All-Hydrocarbon Stapling and Amino Acid Substitution-Modified Antimicrobial Peptide Feleucin-K3 Analogs Enhanced the Stability and Optimized the Therapeutic Index against Multidrug-Resistant Bacteria.

Our previous research found that the poor stability of the antimicrobial peptide Feleucin-K3 (FK3) had limited its transition into clinical application. Herein, we developed a series of FK3 derivatives stapled by all-hydrocarbon and thioether to enhance the stability and then implemented an amino acid substitution strategy to reduce the hemolytic toxicity. Consequently, after replacing the first phenylalanine of FK3 with alanine and conducting (i, i + 4) all-hydrocarbon stapling with (S)-2-(4-pentenyl) alanine at the 5,9-position, analog S1-1A displayed the highest therapeutic index, high stability, and potent antimicrobial effects against multidrug-resistant (MDR) bacteria as well as antibiofilm properties. A striking finding was that S1-1A exhibited 8-fold greater antimicrobial activity against resistant strains of Staphylococcus aureus than vancomycin. The efficacy of S1-1A in vivo was as effective as vancomycin in the skin wound infection model. Overall, stapled peptide S1-1A showed promising potential for being developed into a novel drug for combating MDR bacterial infections.