PROJECT SUMMARY/ABSTRACT The Tier 1 bio-weapon and global health threats Francisella tularensis and Burkholderia pseudomallei exploit the intracellular alveolar macrophage, and have evolved sophisticated immunomodulatory escape mechanisms. New therapeutic strategies are badly needed against these highly lethal and progressively antibiotic resistant agents. This project will identify new host-directed immune therapeutic strategies that can work with macrophage-targeted polymeric prodrugs to overcome these bacterial infections, or prophylactically reduce their disease impact. The polymeric prodrugs achieve these new drug activities by providing targeted and sustained antibiotic pharmacokinetic (PK) profiles within the intracellular lung macrophage compartment, and across whole lung by diffusion. They would potentially allow multi-day efficacy after single administrations with distributable inhalation devices, key advantages for biodefense and global health settings where oral antibiotic adherence is a key issue. Immune-therapy has provided exciting new drug strategies for cancer and other infectious diseases. Here, we aim to identify and exploit host-directed immune modulators that are co-targeted to the lung macrophage reservoir with antibiotic polymeric prodrugs. This combination drug approach is critical in their biodefense settings, where it would often be unknown immediately whether Francisella or Burkholderia was the causative agent. The identification of drug combinations that could work against both is thus essential, and potent host-directed and anti-bacterial activities are likely both needed for symptomatic patient therapy. This project will identify which immune modulators work best against Francisella versus Burkholderia, and especially to identify which immune therapeutics and antibiotics can work effectively against both pathogens. The proposal is structured around 3 specific aims: (1) Develop a panel of host-directed immune modulators as polymeric prodrug candidates that exploit the lung macrophage as a reservoir to focus intracellular drug delivery and to achieve extended dosing pharmacokinetics. (2) Identify promising immune-modulatory pathways and optimize therapeutic and prophylactic activities in ABSL2 aerosolized F. novicida and B. thailandensis mouse models. Favorable immune modulating drugs will be tested with a potent ciprofloxacin polymeric prodrug for combination drug selection. (3) Assess and optimize the up-selected polymeric prodrugs combining host-directed immune modulators and antibiotics against the ABSL3 aerosolized Francisella tularensis and Burkholderia pseudomallei rodent disease models. If successful, this platform may offer new host-drug combination strategies for other pulmonary infections. This platform also meets requirements for rapid development against future pulmonary threats, including antibiotic resistant threats. The polymeric prodrugs have a favorable manufacturing and cost- of-goods-sold profile to...