PROJECT SUMMARY Alzheimer's disease (AD) is the most common form of dementia accompanied by detrimental cognitive deficits and pathological accumulation of amyloid-β (Aβ) plaques and tau-containing neurofibrillary tangles. The majority of AD cases occur late in life, and it usually develops after 65 years of age. The strongest genetic risk factor for late-onset AD (LOAD) is apolipoprotein E (APOE) genotype, with the ε4 allele increasing AD risk and the ε2 allele being protective compared with the common ε3 allele. Increasing evidence indicates that down- regulation of apoE4 protein level and/or inhibition of apoE4 aggregation not only alleviate amyloid pathology but also protect against tau-mediated neurodegeneration. In our preliminary studies, we have developed an apoE4 reporter assay with a split luciferase protein-fragment complementation, enabling us to not only monitor apoE4 protein level but also measure apoE4 self-oligomerization/aggregation by luciferase bioluminescent signals in a high-throughput screening format. Under the support of the Mayo-SBP (Sanford Burnham Prebys) Drug Discovery Collaboration Program, we performed a pilot screen of ~17,000 small molecule compounds with satisfactory performance, and discovered a novel apoE4 modulator that down-regulates apoE4 protein level and inhibits tau phosphorylation in induced pluripotent stem cells (iPSCs)-derived cerebral organoids from AD patient carrying APOE4, demonstrating that our HTS assay is robust and capable of identifying novel apoE4 modulators. Herein, we proposed a collaborative effort to identify apoE4 modulators that down-regulate apoE4 protein level and/or suppress apoE4 aggregation for AD therapy. Aim 1 will complete the apoE4 reporter high-throughput screen on a large chemical library to identify potent and specific apoE4 modulators for suppressing apoE4 level and/or aggregation. Aim 2 will examine the potency, modes of actin (MOA), and therapeutic effects of apoE4 modulators using biochemical and cell-based assays and human iPSC-derived cellular models. Aim 3 will perform SAR-by-catalog and limited chemistry on lead compounds to improve their potency and efficacy and determine the therapeutic efficacy of the most promising candidate compounds in 3-D cerebral organoid models such that our findings may have relevance in a humanized setting. Moreover, the “drug-like” and pharmacokinetics properties and brain penetration will be characterized and benchmarked to position them for future in vivo preclinical animal studies. The identified apoE4 modulators will be promising drug leads in novel therapeutic strategies for AD.