Multiple myeloma (MM) is a plasma B-cell hematologic cancer that causes significant skeletal morbidity. Despite improvements in survival, heterogeneity in response remains a major challenge in MM. Cluster of differentiation 38 (CD38) is a type II transmembrane glycoprotein overexpressed in myeloma cells and is implicated in MM cell signaling. Daratumumab is a U.S. Food and Drug Administration–approved high-affinity monoclonal antibody targeting CD38 that is clinically benefiting refractory MM patients. Here, we evaluated [⁸⁹Zr]Zr-desferrioxamine (DFO)-daratumumab PET/CT imaging in MM tumor models. Methods: Daratumumab was conjugated to DFO-p-benzyl-isothiocyanate (DFO-Bz-NCS) for radiolabeling with ⁸⁹Zr. Chelator conjugation was confirmed by electrospray ionization-mass spectrometry, and radiolabeling was monitored by instant thin-layer chromatography. Daratumumab was conjugated to Cyanine5 (Cy5) dye for cell microscopy. In vitro and in vivo evaluation of [⁸⁹Zr]Zr-DFO-daratumumab was performed using CD38⁺ human myeloma MM1.S-luciferase (MM1.S) cells. Cellular studies determined the affinity, immunoreactivity, and specificity of [⁸⁹Zr]Zr-DFO-daratumumab. A 5TGM1-luciferase (5TGM1)/KaLwRij MM mouse model served as control for imaging background noise. [⁸⁹Zr]Zr-DFO-daratumumab PET/CT small-animal imaging was performed in severe combined immunodeficient mice bearing solid and disseminated MM tumors. Tissue biodistribution (7 d after tracer administration, 1.11 MBq/animal, n = 4–6/group) was performed in wild-type and MM1.S tumor–bearing mice. Results: A specific activity of 55.5 MBq/nmol (0.37 MBq/μg) was reproducibly obtained with [⁸⁹Zr]Zr-daratumumab-DFO. Flow cytometry confirmed CD38 expression (>99%) on the surface of MM1.S cells. Confocal microscopy with daratumumab-Cy5 demonstrated specific cell binding. Dissociation constant, 3.3 nM (±0.58), and receptor density, 10.1 fmol/mg (±0.64), was obtained with a saturation binding assay. [⁸⁹Zr]Zr-DFO-daratumumab/PET demonstrated specificity and sensitivity for detecting CD38⁺ myeloma tumors of variable sizes (8.5–128 mm³) with standardized uptake values ranging from 2.1 to 9.3. Discrete medullar lesions, confirmed by bioluminescence images, were efficiently imaged with [⁸⁹Zr]Zr-DFO-daratumumab/PET. Biodistribution at 7 d after administration of [⁸⁹Zr]Zr-DFO-daratumumab showed prominent tumor uptake (27.7 ± 7.6 percentage injected dose per gram). In vivo blocking was achieved with a 200-fold excess of unlabeled daratumumab. Conclusion: [⁸⁹Zr]Zr-DFO- and Cy5-daratumumab demonstrated superb binding to CD38⁺ human MM cells and significantly low binding to CD38^low cells. Daratumumab bioconjugates are being evaluated for image-guided delivery of therapeutic radionuclides.

多发性骨髓瘤 (MM) 是一种血浆 B 细胞血液肿瘤，可导致严重的骨骼疾病。尽管生存率有所提高，但反应的异质性仍然是 MM 的主要挑战。分化簇 38 (CD38) 是一种在骨髓瘤细胞中过表达的 II 型跨膜糖蛋白，与 MM 细胞信号传导有关。Daratumumab 是美国食品和药物管理局批准的靶向 CD38 的高亲和力单克隆抗体，在临床上有益于难治性 MM 患者。在这里，我们评估了 MM 肿瘤模型中的 [ ⁸⁹ Zr]Zr-去铁胺 (DFO)-daratumumab PET/CT 成像。方法： Daratumumab 与 DFO-对苯甲基异硫氰酸酯 (DFO-Bz-NCS) 偶联，用于用^{89进行放射性标记}锆。通过电喷雾电离质谱法确认螯合剂结合，并通过即时薄层色谱法监测放射性标记。Daratumumab 与 Cyanine5 (Cy5) 染料偶联用于细胞显微镜检查。^{[ 89} Zr]Zr-DFO-daratumumab的体外和体内评估使用 CD38 ⁺人骨髓瘤 MM1.S-荧光素酶(MM1.S) 细胞进行。^{细胞研究确定了 [ 89} Zr]Zr-DFO-daratumumab的亲和力、免疫反应性和特异性。5TGM1-荧光素酶(5TGM1)/KaLwRij MM 小鼠模型用作成像背景噪声的对照。[ ⁸⁹Zr]Zr-DFO-daratumumab PET/CT 小动物成像在患有实体和播散性 MM 肿瘤的严重联合免疫缺陷小鼠中进行。在野生型和 MM1.S 荷瘤小鼠中进行组织生物分布（示踪剂给药后 7 天，1.11 MBq/动物，n = 4-6/组）。结果：使用 [ ⁸⁹ Zr]Zr-daratumumab-DFO可重现地获得 55.5 MBq/nmol (0.37 MBq/μg) 的比活性。流式细胞术证实了 MM1.S 细胞表面的 CD38 表达 (>99%)。使用 daratumumab-Cy5 的共聚焦显微镜显示了特异性细胞结合。通过饱和结合测定获得解离常数 3.3 nM (±0.58) 和受体密度 10.1 fmol/mg (±0.64)。[ ⁸⁹Zr]Zr-DFO-daratumumab/PET 证明了检测具有 2.1 至 9.3 范围内的标准化摄取值的不同大小 (8.5–128 mm ^{3 ) 的 CD38 +骨髓瘤肿瘤的特异性和敏感性。}通过生物发光图像确认的离散髓质病变可使用 [ ⁸⁹ Zr]Zr-DFO-daratumumab/PET 进行有效成像。^{[ 89} Zr]Zr-DFO-daratumumab给药后 7 天的生物分布显示出显着的肿瘤摄取（27.7 ± 7.6% 的注射剂量/克）。体内阻断是通过 200 倍过量的未标记达雷妥尤单抗实现的。结论： [ ^{89 Zr]Zr-DFO- 和 Cy5-daratumumab 表现出与 CD38 +}的极好结合^{人 MM 细胞和与 CD38低}细胞的结合显着降低。正在评估 Daratumumab 生物偶联物用于治疗性放射性核素的图像引导递送。