Molecular Imaging Center, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
Nucl Med Biol. 2011 May;38(4):529-40. doi: 10.1016/j.nucmedbio.2010.11.008. Epub 2011 Feb 4.
The α(V)β(3) integrin is a well-known transmembrane receptor involved in tumor invasion, angiogenesis and metastasis. Our aim was to evaluate a novel positron emission tomography (PET) probe, (64)Cu-cyclam-RAFT-c(-RGDfK-)(4), for noninvasive visualization and quantification of α(V)β(3) integrin expression.
RAFT-c(-RGDfK-)(4), a tetrameric cyclic Arg-Gly-Asp (RGD)-based peptide, was conjugated with a bifunctional chelator, 1,4,8,11-tetraazacyclotetradecane (cyclam), radiolabeled with the positron emitter (64)Cu and evaluated in vitro by cell binding and competitive inhibition assays and in vivo by biodistribution and receptor blocking studies, and PET imaging. The following cell lines, human embryonic kidney HEK293(β(1)) [α(V)β(3)-negative] and HEK293(β(3)) [α(V)β(3)-overexpressing] and human glioblastoma U87MG [naturally expressing α(V)β(3)], together with their subcutaneous xenografts in athymic nude mice, were used for the present study. The expression levels of α(V)β(3) on these cell lines and tumor xenografts were analyzed by flow cytometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis/autoradiography, respectively.
(64)Cu-cyclam-RAFT-c(-RGDfK-)(4) demonstrated the in vitro and in vivo specificity for the α(V)β(3) integrin and displayed rapid blood clearance, predominantly renal excretion and low uptake in nontumor tissues. Tumor uptake of (64)Cu-cyclam-RAFT-c(-RGDfK-)(4) (3 h postinjection) in HEK293(β(3)) (high levels of α(V)β(3)), U87MG (moderate levels of α(V)β(3)) and HEK293(β(1)) (undetectable levels of α(V)β(3)) tumors was 9.35%±1.19%, 3.46%±0.45% and 1.18%±0.30% injected dose per gram, respectively, with a strong and positive correlation with the tumor α(V)β(3) expression levels (correlation coefficient=0.967; P<.0001). Positron emission tomographic images showed that α(V)β(3)-positive tumors were clearly visualized with high tumor-to-background contrast, and agreed well with the biodistribution results.
(64)Cu-cyclam-RAFT-c(-RGDfK-)(4) exhibits potential for noninvasively quantifying α(V)β(3) expression.
α(V)β(3)整合素是一种众所周知的跨膜受体，参与肿瘤侵袭、血管生成和转移。我们的目的是评估一种新型正电子发射断层扫描（PET）探针（64）Cu-环脒-RAFT-c（-RGDfK-）（4），用于非侵入性可视化和定量α(V)β(3)整合素表达。
RAFT-c（-RGDfK-）（4）是一种四聚体环状 Arg-Gly-Asp（RGD）基肽，与双功能螯合剂 1,4,8,11-四氮杂环十四烷（环脒）缀合，用正电子发射体（64）Cu 标记，并通过细胞结合和竞争性抑制试验进行体外评估，以及通过生物分布和受体阻断研究和 PET 成像进行体内评估。使用人胚肾 HEK293（β(1)）[α(V)β(3)-阴性]和 HEK293（β(3)）[α(V)β(3)-过表达]以及人神经胶质瘤 U87MG[天然表达α(V)β(3)]细胞系及其在裸鼠中的皮下异种移植肿瘤进行本研究。通过流式细胞术和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳/放射自显影分别分析这些细胞系和肿瘤异种移植物中α(V)β(3)的表达水平。
（64）Cu-环脒-RAFT-c（-RGDfK-）（4）在体外和体内均表现出对α(V)β(3)整合素的特异性，并显示出快速的血液清除、主要经肾脏排泄和非肿瘤组织摄取低。（64）Cu-环脒-RAFT-c（-RGDfK-）（4）在注射后 3 小时（高水平的α(V)β(3)）、U87MG（中等水平的α(V)β(3)）和 HEK293（β(1)）（检测不到α(V)β(3)）肿瘤中的摄取率分别为 9.35%±1.19%、3.46%±0.45%和 1.18%±0.30%注射剂量/克，与肿瘤α(V)β(3)表达水平呈强正相关（相关系数=0.967；P<.0001）。正电子发射断层扫描图像显示，α(V)β(3)阳性肿瘤具有清晰的可视化和高肿瘤与背景的对比，与生物分布结果吻合良好。
（64）Cu-环脒-RAFT-c（-RGDfK-）（4）具有非侵入性定量检测α(V)β(3)表达的潜力。
