Expression of the chemokine receptor chemokine C-X-C motif receptor 4 (CXCR4) plays an important role in cancer metastasis, in autoimmune diseases, and during stem cell-based repair processes after stroke and myocardial infarction. Previously reported PET imaging agents targeting CXCR4 suffer from either high nonspecific uptake or bind only to the human form of the receptor. The objective of this study was to develop a high-stability 64Cu-labeled small-molecule PET agent for imaging both human and murine CXCR4 chemokine receptors. Methods: Synthesis, radiochemistry, stability and radioligand binding assays were performed for the novel tracer 64Cu-CuCB-bicyclam. In vivo dynamic PET studies were performed on mice bearing U87 (CXCR4 low-expressing) and U87.CXCR4 (human-CXCR4 high-expressing) tumors. Biodistribution and receptor blocking studies were performed on CD1-IGS immunocompetent mice. CXCR4 expression on tumor and liver disaggregates was confirmed using a combination of immunohistochemistry, quantitative polymerase chain reaction, and Western blot. Results: 64Cu-CuCB-bicyclam has a high affinity for both the human and the murine variants of the CXCR4 receptor (half-maximal inhibitory concentration, 8 nM [human]/2 nM [murine]) and can be obtained from the parent chelator that has low affinity. In vitro and in vivo studies demonstrate specific uptake in CXCR4-expressing cells that can be blocked by more than 90% using a higher-affinity antagonist, with limited uptake in non-CXCR4-expressing organs and high in vivo stability. The tracer was also able to selectively displace the CXCR4 antagonists AMD3100 and AMD3465 from the liver. Conclusion: The tetraazamacrocyclic small molecule 64Cu-CuCB-bicyclam has been shown to be an imaging agent for the CXCR4 receptor that is likely to be applicable across a range of species. It has high affinity and stability and is suitable for preclinical research in immunocompetent murine models.

中文翻译：

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CXCR4 趋化因子受体的 64Cu PET 成像，使用交叉桥接的 Cyclam Bis-Tetraazamacrocyclic 拮抗剂。

趋化因子受体趋化因子 CXC 基序受体 4 (CXCR4) 的表达在癌症转移、自身免疫性疾病以及中风和心肌梗塞后基于干细胞的修复过程中发挥重要作用。先前报道的靶向 CXCR4 的 PET 显像剂要么具有高非特异性摄取，要么仅与人类形式的受体结合。本研究的目的是开发一种高稳定性 64Cu 标记的小分子 PET 试剂，用于对人和鼠 CXCR4 趋化因子受体进行成像。方法：对新型示踪剂 64Cu-CuCB-bicyclam 进行合成、放射化学、稳定性和放射性配体结合测定。对携带 U87（CXCR4 低表达）和 U87.CXCR4（人-CXCR4 高表达）肿瘤的小鼠进行体内动态 PET 研究。对 CD1-IGS 免疫活性小鼠进行生物分布和受体阻断研究。使用免疫组织化学、定量聚合酶链反应和蛋白质印迹的组合证实了肿瘤和肝脏分解物上的 CXCR4 表达。结果：64Cu-CuCB-bicyclam 对人和小鼠的 CXCR4 受体变体具有高亲和力（半数最大抑制浓度，8 nM [人]/2 nM [小鼠]），并且可以从亲本螯合剂中获得亲和力低的那个。体外和体内研究表明，在表达 CXCR4 的细胞中，使用更高亲和力的拮抗剂可阻断超过 90% 的特异性摄取，在非表达 CXCR4 的器官中摄取有限且体内稳定性高。示踪剂还能够选择性地从肝脏中置换出 CXCR4 拮抗剂 AMD3100 和 AMD3465。结论：四氮杂大环小分子 64Cu-CuCB-bicyclam 已被证明是 CXCR4 受体的显像剂，可能适用于多种物种。它具有高亲和力和稳定性，适用于免疫活性小鼠模型的临床前研究。