Comparative Mechanistic Studies of Brilacidin, Daptomycin, and the Antimicrobial Peptide LL16

Abstract

b Brilacidin (PMX30063) has shown potent bactericidal activity against drug-resistant and -susceptible strains of multiple Gramnegative and Gram-positive pathogens. In this study, we demonstrate that brilacidin causes membrane depolarization in the Gram-positive bacterium Staphylococcus aureus, to an extent comparable to that caused by the lipopeptidic drug daptomycin. Transcriptional profiling of Staphylococcus aureus by deep sequencing shows that the global response to brilacidin treatment is well correlated to those of treatment with daptomycin and the cationic antimicrobial peptide LL37 and mostly indicates abrogation of cell wall and membrane functions. Furthermore, the upregulation of various chaperones and proteases by brilacidin and daptomycin indicates that cytoplasmic protein misfolding stress may be a contributor to the mechanism of action of these drugs. These stress responses were orchestrated mainly by three two-component systems, GraSR, VraSR, and NsaSR, which have been implicated in virulence and drug resistance against other clinically available antibiotics. The recent rise of multidrug-resistant pathogenic bacteria is an alarming health care crisis that has outpaced the discovery of effective and novel therapeutics (1, 2). Antimicrobial peptides (AMPs), which are evolutionarily conserved, first-line host defense mechanisms, offer an attractive platform for the development of new antibiotics (3-5). Most AMPs are believed to interact with bacterial membranes and cause cell death by dysregulating the properties of the phospholipid bilayer or by causing membrane leakage, although some have been identified to have downstream cytoplasmic targets as well (6). Despite the variety of sequences and secondary and tertiary structures, most AMPs share an amphiphilic topology, with a charged, mostly positive face that allows for interaction with the negatively charged bacterial membrane and a hydrophobic face that allows for insertion into the membrane and interaction with the apolar acyl chains of the bilayer (4, 7-10). Several mechanisms have been suggested for the nature of this interaction with the membrane, including carpet, toroidal pore, and barrel stave mechanisms (6). Development of resistance to these peptides is limited (11), presumably due to the membrane being the primary target (12). As such, several strategies have been employed to mimic the activity of AMPs in order to improve efficacy, selectivity for bacteria, and bioavailability while circumventing issues associated with peptidic drugs, such as proteolytic degradation and difficulties with large-scale synthesis. These include the use of scaffolds such as D-L peptides, ␤-amino acid helices, and antimicrobial polymers (13-15).In previous work, we developed a series of small-molecule arylamide mimics of AMPs that showed potent activity against a broad range of drug-susceptible and multidrug-resistant Gramnegative and Gram-positive bacteria (15-19). These compounds feature a small arylamide backbone that is stabilized by intramolecular hydroge...

β-Lactams Enhance Daptomycin Activity against Vancomycin-Resistant Enterococcus faecalis and Enterococcus faecium in In Vitro Pharmacokinetic/Pharmacodynamic Models

“…LL37 is a human, cationic, cathelicidin antimicrobial peptide that is active through bacterial membrane destabilization (48). LL37 is not only a marker of immune response but also an endogenous analogue to DAP (49). Our data echo previous findings demonstrating the synergistic effects of ␤-lactam agents on LL37 activity in E. faecalis, E. faecium, and Staphylococcus aureus (24,25,50,51).…”

The GraS Sensor in Staphylococcus aureus Mediates Resistance to Host Defense Peptides Differing in Mechanisms of Action

“…The current findings are consistent with prior data which suggested that GraSR is involved in stress responses and potential mechanisms of action of other peptide anti-infective agents, including daptomycin, LL-37, and the experimental agent brilacidin (20). Other studies have suggested that GraX as well as distinct two-component regulatory systems, such as VraSR and NsaSR, are also involved in S. aureus responses to antibiotics (21,22).…”

Synergistic Efficacy of Aedes aegypti Antimicrobial Peptide Cecropin A2 and Tetracycline against Pseudomonas aeruginosa

“…Antimicrobial peptides (AMPs) have been proposed as candidates because of their novel mechanisms of action. AMPs are produced by diverse organisms, including microbes, plants, insects, and mammals, and may replace or complement traditional antibiotics in settings where antibiotics alone have lost efficacy (12)(13)(14). Most AMPs interact with bacterial membranes and cause membrane depolarization, electrolyte leakage, and ultimately cell death (15), but others have cytoplasmic targets (16).…”