(569c) A Toxin-Triggered Vehicle for Targeted Delivery of Antibiotics

Controlled release of antibiotics has the potential to limit exposure of nonpathogenic bacteria to the drug, thus limiting development of secondary infections and slowing development of antibiotic resistance. For example, periodontitis is often treated with systemic antibiotics; while effective in clearing the disease-causing organisms in the mouth, the process exposes the gut microbiota to high concentrations of these drugs and has been associated with increased rates of antibiotic resistance in the relevant organisms. Here, we describe a technique to deliver antibiotics in a controlled fashion to treat localized aggressive periodontitis (LAP), a disease caused by Aggregatibacter actinomycetemcomitans (Aa). Not all strains of Aa are pathogenic, but those that are most closely related to disease have been demonstrated to produce more of a protein toxin, leukotoxin (LtxA). We therefore hypothesized that LtxA could be used as a disease-specific trigger for the controlled release of antibiotics. Previously, we demonstrated that LtxA is able to disrupt model membranes (liposomes), but only when they contain certain lipids, those with a negative spontaneous curvature. Here, we have used this specific membrane-permeabilizing activity to design a “Trojan horse” delivery system for the controlled release of antibiotics to treat LAP. We have demonstrated that LtxA, at physiologically relevant concentrations, efficiently permeabilizes liposomes composed of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-methyl (N-methyl-DOPE), and inclusion of cholesterol enhances this effect. Finally, we found that antibiotic-containing liposomes inhibit growth of the LtxA-producing strain but not that of a non-LtxA-producing strain. Control liposomes, composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), which are not efficiently permeabilized by LtxA, do not inhibit bacterial growth. Together, our results demonstrate that N-methyl-DOPE liposomes provide a suitable platform for the controlled release of antibiotics only in the presence of the specific disease-causing agent.