(472) Synergistic Silver-Tobramycin Nanocomplexes Curtail Pseudomonas Lung Infections in CF Mouse Models.

Background: New approaches are needed to treat Cystic Fibrosis bacterial pathogens, such as Pseudomonas aeruginosa (PA), which persistently colonize lungs due to biofilm formation and cause CF exacerbations even in the era of CFTR modulator therapy. The use of combination therapeutics that act synergistically is a promising treatment strategy; however, the delivery of multiple therapeutics at relevant dosages remains challenging. Even inhaled monotherapies with tobramycin or aztreonam, require multiple doses per day, which remains a barrier for many CF patients due to work or school obligations. We therefore developed a new nanoscale drug carrier by combining approaches from both polyelectrolyte nanocomplex (NC) formation and layer-by-layer electrostatic self-assembly and tested these in mouse models of CF lung infection with PA.

Methods: NC drug carriers were functionalized through polyelectrolyte nanocomplex formation and layer-by-layer electrostatic self-assembly with both tobramycin and silver nanoparticles with high loading efficiencies. The antimicrobial activity of these AgTob-NCs was characterized against planktonic and biofilm PA cultures in vitro and in mouse models of CF lung infection with PA. Mice were pre-treated with intratracheal instillation of either AgTob-NCs, tobramycin alone, or PBS for 2 hours before introduction of ~106 cfu/animal of PA. Mice were sacrificed at 6 hours and the lungs and BAL collected for quantification of bacterial burden. Physiologic data of weight and temperature were measured q2 hrs during the acute lung infection model and during subsequent survival studies.

Results: These positively charged AgTob-NCs demonstrated complete biofilm eradication and increased antibacterial activity compared with tobramycin or silver alone. Mice treated with novel AgTob-NC demonstrated less hypothermia, decreased bacterial burden as measured by recovered CFU/lung at 6 hours, and greater survival at 24 hours compared with controls (PBS) and standard of therapy (tobramycin). PBS-treated control mice demonstrated 0% survival at 24 hours compared with 38% survival in the tobramycin-treated mice and 80% survival in AgTob-NC-treated mice (see Figure).

Conclusions: This work showcases a novel approach to synergistic antimicrobial delivery, utilizing tobramycin and silver nanocomplexes. This novel AgTob-NC effectively reduces PA biofilms in vitro, eliminates bacterial burden, and improves survival in CF mouse models of lung infection. These nanocomplexes offer a new therapeutic approach to overcome PA colonization and infection in CF lung disease.

Acknowledgements: This work is supported by the CFF Basic Science Research Award (835526).

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