Mechanism of Action and Limited Cross-Resistance of New Lipopeptide MX-2401

Abstract

MX-2401 is a semisynthetic calcium-dependent lipopeptide antibiotic (analogue of amphomycin) in preclinical development for the treatment of serious Gram-positive infections. In vitro and in vivo, MX-2401 demonstrates broad-spectrum bactericidal activity against Gram-positive organisms, including antibiotic-resistant strains. The objective of this study was to investigate the mechanism of action of MX-2401 and compare it with that of the lipopeptide daptomycin. The results indicated that although both daptomycin and MX-2401 are in the structural class of Ca 2؉ -dependent lipopeptide antibiotics, the latter has a different mechanism of action. Specifically, MX-2401 inhibits peptidoglycan synthesis by binding to the substrate undecaprenylphosphate (C 55 -P), the universal carbohydrate carrier involved in several biosynthetic pathways. This interaction resulted in inhibition, in a dose-dependent manner, of the biosynthesis of the cell wall precursors lipids I and II and the wall teichoic acid precursor lipid III, while daptomycin had no significant effect on these processes. MX-2401 induced very slow membrane depolarization that was observed only at high concentrations. Unlike daptomycin, membrane depolarization by MX-2401 did not correlate with its bactericidal activity and did not affect general membrane permeability. In contrast to daptomycin, MX-2401 had no effect on lipid flip-flop, calcein release, or membrane fusion with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1-rac-glycerol) (sodium salt) (POPG) liposomes. MX-2401 adopts a more defined structure than daptomycin, presumably to facilitate interaction with C 55 -P. Mutants resistant to MX-2401 demonstrated low cross-resistance to other antibiotics. Overall, these results provided strong evidence that the mode of action of MX-2401 is unique and different from that of any of the approved antibiotics, including daptomycin.MX-2401 is a semisynthetic calcium (Ca 2ϩ )-dependent lipopeptide antibiotic in preclinical development for the treatment of serious Gram-positive infections. An analogue of amphomycin, MX-2401, demonstrates broad-spectrum bactericidal activity against Gram-positive organisms, including strains resistant to vancomycin, macrolides, penicillin, methicillin, gentamicin, and other marketed antimicrobials (12,15). In animal models of infection, MX-2401 exhibits potent dose-dependent activity against Gram-positive organisms, including resistant strains, with an excellent ability to kill bacteria in neutropenic mice (9).MX-2401 ( Fig. 1) is chemically related to a number of antimicrobial lipopeptides, such as amphomycin, friulimicin, and daptomycin (7,11,25,46). Specifically, amphomycin, friulimicin, and MX-2401 share the same cyclopeptide ring core comprising 10 amino acids and differ only in their exocylic amino acids, with asparagine in friulimicin and aspartic acid in MX-2401 and amphomycin (25, 46). MX-2401 differs from amphomycin in the side chain of residue 9 (1). In contrast, daptomycin...

The action mechanism of daptomycin

“…If the same concentrations were added separately to the calcein-loaded DOPC/DOPG liposomes, less than 10% leakage was observed even at 16 µg/mL daptomycin. Later, this same group, in collaboration with others, using essentially the same assay, reported only 7% calcein release from DOPC/PG liposomes at 32 µg/mL of daptomycin, 32 which seems more in line with the previously discussed results obtained with bacterial cells. 76 Using a coupled fluorescence assay that is based on the pH-sensitive indicator pyranine, 80 Zhang et al recently demonstrated that daptomycin can form pores in DMPC/DMPG (1:1) liposomes.…”

“…Using this assay, a fraction of the cells in a liquid culture of Staphylococcus epidermidis were found to be permeabilized after daptomycin treatment. 32 Such findings should be interpreted with caution, however. Propidium is very similar in structure to ethidium, which is widely used as a model substrate for bacterial efflux systems.…”

“…While the structural similarities between both groups have prompted researchers to look for a direct, specific inhibition by daptomycin of peptidoglycan synthesis also, no such effect has yet been substantiated. 32 The similarity between the cyclic lipopeptide antibiotics also pertains to their synthetase systems. Through genetic recombination of these modular synthetases, hybrid lipopeptides can be generated.…”

“…58 A recent study employed bacterial membrane preparations to compare the effect on LTA and peptidoglycan precursor synthesis of daptomycin, amphomycin, and an analogue of the latter (MX-2401). 32 A strong inhibition was seen when amphomycin and its analogue were used in twofold molar excess over their known target bactoprenol phosphate. A twofold excess of daptomycin caused an inhibition by approximately 20%.…”

A High‐Resolution Crystal Structure that Reveals Molecular Details of Target Recognition by the Calcium‐Dependent Lipopeptide Antibiotic Laspartomycin C

“…At present, daptomycin is the only clinically used CDA, and its mode of action is the topic of ongoing investigation 6, 7, 8, 9. By comparison, the structurally similar CDAs laspartomycin C, friulimycin B, tsushimycin, and amphomycin have more clearly understood antibacterial mechanisms 10, 11, 12, 13, 14. It was recently reported that laspartomycin C forms a high‐affinity complex ( K d =7.3±3.8 n m ) with the bacterial cell wall precursor undecaprenyl phosphate (C 55 ‐P) and in doing so inhibits peptidoglycan biosynthesis, ultimately leading to cell death 14.…”