Roshanbin Sahar, Xiong Mengfei, Hultqvist Greta, Söderberg Linda, Zachrisson Olof, Meier Silvio, Ekmark-Lewén Sara, Bergström Joakim, Ingelsson Martin, Sehlin Dag, Syvänen Stina
Department of Public Health and Caring Sciences, Uppsala University, Uppsala, Sweden.
Department of Public Health and Caring Sciences, Uppsala University, Uppsala, Sweden.
Neuropharmacology. 2022 May 1;208:108985. doi: 10.1016/j.neuropharm.2022.108985. Epub 2022 Feb 8.
The protein alpha-synuclein (αSYN) plays a central role in synucleinopathies such as Parkinsons's disease (PD) and multiple system atrophy (MSA). Presently, there are no selective αSYN positron emission tomography (PET) radioligands that do not also show affinity to amyloid-beta (Aβ). We have previously shown that radiolabeled antibodies, engineered to enter the brain via the transferrin receptor (TfR), is a promising approach for PET imaging of intrabrain targets. In this study, we used this strategy to visualize αSYN in the living mouse brain. Five bispecific antibodies, binding to both the murine TfR and αSYN were generated and radiolabeled with iodine-125 or iodine-124. All bispecific antibodies bound to αSYN and mTfR before and after radiolabelling in an ELISA assay, and bound to brain sections prepared from αSYN overexpressing mice as well as human PD- and MSA subjects, but not control tissues in autoradiography. Brain concentrations of the bispecific antibodies were between 26 and 63 times higher than the unmodified IgG format 2 h post-injection, corresponding to about 1.5% of the injected dose per gram brain tissue. Additionally, intrastriatal αSYN fibrils were visualized with PET in an αSYN deposition mouse model with one of the bispecific antibodies, [I]RmAbSynO2-scFv8D3. However, PET images acquired in αSYN transgenic mice with verified brain pathology injected with [I]RmAbSynO2-scFv8D3 and [I]RmAb48-scFv8D3 showed no increase in antibody retention compared to WT mice. Despite successful imaging of deposited extracellular αSYN using a brain-penetrating antibody-based radioligand with no cross-specificity towards Aβ, this proof-of-concept study demonstrates challenges in imaging intracellular αSYN inclusions present in synucleinopathies.
蛋白质α-突触核蛋白（αSYN）在帕金森病（PD）和多系统萎缩（MSA）等突触核蛋白病中起核心作用。目前，尚无对淀粉样β蛋白（Aβ）无亲和力的选择性αSYN正电子发射断层扫描（PET）放射性配体。我们之前已经表明，经工程改造可通过转铁蛋白受体（TfR）进入大脑的放射性标记抗体，是脑内靶点PET成像的一种有前景的方法。在本研究中，我们使用该策略在活体小鼠脑中可视化αSYN。制备了五种与小鼠TfR和αSYN均结合的双特异性抗体，并用碘-125或碘-124进行放射性标记。在ELISA分析中，所有双特异性抗体在放射性标记前后均与αSYN和mTfR结合，并与由过表达αSYN的小鼠以及人类PD和MSA受试者制备的脑切片结合，但在放射自显影中不与对照组织结合。双特异性抗体在注射后2小时的脑浓度比未修饰的IgG形式高26至63倍，相当于每克脑组织约1.5%的注射剂量。此外，在αSYN沉积小鼠模型中，使用双特异性抗体之一[I]RmAbSynO2-scFv8D3通过PET可视化纹状体内αSYN纤维。然而，在注射了[I]RmAbSynO2-scFv8D3和[I]RmAb48-scFv8D3的具有已证实脑病理学的αSYN转基因小鼠中获得的PET图像显示，与野生型小鼠相比，抗体滞留没有增加。尽管使用对Aβ无交叉特异性的基于脑穿透抗体的放射性配体成功地对沉积的细胞外αSYN进行了成像，但这项概念验证研究表明，在对突触核蛋白病中存在的细胞内αSYN包涵体进行成像时存在挑战。
