# Small molecule antagonist probes for the relaxin-3/RXFP3 system

> **NIH NIH R01** · RESEARCH TRIANGLE INSTITUTE · 2021 · $635,310

## Abstract

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.

## Key facts

- **NIH application ID:** 10266756
- **Project number:** 5R01AA028255-02
- **Recipient organization:** RESEARCH TRIANGLE INSTITUTE
- **Principal Investigator:** Joyce Besheer
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $635,310
- **Award type:** 5
- **Project period:** 2020-09-20 → 2023-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10266756

## Citation

> US National Institutes of Health, RePORTER application 10266756, Small molecule antagonist probes for the relaxin-3/RXFP3 system (5R01AA028255-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10266756. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*