Karmanos Cancer Institute, Wayne State University, Detroit, MI, 48202, USA.
PET Center, Wayne State University, Detroit, MI, 48202, USA.
Mol Imaging Biol. 2018 Aug;20(4):594-604. doi: 10.1007/s11307-017-1149-8.
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 (K/K 716.5 ± 72.8, 615.4 ± 50.5, 269.5 ± 52.1/s mol, respectively). Radiosynthesis of 12- [F]fluorododecanoic aminohexanoicanilide (12-[F]DDAHA) was achieved by nucleophilic radiofluorination of 12-iododecanoic-AHA precursor.
A significantly higher accumulation of 12-[F]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-[F]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.
本研究旨在开发一种 SIRT2 特异性底物型放射性示踪剂，用于非侵入性正电子发射断层扫描（PET）成像，以研究 SIRT2 在正常组织和疾病组织中介导的表观遗传调控过程。
用含有叔丁氧羰基-赖氨酸-氨甲基香豆素骨架的化合物库进行衍生化，得到长度为 3-16 个碳原子的氟烷基链。SIRT2 最有效地切割豆蔻酰基，其次是 12-氟十二烷酸和 10-氟癸酸基团（K/K716.5±72.8、615.4±50.5、269.5±52.1/s mol，分别）。通过亲核放射性氟化 12-碘代十二烷酸-AHA 前体，实现了 12-[F]氟十二烷酸氨基己酰苯胺（12-[F]DDAHA）的放射性合成。
与 U87、MiaPaCa 和 MCF10A 相比，MCF-7 和 MDA-MB-435 细胞在体外的 12-[F]DDAHA 积累明显更高，这与 SIRT2 表达水平一致。在 9L 胶质母细胞瘤荷瘤大鼠中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脱氟，这一点可通过 F-18 放射性在颅骨和其他骨骼中的大量积累得到证明，这给肿瘤和大脑其他区域内示踪剂积累的图像解释带来了困难。
应使用 DDAHA 脂肪链上替代的放射性氟化部位开发对全身脱氟具有抗性的新一代 SIRT2 特异性放射性示踪剂。SIRT2 选择性放射性示踪剂可提供关于肿瘤和正常器官和组织中 SIRT2 表达和活性的信息，这可能有助于更好地了解 SIRT2 在不同疾病中的作用。
