Design, Synthesis, Structural and Functional Characterization of Novel Melanocortin Agonists Based on the Cyclotide Kalata B1

Abstract

Background: Cyclotides are useful scaffolds to stabilize bioactive peptides. Results: Four melanocortin analogues of kalata B1 were synthesized. One is a selective MC4R agonist. Conclusion:The analogues retain the native kalata B1 scaffold and introduce a designed pharmacological activity, validating cyclotides as protein engineering scaffolds. Significance: A novel type of melanocortin agonist has been developed, with potential as a drug lead for treating obesity.

Cyclotides: Overview and Biotechnological Applications

“…A similar approach has been used more recently for targeting the bradykinin and melanocortin 4 receptors for pain and obesity management, respectively. [14, 80] It is worth noting that the kalata B1-based bradykinin antagonist was shown to be orally bioavailable [14] highlighting the potential of the cyclotide scaffold for the development of orally-bioavailable peptide-based therapeutics. The cyclotide MCoTI-I has been recently used for the design of a potent (low nM) CXCR4 antagonist.…”

Synthetic Cystine-Knot Miniproteins – Valuable Scaffolds for Polypeptide Engineering

“…Peptide bearing the poly-R motif in loop 3 appeared the most active (IC 50 = 12 nM) and the most stable one [77]. Kalata B1 showed its utility as a scaffold for the development of stabilized melanocortin receptor 4 (MCR4) [78] agonists for the treatment of obesity [79]. To that end, four tetrapeptide epitopes derived from melanocyte-stimulating hormone, which acts against MCR, were incorporated in loop 6.…”

“…To that end, four tetrapeptide epitopes derived from melanocyte-stimulating hormone, which acts against MCR, were incorporated in loop 6. The most potent mutant showed a K i of 29 nM against MCR4 in radiolabeled binding studies [79]. Loop 6 of Kalata B1 was exchanged against a bradykinin (BK) antagonistic peptide [80] in order to develop novel analgesic agents.…”

Cyclotides: a natural combinatorial peptide library or a bioactive sequence player?

“…Probably, the low selectivity and the intrinsic poor stability of peptide molecules are the main problematic steps for the development of chemical entities for clinical trials 38 . Recently, the discovery of cyclotides stimulates the use of their features to solve some of the pharmacokinetic limitations related to peptides; inspired by the use of kalata B1 as scaffold for bradikinine analogues (example A), Eliasen et al 27 proposed Kalata-B1 for the insertion of previously optimized melanocortin agonist sequences ( Table 2, part B).…”

“…This approach consists of grafting an external peptide sequence into a cyclotide loops, so as to obtain chimeric molecules able to bind G protein-coupled receptors 26,27 , e.g. to inactivate VEGF 28 , to stimulate angiogenesis 29 , to block the entry of HIV via CXCR4 30 , and to inhibit serine proteases 31 .…”