Alzheimer's Therapeutics Targeting Amyloid Beta 1–42 Oligomers I: Abeta 42 Oligomer Binding to Specific Neuronal Receptors Is Displaced by Drug Candidates That Improve Cognitive Deficits

Synaptic dysfunction and loss caused by age-dependent accumulation of synaptotoxic beta amyloid (Abeta) 1–42 oligomers is proposed to underlie cognitive decline in Alzheimer's disease (AD). Alterations in membrane trafficking induced by Abeta oligomers mediates reduction in neuronal surface receptor expression that is the basis for inhibition of electrophysiological measures of synaptic plasticity and thus learning and memory. We have utilized phenotypic screens in mature, in vitro cultures of rat brain cells to identify small molecules which block or prevent the binding and effects of Abeta oligomers. Synthetic Abeta oligomers bind saturably to a single site on neuronal synapses and induce deficits in membrane trafficking in neuronal cultures with an EC50 that corresponds to its binding affinity. The therapeutic lead compounds we have found are pharmacological antagonists of Abeta oligomers, reducing the binding of Abeta oligomers to neurons in vitro, preventing spine loss in neurons and preventing and treating oligomer-induced deficits in membrane trafficking. These molecules are highly brain penetrant and prevent and restore cognitive deficits in mouse models of Alzheimer's disease. Counter-screening these compounds against a broad panel of potential CNS targets revealed they are highly potent and specific ligands of the sigma-2/PGRMC1 receptor. Brain concentrations of the compounds corresponding to greater than 80% receptor occupancy at the sigma-2/PGRMC1 receptor restore cognitive function in transgenic hAPP Swe/Ldn mice. These studies demonstrate that synthetic and human-derived Abeta oligomers act as pharmacologically-behaved ligands at neuronal receptors - i.e. they exhibit saturable binding to a target, they exert a functional effect related to their binding and their displacement by small molecule antagonists blocks their functional effect. The first-in-class small molecule receptor antagonists described here restore memory to normal in multiple AD models and sustain improvement long-term, representing a novel mechanism of action for disease-modifying Alzheimer's therapeutics.

由年龄依赖性积累的突触毒性β淀粉样蛋白（beta amyloid, Aβ）1-42寡聚体引发的突触功能障碍与丢失，被认为是阿尔茨海默病（Alzheimer's Disease, AD）认知衰退的核心致病基础。Aβ寡聚体诱导的膜运输异常，会导致神经元表面受体表达水平下调，这正是其抑制突触可塑性的电生理检测指标、进而损害学习记忆能力的关键机制。本研究借助成熟大鼠脑细胞体外培养模型的表型筛选，鉴定出可阻断或抑制Aβ寡聚体结合及其毒性效应的小分子化合物。人工合成的Aβ寡聚体可与神经元突触上的单一结合位点发生可饱和性结合，并诱导神经元培养体系出现膜运输功能缺陷，其半最大效应浓度（EC50）与结合亲和力相一致。本研究发现的先导治疗化合物属于Aβ寡聚体的药理学拮抗剂，可在体外实验中降低Aβ寡聚体与神经元的结合效率，阻止神经元树突棘丢失，并能预防和逆转寡聚体诱导的膜运输功能缺陷。这类化合物具备优异的血脑屏障穿透性，可在阿尔茨海默病小鼠模型中预防并逆转认知功能缺陷。通过针对一系列潜在中枢神经系统（Central Nervous System, CNS）靶点的反向筛选，研究证实这类化合物是σ-2/PGRMC1受体的高效特异性配体。当化合物在脑内浓度达到可与σ-2/PGRMC1受体结合超过80%的受体占有率时，即可恢复转基因hAPP Swe/Ldn小鼠的认知功能。本研究证实，人工合成与人类来源的Aβ寡聚体均可作为神经元受体上的药理学活性配体：具体而言，它们可与靶标发生可饱和性结合，产生与结合水平相关的功能性效应，而小分子拮抗剂可通过竞争性置换结合阻断其毒性功能。本研究报道的这款首创类小分子受体拮抗剂，可在多种AD模型中将记忆恢复至正常水平，并能长期维持改善效果，为阿尔茨海默病的疾病修饰治疗提供了全新的作用机制。