AUTHOR=Fahradpour Mohsen , Keov Peter , Tognola Carlotta , Perez-Santamarina Estela , McCormick Peter J. , Ghassempour Alireza , Gruber Christian W. 

TITLE=Cyclotides Isolated from an Ipecac Root Extract Antagonize the Corticotropin Releasing Factor Type 1 Receptor

JOURNAL=Frontiers in Pharmacology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2017.00616

DOI=10.3389/fphar.2017.00616

ISSN=1663-9812

ABSTRACT=<p>Cyclotides are plant derived, cystine-knot stabilized peptides characterized by their natural abundance, sequence variability and structural plasticity. They are abundantly expressed in Rubiaceae, Psychotrieae in particular. Previously the cyclotide kalata B7 was identified to modulate the human oxytocin and vasopressin G protein-coupled receptors (GPCRs), providing molecular validation of the plants’ uterotonic properties and further establishing cyclotides as valuable source for GPCR ligand design. In this study we screened a cyclotide extract derived from the root powder of the South American medicinal plant ipecac (<italic>Carapichea ipecacuanha</italic>) for its GPCR modulating activity of the corticotropin-releasing factor type 1 receptor (CRF<sub>1</sub>R). We identified and characterized seven novel cyclotides. One cyclotide, caripe 8, isolated from the most active fraction, was further analyzed and found to antagonize the CRF<sub>1</sub>R. A nanomolar concentration of this cyclotide (260 nM) reduced CRF potency by ∼4.5-fold. In contrast, caripe 8 did not inhibit forskolin-, or vasopressin-stimulated cAMP responses at the vasopressin V<sub>2</sub> receptor, suggesting a CRF<sub>1</sub>R-specific mode-of-action. These results in conjunction with our previous findings establish cyclotides as modulators of both classes A and B GPCRs. Given the diversity of cyclotides, our data point to other cyclotide-GPCR interactions as potentially important sources of drug-like molecules.</p>