Targeting Postsynaptic Small G-protein Regulators

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ABSTRACT This application aims to discover and validate small-molecule inhibitors of the Rac guanosine-nucleotide exchange factor (GEF) kalirin, a major signal transduction hub in dendritic spines in the cerebral cortex. Our long-term goal is to translate knowledge about dendritic spine plasticity and synaptic small GTPase signaling, into treatments of neuropsychiatric disorders (NPDs). Dendritic spines are the sites of most excitatory synapses in the brain, and play central roles in the development and plasticity of neuronal circuits, and ultimately in learning, memory, and behavior. Conversely, abnormalities in dendritic spines are extensively involved in NPD pathogenesis. Molecular pathways mediated by small GTPases such as Rac, direct upstream activators (GEFs), and their downstream targets are major pathways that govern dendritic spine plasticity. Furthermore, genetic and postmortem studies demonstrate a key role for these pathways in the pathogenesis of NPDs. Kalirin is the most abundant Rac-GEF in dendritic spines in the cerebral cortex and hippocampus, plays central roles in spine plasticity and pathology as shown by knockdown and knockout studies, and has been implicated in NPDs by genetic, postmortem, and functional studies. Hence, in order to study the role of kalirin in cortical plasticity and NPD pathogenesis, and of Rac-GTPase signaling in general, here we aim to develop novel, potent, specific, inhibitors of kalirin with biological activity in neurons. We have established a collaboration between experts in synapse biology and NPDs, high- throughput screening and computational pharmacology, medicinal chemistry, and crystallography, and performed extensive preliminary studies that demonstrate the validity of our hypothesis and the feasibility of our approach. We propose the following Specific Aims: 1) Hit discovery by HTS to identify small molecules binding to kalirin's DHPH domain and inhibiting its GEF activity. 2) Hit validation in cellular and neuronal assays. 3) Characterization of the mechanism of action of hit compounds. 4) Medicinal chemistry optimization of new GEF inhibitors