Overexpression of manganese superoxide dismutase (MnSOD) by transgene therapy prior to (or after) ionizing irradiation exposure significantly decreases both acute and chronic irradiation-induced damage and reduces radical oxygen species production by pulmonary, esophageal, oral cavity, intestinal, and bladder tissues in rodent models. Our laboratory has demonstrated that MnSOD transgene mRNA, and epitope-tagged HA-hemagglutinin MnSOD protein overexpression are detectable for 48 to 72 hours after organ specific gene therapy and that sequential administration of multiple doses of MnSOD-Plasmid Liposomes (PL) results in stable radioprotective transgene expression by the intra-oral or inhalation route. We have also shown that small molecule SOD mimetic compounds decrease acute and chronic irradiation damage. We will now optimize SOD antioxidant therapy for radiation protection and radiation injury mitigation. The first specific aim tests the hypothesis that MnSOD-PL will be an effective systemic protector against whole body irradiation (WB1). We will measure radical oxygen species (ROS) production, changes in thiols and antioxidant pools in tissues from MnSOD-PL treated, and MnSOD-transgenic mice; and in a novel tet-inducible MnSOD transgenic mouse model, will determine the level of radioprotection, toxicity, carcinogenicity and late effects of MnSOD overexpression relative to time before or after WBI. The second specific aim tests the hypothesis that newly designed and synthesized small molecule SOD mimetic compounds which are mitochondrially targeted by peptide dragging, and benchmarked to the antioxidant, EUK-134, will effectively substitute for or synergize with MnSOD-PL gene therapy. The Innovative Medicinal Chemistry: Discovery and Screening Core will collaborate with us to develop a systemic oral or skin patch absorbable drug product. The third specific aim tests the hypothesis that adding nitroxide, catalase or glutathione peroxidase (GPX) to the optimized protocol of mitochondrial targeted SOD mimetic and MnSOD-PL will further improve both radioprotection and radiation mitigation. These studies should optimize utilization of both antioxidant transgene and small molecule SOD mimetic therapy for protection from ionizing irradiation damage.