PURPOSE Abnormal CD38 expression in some hematologic malignancies, including lymphoma, has made it a biomarker for targeted therapies. Daratumumab (Dara) is the first FDA-approved CD38-specific monoclonal antibody, enabling successfully immunoPET imaging over the past years. Radiolabeled Dara however has a long blood circulation and delayed tumor uptake which can limit its applications. The focus of this study is to develop 64Cu-labeled Dara-F(ab')2 for the visualization of CD38 in lymphoma models. METHODS F(ab')2 fragment was prepared from Dara using an IdeS enzyme and purified with Protein A beads. Western blotting, flow cytometry, and surface plasmon resonance (SPR) were performed for in vitro assay. Probes were labeled with 64Cu after the chelation of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). Small animal PET imaging and quantitative analysis were performed after injection of 64Cu-labeled Dara-F(ab')2, IgG-F(ab')2, and Dara for evaluation in lymphoma models. RESULTS Flow cytometry and SPR assay proved the specific binding ability of Dara-F(ab')2 and NOTA-Dara-F(ab')2 in vitro. Radiolabeling yield of [64Cu]Cu-NOTA-Dara-F(ab')2 was over 90% and with a specific activity of 4.0 ± 0.6 × 103 MBq/μmol (n = 5). PET imaging showed [64Cu]Cu-NOTA-Dara-F(ab')2 had a rapid and high tumor uptake as early as 2 h (6.9 ± 1.2%ID/g) and peaked (9.5 ± 0.7%ID/g) at 12 h, whereas [64Cu]Cu-NOTA-Dara reached its tumor uptake peaked at 48 h (8.3 ± 1.4%ID/g, n = 4). In comparison, IgG-F(ab')2 and HBL-1 control groups found no noticeable tumor uptake. [64Cu]Cu-NOTA-Dara-F(ab')2 had significantly lower uptake in blood pool, bone, and muscle than [64Cu]Cu-NOTA-Dara and its tumor-to-blood and tumor-to-muscle ratios were significantly higher than controls. CONCLUSIONS [64Cu]Cu-NOTA-Dara-F(ab')2 showed a rapid and high tumor uptake in CD38-positive lymphoma models with favorable imaging contrast, showing its promise as a potential PET imaging agent for future clinical applications.

中文翻译：

---

64Cu 标记的 daratumumab F(ab')2 片段可实现 CD38 阳性淋巴瘤的早期可视化。

目的 CD38 在某些血液系统恶性肿瘤（包括淋巴瘤）中的异常表达使其成为靶向治疗的生物标志物。Daratumumab (Dara) 是第一个获得 FDA 批准的 CD38 特异性单克隆抗体，在过去几年中成功实现了免疫 PET 成像。然而，放射性标记的 Dara 具有较长的血液循环和延迟的肿瘤摄取，这可能会限制其应用。本研究的重点是开发 64Cu 标记的 Dara-F(ab')2，用于淋巴瘤模型中 CD38 的可视化。方法 F(ab')2 片段是使用 IdeS 酶从 Dara 制备的，并用蛋白 A 珠纯化。对体外测定进行了蛋白质印迹、流式细胞术和表面等离子体共振 (SPR)。在螯合 1,4,7-三氮杂环壬烷-1,4,7-三乙酸 (NOTA) 后，用 64Cu 标记探针。在注射 64Cu 标记的 Dara-F(ab')2、IgG-F(ab')2 和 Dara 后进行小动物 PET 成像和定量分析，以评估淋巴瘤模型。结果流式细胞术和SPR实验证明了Dara-F(ab')2和NOTA-Dara-F(ab')2在体外具有特异性结合能力。[64Cu]Cu-NOTA-Dara-F(ab')2 的放射性标记产率超过 90%，比活性为 4.0 ± 0.6 × 103 MBq/μmol (n = 5)。PET 成像显示 [64Cu]Cu-NOTA-Dara-F(ab')2 早在 2 小时 (6.9 ± 1.2%ID/g) 就具有快速和高的肿瘤摄取，并达到峰值 (9.5 ± 0.7%ID/g)在 12 小时，而 [64Cu]Cu-NOTA-Dara 在 48 小时达到其肿瘤摄取峰值（8.3 ± 1.4%ID/g，n = 4）。相比之下，IgG-F(ab')2 和 HBL-1 对照组没有发现明显的肿瘤摄取。[64Cu]Cu-NOTA-Dara-F(ab')2 在血池、骨骼、和肌肉比 [64Cu]Cu-NOTA-Dara 及其肿瘤与血液和肿瘤与肌肉的比率显着高于对照组。结论 [64Cu]Cu-NOTA-Dara-F(ab')2 在 CD38 阳性淋巴瘤模型中表现出快速和高肿瘤摄取，具有良好的成像对比度，显示其作为未来临床应用的潜在 PET 成像剂的前景。