Novel Polymyxin Derivatives Carrying Only Three Positive Charges Are Effective Antibacterial Agents

Abstract

The lack of novel antibiotics against gram-negative bacteria has reinstated polymyxins as the drugs of last resort to treat serious infections caused by extremely multiresistant gram-negative organisms. However, polymyxins are nephrotoxic, and this feature may complicate therapy or even require its discontinuation. Like that of aminoglycosides, the nephrotoxicity of polymyxins might be related to the highly cationic nature of the molecule. Colistin and polymyxin B carry five positive charges. Here we show that novel polymyxin derivatives carrying only three positive charges are effective antibacterial agents. NAB739 has a cyclic peptide portion identical to that of polymyxin B, but in the linear portion of the peptide, it carries the threonyl-D-serinyl residue (no cationic charges) instead of the diaminobutyryl-threonyl-diaminobutyryl residue (two cationic charges). The MICs of NAB739 for 17 strains of Escherichia coli were identical, or very close, to those of polymyxin B. Furthermore, NAB739 was effective against other polymyxin-susceptible strains of Enterobacteriaceae and against Acinetobacter baumannii. At subinhibitory concentrations, it dramatically sensitized A. baumannii to low concentrations of antibiotics such as rifampin, clarithromycin, vancomycin, fusidic acid, and meropenem. NAB739 methanesulfonate was a prodrug analogous to colistin methanesulfonate. NAB740 was the most active derivative against Pseudomonas aeruginosa. NAB7061 (linear portion of the peptide, threonyl-aminobutyryl) lacked direct antibacterial activity but sensitized the targets to hydrophobic antibiotics by factors up to 2,000. The affinities of the NAB compounds for isolated rat kidney brush border membrane were significantly lower than that of polymyxin B.

Lipopeptides as anti-infectives: a practical perspective

“…Nephrotoxicity is probably due to the interaction of polymyxins with megalin, a giant endocytic receptor abundant in the apical membrane of proximal tubules [76]. In fact, NAB739 and NAB7061 bind to the isolated brush-border membrane of rat kidney at an affinity which is only 1/7-1/5 of that for PMB, indicating a lower potential for nephrotoxicity [77]. Figure 2 depicts modifications introduced into PMB in order to create NAB739 and NAB7061, by reducing both the number of charges and changing the identity of the fatty acyl chain.…”

Development of new polymyxin derivatives for multi-drug resistant Gram-negative infections

“…This approach has since been followed by several groups, each attempting to overcome some of the drawbacks, including the slow cyclisation step, and the careful cleavage from resin to avoid concomitant deprotection. A similar approach using TCP resin and iv(Dde) orthogonal protection has been used by Velkov et al 45 Vaara et al, 41 used benzyloxycarbonyl (CBZ) protection on the Dab groups allowing facile acid-induced cleavage from the resin, while Kanazawa 46 utilized 2-Chloro CBZ protection which required final removal with HF. A recent publication by Ramesh et al 47 reports a clean cyclisation reaction off-resin using PyAOP (7-azabenzotriazol-1-yloxy)tripyrroldinophosphonium hexafluorophosphate) as coupling agent.…”

“…A range of fatty acyl nonapeptide derivatives has been reported where amino acid 3 is replaced with amino acids without an amine in the side chain thus resulting in molecules with only three positive charges. 70,71 For optimal activity it appeared to be necessary to have a hydroxyl containing side chain, with D-serine or D-threonine apparently superior to L-serine. Compounds with aminobutyrate at amino acid 3, eg, NAB7061, had weak direct antimicrobial activity but retained the ability to potentiate other antibiotics such as rifampin.…”

“…40 Polymyxins demonstrate binding to the brush border membrane of the renal cortex as measured by the displacement of radiolabelled gentamicin. 41 A range of immortalized cell lines derived from kidney proximal …”

Characterization of Protamine Uptake by Opossum Kidney Epithelial Cells

“…5A, gentamicin inhibited the association of FITC-protamine in a concentration-dependent manner. In addition, polymixin B, a cationic peptide antibiotic that binds to megalin, 24,25) greatly decreased the association of FITC-protamine (Fig. 5B).…”