Optimization of microtubule-stabilizing triazolopyrimidines as therapeutics for Alzheimer's disease and related tauopathies

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PROJECT SUMMARY A group of neurodegenerative diseases referred to as tauopathies, which includes Alzheimer’s disease (AD), are characterized by the presence within brain neurons of inclusions comprised of hyperphosphorylated forms of tau protein. Tau is normally a microtubule (MT)-associated protein that appears to provide stability to MTs in axons, and excessive phosphorylation of tau in tauopathies promotes its disengagement from MTs and misfolding into oligomeric and fibrillar structures. This results in increased MT dynamicity, reduced MT density and altered axonal transport in transgenic (Tg) mouse tauopathy models, with evidence of similar MT deficits in AD brain that likely contribute to neurodegeneration. We previously demonstrated that administration of the brain-penetrant MT-stabilizing natural product, epothilone D (EpoD), to Tg tauopathy mice resulted in dramatic improvements in several key endpoints, including increased MT density, reduced axonal dystrophy, diminished tau pathology and a lowering of neuron loss with improved cognitive performance. Although EpoD progressed to a small Phase 1b clinical trial in AD patients, its future clinical advancement is uncertain. Thus, there would be considerable value in identifying alternative MT-stabilizing agents that could undergo more thorough testing in AD and tauopathy patients. In this regard, we have synthesized and evaluated a series of non-natural product MT-stabilizing compounds (triazolopyrimidines or TPDs, and phenylpyrimidines), and an evaluation of these compounds has led to an understanding of key structure-activity correlates. An assessment of pharmacokinetic (PK) and pharmacodynamics (PD) profiles of select examples resulted in the identification of a lead TPD that has recently shown highly beneficial activity in a Tg mouse tauopathy model. We propose in this early-stage U01 program to utilize lessons learned in our initial medicinal chemistry exploration to conduct a highly focused chemical optimization program to identify a candidate TPD compound suitable for entry into IND-enabling pre- clinical safety pharmacology and toxicology studies. We will utilize in silico computational docking studies to select and prioritize patentable TPD congeners for activity testing in established cellular assays. Data from these studies will be utilized to refine the scoring method and re-evaluate the prioritization of in silico hits, leading to additional iterative cycles of synthesis and biological evaluations. The most active compounds identified through this process will be assessed for brain exposure in mice, and preferred examples will undergo complete PK and PD testing. Ultimately, a select few analogs with superior PK/PD properties will be assessed for safety/tolerability in mice, with the best candidate advancing to efficacy studies in an established Tg mouse tauopathy model. The overall project objective is to identify a patentable lead candidate TPD that would be eligible for entry in IND-enabling studies to be conducted after completion of this early-stage U01 program.