Study on the synergistic activity of G-749 and colistin against Escherichia coli.

OBJECTIVES: In order to investigate the synergistic antibacterial effects of the novel FLT3 inhibitor G-749 in combination with colistin against Escherichia coli (E. coli). METHODS: The in vitro antibacterial activity of G-749 combined with colistin was evaluated by MIC using the broth microdilution method, followed by checkerboard synergy testing and time-kill assays. The in vivo efficacy was assessed in a murine thigh infection model using mcr-positive colistin-resistant strain M17GZZ15. Mechanistic studies employed propidium iodide (PI) and 4',6-diamidino-2-phenylindole (DAPI) staining to evaluate bacterial membrane integrity and nucleic acid content. The pharmacokinetic profile of G-749 was characterized in mice after a single oral dose of 100 mg/kg body weight. RESULTS: G-749 significantly potentiated colistin activity, reducing the MIC of colistin by 16- to 64-fold against susceptible E. coli ATCC25922 and by 8- to 32-fold against the resistant strain M17GZZ15. Time-kill assays revealed rapid bactericidal effects within 4 h. In the murine thigh infection model, the combination therapy significantly reduced bacterial burdens compared with monotherapy (P < 0.01). Mechanistic investigations showed enhanced PI uptake, indicating increased membrane permeability, and diminished DAPI fluorescence, suggesting intracellular nucleic acid leakage. Pharmacokinetic profiling of G-749 yielded a Cmax of 17.94 mg/L at Tmax 0.67 h, an AUC0-24 of 44.91 mg·h/L, and an elimination half-life of 3.34 h. CONCLUSIONS: These findings establish G-749 as a potent colistin adjuvant that acts primarily by augmenting membrane disruption, with oxidative stress and energy suppression potentially contributing at higher concentrations, thereby improving antibacterial efficacy against Gram-negative bacteria. This multi-mechanistic and concentration-dependent synergistic profile offers a promising strategy to combat multidrug-resistant infections.