Chemical-Driven Amyloid Clearance for Therapeutics and Diagnostics of Alzheimer’s Disease

ConspectusA century ago, German neurologist Alois Alzheimer documented the first case of Alzheimer's disease (AD), illuminating cognitive impairments associated with the presence of abnormal protein clusters, including amyloid plaques and tau tangles, within the brain. In a typical physiological state, the equilibrium of amyloid-β (Aβ) levels is maintained, but aging can precipitate disruptions in the homeostasis of Aβ due to its overproduction, impaired clearance, and other factors, ultimately leading to its accumulation. Although the link between Aβ aggregates and neurodegeneration has long made Aβ a promising target for AD, decades without successful drug development targeting Aβ have generated skepticism regarding the efficacy of this strategy for AD therapy. However, recent approvals of anti-Aβ antibody drugs by the FDA, including aducanumab (Aduhelm), lecanemab (Leqembi), and donanemab (Kisunla), have prompted a re-evaluation of this perspective. These therapies have demonstrated efficacy in reducing brain Aβ levels, thereby decelerating disease progression and reaffirming Aβ as a key target. Despite advancements, immunotherapies are accompanied by considerable disadvantages, including adverse effects, high costs, and cumbersome administration. To address these limitations, our research has focused on developing small molecules that can mitigate the challenges of antibody treatments while offering practical and accessible options. We identified 4-(2-hydroxyethyl)-1-piperazine propanesulfonic acid (EPPS) as a promising compound that significantly reduces aggregated Aβ in the brain and enhances behavior in AD rodent models. Following administration, EPPS penetrates the blood-brain barrier (BBB) and binds to toxic Aβ aggregates, subsequently breaking them down into nontoxic monomers. This leads to two significant outcomes: a reduction of Aβ aggregates in the brain and a subsequent increase in Aβ monomers in blood. The monomeric Aβ, unlike its aggregated form, can now traverse the BBB and enter the bloodstream. This mechanism provides an innovative approach to AD treatment and diagnosis. By detaching cerebral Aβ aggregates, EPPS facilitates Aβ clearance and addresses a key pathological feature of AD. Concurrently, the increase in blood Aβ levels offers a potential biomarker for monitoring treatment efficacy and disease progression, thereby revolutionizing both AD treatment and diagnosis. Investigating the detailed mode of action of drug candidates requires structural information about a target protein. Unfortunately, the unstable and heterogeneous nature of Aβ aggregates, which form larger clusters, complicates the identification of these structures. Therefore, we developed new tools for screening small molecules by immobilizing monomeric Aβ and its fragments on plates. This allows us not only to identify novel compounds that target Aβ but also to elucidate their mechanisms of action, enabling the development of Aβ-targeting therapeutic avenues in AD. We believe that our work on chemical-driven amyloid clearance through small molecules represents an advance in AD research, offering chemical diversity and straightforward, economical development processes. In clinical practice, we anticipate that these findings will contribute to the development of patient-friendly therapeutic and diagnostic interventions, including self-administered and orally available options, thereby enhancing disease management and overall quality of life for individuals with AD. Furthermore, this research extends beyond AD, potentially offering insights into other neurodegenerative diseases characterized by protein aggregation.