A Novel Substrate Radiotracer for Molecular Imaging of SIRT2 Expression and Activity with Positron Emission Tomography
作者:Robin E. Bonomi、Maxwell Laws、Vadim Popov、Swatabdi Kamal、Shreya Potukutchi、Aleksandr Shavrin、Xin Lu、Nashaat Turkman、Ren-Shyan Liu、Thomas Mangner、Juri G. Gelovani
DOI:10.1007/s11307-017-1149-8
日期:2018.8
The purpose of this study was to develop a SIRT2-specific substrate-type radiotracer for non-invasive PET imaging of epigenetic regulatory processes mediated by SIRT2 in normal and disease tissues. A library of compounds containing tert-butyloxycarbonyl-lysine-aminomethylcoumarin backbone was derivatized with fluoroalkyl chains 3–16 carbons in length. SIRT2 most efficiently cleaved the myristoyl, followed by 12-fluorododecanoic and 10-fluorodecanoic groups (Kcat/Km 716.5 ± 72.8, 615.4 ± 50.5, 269.5 ± 52.1/s mol, respectively). Radiosynthesis of 12- [18F]fluorododecanoic aminohexanoicanilide (12-[18F]DDAHA) was achieved by nucleophilic radiofluorination of 12-iododecanoic-AHA precursor. A significantly higher accumulation of 12-[18F]DDAHA was observed in MCF-7 and MDA-MB-435 cells in vitro as compared to U87, MiaPaCa, and MCF10A, which was consistent with levels of SIRT2 expression. Initial in vivo studies using 12-[18F]DDAHA conducted in a 9L glioma-bearing rats were discouraging, due to rapid defluorination of this radiotracer upon intravenous administration, as evidenced by significant accumulation of F-18 radioactivity in the skull and other bones, which confounded the interpretation of images of radiotracer accumulation within the tumor and other regions of the brain. The next generation of SIRT2-specific radiotracers resistant to systemic defluorination should be developed using alternative sites of radiofluorination on the aliphatic chain of DDAHA. A SIRT2-selective radiotracer may provide information about SIRT2 expression and activity in tumors and normal organs and tissues, which may help to better understand the roles of SIRT2 in different diseases.
本研究的目的是开发一种特异性针对SIRT2的底物型放射性示踪剂,以便对正常和病变组织中由SIRT2介导的表观遗传调控过程进行非侵入性PET成像。我们制备了一系列包含叔丁氧羰基-赖氨酸-氨甲基香豆素主链的化合物,并用长度为3至16个碳的氟烷基链进行衍生化。SIRT2最有效地切割肉豆蔻酰基,其次是12-氟十二酸和10-氟十酸基团(Kcat/Km 716.5 ± 72.8、615.4 ± 50.5、269.5 ± 52.1/s mol,分别)。通过对12-碘十二酸-AHA前体进行亲核放射性氟化,成功合成了12-[18F]氟十二酸氨己酰胺(12-[18F]DDAHA)。在体外研究中,MCF-7和MDA-MB-435细胞中观察到12-[18F]DDAHA的显著更高积累,与U87、MiaPaCa和MCF10A细胞相比,这与SIRT2的表达水平一致。对9L胶质瘤-bearing大鼠进行的初步体内研究结果令人沮丧,因为该放射性示踪剂在静脉给药后迅速去氟化,导致F-18放射活性在颅骨和其他骨骼中的显著积累,从而使得肿瘤及脑部其他区域示踪剂积累图像的解读变得困难。下一代抵抗系统性去氟化的SIRT2特异性放射性示踪剂应使用DDAHA脂肪链上的其他氟化位点进行开发。SIRT2选择性放射性示踪剂可能提供肿瘤和正常器官及组织中SIRT2表达和活性的信息,帮助更好地理解SIRT2在不同疾病中的作用。