Revisiting aminocoumarins for the treatment of melioidosis

Abstract

Burkholderia pseudomallei causes melioidosis, a potentially lethal disease that can establish both chronic and acute infections in humans. It is inherently recalcitrant to many antibiotics, there is a paucity of effective treatment options and there is no vaccine. In the present study, the efficacies of selected aminocoumarin compounds, DNA gyrase inhibitors that were discovered in the 1950s but are not in clinical use for the treatment of melioidosis were investigated. Clorobiocin and coumermycin were shown to be particularly effective in treating B. pseudomallei infection in vivo. A novel formulation with dl-tryptophan or l-tyrosine was shown to further enhance aminocoumarin potency in vivo. It was demonstrated that coumermycin has superior pharmacokinetic properties compared with novobiocin, and the coumermycin in l-tyrosine formulation can be used as an effective treatment for acute respiratory melioidosis in a murine model. Repurposing of existing approved antibiotics offers new resources in a challenging era of drug development and antimicrobial resistance.

Keywords: Aminocoumarin; Burkholderia pseudomallei; Clorobiocin; Coumermycin; Melioidosis; Novobiocin.

Fig. 1

The novobiocin formulation modifies in vivo potency in Galleria mellonella larvae. Galleria larvae (n = 5 per group) were infected with Burkholderia pseudomallei K96243 (110–178 CFU) for 1 h at 37 °C and were then treated with different aminocoumarins (10 μL of 1 mg/mL stock solution) or novobiocin in different formulations as indicated. One-way analysis of variance (ANOVA) was performed with Dunnett's multiple comparisons test versus (A,B) untreated larvae or (C,D) novobiocin formulation in phosphate-buffered saline (PBS). Representative figures from at least three independent biological replicates are shown. Error bars represent the standard deviation from the mean. ** P < 0.01; *** P < 0.001; **** P < 0.0001; ^NS, not significant.

Fig. 2

Pharmacokinetics of novobiocin and coumermycin. Female BALB/c mice (n = 3 per group) were intraperitoneally administered (A) 15 mg/kg coumermycin or (B) 15 mg/kg novobiocin with or without formulation in an equimolar concentration of dl-tryptophan (dose volume 10 mL/kg). Error bars represent the standard deviation from the mean. Plasma concentrations of the compound were assessed by mass spectrometry at different time points as indicated.

Fig. 3

Coumermycin treatment significantly improved survival in a murine model of melioidosis. Female BALB/c mice were infected intranasally with 500 CFU of Burkholderia pseudomallei K96243 (n = 5 per group). Ceftazidime (CFT) (1200 mg/kg, intraperitoneal) or coumermycin ± l-tyrosine (Tyr) (30 mg/kg, subcutaneous) was administered at 6 h post-infection, with subsequent treatments every 24 h for 4 days thereafter. (A) Survival and (B) body weight was assessed until the end of the experiment at 30 days post-infection. Statistical comparison of survival curves was performed by log-rank (Mantel–Cox) test.