Coordination-Mediated Synthesis of <sup>67</sup>Ga-Labeled Purification-Free Trivalent Probes for in Vivo Imaging of Saturable Systems
作者:Holis A. Holik、Tomoya Uehara、Soki Nemoto、Takemi Rokugawa、Yuumi Tomizawa、Ayako Sakuma、Yuki Mizuno、Hiroyuki Suzuki、Yasushi Arano
DOI:10.1021/acs.bioconjchem.8b00337
日期:2018.9.19
A large excess of unlabeled ligands over gallium-67 (67Ga) provides 67Ga-labeled probes with high radiochemical yields in a short reaction time. However, the unlabeled ligands hinder target accumulation of radiolabeled probes by competing for target molecules. To circumvent the problem, we investigated the way to prepare 67Ga-labeled multivalent probes from monovalent ligands. The reaction of a bi- or tridentate ligand with [67Ga]Ga-citrate resulted in 67Ga-labeled probes of insufficient stability. However, the reaction of [67Ga]Ga-citrate with a mixture of RGD-conjugated salicylaldehyde and triamine provided a 67Ga-labeled trivalent probe with stability sufficient for in vivo applications. Since the free Schiff base ligand decomposed rapidly upon injection, the 67Ga-labeled trivalent probe visualized the murine tumor without postlabeling purification, which was not achieved with a 67Ga-labeled trivalent probe from a trivalent ligand. These findings indicate the availability of Schiff base ligands to prepare 67Ga-labeled trivalent probes by a simple radiolabeling procedure.
大量未标记的配体相对于镓-67 (67Ga) 的过量提供了在短时间内获得高放射化学产率的67Ga标记探针。然而,未标记的配体通过竞争靶分子而妨碍了放射性标记探针的靶向聚集。为了解决这个问题,我们研究了如何从单价配体制备67Ga标记的多价探针。双齿或三齿配体与[67Ga]Ga-柠檬酸的反应产生的67Ga标记探针稳定性不足。然而,[67Ga]Ga-柠檬酸与RGD结合的水杨醛和三胺混合物的反应则提供了一种具有足够稳定性用于体内应用的67Ga标记三价探针。由于游离的希夫碱配体在注射后迅速降解,因此67Ga标记的三价探针能够在没有后标记纯化的情况下可视化小鼠肿瘤,而这在由三价配体制备的67Ga标记三价探针中无法实现。这些发现表明希夫碱配体可通过简单的放射性标记程序制备67Ga标记的三价探针。