Authors' Affiliations: Molecular Imaging Program at Stanford (MIPS), Department of Radiology; and Bioengineering, Materials Science & Engineering, Stanford University, Stanford, California.
Clin Cancer Res. 2013 Dec 15;19(24):6820-9. doi: 10.1158/1078-0432.CCR-13-0626. Epub 2013 Oct 4.
The aim of this article was to evaluate the use of a novel engineered anti-CD20 protein based on the 10 kDa human fibronectin type 3 domain (FN3) and subsequently compare with (64)Cu-rituximab for positron emission tomography (PET) imaging of CD20.
The engineered FN3(CD20) and FN3(WT) were produced in Escherichia coli cells at 2 to 5 mg/L, conjugated to DOTA, labeled with (64)Cu, and used for PET imaging of huCD20 expression in B cells. Humanized transgenic mice and subcutaneously xenografted mice each received intravenous (64)Cu-FN3(CD20) or FN3(WT) (3.7 MBq/4 μg Do-FN3 in 200 μL PBS). Control group received a blocking dose (50-fold excess) of unconjugated FN3(CD20) two hours before radiotracer injection. PET imaging was carried out at 1 to 24 hours postinjections.
In vitro assay demonstrated FN3 binds CD20 with 20 nmol/L affinity on CD20-expressing cells. (64)Cu-FN3(CD20) showed clear, high-contrast visualization of huCD20-expressing B cells in the spleen of transgenic mice as early as 1 hour postinjection [38 ± 3% injected dose (ID)/g] and exhibited a spleen-to-blood ratio of 13 by 4 hours. This is higher uptake (P = 0.04) and 10-fold greater signal-to-background (P = 0.04) than the (64)Cu-rituximab antibody radiotracer. Tumor uptake (16.8 ± 1.6 vs. 5.6 ± 1.4%ID/g) and tumor:background ratios were superior for FN3CD20 relative to rituximab in xenograft studies as well.
The (64)Cu-Do-FN3(CD20) radiotracer represents a novel small, high-affinity binder for imaging human CD20, which may be well suited for B-cell non-Hodgkin's lymphoma imaging in patients at early time points.
本文旨在评估一种新型的基于 10kDa 人纤维连接蛋白 3 结构域（FN3）的工程化抗 CD20 蛋白的应用，并与（64）Cu-利妥昔单抗进行比较，用于 CD20 的正电子发射断层扫描（PET）成像。
该工程 FN3（CD20）和 FN3（WT）在大肠杆菌细胞中以 2 至 5mg/L 的产量进行生产，与 DOTA 缀合，用（64）Cu 标记，用于 B 细胞中 huCD20 表达的 PET 成像。人源化转基因小鼠和皮下异种移植小鼠分别静脉内给予（64）Cu-FN3（CD20）或 FN3（WT）（3.7MBq/4μg Do-FN3 在 200μL PBS 中）。对照组在放射性示踪剂注射前两小时给予未结合的 FN3（CD20）的阻断剂量（50 倍过量）。在注射后 1 至 24 小时进行 PET 成像。
体外试验表明，FN3 以 20nmol/L 的亲和力与表达 CD20 的细胞上的 CD20 结合。（64）Cu-FN3（CD20）在注射后 1 小时即可清晰、高对比度地显示转基因小鼠脾脏中表达 huCD20 的 B 细胞[38±3%注射剂量（ID）/g]，4 小时时脾脏与血液的比值为 13。与（64）Cu-利妥昔单抗抗体放射性示踪剂相比，这是更高的摄取（P=0.04）和 10 倍的信号与背景比（P=0.04）。在异种移植研究中，FN3CD20 也具有更高的肿瘤摄取（16.8±1.6 比 5.6±1.4%ID/g）和肿瘤：背景比值。
（64）Cu-Do-FN3（CD20）放射性示踪剂是一种新型的高亲和力小分子人类 CD20 成像剂，可能非常适合患者早期的 B 细胞非霍奇金淋巴瘤成像。
