Zeng Jun, Liu Ci-yi, Xie Wen-hui, Hu Si-long, Jin Mu-xiu
Department of Nuclear Medicine, Shanghai Chest Hospital, Shanghai Jiao-Tong University, 241 Hui-hai Road, Shanghai 200030, China.
Chin Med J (Engl). 2006 Sep 5;119(17):1435-43.
Screening libraries against a molecular target in vitro are idealized models that cannot reflect the real state in vivo where biomolecules coexist and interact. C-terminal amide tripeptides labelled with Technetium-99m can provide a unique noninvasive approach to trace a large number of compounds in vivo.
The C-terminal amide tripeptide libraries were synthesized on Rink Amide-MBHA resin using iterative and pooling protocol. Technetium (V) oxo core [TcO(3+)] was bound to each tripeptide via 4 deprotonated nitrogen atoms to form a library of 8000 (99m)Tc tripeptoid complexes. The radiocombinatorial screening (RCS) in vivo was carried out on SD rats and A549 tumour bearing mice.
Signals of tissue distribution and metabolism of libraries were recorded by counting or imaging and tissue targeting leads identified by both random and directed RCS. Among them, (99m)Tc RPA, (99m)Tc VIG and (99m)Tc RES had specific tissue targeting in kidney, liver and tumour respectively. The percent injected dose per gram tissue of (99m)Tc labelled leads in their target tissue was highly structure dependent. Because the nontarget tissue binding and the metabolism of (99m)Tc tripeptoid sublibraries were simultaneously monitored successfully by RCS, the interference of background activity was limited to the lowest level. Optimization of renal function agent from the labelled libraries was carried out by directed screening. (99m)Tc DSG was finally identified the most promising agent for renal function studies.
RCS in vivo is a powerful tool for the discovery of tissue targeting drugs. The potential screening bias is probably the major limitation of labelled libraries.
体外针对分子靶点筛选文库是理想化模型，无法反映生物分子共存并相互作用的体内真实状态。用99m锝标记的C末端酰胺三肽可为体内追踪大量化合物提供独特的非侵入性方法。
采用迭代和混合方案在Rink酰胺-MBHA树脂上合成C末端酰胺三肽文库。锝（V）氧核心[TcO(3+)]通过4个去质子化氮原子与每个三肽结合，形成一个包含8000个99mTc三肽类配合物的文库。对SD大鼠和荷A549肿瘤小鼠进行体内放射组合筛选（RCS）。
通过计数或成像记录文库的组织分布和代谢信号，并通过随机和定向RCS识别组织靶向先导物。其中，99mTc RPA、99mTc VIG和99mTc RES分别在肾脏、肝脏和肿瘤中具有特异性组织靶向性。99mTc标记先导物在其靶组织中的每克组织注射剂量百分比高度依赖于结构。由于通过RCS成功同时监测了99mTc三肽类亚文库的非靶组织结合和代谢，背景活性干扰被限制到最低水平。通过定向筛选对标记文库中的肾功能剂进行优化。最终确定99mTc DSG是最有前景的肾功能研究药物。
体内RCS是发现组织靶向药物的有力工具。潜在的筛选偏差可能是标记文库的主要局限性。
