用 18F 标记的亲和体分子进行表皮生长因子受体的 PET 显像。
PET of EGFR expression with an 18F-labeled affibody molecule.
机构信息
Molecular Imaging Program at Stanford (MIPS), Bio-X Program, Department of Radiology, Stanford University, Stanford, CA 94305, USA.
出版信息
J Nucl Med. 2012 Jul;53(7):1110-8. doi: 10.2967/jnumed.111.100842. Epub 2012 Jun 11.
UNLABELLED
Epidermal growth factor receptor (EGFR) is often overexpressed in a variety of human cancers, and its expression is associated with poor prognosis for many cancer types. However, an accurate technique to noninvasively image EGFR expression in vivo is not available in the clinical setting. In this research, an Affibody analog, anti-EGFR Ac-Cys-Z(EGFR:1907), was successfully site-specifically (18)F-labeled for PET of EGFR expression.
METHODS
The prosthetic group N-[2-(4-(18)F-fluorobenzamido) ethyl] maleimide ((18)F-FBEM) was conjugated to Ac-Cys-Z(EGFR:1907) under mild conditions (pH 7) to produce the probe (18)F-FBEM-Cys-Z(EGFR:1907). The binding affinity and specificity tests of (18)F-FBEM-Cys-Z(EGFR:1907) to EGFR were conducted using A431 cancer cells. Small-animal PET and biodistribution studies were conducted on various mice tumor xenograft models with EGFR overexpression (6 types) after injection of approximately 2.0 MBq of (18)F-FBEM-Cys-Z(EGFR:1907) with or without coinjection of unlabeled Ac-Cys-Z(EGFR:1907) for up to 3 h after injection. A correlation study between (18)F-FBEM-Cys-Z(EGFR:1907) small- animal PET quantification and ex vivo Western blot analysis of tumor EGFR expression was conducted in those 6 types of tumor models.
RESULTS
(18)F-FBEM-Cys-Z(EGFR:1907) binds to EGFR with low nanomolar affinity (37 nM) in A431 cells. (18)F-FBEM-Cys-Z(EGFR:1907) rapidly accumulated in the tumor and cleared from most of the normal organs except the liver and kidneys at 3 h after injection, allowing excellent tumor-to-normal tissue contrast to be obtained. In the A431 tumor xenograft model, coinjection of the PET probe with 45 μg of Ac-Cys-Z(EGFR:1907) was able to improve the tumor uptake (3.9 vs. 8.1 percentage of the injected radioactive dose per gram of tissue, at 3 h after injection) and tumor imaging contrast, whereas coinjection with 500 μg of Ac-Cys-Z(EGFR:1907) successfully blocked the tumor uptake significantly (8.1 vs. 1.0 percentage of the injected radioactive dose per gram of tissue, at 3 h after injection, 88% inhibition, P < 0.05). Moderate correlation was found between the tumor tracer uptake at 3 h after injection quantified by PET and EGFR expression levels measured by Western blot assay (P = 0.007, R = 0.59).
CONCLUSION
(18)F-FBEM-Cys-Z(EGFR:1907) is a novel protein scaffold-based PET probe for imaging EGFR overexpression of tumors, and its ability to differentiate tumors with high and low EGFR expression in vivo holds promise for future clinical translation.
目的
表皮生长因子受体（EGFR）在多种人类癌症中常过度表达，其表达与许多癌症类型的不良预后相关。然而，目前临床上还没有一种准确的无创性方法来对体内 EGFR 表达进行成像。本研究中，成功地对一种 Affibody 类似物，抗 EGFR Ac-Cys-Z（EGFR：1907）进行了位点特异性（18）F 标记，用于 EGFR 表达的 PET 成像。
方法
将亲电子试剂 N-[2-（4-（18）F-氟苯甲酰胺基）乙基]马来酰亚胺（（18）F-FBEM）在温和条件（pH 7）下与 Ac-Cys-Z（EGFR：1907）缀合，生成探针（18）F-FBEM-Cys-Z（EGFR：1907）。使用 A431 癌细胞进行（18）F-FBEM-Cys-Z（EGFR：1907）与 EGFR 结合亲和力和特异性测试。在 6 种具有过表达 EGFR（6 种）的小鼠肿瘤异种移植模型中，在注射约 2.0 MBq 的（18）F-FBEM-Cys-Z（EGFR：1907）后，进行小动物 PET 和生物分布研究，在注射后长达 3 小时内，进行或不进行未标记的 Ac-Cys-Z（EGFR：1907）的共注射。在这 6 种肿瘤模型中，进行了（18）F-FBEM-Cys-Z（EGFR：1907）小动物 PET 定量与肿瘤 EGFR 表达的体外 Western blot 分析之间的相关性研究。
结果
（18）F-FBEM-Cys-Z（EGFR：1907）在 A431 细胞中以低纳摩尔亲和力（37 nM）与 EGFR 结合。（18）F-FBEM-Cys-Z（EGFR：1907）在注射后 3 小时内迅速在肿瘤中积累，并从除肝脏和肾脏以外的大多数正常器官中清除，从而获得出色的肿瘤与正常组织对比。在 A431 肿瘤异种移植模型中，与 45 μg 的 Ac-Cys-Z（EGFR：1907）共注射 PET 探针能够提高肿瘤摄取（3 小时后注射，每克组织注射放射性剂量的 3.9%比 8.1%）和肿瘤成像对比，而与 500 μg 的 Ac-Cys-Z（EGFR：1907）共注射则成功地显著阻断了肿瘤摄取（3 小时后注射，每克组织注射放射性剂量的 8.1%比 1.0%，88%抑制，P < 0.05）。在注射后 3 小时定量 PET 测定的肿瘤示踪剂摄取与 Western blot 测定的 EGFR 表达水平之间发现中度相关性（P = 0.007，R = 0.59）。
结论
（18）F-FBEM-Cys-Z（EGFR：1907）是一种新型的基于蛋白质支架的 PET 探针，用于成像肿瘤中 EGFR 的过度表达，其在体内区分高表达和低表达 EGFR 肿瘤的能力为未来的临床转化提供了希望。
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