Synthesis of α,ε-N,N’-Di-stearoyl Lysine-Derived Amide Lipids and Their Application to Liposome Formulation: Incorporation of Lipid A-Ligand for Bacterial Targeting and Sialic Acid for Phagocytosis Resistance

As part of an antimicrobial resistance (AMR) strategy, we have prepared α,ε-N,N’-di-stearoyl lysine-based amide lipids to improve the chemical and biological stabilities of nanoparticles. Those amide lipids incorporated a variety of head groups, including lipid A-binding ligand (polymyxin B nonapeptide, PMBN) for bacterial targeting and sialic acid as an alternative to PEGylation for phagocytosis resistance. The study demonstrated that the PMBN-liposome specifically targeted lipid A-containing Gram-negative Acinetobacter baumannii bacteria, but not Gram-positive Staphylococcus aureus. However, such interaction was interrupted by the adsorption of serum proteins onto liposomes, demonstrating the complexity and challenge of targeted delivery. As expected, slower uptake of sialic acid-liposomes by human leukemia monocytic THP-1 cells was observed, suggesting their resistance to phagocytosis. Additionally, in a mouse model, the sialic acid-containing liposomes showed more favorable biodistribution and longer retention time than the comparable phospholipid-only liposomes. We observed that both sialic acid-incorporated and PEGylated liposomes distributed over the whole mouse bodies and remained for over 48 h. In contrast, the phospholipid-only liposomes rapidly migrated to the liver (5–15 min). In conclusion, although this study did not achieve bacteria-targeted liposome delivery, it provided evidence that the sialic acid-amide lipid can serve as an alternative to PEGylation in future nanomedicine.