Lysine-Tethered Stable Bicyclic Cationic Antimicrobial Peptide Combats Bacterial Infection in Vivo

Abstract

Antimicrobial peptides (AMPs) have attracted great attention as next generation antibiotics for the treatment of multidrug-resistant (MDR) bacterial infections. Poor proteolytic stability has however undermined clinical applications of AMPs. A novel peptide cyclization approach is described to enhance the in vivo antibacterial activity of AMPs. Bicyclic antimicrobial peptides were synthesized by cross-linking the ε-amino groups of three lysine residues with a 1,3,5-trimethylene benzene spacer. In a proof of principal study, four bicyclic peptides were synthesized from the cationic AMP OH-CM6. One bicyclic peptide retained strong antimicrobial activity and low toxicity but exhibited a prolonged half-life in serum. Antibacterial activity was consequently improved in vivo without renal or hepato-toxicity. The novel peptide cyclization approach represents an important tool for enhancing AMP proteolytic stability for improved treatment of bacterial infection.

All‐hydrocarbon stapling enables improvement of antimicrobial activity and proteolytic stability of peptide Figainin 2

“…According to previous studies, amino acid residues with hydrophobic or positive charges play a vital role in the activity of Figainin 2, where positively charged lysines may facilitate electrostatic interactions of the peptide with negatively charged components of the cell membrane 34–36 . Therefore, we adopted a more comprehensive short‐chain scanning approach by introducing the unnatural amino acids Fmoc‐S 5 ‐OH (Fmoc‐( S )‐2‐(4‐pentenyl)alanine) and Fmoc‐R 8 ‐OH (Fmoc‐( R )‐2‐(7‐octenyl)alanine) at different positions while retaining the positively charged lysine residues (Lys7, Lys14, Lys25, and Lys27) and the hydrophobic amino acid leucine (Leu2, Leu6, Leu12, and Leu17), which play an important role in maintaining the secondary structure of the peptide 37 .…”

“…According to previous studies, amino acid residues with hydrophobic or positive charges play a vital role in the activity of Figainin 2, where positively charged lysines may facilitate electrostatic interactions of the peptide with negatively charged components of the cell membrane. [34][35][36] Therefore, we adopted a more comprehensive shortchain scanning approach by introducing the unnatural amino acids and the hydrophobic amino acid leucine (Leu2, Leu6, Leu12, and Leu17), which play an important role in maintaining the secondary structure of the peptide. 37 One or two helical spaces are stapled to the positions i, i + 4 and i, i + 7 to obtain the corresponding helical structure diagram (Figure 1A,B).…”

A guided tour through α-helical peptide antibiotics and their targets

“…Indeed, stapled αAMPs have been shown to be highly resistant to proteolytic degradation [226,227,229], which provided the basis for efficacy in animal infection models [226,229]. A bicyclic stapling approach has been reported, tethering three lysine residues positioned at i, (i + 4) and (i + 8) [230]. Even though the bicyclic stapled peptide showed a decreased helical propensity compared with its linear parent peptide, the trifunctional staple increased the resistance to enzymatic proteolysis rendering the peptide effective in a murine MRSA infection model [230].…”

To Fold or Not to Fold: Diastereomeric Optimization of an α-Helical Antimicrobial Peptide

“…Membrane disruptive antimicrobial peptides (AMPs), which occur naturally as part of the innate immune system, offer an opportunity to address multidrug-resistant (MDR) bacteria because of their unspecific mechanism of action, against which resistance does not occur easily. − Such AMPs are however unstable in serum and most often toxic owing to their membrane disruptive amphiphilic and usually α-helical structure triggering their antibacterial effect. Their properties can be improved by sequence optimization, − whereby the most versatile approach consists in introducing non-natural structural elements such as d -amino acids, − non-natural residues, β- or γ-amino acids, , isopeptide bonds, or entirely non-peptidic elements such as spermine or fatty acids. , A complete redesign of AMPs is also possible in the form of dimers, cyclic or bicyclic staples, − small molecules, peptoids, , foldamers, or dendrimers. , …”

“…Their properties can be improved by sequence optimization, 4 − 7 whereby the most versatile approach consists in introducing non-natural structural elements 8 such as d -amino acids, 9 − 13 non-natural residues, 14 β- or γ-amino acids, 15 , 16 isopeptide bonds, 17 or entirely non-peptidic elements such as spermine 18 or fatty acids. 19 , 20 A complete redesign of AMPs is also possible in the form of dimers, 21 cyclic or bicyclic staples, 22 − 24 small molecules, 25 peptoids, 26 , 27 foldamers, 28 or dendrimers. 29 , 30 …”