Albumin hitchhiking siRNAs for gene targeting in aged brain

目前治疗阿尔茨海默病（AD）的一个障碍是在大脑中施用有效剂量的生物药物。阿尔茨海默病的最大危险因素是衰老，这与血脑屏障（BBB）的进行性功能障碍相吻合，导致正常情况下被排除在健康大脑之外的血清蛋白进入和滞留。其中一种蛋白质是白蛋白，它在年轻的脑组织中检测不到，但随着年龄的增长逐渐在大脑中积累。在这里，我们提出了一种治疗AD的新策略，该策略将利用白蛋白作为“天然”载体来增强衰老大脑中sirna介导的基因靶向。我们假设在静脉给药后，将siRNA“搭便车”到白蛋白上将改善siRNA在老年大脑中的积累和基因沉默活性，从而提供一种针对AD相关基因的定制策略。我们实验室开发的一种新型二酰基脂肪酸载体（“EG18”）促进了这种方法的实现，该载体可以直接与siRNA（“siRNA-EG18”）结合。我们有相关的初步数据显示：1)相对于我们之前发表的siRNA-L2载体，siRNA-EG18对白蛋白的亲和力和特异性增强，循环半衰期延长；

A current hurdle for the treatment of Alzheimer’s disease (AD) is administration of efficacious doses of biological drugs in the brain. The strongest risk factor for AD is aging, which coincides with progressive dysfunction of the blood-brain barrier (BBB) leading to entry and retention of serum proteins that are normally excluded from healthy brain. One of these proteins is albumin, which is not detected in young brain tissue but gradually accumulates in the brain with age. Here, we propose to a novel strategy for treating AD that will leverage albumin as a “natural” carrier to enhance siRNA-mediated gene targeting in the aged brain. We hypothesize that “hitchhiking” siRNA onto albumin will improve siRNA accumulation and gene silencing activity in the aged brain after intravenous administration, thereby providing a customizable strategy to target genes associated with AD. This approach is facilitated by a novel diacyl fatty acid carrier developed in our lab (“EG18”) that can be directly conjugated to siRNA (“siRNA-EG18”). We have relevant preliminary data showing that: 1) siRNA-EG18 has enhanced affinity and specificity for albumin and increased circulation half-life relative to our previously published siRNA-L2 carrier; 2) siRNA-EG18 exerts sustained gene knockdown in a mouse model of osteoarthritis that leads to albumin accumulation in the inflamed knee joint; 3) siRNA-EG18 accumulates in the brains of old but not young mice 24 hours after intravenous delivery of a modest 1 mg/kg dose. Aim 1 of this proposal will build on these results by examining the pharmacokinetics, biodistribution, and toxicity of siRNA-EG18 as a function of age and dosing scheme. Aim 2 will examine the bioactivity of siRNA-EG18 in the aged brain, with a focus on targeting APOE, the strongest known genetic risk factor for AD. Collectively, this proposal will establish working parameters for achieving gene silencing in the aged brain via albumin hitchhiking of siRNA, thereby providing new opportunities for personalized medicine in AD.