Data Sheet 1_The Alzheimer's disease 5xFAD mouse model is best suited to investigate pretargeted imaging approaches beyond the blood-brain barrier.docx

Alzheimer's disease (AD) is the most common neurodegenerative disease, with an increasing prevalence. Currently, there is no ideal diagnostic molecular imaging agent for diagnosing AD. Antibodies (Abs) have been proposed to close this gap as they can bind selectively and with high affinity to amyloid β (Aβ)—one of the molecular hallmarks of AD. Abs can even be designed to selectively bind Aβ oligomers or isoforms, which are difficult to target with small imaging agents. Conventionally, Abs must be labeled with long-lived radionuclides which typically results in in high radiation burden to healthy tissue. Pretargeted imaging could solve this challenge as it allows for the use of short-lived radionuclides. To develop pretargeted imaging tools that can enter the brain, AD mouse models are useful as they allow testing of the imaging approach in a relevant animal model that could predict its clinical applicability. Several mouse models for AD have been developed with different characteristics. Commonly used models are: 5xFAD, APP/PS1 and tg-ArcSwe transgenic mice. In this study, we aimed to identify which of these models were best suited to investigate pretargeted imaging approaches beyond the blood brain barrier. We evaluated this by pretargeted autoradiography using the Aβ-targeting antibody 3D6 and an 111In-labeled Tz. Evaluation criteria were target-to-background ratios and accessibility. APP/PS1 mice showed Aβ accumulation in high and low binding brain regions and is as such less suitable for pretargeted purposes. 5xFAD and tg-ArcSwe mice showed similar uptake in high binding regions whereas low uptake in low binding regions and are better suited to evaluate pretargeted imaging approaches. 5xFAD mice are advantaged over tg-ArcSwe mice as pathology can be traced early (6 months compared to 18 months of age) and as 5xFAD mice are commercially available.

阿尔茨海默病（Alzheimer's disease, AD）是最常见的神经退行性疾病，其患病率逐年攀升。目前尚无理想的诊断用分子显像剂用于AD的临床诊断。抗体（antibodies, Abs）被认为可填补这一空白，因其能够选择性地与AD的核心分子标志物之一——β淀粉样蛋白（amyloid β, Aβ）以高亲和力结合。抗体甚至可被定制化设计为选择性结合Aβ寡聚体或亚型，而这类靶点难以通过小分子显像剂实现靶向结合。传统显像方案中，抗体需通过长寿命放射性核素进行标记，这通常会给健康组织带来较高的辐射负荷。预靶向显像（pretargeted imaging）可有效解决这一难题，因其允许使用短寿命放射性核素。为开发可穿透血脑屏障（blood brain barrier）的预靶向显像工具，AD小鼠模型是极为实用的研究载体，可在具有临床相关性的动物模型中对显像方法进行验证，进而预测其临床应用潜力。目前已开发出多种具有不同特征的AD转基因小鼠模型，其中常用模型包括5xFAD、APP/PS1及tg-ArcSwe转基因小鼠。本研究旨在明确上述三类模型中，哪一种最适合用于评估血脑屏障之外的预靶向显像策略。我们采用靶向Aβ的抗体3D6与111铟标记四嗪（111In-labeled Tz）开展预靶向放射自显影（autoradiography）实验以完成评估。评估指标为靶本比与组织可及性。实验结果显示，APP/PS1小鼠在脑内高结合区域与低结合区域均存在明显的Aβ沉积，因此不太适合用于预靶向相关研究。5xFAD与tg-ArcSwe小鼠在高结合区域的放射性摄取水平相近，而在低结合区域摄取量较低，二者更适合用于预靶向显像方法的评估。相较于tg-ArcSwe小鼠，5xFAD小鼠具备显著优势：其AD病理特征可在更早的月龄（6月龄，相较tg-ArcSwe小鼠的18月龄）被观测到，且5xFAD小鼠可通过商业渠道购得。