for better enhancement of brain uptake and for sufficient metabolic stability.
使用正电子发射断层扫描 (PET) 和合适的放射性示踪剂来研究活体中的 2 型环氧合酶 (COX-2) 具有巨大的潜力。在本研究中,我们制备并评估了五种源自吲哚美辛的 11C 标记的酯和酰胺类似物,作为脑 COX-2 酶体内可视化的潜在 PET 成像剂。通过用[11C]三氟甲磺酸甲酯处理相应的O-去甲基前体,制备了五种具有不同亲脂性和中等COX-2抑制活性的11C标记COX-2抑制剂,并通过HPLC纯化(放射化学收率55-71%,放射化学纯度>93%,比活度22—331 GBq/μmol)。在小鼠中,所有放射性示踪剂的大脑中的放射性都很低,脑与血液的比率非常低。注射后 1 分钟的脑摄取与所研究的 11C 放射性示踪剂的亲脂性(实验日志 P7.4)之间观察到明显的负相关关系。与对照组相比,用环孢菌素 A 预处理小鼠以阻断 P-糖蛋白,在注射 11C-放射性示踪剂后,小鼠大脑对放射性的吸收显着增加。 HPLC分析表明,每种放射性示踪剂都迅速代谢,并且在血浆和脑中都发现了一些比原始放射性示踪剂极性更强的代谢物。体内阻断研究清楚地揭示了示踪剂与大脑中 COX-2 酶没有特异性结合。示踪剂的进一步结构细化对于更好地增强大脑摄取和足够的代谢稳定性是必要的。