Self-enhanced targeted delivery of a cell wall– and membrane-active antibiotics, daptomycin, against staphylococcal pneumonia

Considering that some antibacterial agents can identify the outer structure of pathogens like cell wall and/or cell membrane, we explored a self-enhanced targeted delivery strategy by which a small amount of the antibiotic molecules were modified on the surface of carriers as targeting ligands of certain bacteria while more antibiotic molecules were loaded inside the carriers, and thus has the potential to improve the drug concentration at the infection site, enhance efficacy and reduce potential toxicity. In this study, a novel targeted delivery system against methicillin-resistant Staphylococcus aureus (MRSA) pneumonia was constructed with daptomycin, a lipopeptide antibiotic, which can bind to the cell wall of S. aureus via its hydrophobic tail. Daptomycin was conjugated with N-hydroxysuccinimidyl–polyethylene glycol–1,2-distearoyl-sn-glycero-3-phosphoethanolamine to synthesize a targeting compound (Dapt–PEG–DSPE) which could be anchored on the surface of liposomes, while additional daptomycin molecules were encapsulated inside the liposomes. These daptomycin-modified, daptomycin-loaded liposomes (DPD-L[D]) showed specific binding to MRSA as detected by flow cytometry and good targeting capabilities in vivo to MRSA-infected lungs in a pneumonia model. DPD-L[D] exhibited more favorable antibacterial efficacy against MRSA than conventional PEGylated liposomal daptomycin both in vitro and in vivo. Our study demonstrates that daptomycin-modified liposomes can enhance MRSA-targeted delivery of encapsulated antibiotic, suggesting a novel drug delivery approach for existing antimicrobial agents.