Locoregionally administered, NK1 receptor (NK1R) targeted radionuclide therapy is a promising strategy for the treatment of glioblastoma multiforme. So far, the radiopharmaceuticals used in this approach have been based on the endogenous agonist of NK1R, Substance P or on its close analogues. Herein, we used a well-known, small molecular NK1R antagonist, L732,138, as the basis for the radiopharmaceutical vector. First, 14 analogues of this compound were evaluated to check whether extending the parent structure with linkers of different lengths would not deteriorate the NK1R binding. The tested analogues had affinity similar to or better than the parent compound, and none of the linkers had a negative impact on the binding. Next, five DOTA conjugates were synthesized and used for labelling with 68Ga and 177Lu. The obtained radioconjugates turned out to be fairly lipophilic but showed rather limited stability in human plasma. Evaluation of the receptor affinity of the (radio)conjugates showed that neither the chelator nor the metal negatively impacts the NK1R binding. The 177Lu-radioconjugates exhibited the binding characteristics towards NK1R similar or better than that of the 177Lu-labelled derivative of Substance P, which is in current clinical use. The experimental results presented herein, along with their structural rationalization provided by modelling, give insight for the further molecular design of small molecular NK1R-targeting vectors.
局部注射的NK1受体(NK1R)靶向放射性药物治疗是治疗多形性胶质母细胞瘤的一种有前途的策略。目前,这种方法中使用的放射性药物基于NK1R的内源性激动剂物质P或其近似物。在这里,我们使用一种广为人知的小分子NK1R拮抗剂L732,138作为放射性药物载体的基础。首先,评估了14个这种化合物的类似物,以检查使用不同长度的连接剂扩展父结构是否会恶化NK1R结合。测试的类似物具有与父化合物相似或更好的亲和力,而且连接剂都没有对结合产生负面影响。接下来,合成了五个DOTA结合物,并用68Ga和177Lu进行标记。获得的放射性结合物相当亲脂性,但在人类血浆中的稳定性相当有限。评估(放射性)结合物的受体亲和力表明,螯合剂或金属都不会对NK1R结合产生负面影响。177Lu-放射性结合物表现出与目前临床使用的物质P的177Lu标记衍生物相似或更好的NK1R结合特性。本文所提供的实验结果以及建模提供的结构合理化为小分子NK1R靶向载体的进一步分子设计提供了见解。