As a disease-modifying approach for Alzheimer's disease (AD), clioquinol (CQ) targets beta-amyloid (Abeta) reactions with synaptic Zn and Cu yet promotes metal uptake. Here we characterize the second-generation 8-hydroxy quinoline analog PBT2, which also targets metal-induced aggregation of Abeta, but is more effective as a Zn/Cu ionophore and has greater blood-brain barrier permeability. Given orally to two types of amyloid-bearing transgenic mouse models of AD, PBT2 outperformed CQ by markedly decreasing soluble interstitial brain Abeta within hours and improving cognitive performance to exceed that of normal littermate controls within days. Nontransgenic mice were unaffected by PBT2. The current data demonstrate that ionophore activity, inhibition of in vitro metal-mediated Abeta reactions, and blood-brain barrier permeability are indices that predict a potential disease-modifying drug for AD. The speed of recovery of the animals underscores the acutely reversible nature of the cognitive deficits associated with transgenic models of AD.

Summary Alzheimer’s Disease (AD) is complicated by pro-oxidant intraneuronal Fe2+ elevation as well as extracellular Zn2+ accumulation within amyloid plaque. We found that the AD β-amyloid protein precursor (APP) possesses ferroxidase activity mediated by a conserved H-ferritin-like active site, which is inhibited specifically by Zn2+. Like ceruloplasmin, APP catalytically oxidizes Fe2+, loads Fe3+ into transferrin, and has a major interaction with ferroportin in HEK293T cells (that lack ceruloplasmin) and in human cortical tissue. Ablation of APP in HEK293T cells and primary neurons induces marked iron retention, whereas increasing APP695 promotes iron export. Unlike normal mice, APP−/− mice are vulnerable to dietary iron exposure, which causes Fe2+ accumulation and oxidative stress in cortical neurons. Paralleling iron accumulation, APP ferroxidase activity in AD post-mortem neocortex is inhibited by endogenous Zn2+, which we demonstrate can originate from Zn2+-laden amyloid aggregates and correlates with Aβ burden. Abnormal exchange of cortical zinc may link amyloid pathology with neuronal iron accumulation in AD.

Cognitive decline in Alzheimer's disease (AD) involves pathological accumulation of synaptotoxic amyloid-␤ (A␤) oligomers and hyperphosphorylated tau. Because recent evidence indicates that glycogen synthase kinase 3␤ (GSK3␤) activity regulates these neurotoxic pathways, we developed an AD therapeutic strategy to target GSK3␤. The strategy involves the use of copper-bis(thiosemicarbazonoto) complexes to increase intracellular copper bioavailability and inhibit GSK3␤ through activation of an Akt signaling pathway. Our lead compound Cu II (gtsm) significantly inhibited GSK3␤ in the brains of APP/PS1 transgenic AD model mice. Cu II (gtsm) also decreased the abundance of A␤ trimers and phosphorylated tau, and restored performance of AD mice in the Y-maze test to levels expected for cognitively normal animals. Improvement in the Y-maze correlated directly with decreased A␤ trimer levels. This study demonstrates that increasing intracellular copper bioavailability can restore cognitive function by inhibiting the accumulation of neurotoxic A␤ trimers and phosphorylated tau.Alzheimer's disease ͉ bioinorganic chemistry ͉ glycogen synthase kinase ͉ therapeutic ͉ animal model A lzheimer's disease (AD) is a neurodegenerative disorder characterized clinically by impaired cognitive performance and pathologically by cerebral deposition of extracellular amyloid plaques and intracellular neurofibrillary tangles. Amyloid plaques in AD contain aggregated forms of the 39-to 43-aa amyloid-␤ peptide (A␤) and A␤ is strongly implicated as a causative agent responsible for cognitive failure in AD. A diverse range of mechanisms for A␤ toxicity has been reported (1). A␤ is produced from the amyloid precursor protein (APP) (2-5) and readily aggregates to form insoluble, high-molecular-mass amyloid structures. Intermediates on the A␤ aggregation pathway, primarily low-molecular-mass oligomers such as dimers and trimers, exhibit the greatest neurotoxicity (6-8). In addition to A␤ oligomers, aberrantly phosphor ylated microtubuleassociated protein tau is also associated with cognitive decline in AD (9). Intracellular neurofibrillary tangles in the AD brain contain hyperphosphorylated tau, and A␤ induced cognitive deficits characteristic of AD transgenic mice are attenuated by decreasing levels of endogenous tau (10).It is now widely recognized that a truly effective therapeutic compound for treating AD needs to attenuate both the A␤-and tau-mediated pathologies. Recent positive outcomes for PBT2 in clinical and preclinical trials are therefore pertinent. Lannfelt et al.(11) demonstrated in phase IIa clinical trials that PBT2 lowers plasma A␤ levels and attenuates cognitive decline, and Adlard et al. (12) have shown that PBT2 decreases interstitial A␤ and phosphorylated tau in the brains of AD model mice. PBT2 is a secondgeneration 8-OH quinoline, which, unlike its predecessor clioquinol, lacks iodine and was selected for clinical development because of its easier chemical synthesis, higher solubility, and increased blood-brain barrier perme...