The goal of this project is to develop and test small-molecule antagonist probes of the relaxin-3/RXFP3 system for behavioral studies in alcohol addiction and relapse. Alcohol addiction is a heterogeneous, chronic relapsing disorder. Current therapies are inadequate, and therefore new medications based on novel targets are needed. The recently deorphanized relaxin-3/RXFP3 system comprises the endogenous neuropeptide relaxin-3 and its cognate G protein-coupled receptor RXFP3. Multiple lines of evidence suggest that RXFP3 antagonism is a novel target for therapeutics to treat alcohol addiction and relapse. Although RXFP3 antagonist peptides are available, there are unmet needs for non-peptide small-molecule antagonists, which are systemically bioavailable and can penetrate the blood-brain barrier, to further validate the relaxin-3/RXFP3 system as a novel drug target. To date, our group has made significant progress in this regard. We have developed a stable RXFP3 cell-based cAMP high-throughput screening assay and completed a screening campaign to identify antagonist hits. Focused structure-activity relationship studies of the hit compound have resulted in the first series of small-molecule antagonists that have Ke <500 nM and are highly selective for RXFP3 over another receptor subtype RXFP1 and can penetrate into the brain. In this application, we propose to further refine our early lead-like compounds to produce antagonist probes for in vivo studies through three iterative specific aims.
In Aim 1, we will optimize potency, receptor selectivity, and drug-like properties of RXFP3 antagonists using medicinal chemistry.
In Aim 2, we will characterize compounds using an RXFP3 functional cAMP assay and a radioligand binding assay. Select compounds will be assessed for receptor selectivity against RXFP1 and RXFP4, two subtypes of the relaxin family, and further evaluated in a target profiling screen. Potent and selective compounds will then be characterized using a battery of ADME and pharmacokinetic assays.
In Aim 3, we will test the best compounds, developed in Aims 1 and 2, in animal models of alcohol reinforcement and stress-induced reinstatement. Overall, completion of this project will provide in vivo antagonist probes to pharmacologically validate the relaxin-3/RXFP3 system as a novel target for treatment of alcoholism.

Public Health Relevance

The recently deorphanized relaxin-3/RXFP3 system has been implicated in regulating the stress response and plays an important role in behaviors related to alcohol abuse and relapse. In this project, we propose to develop potent, selective, and brain-penetrant small-molecule RXFP3 antagonists, which will serve as pharmacological tools to probe the RXFP3 functions in animal models of alcoholism.

National Institute of Health (NIH)
National Institute on Alcohol Abuse and Alcoholism (NIAAA)
Research Project (R01)
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Drug Discovery for the Nervous System Study Section (DDNS)
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Egli, Mark
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Research Triangle Institute
Research Triangle Park
United States
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