(472b) Block Ionomer Complexes Containing Gentamicin to Kill Intracellular Brucella Melitensis

Brucellosis, caused by intracellular Brucella spp., is the most common disease that can be passed from infected animals to humans. It is difficult to eliminate as the pathogen resides partially within phagocytic host cells and the recommended polar antibiotics for treatment do not enter these cells efficiently. Core-shell block ionomer complexes (BICs) carrying antibiotics in their cores were designed to transport these drugs into cells. Polyether-polyacrylate copolymers were complexed with cationic aminoglycoside antibiotics to form BICs with hydrodynamic diameters of 170-340 nm in water. An anionic poly(acrylate-b-ethylene oxide-b-propylene oxide-b-ethylene oxide-b-acrylate) copolymer blended with a poly(ethylene oxide-b-acrylate) diblock was complexed with the cationic drug gentamicin in PBS to form complexes containing up to 42 wt% of the antibiotic. The poly(propylene oxide) provided hydrophobic interactions that enhanced complex stability in aqueous media while the hydrophilic blocks generated steric interactions to disperse the MBICs. These core-shell BICs were fabricated in a multi-inlet-vortex mixer that involved mixing solutions of the cationic drug and anionic block copolymers under turbulent flow conditions so that the mixing time was rapid (<50 ms). This promoted reproducible and uniform complex formation. The drug release profiles in PBS showed two distinctly different regimes - a "burst" phase within the first ~10 hours followed by slower release over the next 40-60 hours. In vitro efficacy of the BICs to reduce intracellular Brucella was studied in murine macrophage-like cells. Significant reductions of 2.78 and 2.85 logs were obtained, while free gentamicin reduced the bacteria by only 0.75 logs. This suggests that the BICs are efficient transporters of polar antibiotics into phagocytic cells. No cell toxicity or nitric oxide production was detected on incubation of the macrophages with a range of BIC concentrations. These BICs were, however, ineffective in significantly reducing Brucella melitensis in the spleens and livers of infected mice, either alone or in combination with doxycycline.