[18F]- and [11C]-Labeled N-benzyl-isatin sulfonamide analogues as PET tracers for Apoptosis: synthesis, radiolabeling mechanism, and in vivo imaging study of apoptosis in Fas-treated mice using [11C]WC-98
作者:Dong Zhou、Wenhua Chu、Delphine L. Chen、Qi Wang、David E. Reichert、Justin Rothfuss、Andre D'Avignon、Michael J. Welch、Robert H. Mach
DOI:10.1039/b819024k
日期:——
The radiolabeled isatin sulfonamide caspase-3 inhibitor, [18F]2 (WC-II-89), is a potential PET radiotracer for noninvasive imaging of apoptosis. The radiolabeling mechanism was studied by 13C NMR, ESI/MS, and computational calculations. It was found that the high electrophilicity of the C3 carbonyl group in the isatin ring, which served as a trap for [18F]fluoride, was responsible for the failure of the radiolabeling via nucleophilic substitution of the mesylate group in 7a by [18F]fluoride. Once treated with a strong base, 7a opened the isatin ring completely to form an isatinate intermediate 16, which lost the ability to trap [18F]fluoride, thereby allowing the displacement of the mesylate group to afford the 18F-labeled isatinate 17. [18F]17 can be converted to isatin [18F]2 efficiently under acidic conditions. The ring-opening and re-closure of the isatin ring under basic and acidic conditions were confirmed by reversed phase HPLC analysis, ESI/MS and 13C NMR studies. Computational studies of model compounds also support the above proposed mechanism. Similarly, the ring-opening and re-closure method was used successfully in the synthesis of the 11C labeled isatin sulfonamide analogue [11C]4 (WC-98). A microPET imaging study using [11C]4 in the Fas liver apoptosis model demonstrated retained activity in the target organ (liver) of the treated mice. Increased caspase-3 activation in the liver was verified by the fluorometric caspase-3 enzyme assay. Therefore, this study provides a useful method for radio-synthesis of isatin derivative radiotracers for PET and SPECT studies, and [11C]4 is a potential PET radiotracer for noninvasive imaging of apoptosis.
放射性标记的isatin磺酰胺类caspase-3抑制剂[18F]2 (WC-II-89)是一种潜在的PET放射性示踪剂,可用于细胞凋亡的无创成像。研究人员通过 13C NMR、ESI/MS 和计算对其放射性标记机制进行了研究。研究发现,isatin 环中 C3 羰基的亲电性很高,是[18F]氟化物的捕获物,这也是 7a 中的甲磺酸基团被[18F]氟化物亲核取代而导致放射性标记失败的原因。经强碱处理后,7a 完全打开了异汀环,形成了异汀酸酯中间体 16,该中间体失去了捕获[18F]氟化物的能力,从而使间苯二甲酸酯基团发生位移,得到了 18F 标记的异汀酸酯 17。在酸性条件下,[18F]17 可以高效地转化为异汀[18F]2。反相 HPLC 分析、ESI/MS 和 13C NMR 研究证实了在碱性和酸性条件下异atin 环的开环和再闭环。对模型化合物的计算研究也支持上述机制。同样,开环和再闭环法也被成功用于合成 11C 标记的靛红磺酰胺类似物 [11C]4 (WC-98)。在 Fas 肝细胞凋亡模型中使用 [11C]4 进行的 microPET 成像研究表明,经处理的小鼠的靶器官(肝脏)中保留了[11C]4 的活性。肝脏中激活的 Caspase-3 增加通过荧光法 Caspase-3 酶测定得到了验证。因此,这项研究为 PET 和 SPECT 研究提供了一种放射性合成异汀衍生物放射性示踪剂的有用方法,[11C]4 是一种潜在的 PET 放射性示踪剂,可用于细胞凋亡的无创成像。