Li Zi-Bo, Niu Gang, Wang Hui, He Lina, Yang Lily, Ploug Michael, Chen Xiaoyuan
Molecular Imaging Program at Stanford, Department of Radiology and Bio-X Program, Stanford University School of Medicine, Stanford, California 94305-5484, USA.
Clin Cancer Res. 2008 Aug 1;14(15):4758-66. doi: 10.1158/1078-0432.CCR-07-4434.
Malignant tumors are capable of degrading the surrounding extracellular matrix, resulting in local invasion or metastasis. Urokinase-type plasminogen activator (uPA) and its cell surface receptor (uPAR) are central molecules in one of the major protease systems involved in extracellular matrix degradation. Noninvasive imaging of this receptor in vivo with radiolabeled peptides that specifically target uPAR may therefore be useful to decipher the potential invasiveness of malignant lesions.
In this study, we developed a (64)Cu-labeled uPAR-binding peptide for positron emission tomography (PET) imaging. A linear, high-affinity uPAR-binding peptide antagonist AE105 was conjugated with 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid (DOTA) and labeled with (64)Cu for microPET imaging of mice bearing U87MG human glioblastoma (uPAR positive) and MDA-MB-435 human breast cancer (uPAR negative).
Surface plasmon resonance measurements show that AE105 with DOTA conjugated at the alpha-amino group (DOTA-AE105) has high affinity toward uPAR. microPET imaging reveals a rapid and high accumulation of (64)Cu-DOTA-AE105 in uPAR-positive U87MG tumors (10.8 +/- 1.5%ID/g at 4.5 hours, n = 3) but not in uPAR-negative MDA-MB-435 tumors (1.2 +/- 0.6%ID/g at 4.5 hours, n = 3). Specificity of this peptide-based imaging of uPAR was validated by further control experiments. First, a nonbinding variant of AE105 carrying a single amino acid replacement (Trp-->Glu) does not target U87MG tumors in vivo. Second, targeting of U87MG tumors by (64)Cu-DOTA-AE105 is specifically inhibited by a nonlabeled antagonist.
The successful demonstration of the ability of a (64)Cu labeled uPAR-specific probe to visualize uPAR expression in vivo may allow clinical translation of this class of radiopharmaceuticals for uPAR-positive cancer detection and patient stratification for uPA/uPAR system-based cancer therapy.
恶性肿瘤能够降解周围的细胞外基质，导致局部侵袭或转移。尿激酶型纤溶酶原激活剂（uPA）及其细胞表面受体（uPAR）是参与细胞外基质降解的主要蛋白酶系统之一的核心分子。因此，用特异性靶向uPAR的放射性标记肽在体内对该受体进行无创成像，可能有助于解读恶性病变的潜在侵袭性。
在本研究中，我们开发了一种用于正电子发射断层扫描（PET）成像的（64）Cu标记的uPAR结合肽。将线性、高亲和力的uPAR结合肽拮抗剂AE105与1,4,7,10-四氮杂十二烷-N,N',N'',N'''-四乙酸（DOTA）偶联，并用（64）Cu标记，用于对携带U87MG人胶质母细胞瘤（uPAR阳性）和MDA-MB-435人乳腺癌（uPAR阴性）的小鼠进行微型PET成像。
表面等离子体共振测量表明，在α-氨基处偶联DOTA的AE105（DOTA-AE105）对uPAR具有高亲和力。微型PET成像显示，（64）Cu-DOTA-AE105在uPAR阳性的U87MG肿瘤中快速且高度聚集（4.5小时时为10.8±1.5%ID/g，n = 3），但在uPAR阴性的MDA-MB-435肿瘤中则没有（4.5小时时为1.2±0.6%ID/g，n = 3）。通过进一步的对照实验验证了这种基于肽的uPAR成像的特异性。首先，携带单个氨基酸替换（Trp→Glu）的AE105非结合变体在体内不靶向U87MG肿瘤。其次，（64）Cu-DOTA-AE105对U87MG肿瘤的靶向作用被未标记的拮抗剂特异性抑制。
成功证明（64）Cu标记的uPAR特异性探针在体内可视化uPAR表达的能力，可能使这类放射性药物能够临床转化，用于uPAR阳性癌症检测以及基于uPA/uPAR系统的癌症治疗的患者分层。
