Author ORCID Identifier
0000-0003-3958-7403
Date of Graduation
8-2019
Document Type
Dissertation (PhD)
Program Affiliation
Cancer Biology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Helen Piwnica-Worms
Committee Member
Cullen M. Taniguchi
Committee Member
Michelle Barton
Committee Member
Russell Broaddus
Committee Member
Anirban Maitra
Abstract
Surgical resection is the only potentially curative treatment for pancreatic cancer, but only 15-20% of patients have resectable tumors. In unresectable cases, stereotactic body radiotherapy (SBRT) may be used to give tumor-directed radiotherapy (RT). Unfortunately, this can cause severe gastrointestinal (GI) toxicity due to proximity of the pancreatic head to the duodenum. Protecting the intestine from the toxic side-effects of radiation may enable dose-escalation that could achieve more effective local control of disease. We and others have previously shown that a fast of 24 hours protects mice from lethal doses of the DNA-damaging agent etoposide. In this study, we demonstrate that a 24 hour fast also protects mice from lethal doses of total-abdominal radiation. Histologic analyses using the Withers-Elkind microcolony assay show that fasting protected small intestinal (SI) stem cells from radiation damage and promoted early regeneration. To show a proof-of-principle for the use of this radioporotective maneuver in cancer therapy, we used an orthotopic model of pancreatic cancer using KPC tumor cells syngeneic to C57BL/6. Here, we show that fasting-mediated intestinal protection enabled dose escalated SBRT for treatment of these orthotopic tumors. RT with fasting-mediated radioprotection delayed tumor growth and improved survival compared to controls. Given this robust phenotype, we developed a 3D culture ex vivo assay using intestinal stem cell-enriched epithelial spheroid cultures. We modified these intestinal spheroids with a bioluminescent reporter and used these cells to develop a modified clonogenic assay for 3D culture that can be used to identify novel radioprotectors, such as a fasting mimetic. Taken together, these results suggest that fasting protects small intestinal stem cells, allowing animals to receive potentially curative doses of abdominal radiation that would otherwise be lethal. Future work will aim to identifying the mechanisms by which fasting confers intestinal protection and drug candidates that can be used to mimic this fasting-mediated protection.
Keywords
radiation, small intestine, toxicity, pancreas, pdac, stem cells, fasting