Radiosynthesis and Evaluation of 11C-Labeled Diaryl-Substituted Imidazole and Indole Derivatives for Mapping Cyclooxygenase-2
作者:Mariko Tanaka、Yoshihiko Fujisaki、Kazunori Kawamura、Kiichi Ishiwata、Qinggeletu、Fumihiko Yamamoto、Takahiro Mukai、Minoru Maeda
DOI:10.1248/bpb.29.2087
日期:——
11C-Labeled analogs of 4-chloro-5-(3-fluoro-4-methoxyphenyl)-1-(4-methylsulfonylphenyl)imidazole ([11C]1), 4-[4-chloro-5-(3-fluoro-4-methoxyphenyl)imidazol-1-yl]benzenesulfonamide ([11C]2) and 2-(4-aminosulfonylphenyl)-3-(4-methoxyphenyl)indole ([11C]3), which have been shown to have excellent potency and high selectivity for cyclooxygenase isoform 2 (COX-2) inhibiting activity, were prepared and evaluated in rats as potential radiopharmaceuticals for imaging the COX-2 enzyme by positron emission tomography. These 11C-labeled COX-2 inhibitors were synthesized in high radiochemical yields by O-[11C]methylation of phenolic precursors with [11C]methyl triflate in acetone containing NaOH as a base. In vivo evaluation in rats bearing AH109A hepatoma showed no specific binding of any tracer to COX-2 in any tissue such as the brain, heart, lung, kidney, and AH109A hepatoma. In ex vivo autoradiography, [11C]1 showed regionally different distribution in the brain, while [11C]2 and [11C]3 were not substantially taken up by the brain. In in vitro monolayer efflux assays, compound 3 was found to be a substrate for the P-glycoprotein (P-gp) efflux pump, but pretreatment of rats with the potent P-gp inhibitor, cyclosporine A, did not have any significant influence on the cerebral uptake of [11C]3. These results indicate that all three tracers were not suitable for in vivo imaging of COX-2. There seem to be some obstacles to finding a useful candidate for in vivo imaging application of COX-2 selective inhibitors only by standard consideration of in vitro affinity and selectivity, and the lipophilicity of the compound.
11C 标记的 4-氯-5-(3-氟-4-甲氧基苯基)-1-(4-甲磺酰基苯基)咪唑类似物([11C]1)、4-[4-氯-5-(3-氟-4-甲氧基苯基)咪唑-1-基]苯磺酰胺类似物([11C]2)和 2-(4-氨基磺酰基苯基)-3-(4-甲氧基苯基)吲哚类似物([11C]3)、制备出了对环氧化酶同工酶 2(COX-2)抑制活性具有卓越效力和高选择性的 11C 标记 COX-2 放射性药物,并在大鼠体内进行了评估,以作为通过正电子发射断层扫描对 COX-2 酶进行成像的潜在放射性药物。这些 11C 标记的 COX-2 抑制剂是通过在含 NaOH 作为碱的丙酮中用 [11C]methyl triflate 对酚类前体进行 O-[11C]methylation 合成的,具有很高的放射化学收率。在患有 AH109A 肝瘤的大鼠身上进行的体内评估显示,在大脑、心脏、肺、肾和 AH109A 肝瘤等任何组织中,任何示踪剂都没有与 COX-2 发生特异性结合。在体外自显影中,[11C]1 在大脑中显示出不同的区域分布,而[11C]2 和[11C]3 并未被大脑大量吸收。在体外单层外排试验中,发现化合物 3 是 P-糖蛋白(P-gp)外排泵的底物,但用强效 P-gp 抑制剂环孢素 A 预处理大鼠并没有对大脑摄取 [11C]3 产生任何显著影响。这些结果表明,这三种示踪剂都不适合用于 COX-2 的体内成像。仅从体外亲和性和选择性以及化合物的亲脂性等标准考虑,要找到一种适用于 COX-2 选择性抑制剂体内成像应用的候选化合物似乎还存在一些障碍。