Liposomal Fluopsin C: Physicochemical Properties, Cytotoxicity, and Antibacterial Activity In Vitro and over In Vivo MDR Klebsiella pneumoniae Bacteremia Model

<b>Introduction:</b> Antimicrobial resistance has become a global concern, and few new antimicrobials are currently being developed. Fluopsin C has proven broad-spectrum activity, being a promising candidate for new antimicrobial development. To optimize antimicrobial activity, this research aimed at fluopsin C (Flp) encapsulation in liposomes to achieve controlled release and reduce cytotoxicity. <b>Methods:</b> Liposomal formulations were prepared by extruding formulations based on soy phosphatidylcholine (SPC) or poly (ethylene glycol)-distearoylphosphatidylethanolamine (DSPE-PEG) plus cholesterol, and were characterized by their size, polydispersity index, zeta potential, encapsulation efficiency, shelf-life stability, in vitro release profile, cytotoxicity, and antimicrobial activity against <i>Klebsiella pneumoniae</i> in vitro and in vivo. <b>Results:</b> The results indicated that the DSPE-PEG DMSO+Flp formulation presented superior physicochemical stability and unaltered antimicrobial activity. In vitro, CC₅₀ decreased by 54%. No lethal dose was obtained in mice within the concentration range tested. The most effective doses in vivo were 2 × 2 mg/kg for free fluopsin C and 1 × 2 mg/kg for DSPE-PEG DMSO+Flp, resulting in a 40% reduction in mortality from bacteremia. Only discrete inflammatory infiltration was detected in the liver, while kidney necrosis ranged from discrete to moderate. Encapsulation of fluopsin C in liposomes showed promising features supporting to use against infections by MDR <i>K. pneumoniae</i>.