Development of Melanocortin 4 Receptor Agonists by Exploiting Animal-Derived Macrocyclic, Disulfide-Rich Peptide Scaffolds

Discovery and development of macrocyclic peptide modulators of the cannabinoid 2 receptor

The cannabinoid type 2 receptor (CB2R), a G protein-coupled receptor, is an important regulator of immune cell function and a promising target to treat chronic inflammation and fibrosis. While CB2R is typically targeted by small molecules, including endo-, phyto-, and synthetic cannabinoids, peptides-owing to their size-may offer a different interaction space to facilitate differential interactions with the receptor. Here, we explore plant-derived cyclic cystine-knot peptides as ligands of the CB2R. Cyclotides are known for their exceptional biochemical stability. Recently, they gained attention as G protein-coupled receptor modulators and as templates for designing peptide ligands with improved pharmacokinetic properties over linear peptides. Cyclotide-based ligands for CB2R were profiled based on a peptide-enriched extract library comprising nine plants. Employing pharmacology-guided fractionation and peptidomics, we identified the cyclotide vodo-C1 from sweet violet (Viola odorata) as a full agonist of CB2R with an affinity (Ki) of 1 μM and a potency (EC50) of 8 μM. Leveraging deep learning networks, we verified the structural topology of vodo-C1 and modeled its molecular volume in comparison to the CB2R ligand binding pocket. In a fragment-based approach, we designed and characterized vodo-C1-based bicyclic peptides (vBCL1-4), aiming to reduce size and improve potency. Opposite to vodo-C1, the vBCL peptides lacked the ability to activate the receptor but acted as negative allosteric modulators or neutral antagonists of CB2R. This study introduces a macrocyclic peptide phytocannabinoid, which served as a template for the development of synthetic CB2R peptide modulators. These findings offer opportunities for future peptide-based probe and drug development at cannabinoid receptors.

Novel BRICHOS-Related Antimicrobial Peptides from the Marine Worm Heteromastus filiformis: Transcriptome Mining, Synthesis, Biological Activities, and Therapeutic Potential

Marine polychaetes represent an extremely rich and underexplored source of novel families of antimicrobial peptides (AMPs). The rapid development of next generation sequencing technologies and modern bioinformatics approaches allows us to apply them for characterization of AMP-derived genes and the identification of encoded immune-related peptides with the aid of genome and transcriptome mining. Here, we describe a universal bioinformatic approach based on the conserved BRICHOS domain as a search query for the identification of novel structurally unique AMP families in annelids. In this paper, we report the discovery of 13 novel BRICHOS-related peptides, ranging from 18 to 91 amino acid residues in length, in the cosmopolitan marine worm Heteromastus filiformis with the assistance of transcriptome mining. Two characteristic peptides with a low homology in relation to known AMPs-the α-helical amphiphilic linear peptide, consisting of 28 amino acid residues and designated as HfBRI-28, and the 25-mer β-hairpin peptide, specified as HfBRI-25 and having a unique structure stabilized by two disulfide bonds-were obtained and analyzed as potential antimicrobials. Interestingly, both peptides showed the ability to kill bacteria via membrane damage, but mechanisms of their action and spectra of their activity differed significantly. Being non-cytotoxic towards mammalian cells and stable to proteolysis in the blood serum, HfBRI-25 was selected for further in vivo studies in a lethal murine model of the Escherichia coli infection, where the peptide contributed to the 100% survival rate in animals. A high activity against uropathogenic strains of E. coli (UPEC) as well as a strong ability to kill bacteria within biofilms allow us to consider the novel peptide HfBRI-25 as a promising candidate for the clinical therapy of urinary tract infections (UTI) associated with UPEC.