PROJECT 2- SUMMARY/ABSTRACT The pathological accumulation of Aβ peptides as toxic oligomers, amyloid plaques and cerebral amyloid angiopathy (CAA), either from increased production of Aβ peptides or from their inadequate clearance, is critical in the pathogenesis of Alzheimer’s disease (AD). The apolipoprotein E4 (apoE4) allele, a major genetic risk factor for late-onset AD, was strongly associated with increased amyloid plaque and vascular amyloid pathology. We have shown that using Aβ12-28P peptides to block the apoE/Aβ interaction constitutes a novel treatment for AD by reducing brain parenchymal and vascular amyloid burden as well as tau -related pathology in multiple AD transgenic (Tg) lines. We also showed that Aβ12-28P penetrates the blood-brain-barrier (BBB). In our preliminary studies, we designed a peptoid library derived from the Aβ12 -28P sequence to screen for apoE/Aβ binding inhibitors with higher efficacy and safety compared to Aβ12-28P. Cyclic peptoids typically have better cell permeability compared to the linear peptides of the same or similar sequence. Indeed, our lead peptoid CPO_Aβ17-21P is cyclic, has a Ki of 1.02 nM against the binding of apoE4 and Aβ, and has therapeutic efficacy in an APP/PS1 AD Tg model. Our preliminary experiments clearly show it is highly effective at reducing the amyloid burden at a dosage 7.5-fold lower than that used with the parent Aβ12-28P. CPO_Aβ17-21P is therefore an outstanding starting point for further biochemical and medicinal chemistry development of both novel peptoid and drug-like, small molecules. We propose testing our lead small, BBB- penetrant, peptoid molecule and analogous drug-like, small molecules in vivo, hypothesizing that these will reduce both neuronal and synaptic toxicity by inhibiting the apoE4/Aβ interaction. We will investigate how these treatments affect the amyloid proteome, and correlate changes to findings in human tissue ( Project 1) and the proteome in the same AD Tg models after immunotherapy (Project 3). We hypothesize that the treated amyloid proteome in apoE4 mice will convert to a more apoE3-like proteome. Aim 1: Design non-toxic, pharmacokinetically favorable peptoid and drug-like, small molecule antagonists of the apoE/Aβ interaction, and characterize their effects in vitro. Aim 2: Te st the lead peptoid and analogous drug -like, small molecules in vivo using 3xTg mice, APP/PS1 and TgSwDI mice crossed onto human knock-in (KI) apoE2, E3 or E4, or apoE knock-out (KO) backgrounds. Aim 3: Compare the amyloid plaque and vessel proteomes in peptoid and drug-like, small molecule tre ated Tg and control mice on KI apoE2, E3 or E4, or apoE KO backgrounds .