Intranasal administration of a stapled relaxin-3 mimetic has anxiolytic- and antidepressant-like activity in rats.

BACKGROUND AND PURPOSE: Depression and anxiety are common causes of disability, and innovative tools and potential pharmacological targets are actively sought for prevention and treatment. Therapeutic strategies targeting the relaxin-3 peptide or its primary endogenous receptor, RXFP3, for the treatment of major depression and anxiety disorders have been limited by a lack of compounds with drug-like properties. We proposed that a hydrocarbon-stapled mimetic of relaxin-3, when administered intranasally, might be uniquely applicable to the treatment of these disorders. EXPERIMENTAL APPROACH: We designed a series of hydrocarbon-stapled relaxin-3 mimetics and identified the most potent compound using in vitro receptor binding and activation assays. Further, we assessed the effect of intranasal delivery of relaxin-3 and the lead stapled mimetic in rat models of anxiety and depression. KEY RESULTS: We developed an i,i+7 stapled relaxin-3 mimetic that manifested a stabilized α-helical structure, proteolytic resistance, and confirmed agonist activity in receptor binding and activation in vitro assays. The stapled peptide agonist enhanced food intake after intracerebral infusion in rats, confirming in vivo activity. We showed that intranasal delivery of the lead i,i+7 stapled peptide or relaxin-3 had orexigenic effects in rats, indicating a potential clinically translatable route of delivery. Further, intranasal administration of the lead i,i+7 stapled peptide exerted anxiolytic and antidepressant-like activity in anxiety- and depression-related behaviour paradigms. CONCLUSIONS AND IMPLICATIONS: Our preclinical findings demonstrate that targeting the relaxin-3/RXFP3 receptor system via intranasal delivery of an i,i+7 stapled relaxin-3 mimetic may represent an effective treatment approach for depression, anxiety, and related neuropsychiatric disorders.

Hydrocarbon stapled B chain analogues of relaxin-3 retain biological activity.

Relaxin-3 or insulin-like peptide 7 (INSL7) is the most recently discovered relaxin/insulin-like family peptide. Mature relaxin-3 consists of an A chain and a B chain held by disulphide bonds. According to structure activity relationship studies, the relaxin-3 B chain is more important in binding and activating the receptor. RXFP3 (also known as Relaxin-3 receptor 1, GPCR 135, somatostatin- and angiotensin- like peptide receptor or SALPR) was identified as the cognate receptor for relaxin-3 by expression profiles and binding studies. Recent studies imply roles of this system in mediating stress and anxiety, feeding, metabolism and cognition. Stapling of peptides is a technique used to develop peptide drugs for otherwise undruggable targets. The main advantages of stapling include, increased activity due to reduced proteolysis, increased affinity to receptors and increased cell permeability. Stable agonists and antagonists of RXFP3 are crucial for understanding the physiological significance of this system. So far, agonists and antagonists of RXFP3 are peptides. In this study, for the first time, we have introduced stapling of the relaxin-3 B chain at 14th and 18th positions (14s18) and 18th and 22nd position (18s22). These stapled peptides showed greater helicity than the unstapled relaxin-3 B chain in circular dichroism analysis. Both stapled peptides bound RXFP3 and activated RXFP3 as observed in an inhibition of forskolin-induced cAMP assay and a ERK1/2 activation assay, although with different potencies. Therefore, we conclude that stapling of the relaxin3 B chain does not compromise its ability to activate RXFP3 and is a promising method for developing stable peptide agonists and antagonists of RXFP3 to aid relaxin-3/RXFP3 research.

Cascade fluorofunctionalisation of 2,3-unsubstituted indoles by means of electrophilic fluorination.

Cascade fluorofunctionalisation of 2,3-unsubstituted indoles featuring the formation of C-C, C-F and C-O bonds via electrophilic fluorination using N-fluorobenzenesulfonimide is described. The use of an O-nucleophile tethered to the nitrogen of indoles enables the synthesis of polycyclic fluorinated indoline derivatives from simple precursors in 40-63% yields.