THE PRIMARY RISK FACTOR LIMITING THE AMOUNT OF TIME AN ASTRONAUT CAN SPEND IN FLIGHT IS THE RISK OF CANCER INDUCTION RESULTING FROM THE UNIQUE RADIATIONS INHERENT TO THE DEEP SPACE ENVIRONMENT. ONE STRATEGY FOR MITIGATING RADIATION INDUCED CARCINOGENESIS IS TO PROVIDE BIOLOGICAL COUNTERMEASURES THAT MITIGATE RADIATION INJURY AND CANCER INDUCTION. TO DATE THE ONLY FDA APPROVED RADIOPROTECTOR IS THE FREE RADICAL SCAVENGER AMIFOSTINE; HOWEVER CONCERNS ABOUT TOXICITY AND REPORTS OF SEVERE ANAPHYLACTIC REACTIONS TO THIS DRUG PREVENT ITS USE IN SPACEFLIGHT. THEREFORE THERE IS A NEED TO DETERMINE AND VALIDATE APPROPRIATE BIOLOGICAL COUNTERMEASURES TO MITIGATE SPACE RADIATION CARCINOGENESIS THEREBY INCREASING THE AMOUNT OF TIME ASTRONAUTS CAN SAFELY SPEND IN SPACE. IN THE PROPOSED STUDIES WE WILL EVALUATE THE RADIO PROTECTIVE POTENTIAL OF GC4419 A NOVEL SUPEROXIDE DISMUTASE MIMETIC DEVELOPED BY GALERA THERAPUTICS (ST. LOUIS MO) IN MITIGATING SPACE RADIATION CARCINOGENESIS. DUE TO ITS EFFICACY IN PHASE 1 CLINICAL TRIALS AND PRE-CLINICAL DATA GENERATED BY OUR GROUP GC4419 IS CURRENTLY BEING FAST TRACKED INTO FDA PHASE II HUMAN CLINICAL TRIALS AS A RADIOPROTECTOR FOR PATIENTS UNDERGOING CHEMORADIATION THERAPY FOR THE TREATMENT OF HEAD AND NECK CANCER. NOT ONLY DOES GC4419 REDUCE THE FREQUENCY OF RADIATION INDUCED ADVERSE EFFECTS PRE-CLINICAL DATA SUGGEST IT HAS POTENT ANTI-CARCINOGENIC AND ANTI-TUMOR EFFECTS AS WELL. THEREFORE GC4419 REPRESENTS A SAFE CLINICALLY TESTED COUNTERMEASURE TO REDUCE RADIATION INJURY. IN THE PROPOSED STUDIES WE WILL EVALUATE THE EFFICACY OF GC4419 IN PREVENTING SPACE RADIATION INDUCED CARCINOGENESIS FOCUSING SPECIFICALLY ON THE LUNG AS A PRIMARY TUMOR SITE.