Small-molecule lead identification for inhibition of tau oligomer formation

Abstract

There is a need for alternative approaches for the development of disease-modifying therapeutics for Alzheimer's disease (AD) as all phase III drug development programs to-date based on the amyloid hypothesis have failed to meet their clinical endpoints. Research advances indicate that pre-tangle aggregates of tau cause transmission of pathology and symptoms related to memory formation validating tau oligomers as a target for drug discovery. A highly differentiated HTS assay (proximity-based) was developed to discover inhibitors of tau oligomer formation and transferred to MHTSC to screen a drug-like library of 100,000 compounds. Cytotoxicity studies were performed using SH-SY5Y neuroblastoma cells on a high throughput platform. Medicinal chemistry analysis was performed that enabled clustering of hits into chemical series that demonstrated a preliminary SAR. HTS hit triage was performed including confirmation of activity in primary assays with dose response, mass spec evaluation of structure and purity, elimination of reactive species, and removal of known/suspected promiscuous inhibitors or compounds that may contribute to tau aggregation at high concentrations. Lastly, lead series were prioritized based on an analysis of novelty, freedom-to-operate, and the potential for intellectual property on composition of matter. For neurocytotoxicity, 338 active hits and 3 toxic control compounds were evaluated. Cell growth was inhibited at less than 50 uM by fifty compounds and the controls. Only 14 compounds had IC50 values <10 uM. Medicinal chemistry analysis was performed on the 576 most active inhibitors from the HTS assay. Cytotoxic compounds were eliminated and initial SAR was developed with compounds clustered by structure type. The clustering revealed that there are 3 large series (>10 compounds), 6 medium series (4 - 5 compounds), 8 small sized series (2 - 3 compounds), and 22 singletons. The preliminary analysis of the structures clearly demonstrates that certain structural classes are active in this assay. It also indicates that hit optimization is possible since a range of potency is observed within structural classes. The HTS has achieved the important goal of finding viable compounds as starting points for medicinal chemical optimization to generate leads.