Proline-Hinged α-Helical Peptides Sensitize Gram-Positive Antibiotics, Expanding Their Physicochemical Properties to Be Used as Gram-Negative Antibiotics.

The outer membrane (OM) of Gram-negative bacteria is the most difficult obstacle for small-molecule antibiotics to reach their targets in the cytosol. The molecular features of Gram-negative antibiotics required for passing through the OM are that they should be positively charged rather than neutral, flat rather than globular, less flexible, or more increased amphiphilic moment. Because of these specific molecular characteristics, developing Gram-negative antibiotics is difficult. We focused on sensitizer peptides to facilitate the passage of hydrophobic Gram-positive antibiotics through the OM. We explored ways of improving the sensitizing ability of proline-hinged α-helical peptides by adjusting their length, hydrophobicity, and N-terminal groups. A novel peptide, 1403, improves the potentiation of rifampicin in vitro and in vivo and potentiates most Gram-positive antibiotics. The "sensitizer" approach is more plausible than those that rely on conventional drug discovery methods concerning drug development costs and the development of drug resistance.

Proline Hinged Amphipathic α-Helical Peptide Sensitizes Gram-Negative Bacteria to Various Gram-Positive Antibiotics.

Gram-negative bacteria are becoming resistant to almost all currently available antibiotics. Systemically designed antimicrobial peptides (AMPs) are attractive agents to enhance the activities of antibiotics. We constructed a small Pro-scanning library using amphipathic model peptides. Measurements of minimum inhibitory concentration (MIC) against Escherichia coli and hemolytic activities showed that one of the Pro-hinged peptides, KL-L9P, displays the highest specificity toward E. coli. Moreover, KL-L9P sensitizes E. coli to be responsive to most antibiotics that are not active against Gram-negative bacteria. The results of biochemical experiments show that KL-L9P promotes the rearrangement of the bacterial membrane that enables hydrophobic antibiotics to permeate. Finally, the results of animal tests demonstrate that KL-L9P strongly sensitizes Gram-negative bacteria to linezolid (Lzd), rifampicin (Rif), or clarithromycin (Clr). Thus, KL-L9P operates as a sensitizer to extend the antibacterial activity of most antibiotics to Gram-negative bacteria.