Development of Novel Melanocortin Receptor Agonists Based on the Cyclic Peptide Framework of Sunflower Trypsin Inhibitor-1

Abstract

Ultrastable cyclic peptide frameworks offer great potential for drug design due to their improved bioavailability compared to their linear analogues. Using the sunflower trypsin inhibitor-1 (SFTI-1) peptide scaffold in combination with systematic N-methylation of the grafted pharmacophore led to the identification of novel subtype selective melanocortin receptor (MCR) agonists. Multiple bicyclic peptides were synthesized and tested toward their activity at MC1R and MC3–5R. Double N-methylated compound 18 showed a pKi of 8.73 ± 0.08 (Ki = 1.92 ± 0.34 nM) and a pEC50 of 9.13 ± 0.04 (EC50 = 0.75 ± 0.08 nM) at the human MC1R and was over 100 times more selective for MC1R. Nuclear magnetic resonance structural analysis of 18 emphasized the role of peptide bond N-methylation in shaping the conformation of the grafted pharmacophore. More broadly, this study highlights the potential of cyclic peptide scaffolds for epitope grafting in combination with N-methylation to introduce receptor subtype selectivity in the context of peptide-based drug discovery.

Rapid and Scalable Plant-Based Production of a Potent Plasmin Inhibitor Peptide

“…SFTI-1 peptide analogues have been engineered for diverse therapeutic applications ranging from anti-cancer (Swedberg et al., 2009, 2011), anti-obesity (Durek et al., 2018), pro and anti-angiogenesis (Chan et al., 2011; Qiu et al., 2017) as well as for treatment of a range of skin conditions (Chen et al., 2016; Zhu et al., 2017). Here, we have shown that like SFTI-1, the engineered plasmin inhibitor [T4Y,I7R]SFTI-1 (Swedberg et al., 2019) is amenable to plant-based production with the resultant purified peptide displaying both structural and functional equivalence to synthetically produced material.…”

“…Furthermore, SFTI-1 is readily tolerant of residue substitutions, exemplified by a wide range of combinatorial and rational design variants that have been applied to convert SFTI-1 into potent and stable inhibitors of therapeutically relevant proteases, including matriptases (Quimbar et al., 2013; Fittler et al., 2014; Gitlin et al., 2015), kallikreins (Shariff et al., 2014; Chen et al., 2016; de Veer et al., 2016; Jendrny and Beck-Sickinger, 2016), chymotrypsin (Swedberg et al., 2017), and furin (Fittler et al., 2015). SFTI-1 has also proven to be a useful scaffold for presenting and stabilizing small bioactive epitopes that by themselves would be unstable and not effective as pharmaceuticals (Chan et al., 2011; Qiu et al., 2017; Durek et al., 2018). These engineered cyclic SFTI-1 analogues uniformly display significantly enhanced serum stability compared with their linear counterparts, overcoming a major limitation of peptide-based therapeutics (Wang and Craik, 2018).…”

Using backbone-cyclized Cys-rich polypeptides as molecular scaffolds to target protein–protein interactions

“…The nuclear magnetic resonance structural analysis of this grafted peptide revealed the key role of peptide bond N-methylation in shaping the conformation of the grafted peptide pharmacophore. This work highlights the potential of cyclic peptide scaffolds for epitope grafting in combination with N-methylation to introduce receptor subtype selectivity in the context of peptide-based drug discovery (106).…”

“…The SFTI-1 scaffold was also recently employed for the production of a novel subtype of selective melanocortin receptor (MCR) agonists (106). This was accomplished by grafting the α/β/γ-melanocyte stimulating hormone (MSH)-derived HFRW tetrapeptide into the different loops of SFTI-1 in combination with systematic N-methylation of the grafted pharmacophore.…”

Linking inhibitor motions to proteolytic stability of sunflower trypsin inhibitor-1

“…[15][16][17][18][19][20] Sequences with completely novel function can be graed into the SFTI-1 framework, for engineering of radiopharmaceuticals, antimicrobials, proangiogenic compounds, and rheumatoid arthritis and autoimmune disease peptides. [21][22][23][24][25][26][27][28] SFTI-1 binds to trypsin in a substrate manner but can resist proteolysis for a quite long time. The hydrolysis rates of SFTI-1 and its analogs have been studied extensively.…”