Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.
Proc Natl Acad Sci U S A. 2013 Sep 3;110(36):14598-603. doi: 10.1073/pnas.1311333110. Epub 2013 Aug 15.
Central nervous system tumors carry grave clinical prognoses due to limited effectiveness of surgical resection, radiation, and chemotherapy. Thus, improved strategies for brain tumor visualization and targeted treatment are critically needed. We demonstrate that mouse cerebellar medulloblastoma (MB) can be targeted and illuminated with a fluorescent, engineered cystine knot (knottin) peptide that binds with high affinity to αvβ3, αvβ5, and α5β1 integrin receptors. This integrin-binding knottin peptide, denoted EETI 2.5F, was evaluated as a molecular imaging probe in both orthotopic and genetic models of MB. Following tail vein injection, fluorescence arising from dye-conjugated EETI 2.5F was localized to the tumor compared with the normal surrounding brain tissue, as measured by optical imaging. The imaging signal intensity correlated with tumor volume. Due to its unique ability to bind to α5β1 integrin, EETI 2.5F showed superior in vivo and ex vivo brain tumor imaging contrast compared with other engineered integrin-binding knottin peptides and with c(RGDfK), a well-studied integrin-binding peptidomimetic. Next, EETI 2.5F was fused to an antibody fragment crystallizable (Fc) domain (EETI 2.5F-Fc) to determine if a larger integrin-binding protein could also target intracranial brain tumors. EETI 2.5F-Fc, conjugated to a fluorescent dye, illuminated MB following i.v. injection and was able to distribute throughout the tumor parenchyma. In contrast, brain tumor imaging signals were not detected in mice injected with EETI 2.5F proteins containing a scrambled integrin-binding sequence, demonstrating the importance of target specificity. These results highlight the potential of using EETI 2.5F and EETI 2.5-Fc as targeted molecular probes for brain tumor imaging.
中枢神经系统肿瘤由于手术切除、放疗和化疗效果有限，临床预后较差。因此，迫切需要改善脑肿瘤可视化和靶向治疗的策略。我们证明，荧光工程半胱氨酸环（knottin）肽可以靶向并照亮小鼠小脑髓母细胞瘤（MB），该肽与 αvβ3、αvβ5 和 α5β1 整合素受体具有高亲和力。这种整合素结合 knottin 肽，称为 EETI 2.5F，在 MB 的原位和遗传模型中被评估为分子成像探针。尾静脉注射后，与正常周围脑组织相比，荧光染料缀合的 EETI 2.5F 的荧光定位于肿瘤，通过光学成像测量。成像信号强度与肿瘤体积相关。由于其与 α5β1 整合素结合的独特能力，EETI 2.5F 与其他工程整合素结合 knottin 肽和研究充分的整合素结合肽模拟物 c(RGDfK)相比，在体内和体外脑肿瘤成像对比方面表现出优异的性能。接下来，EETI 2.5F 与抗体片段结晶（Fc）结构域融合（EETI 2.5F-Fc），以确定更大的整合素结合蛋白是否也可以靶向颅内脑肿瘤。EETI 2.5F-Fc 与荧光染料缀合，静脉注射后可照亮 MB，并能够分布在肿瘤实质中。相比之下，在注射含有乱序整合素结合序列的 EETI 2.5F 蛋白的小鼠中未检测到脑肿瘤成像信号，这表明靶向特异性的重要性。这些结果突出了使用 EETI 2.5F 和 EETI 2.5-Fc 作为脑肿瘤成像的靶向分子探针的潜力。
