GALACTIC COSMIC RAYS (GCR) AND SOLAR PARTICLE EVENTS (SPES) ARE A MAJOR SOURCE OF CARCINOGENIC RISK FOR ASTRONAUTS ON PROLONGED SPACE MISSIONS. LARGE UNCERTAINTIES EXIST IN THE EXACT ESTIMATION OF CANCER RISKS FROM CHARGED PARTICLES DUE TO THE PAUCITY OF EPIDEMIOLOGICAL DATA IN THIS AREA. FURTHERMORE A MECHANISTIC UNDERSTANDING OF GENETIC CHANGES UNDERLYING TRANSFORMATION BY PARTICLE RADIATION IS NECESSARY FOR THE DEVELOPMENT OF APPROPRIATE COUNTERMEASURES. THUS EXPERIMENTAL ANIMAL MODELS THAT CLOSELY MIMIC THE PROCESS OF CARCINOGENESIS IN HUMANS ARE ESSENTIAL FOR ONCOGENIC RISK ASSESSMENT. IN THE COURSE OF OUR CURRENTLY FUNDED 3 YR. NASA PROJECT (2013 2016) WE CHARACTERIZED TWO SENSITIVE AND COMPLEMENTARY MOUSE MODELS THAT CAN BE USED TO ELUCIDATE MOLECULAR MECHANISMS UNDERLYING THE PROCESS OF PARTICLE RADIATION-INDUCED GLIOBLASTOMA (GBM) DEVELOPMENT. GBMS ARE LETHAL BRAIN TUMORS WITH VERY DISMAL PROGNOSIS FOR WHICH RADIATION IS THE ONLY KNOWN RISK FACTOR. GBMS REPRESENT THE THIRD LEADING CAUSE OF CANCER-RELATED DEATH AMONG ADULTS AGED 30 50 YEARS (THE AVERAGE AGE OF ASTRONAUTS) THE MEAN SURVIVAL AFTER DIAGNOSIS BEING ONLY ABOUT 14 MONTHS. GBM WAS THE FIRST CANCER TO BE ANALYZED BY THE CANCER GENOME ATLAS NETWORK (TCGA) AND THE KEY GENETIC ALTERATIONS OCCURRING IN GBM ARE NOW WELL DEFINED. BASED ON THIS INFORMATION WE UTILIZED TRANSGENIC MICE WITH BRAIN-RESTRICTED DELETIONS OF GBM-RELEVANT TUMOR SUPPRESSORS IN LOGICAL COMBINATIONS TO ANALYZE THE PROCESS OF CHARGED PARTICLE-INDUCED CARCINOGENESIS. WE IDENTIFIED AND CHARACTERIZED TWO COMPLEMENTARY MOUSE GBM MODELS THAT WOULD BE IDEAL FOR STUDYING PARTICLE RADIATION-INDUCED CARCINOGENESIS - NESTIN-CRE INK4AB-/-ARF F/F AND NESTIN-CRE P53F/+PTENF/+. THESE MODELS EXHIBIT A LOW FREQUENCY OF SPONTANEOUS GBMS BUT READILY DEVELOP BRAIN TUMORS AFTER EXPOSURE TO HZE PARTICLES WHICH RESEMBLE HUMAN HIGH GRADE GLIOMAS IN THEIR GENETIC AND MOLECULAR SIGNATURES. USING THESE MICE WE HAVE CLEARLY DEMONSTRATED THAT HIGHLINEAR ENERGY TRANSFER (LET) CHARGED PARTICLES HAVE A GREATER TRANSFORMING POTENTIAL COMPARED TO LOW-LET RADIATION AND HAVE CHARACTERIZED THE MOLECULAR EVENTS UNDERLYING FE ION-INDUCED GLIOMAGENESIS IN THESE MODELS THIS WORK SETS THE STAGE FOR QUANTITATIVE STUDIES ON RADIATION QUALITY EFFECTS ON CARCINOGENESIS FOR AN ARRAY OF CHARGED PARTICLES REPRESENTING THE GCR (AS PROPOSED IN AIM 1). THESE CHARGED PARTICLES INDUCE COMPLEX DNA DOUBLE-STRAND BREAKS (DSBS) THE ACCURATE REPAIR OF WHICH IS CRITICAL FOR PREVENTING TRANSFORMATION. OUR MODELS WILL ALSO ALLOW US TO DETERMINE WHICH DSB REPAIR PATHWAY REPRESENTS A MAJOR BARRIER TO CHARGED PARTICLE-INDUCED GLIOMAGENESIS (AS PROPOSED IN AIM 2). THIS INFORMATION WOULD BE FUNDAMENTAL TO THE DEVELOPMENT OF A MECHANISTIC UNDERSTANDING OF CHARGED PARTICLE-INDUCED CARCINOGENESIS. WE WILL CROSS THE TRANSGENIC MICE CHARACTERIZED BY US WITH MICE HARBORING BRAIN-SPECIFIC ABLATION OF NON-HOMOLOGOUS END JOINING (NHEJ) OR HOMOLOGOUS RECOMBINATION (HR) REPAIR PATHWAYS - NESTIN-CRE LIGASE4F/F AND NESTIN-CRE BRCA2F/F THAT WERE ESTABLISHED IN THE LABORATORY OF PROF. PETER MCKINNON (COLLABORATOR ON PROJECT). FINALLY GENOMIC AND BIOINFORMATICS ANALYSES WILL BE USED TO DEFINE GENETIC SIGNATURES UNIQUE TO PARTICLE-RADIATION INDUCED GLIOBLASTOMAS AND TO DELINEATE KEY PATHWAYS THAT ARE DE-REGULATED DURING HZEINDUCED GLIOMAGENESIS (AS PROPOSED IN AIM 3). WE ARE HOPEFUL THAT AN IN-DEPTH MECHANISTIC ANALYSIS OF CHARGED PARTICLE-INDUCED GLIOMAGENESIS IN THESE VALIDATED MOUSE MODELS WILL HELP US TO MAKE SIGNIFICANT PROGRESS TOWARDS CANCER RISK ASSESSMENTS AND DEVELOPMENT OF PROTECTIVE STRATEGIES FOR CHARGED PARTICLE EXPOSURE.