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Updated: Aug 22, 2025

Methods for the Discovery of Novel Compounds Modulating a Gamma-Aminobutyric Acid Receptor Type A Neurotransmission
Published on: August 16, 2018
The first structure-activity relationship study of oxytocin as a positive allosteric modulator for the µ opioid
Takaaki Mizuguchi1, Kanako Miyano2, Risa Yamauchi3
1Laboratory of Medicinal Chemistry, School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan; Medicinal Research Laboratories, School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan.
Abstract:
Positive allosteric modulators (PAMs) of G protein-coupled receptors (GPCRs) have drawn attention as novel drug candidates. PAMs can enhance the activities of endogenous agonists which are not only secreted at appropriate times and in parts of the body, but also are immediately metabolized. Therefore, they are expected to show fewer side effects than exogeneous orthosteric ligands. Recently, we have reported that oxytocin (OT) functioned as a PAM of the μ opioid receptor (MOR) which was one of the most potent targets for analgesics. OT is thus thought to be a useful compound for the development of novel analgesics. In this study, several OT analogs were synthesized and evaluated with an intact cell-based assay to investigate the crucial structures of OT for exerting the PAM activity. The assay results indicated that the cyclic structure formed by an intramolecular disulfide bond and the three C-terminal residues containing a small Gly residue of OT were essential for their function as a MOR-PAM. Intriguingly, two analogs having an amide or an ethylene tether instead of the intramolecular disulfide bridge did not have any PAM effects. The results suggested that the disulfide linkage of OT would be a key structure for exerting the PAM activity at the MOR.
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