(197m) Formulation of Peptide Antimicrobials for Treatment of Wound Infections

Cationic antimicrobial peptides (CAMPs) have shown great potential for the treatment of infections involving gram-negative bacteria. However, they are hindered by their short biological life due to hydrolytic degradation in human plasma by proteolytic enzymes. Furthermore, they are not particularly effective once biofilm formation occurs. In order to overcome these challenges, we are developing polyelectrolyte copolymers for the nanoencapsulation of CAMPs. These complexes are formulated to extend the biological lifetime of CAMPs, to provide controlled release from the delivery complex, and to disrupt bacterial biofilms thereby augmenting the activity of the antimicrobial peptide.

Poly(alkylacrylic acid) polymers were prepared via free radical polymerization under N₂ using azobisisobutyronitrile as the initiator. Next, grafted copolymers were prepared by attaching polyetheramine chains to the poly(alkylacrylaic acid) backbones through carbodiimide coupling. All polymers were characterized by NMR and GPC and tested for their ability to form sub-micron particles encapsulating CAMPs that include well established CAMPs such as KSL-W and polymyxin B as well as novel cyclic lipopeptide provided by a collaborator. In contrast to our previous work using these polymers to coat lipoplexes for oligonucleotide delivery, here graft copolymers with poly(methacrylic acid) backbones proved more effective than those built on poly(propylacrylic acid) in encapsulation of peptides and forming stable nano-sized complexes. These complexes are to protect KSL-W, from degradation in human plasma for up to 24 hours while maintaining the free peptide’s activity against the gram-positive bacteria, S. aureus. By varying the graft percentage in the range of 0-10%, we are able to tune the release rate of polymyxin B from 1-10 days. Furthermore, the nanocomplexes were active against Klebsiella pnemoniae biofilms, with additive activity resulting from the polymer and the peptide in the nanocomplex.

Together, these results indicate that our graft copolymer formulation is effective at protecting, releasing and potentiating the activity of CAMPs. Future work will explore the formulation of these nanocomplexes within gels for topical administration.