Small Molecule Ligands Targeting Pathological Tau Signaling In AD And Related Dementias - Abstract Tau plays a significant role in pathogenesis of many adult-onset neurodegenerative diseases. Misfolded and hyperphosphorylated tau is pathognomic for Alzheimer’s disease and Chronic Traumatic Encephalopathy, as well as playing a secondary role in other diseases such as Parkinson’s disease. In addition, tau mutations cause diseases such as Progressive Supranuclear Palsy, Corticobasal Degeneration and Frontotemporal Lobe Degeneration-17. Although each tauopathy has a disease specific phenotype, histological presentation, morphology and neurological presentation, all are associated with misfolded tau and tau hyperphosphorylation suggesting a common gain of toxic function. Misregulation of neuronal signaling involving Protein Phosphatase 1 (PP1) and GSK3b (GSK3) by misfolded tau has been identified as a toxic gain of function for all pathological tau examined. The activity is mediated by exposure of an N-terminal 17aa domain, the tau Phosphatase Activating Domain (PAD). The PAD is aberrantly exposed in all forms of pathogenic tau identified to date and leads to disruption of synaptic function and inhibition of fast axonal transport. A monoclonal antibody (TNT1) to the PAD eliminates toxicity of pathogenic tau. Since antibody-based therapies are impractical for intracellular neuronal targets, we devised a high throughput screen to identify small molecule ligands that block TNT1 binding to the PAD and prevent activation of PP1/GSK3 signaling. We identified a series of candidate molecules that prevent PP1 binding to tau and following initial optimization, we have focused on 3 PAD ligands (PADL) that successfully block toxic effects of pathogenic tau with IC50 of 18-195 nM in neurons, while exhibiting low toxicity in both neuronal and non-neuronal cells in culture (CC50 > 100µM). These PADLs prevent both axonal degeneration and cell death in cell-based models of tau pathology. In Aim 1, we will optimize early leads in the current chemical series to retain or improve potency and enhance brain bioavailability. In Aim 2, PADLs with suitable properties will be evaluated for therapeutic potential by phenotypic characterization of candidate PADLs in rodent neurons with mutant tau and IPSC-derived neurons from patients with tau mutations to assess the ability of PADL to prevent tau pathology in cultured human neurons These will determine effective doses and toxicity in cultured neurons. The distribution and tolerability of PADLs in wild type mice will establish their suitability for treating tauopathies. Finally, in Aim 3 we will conduct preclinical trials using a well-characterized mouse model of Progressive Supranuclear Palsy (JNPL3, MAPT P301L). Target engagement will be assessed by immunoblots and immunohistochemistry to evaluate acute effects of candidate PADLs on GSK3b activity and tau phosphorylation in brains of WT and P301L tau transgenic mice. Preclinical studies will assess the ability of PADLs to prevent neurodegeneration in P301L mice. Efficacy will be determined by prevention of cognitive and motor symptoms, as well as reduction of indicators of neurodegeneration and longer lifespan.
