Development of STEP Allosteric Inhibitors as Novel Therapeutics for Alzheimer's Disease

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PROJECT SUMMARY STriatal-Enriched Tyrosine Phosphatase (STEP) is a neuron-specific protein tyrosine phosphatase (PTP) and a novel therapeutic target for Alzheimer's disease (AD), a debilitating neurodegenerative disorder for which currently no cure exists. Recent studies indicate that STEP is overactive in AD and other neurodegenerative and neuropsychiatric disorders. The emergent model suggests that the increase in STEP activity interferes with synaptic function and contributes to the characteristic cognitive and behavioral deficits in these diseases. Knockout or pharmacological inhibition of STEP in a mouse model of AD decreases the biochemical and cognitive deficits in these mice, validating STEP as a novel drug target for the treatment of AD. However, the only reported STEP inhibitor with cellular and in vivo activity is a benzopentathiepin (TC-2153) that is known to modify DNA, thus likely causing adverse effects when given chronically. In this proposal we plan to develop the first selective and drug-like inhibitors of STEP for proof-of-concept (POC) studies in AD mouse models. Previous efforts to generate more drug-like STEP inhibitors have failed. These prior high-throughput screening (HTS) efforts utilized simple biochemical screening assays with truncated STEP constructs that only contained the catalytic domain. Thus, they favored the identification of compounds that target the highly conserved active site and are not selective for STEP. We have developed a robust HTS platform based on protein thermal shift (PTS) technology that can detect small molecule binding to full-length STEP in 384-well format. A sequence of secondary assays to further characterize hits is in place, as well as crucial collaborations, ensuring the greatest likelihood of success in the search for small molecules that are suitable for POC studies aimed at establishing a STEP-based treatment strategy in AD. In Aim 1 we will perform HTS for STEP allosteric inhibitors using our PTS- based screening platform. We will confirm and characterize hit compounds and select the most promising scaffolds for chemical optimization in Aim 2, where we will improve STEP inhibitor potency, selectivity, and drug- like properties. In Aim 3, we will evaluate selected inhibitors in cellular models for efficacy and specificity. Our overall goal is to develop at least one lead series and one back-up series of potent and specific STEP inhibitor probes that are ready for subsequent testing and optimization for in vivo studies.