PROJECT SUMMARY The majority of patients diagnosed with rectal cancer will receive radiation therapy to treat their tumors. Long- term complications from radiation therapy directed to the colorectal region are bowel fibrosis, rectal wall damage, bowel incontinence, rectal and bladder bleeding and pelvic fracture and there are no FDA approved treatments to protect normal rectal and anal tissues from radiation-induced damage. Radiation exposure leads to free radical-mediated oxidative damage to normal tissues leading to fibrosis. Cancer cells have increased metabolic production of reactive oxygen species (ROS), relative to normal cells, which have been shown to drive cancer progression. Thus, suppressing radiation-induced ROS would act as both a radioprotector in normal tissues while inhibiting pro-survival and progression pathways in cancer cells. BMX-001 is a small molecule antioxidant, which scavenges ROS. Preliminary data demonstrate that BMX-001 protects rectal tissues from radiation- induced damage, while enhancing colorectal cancer killing. The overall hypothesis of this proposal is that BMX- 001 will protect normal tissues from radiation-induced damage, while not protecting the cancer cells in patients undergoing radiation therapy of rectal and anal cancers. Specific Aim 1 will determine the mechanism(s) by which BMX-001 protects from radiation-induced epithelial dysfunction and how BMX-001 prevents blood chemo- radiation toxicity. It will be determined whether BMX-001 prevents hematological chemoradiation toxicity through the NRF2/MnSOD signaling and potential biomarkers of oxidative stress and GI damage will be identified in a chronic in vivo model of radiation-induced damage. Specific Aim 2 will determine the safety and efficacy in patients through Phase II clinical trials as a radioprotector of rectal cancers. A randomized phase II clinical trial will determine whether BMX-001 is an efficacious radioprotector of normal tissues in rectal cancer patients undergoing total neoadjuvant chemoradiation therapy followed by surgery. Specific Aim 3 will identify potential biomarkers that can be used to demonstrate radiation damage and radioprotector efficacy of BMX-001 in human clinical specimens obtained from the Phase II trial. Surgically resected tumor and adjacent normal rectal tissues from BMX-001 or placebo controlled patients after chemoradiation will be evaluated for inflammation, normal tissue damage, fibrosis and oxidative stress. In addition, oxidative stress markers will be evaluated in blood and urine samples. The completion of the studies will provide an in depth mechanistic understanding of the mechanisms by which BMX-001 inhibits normal tissue injury and whether BMX-001 can be used in rectal cancer patients as an effective radioprotector and could be universally adapted for treatment of other cancers receiving pelvic irradiation.