Project Summary Aim 1 addresses the dearth of drugs for dementia, by structure-based drug design. This approach, so fruitful for treating cancer and HIV-AIDS, is opening for Alzheimer’s Disease (AD) because of advances in diffraction and cryoEM. Aggregation of protein tau is strongly correlated with the onset of dementia. Based on atomic structures, 9 inhibitors of tau aggregation have been designed. Aim 1 proposes determination of the atomic structure of one of these inhibitors on the tip of tau fibrils extracted from the autopsied brain of an AD patient. By binding to fibril tips, our designed inhibitors halt “seeding” of new tau fibrils in connected cells. This atomic structure will reveal how to increase the affinity and specificity of the inhibitor. Aim 1 will also focus on the discovery of the identity and binding sites on tau of molecular factors that drive its aggregation. These structures will enable design of small molecules and peptides that mask the binding site, thereby interfering with factor binding, and hence producing prophylactic drugs for AD. The same approach will visualize binding sites of post-translational modifications of tau, including phosphorylation, offering a related strategy for drug design. Aim 2 proposes to fill the vacuum of knowledge of the structures of small aggregates of tau and beta- amyloid, known as oligomers. Numerous studies of others provide evidence that oligomers are more cytotoxic on a weight basis (but not a mole basis) than fibrils of the same protein. And, somewhat mysteriously, oligomers of different fibril-forming proteins share structural similarities in that a particular antibody (A11) recognizes them, but not their corresponding fibrils. The transient nature of oligomers has defeated previous attempts to learn their atomic structures, but fortunately our collaborators in the Kayed and Raskatov labs have found methods to stabilize oligomers of tau and beta-amyloid, respectively, long enough for us to make grids suitable for cryoEM structure determination. Preliminary micrographs are encouraging. Aim 3 proposes tests of AD drugs in “mini-brains” which are grown in the lab of our collaborator UCLA Prof. Novitch. These organoids are about the size of a BB yet display structure and electrical properties of actual human brains. They are made from human cells and display the cell types and electrical messaging of human brains. Preliminary work shows these mini-brains can be infected with tau pathology, and now the ability of our various drug candidates to interfere with the spreading and damage of aggregated tau will be tested in them. If successful, this approach can provide a new avenue for testing Alzheimer’s drugs prior to human trials.