Li Feng, Jiang Sheng, Zu Youli, Lee Daniel Y, Li Zheng
Department of Translational Imaging, Houston Methodist Research Institute, Weill Cornell Medical College, Houston, Texas
Laboratory of Medicinal Chemistry, Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, China; and.
J Nucl Med. 2014 Sep;55(9):1525-31. doi: 10.2967/jnumed.114.138925. Epub 2014 Jun 26.
Tyrosine kinase receptors including vascular endothelial growth factor receptor (VEGFR) have gained significant attention as pharmacologic targets. However, clinical evaluation of small-molecule drugs or biologics that target these pathways has so far yielded mixed results in a variety of solid tumors. The reasons for response variability remain unknown, including the temporal and spatial patterns of receptor tyrosine kinase expression. Methods to detect and quantify the presence of such cellular receptors would greatly facilitate drug development and therapy response assessment. We aimed to generate specific imaging agents as potential companion diagnostics that could also be used for targeted radionuclide therapy. Here, we report on the synthesis and initial preclinical performance of (64)Cu-labeled probes that were based on the kinase inhibitor already in clinical use, vandetanib (ZD6474), as a VEGFR-selective theranostic radiopharmaceutical.
A monomeric (ZD-G1) and a dimeric (ZD-G2) derivative of ZD6474 were synthesized and conjugated with DOTA for chelation with (64)Cu to produce the probes (64)Cu-DOTA-ZD-G1 and (64)Cu-DOTA-ZD-G2. The binding affinity and specificity to VEGFR were measured using U-87 MG cells known to overexpress VEGFR. Small-animal PET and biodistribution studies were performed with (64)Cu-labeled probes (3-4 MBq) intravenously administered in U-87 MG tumor-bearing mice with or without coinjection of unlabeled ZD-G2 for up to 24 h after injection.
Receptor-binding assays yielded a mean equilibrium dissociation constant of 44.7 and 0.45 nM for monomeric and dimeric forms, respectively, indicating a synergistic effect in VEGFR affinity by multivalency. Small-animal PET/CT imaging showed rapid tumor accumulation of (64)Cu-DOTA-ZD-G2, with excellent tumor-to-normal tissue contrast by 24 h. Coinjection of the (64)Cu-DOTA-ZD-G2 with 50 nmol (60 μg) of nonradioactive ZD-G2 effectively blocked tumor uptake.
A (64)Cu-labeled probe derived from an approved oncologic drug selective for VEGFR demonstrates excellent tumor targeting, particularly for the dimeric form. The multivalent probe yielded a 100-fold improvement in receptor affinity while maintaining pharmacokinetic and biodistribution properties well suited for PET imaging in our preclinical model. These results indicate that a clinically relevant theranostic platform can be rapidly developed from known small molecules that target key cellular receptors.
包括血管内皮生长因子受体（VEGFR）在内的酪氨酸激酶受体作为药物靶点已受到广泛关注。然而，针对这些通路的小分子药物或生物制剂的临床评估在多种实体瘤中迄今产生了喜忧参半的结果。反应变异性的原因尚不清楚，包括受体酪氨酸激酶表达的时间和空间模式。检测和量化此类细胞受体存在的方法将极大地促进药物开发和治疗反应评估。我们旨在生成特定的成像剂作为潜在的伴随诊断工具，也可用于靶向放射性核素治疗。在此，我们报告基于已在临床使用的激酶抑制剂凡德他尼（ZD6474）合成的（64）Cu标记探针作为VEGFR选择性诊疗放射性药物的合成及初步临床前性能。
合成ZD6474的单体（ZD-G1）和二聚体（ZD-G2）衍生物，并与DOTA偶联以与（64）Cu螯合，制备探针（64）Cu-DOTA-ZD-G1和（64）Cu-DOTA-ZD-G2。使用已知过表达VEGFR的U-87 MG细胞测量对VEGFR的结合亲和力和特异性。在荷U-87 MG肿瘤小鼠中静脉注射（64）Cu标记的探针（3 - 4 MBq），有或没有同时注射未标记的ZD-G2，进行小动物PET和生物分布研究，注射后长达24小时。
受体结合试验得出单体和二聚体形式的平均平衡解离常数分别为44.7和0.45 nM，表明多价性对VEGFR亲和力有协同作用。小动物PET/CT成像显示（64）Cu-DOTA-ZD-G2在肿瘤中快速聚集，到24小时时肿瘤与正常组织对比度极佳。将（64）Cu-DOTA-ZD-G2与50 nmol（60 μg）非放射性ZD-G2同时注射可有效阻断肿瘤摄取。
源自一种已获批准的对VEGFR有选择性的肿瘤药物的（64）Cu标记探针显示出优异的肿瘤靶向性，特别是二聚体形式。在我们的临床前模型中，多价探针在保持适合PET成像的药代动力学和生物分布特性的同时，使受体亲和力提高了100倍。这些结果表明，可以从靶向关键细胞受体的已知小分子快速开发出临床相关的诊疗平台。
