The chemokine receptor 4 (CXCR4) is an important molecular target for both visualization and therapy of tumors. The aim of the present study was the synthesis and preclinical evaluation of a 64Cu-labeled, CXCR4-targeting peptide for positron emission tomography (PET) imaging of CXCR4 expression in vivo. For this purpose, 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), or 1,4,7-triazacyclononane-triacetic acid (NOTA) was conjugated to the highly affine CXCR4-targeting pentixather scaffold. Affinities were determined using Jurkat T-lymphocytes in competitive binding assays employing [125I]FC131 as the radioligand. Internalization and efflux studies of [64Cu]NOTA-pentixather were performed in chem-1 cells, stably transfected with hCXCR4. The stability of the tracer was evaluated in vitro and in vivo. Small-animal PET and biodistribution studies at different time points were performed in Daudi lymphoma-bearing severe combined immunodeficiency (SCID) mice. [64Cu]NOTA-pentixather was rapidly radiolabeled at 60 °C with high radiochemical yields ≥90% and purities >99%. [64Cu]NOTA-pentixather offered the highest affinity of the evaluated peptides in this study (IC50 = 14.9 ± 2.1 nM), showed efficient CXCR4-targeting in vitro and was stable in blood and urine with high resistance to transchelation in ethylenediaminetetraacetic acid (EDTA) challenge studies. Due to the enhanced lipophilicity of [64Cu]NOTA-pentixather (logP = -1.2), biodistribution studies showed some nonspecific accumulation in the liver and intestines. However, tumor accumulation (13.1 ± 1.5% ID/g, 1.5 h p.i.) was CXCR4-specific and higher than in all other organs and resulted in high resolution delineation of Daudi tumors in PET/CT images in vivo. [64Cu]NOTA-pentixather was fast and efficiently radiolabeled, showed effective CXCR4-targeting, high stability in vitro and in vivo and resulted in high resolution PET/CT images accompanied with a suitable biodistribution profile, making [64Cu]NOTA-pentixather a promising tracer for future application in humans.

中文翻译：

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[64Cu]NOTA-pentixather 能够对临床前淋巴瘤模型中的 CXCR4 表达进行高分辨率 PET 成像。

趋化因子受体 4 (CXCR4) 是肿瘤可视化和治疗的重要分子靶点。本研究的目的是合成 64Cu 标记的 CXCR4 靶向肽，用于体内 CXCR4 表达的正电子发射断层扫描 (PET) 成像，并进行临床前评估。为此，将 1,4,7-三氮杂环壬烷,1-戊二酸-4,7-乙酸 (NODAGA) 或 1,4,7-三氮杂环壬烷-三乙酸 (NOTA) 缀合至高度亲和力的 CXCR4 靶向pentixather 支架。在使用[125I]FC131作为放射性配体的竞争性结合测定中，使用Jurkat T淋巴细胞测定亲和力。[64Cu]NOTA-pentixather 的内化和外排研究在稳定转染 hCXCR4 的 chem-1 细胞中进行。在体外和体内评估了示踪剂的稳定性。在患有 Daudi 淋巴瘤的严重联合免疫缺陷 (SCID) 小鼠中进行了不同时间点的小动物 PET 和生物分布研究。[64Cu]NOTA-pentixather 在 60 °C 下快速放射性标记，放射化学产率高达 ≥90%，纯度 >99%。[64Cu]NOTA-pentixather 在本研究中提供了所评估肽的最高亲和力 (IC50 = 14.9 ± 2.1 nM)，在体外表现出高效的 CXCR4 靶向性，并且在血液和尿液中稳定，对乙二胺四乙酸 (EDTA) 中的转螯合具有高抗性）挑战研究。由于[64Cu]NOTA-pentixather 的亲脂性增强（logP = -1.2），生物分布研究显示在肝脏和肠道中存在一些非特异性积累。然而，肿瘤积累（13.1 ± 1.5% ID/g，注射后 1.5 小时）是 CXCR4 特异性的，并且高于所有其他器官，并导致体内 PET/CT 图像中 Daudi 肿瘤的高分辨率描绘。[64Cu]NOTA-pentixather 可以快速有效地进行放射性标记，显示出有效的 CXCR4 靶向性、体外和体内的高稳定性，并产生高分辨率 PET/CT 图像以及合适的生物分布曲线，使 [64Cu]NOTA-pentixather 成为一种有前景的药物未来在人类中应用的示踪剂。