Varlow Cassis, Mathis Chester A, Vasdev Neil
Institute of Medical Science, University of Toronto, ON M5S 1A8, Canada; Brain Health Imaging Centre, Centre for Addiction and Mental Health, Toronto, ON M5T 1R8, Canada.
Department of Radiology, University of Pittsburgh, PA 15213, USA.
Nucl Med Biol. 2024 Mar-Apr;130-131:108891. doi: 10.1016/j.nucmedbio.2024.108891. Epub 2024 Feb 19.
Alzheimer's disease (AD) and non-AD tauopathies such as chronic traumatic encephalopathy (CTE), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) are characterized by the abnormal aggregation of three-repeat (3R) and/or four-repeat (4R) tau isoforms. Several tau-PET tracers have been applied for human imaging of AD and non-AD tauopathies including [F]PI-2620. Our objective is to evaluate [H]PI-2620 and two promising structural derivatives, [H]PI-2014 and [H]F-4, using in vitro saturation assays and competitive binding assays against new chemical entities based on this scaffold in human AD tissues for comparison with PSP, CBD and CTE tissues. Thin section autoradiography was employed to assess specific binding and distribution of [H]PI-2620 and [H]F-4 in fresh-frozen human post-mortem AD, PSP, CBD and CTE tissues. Immunohistochemistry was performed for phospho-tau (AT8) and 4R-tau (RD4). Homogenate filtration binding assays were performed for saturation analysis and competitive binding studies against [H]PI-2620. All compounds bound with high affinity in AD tissue. In PSP tissue [H]PI-2620 demonstrated the highest affinity (5.3 nM) and in CBD tissue [H]F-4 bound with the highest affinity (9.4 nM). Over 40 fluorinated derivatives based on PI-2620 and F-4 were screened in AD and PSP tissue. Notably, compound 2 was the most potent derivative in PSP tissue (K = 7.3 nM). By autoradiography, [H]PI-2620 and [H]F-4 demonstrated positive signals similar in intensity in AD, PSP and CTE tissues that were displaced by homologous blockade. Binding of both radiotracers aligned with immunostaining for 4R-tau. This work demonstrates that [H]PI-2620 and [H]F-4 show promise for imaging 4R-tau aggregates in non-AD tauopathies. PI-2620 continues to serve as a structural scaffold for PET radiotracers with higher affinity for non-AD tau over AD tau.
阿尔茨海默病（AD）以及诸如慢性创伤性脑病（CTE）、进行性核上性麻痹（PSP）和皮质基底节变性（CBD）等非AD tau蛋白病的特征是三重复（3R）和/或四重复（4R）tau蛋白异构体的异常聚集。几种tau蛋白正电子发射断层扫描（PET）示踪剂已应用于AD和非AD tau蛋白病的人体成像，包括[F]PI - 2620。我们的目标是使用体外饱和测定法和针对基于该支架的新化学实体的竞争性结合测定法，在人AD组织中评估[H]PI - 2620以及两种有前景的结构衍生物[H]PI - 2014和[H]F - 4，并与PSP、CBD和CTE组织进行比较。采用薄切片放射自显影术评估[H]PI - 2620和[H]F - 4在新鲜冷冻的人死后AD、PSP、CBD和CTE组织中的特异性结合和分布。对磷酸化tau蛋白（AT8）和4R - tau蛋白（RD4）进行免疫组织化学检测。进行匀浆过滤结合测定以进行饱和分析以及针对[H]PI - 2620的竞争性结合研究。所有化合物在AD组织中均以高亲和力结合。在PSP组织中，[H]PI - 2620表现出最高亲和力（5.3 nM），在CBD组织中，[H]F - 4以最高亲和力结合（9.4 nM）。在AD和PSP组织中筛选了40多种基于PI - 2620和F - 4的氟化衍生物。值得注意的是，化合物2是PSP组织中最有效的衍生物（K = 7.3 nM）。通过放射自显影术，[H]PI - 2620和[H]F - 4在AD、PSP和CTE组织中显示出强度相似的阳性信号，这些信号被同源阻断所取代。两种放射性示踪剂的结合与4R - tau蛋白的免疫染色一致。这项工作表明，[H]PI - 2620和[H]F - 4在非AD tau蛋白病中对4R - tau蛋白聚集体成像显示出前景。PI - 2620继续作为PET放射性示踪剂的结构支架，对非AD tau蛋白的亲和力高于AD tau蛋白。
