PROJECT SUMMARY As one of the most common brain disorders, epilepsy afflicts about 1% of the world population. Despite recent marked advances in seizure management, there are still more than 30% of patients poorly responding to current anti-seizure drugs (ASDs), which can cause wide-ranging and often unbearable side effects. It is another very unfortunate fact that current ASDs merely provide symptomatic relief, and no FDA-approved medication has been demonstrated to prevent the development of epilepsy in people at risks or modify the disease progression in those diagnosed with epilepsy. Developing safer, more effective anti-seizure and/or anti-epileptogenic therapies is in urgent unmet demand. Transient receptor potential canonical 3 (TRPC3) is a member of TRP family channels that control Ca2+ influxes. TRPC3 is found abundant in neocortex and hippocampus, where it colocalizes with brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase receptor B (TrkB), regulating BDNF/TrkB signaling- mediated dendritic remodeling in pyramidal neurons. Mounting evidence from recent studies suggest that the excessive BDNF/TrkB activity contributes to spontaneous recurrent seizures (SRSs) after status epilepticus (SE), indicative of a role of TRPC3 in epileptic seizures. Genetic ablation of TRPC3 reduces pilocarpine- induced seizures in mice, suggesting that TRPC3 inhibition might represent a novel anti-seizure and/or anti- epileptogenic strategy. Among TRPC3 inhibitors that emerged during the past decade, Pyr3 is most selective and thus widely used to study TRPC3-mediated Ca2+ entry in various pathological conditions. However, the chemical structure of Pyr3 poses a number of major liabilities including low metabolic stability caused by rapid hydrolysis of its ester moiety, leading to inactive carboxylic acid metabolite. Our overarching goal is to – using rationale design – develop a lead TRPC3 inhibitor with high metabolic stability, low toxicity, as well as favorable pharmacodynamic and pharmacokinetic properties (R61 phase). We will then determine its ability to suppress acute seizures, prevent SRSs (epileptogenesis), and/or improve cognitive outcomes (R33 phase). Upon successful completion, we will have established a proof-of-concept for TRPC3 inhibition as a novel anti- seizure and/or anti-epileptogenic strategy in a classical mouse model of epilepsy and a patented lead molecule for further development. Anticipated results will justify future studies on safety, efficacy, and more extensive lead-optimization if needed to develop a new therapy to prevent and/or suppress acquired epilepsy in patients suffering from putative seizure-precipitating events, such as de novo SE, traumatic brain injuries, etc.

RELEVANCE Despite the introduction of the third-generation anti-seizure drugs, epilepsy remains one of the most common and devastating neurological disorders. The current FDA-approved medications merely provide symptomatic relief, lack efficacy in controlling seizures among approximately one-third of epilepsy patients, and often impose wide-ranging, sometimes unbearable, side effects. The proposed research will develop novel drug-like inhibitors for the TRPC3 channel, an emerging therapeutic target for epileptic seizures, and may lead to a new treatment for acute seizures and/or chronic epilepsy.