Novel medical countermeasure to mitigate potentially lethal acute radiation syndrome

Project Summary/Abstract Despite significant advances, gaps remain in developing treatments that address persistent inflammation that ensue after acute radiation exposure. The long-term objective of the proposed project is to develop a well-tolerable and effective first-in-class medical countermeasure (MCM) designed for mitigation and treatment of potentially lethal acute radiation syndrome (ARS) and administered at least 24 h post-radiation to significantly extend survival of irradiated patients and radiation casualties. Radiation injury is accompanied by macrophage-driven uncontrolled inflammation. Ionizing radiation increases expression of Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) in macrophages. In animals, TREM-1 has been shown to contribute to worse survival after total body irradiation (TBI). This implicates TREM-1 as a promising emerging target to develop a novel MCM for radiation injury. Current TREM-1 blockers are all ligand-dependent and attempt to block binding of TREM-1 to its multiple known and unknown ligands, bearing thus high risk of drug failure in clinical efficacy testing. First clinical TREM-1 blocker LR12 recently failed to reach significance for the primary endpoint in phase IIb sepsis trial. To minimize the risk of failure in the clinic, we developed ligand-independent TREM-1 inhibitory peptide sequence GF9 that can be used as a part of trifunctional peptide GA31 formulated into macrophage- specific lipopeptide complexes (LPC) to improve its half-life and targeting. Macrophage-targeted delivery also addresses the potential for different TREM-1-expressing cell types (e.g., neutrophils vs macrophages) playing different roles in the pathogenesis of inflammatory diseases. TREM-1 blockade by GA31-LPC inhibits uncontrolled inflammatory response and ameliorates the disease in animal models of sepsis, acute respiratory distress syndrome, sulfur mustard-induced lung injury, cancer, arthritis, retinopathy, and other inflammation-associated diseases. GA31-LPC is safe and well-tolerable by healthy and diseased animals. The major goal of the proposed research is to test the hypothesis that therapeutic blockade of TREM-1 by using GA31-LPC will significantly extend survival of mice exposed to LD70/30 radiation dose when administered at 24 h or later post-radiation. Specific aims of this project are to: 1) generate, characterize and test GA31-LPC in vitro; and 2) determine the in vivo feasibility of using GA31-LPC as a therapeutic MCM to significantly extend survival of mice exposed to LD70/30 radiation dose. We will generate GA31-LPC, characterize its composition, size and stability, and test in vitro in cell- based assays. We will next test GA31-LPC in mice exposed to LD70/30 radiation dose for its ability to improve 30 day animal survival when systemically administered 24 or 48 h post-TBI. If successful, this project will generate preliminary data supporting the development of a new mechanism-based, well- tolerable and effective MCM for mitigation and treatment of potentially lethal ARS.