SUMMARY To address challenges of the anticipated diversity of target classes for AD drug discovery, the Open-AD Assay Development and High Throughput Screening (HTS) Core (Assay and Screen Core) has established an innovative operational structure that harnesses a wide range of expertise and capabilities for AD target evaluation and chemical probe discovery from both public and private sectors. The Core will be organized with an operational hub at Emory University and spokes of expanded capabilities with world-leading Associated Partners, who will contribute specialized assays, screens, and libraries. Associated Partners include Baylor College of Medicine with highly efficient Drosophila models, the University of Washington with human iPSC- based assays for target validation, the Diamond Synchrotron for fragment-based screens, the Structural Genomics Consortium (SGC) for rich experience in diverse assays and screens, Charles River Laboratories with its diversity libraries for HTS and pharmacology, X-Chem with its unique DNA-encoded libraries, Alzheimer?s Research UK Oxford Drug Discovery Institute for a suite of cell-based functional assays for chemical probe characterization, the University of Pittsburgh with AD animal models for in vivo target engagement and efficacy studies, and Eli Lilly for their expertise in AD targets and drug development. With our combined complementary expertise and capabilities and integrated operation with Bioinformatics, Structural Biology, MedChem, and Admin and Data Cores, we will support the overarching goal of Open-AD by creating experimental reagents and validated hits to populate Target Enabling Packages (TEPs) for each prioritized target in order to catalyze robust evaluation of a diverse set of therapeutic hypotheses. The Assay and Screen Core aims (i) to provide experimental validation for nominated targets followed by development of primary and secondary assays to enable hit discovery, (ii) implement HTS and high content screening (HCS) campaigns for prioritized targets to discover validated hits, and (iii) to develop and utilize functional assays for chemical probe characterization. Over the 5-year project, completion of these aims will generate experimental evidence for up to 100 nominated targets, advance 50 targets for development of assay packages, execute 30 HTS or HCS campaigns for hit discovery, and deliver validated hit series for 15 targets to Open-AD. For each target, all reagents and tools will be released as TEPs to the scientific community. 1