ASCORBATE-INDUCED RADIOSENSITIZATION IN PANCREATIC CANCER

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DESCRIPTION (provided by applicant): Adenocarcinoma of the pancreas is the fourth leading cause of cancer death in the United States and is increasing in incidence; the prognosis remains dismal. We propose to investigate an entirely new approach, using pharmacological ascorbate as an adjuvant to radio-therapy, to treat pancreas cancer. Intravenous ascorbate (i.e., ascorbic acid, vitamin C), but not oral ascorbate, produces high plasma concentrations, which are in the range that are cytotoxic to tumor cells. Preliminary studies from our group have demonstrated that ascorbate induces oxidative stress and cytotoxicity in pancreatic cancer cells; this cytotoxicity appears to be greater in tumor vs. normal cells. We have firmly established that pharmacological ascorbate is a pro-drug for delivery of hydrogen peroxide (H2O2) in vitro and in vivo via its autoxidation. Studies from our previously funded R21 grant CA137230 "Mechanisms of ascorbate-induced cytotoxicity in pancreatic cancer" have demonstrated that ascorbate, in doses achievable in humans, decreases viability and proliferation in all pancreatic cancer cell lines examined, via a H2O2-mediated mechanism. The current application extends this preclinical work to determine if this strategy can be used effectively as an adjuvant in radiotherapy for pancreatic cancer. If pancreatic cancer cells (relative to normal cells) are more susceptible to ascorbate-induced cytotoxicity due to increased metal ion catalyzed ascorbate autoxidation leading to increased production of H2O2, then using ascorbate as an adjuvant would be expected to sensitize pancreatic tumor cells to standard therapies such as ionizing radiation that increase levels of reactive oxygen species. We will use biochemistry/molecular biology techniques to determine relative susceptibility to ascorbate-induced radiosensitization and oxidative stress in vitro and in vivo; we will employ FLT-PET (fluoro-labeled thymidine positron emission tomography) as a non- invasive in vivo index of cell proliferation. This proposal focuses on improvement of the therapeutic ratio of a standard anti-cancer therapy (ionizing radiation) using a complementary approach (high dose ascorbate), in the treatment of pancreatic cancer. The current proposal will test the hypothesis that metal ion catalyzed H2O2 generation from the auto-oxidation of ascorbate induces radiosensitization of human pancreatic cancer cells in vitro and in vivo. We will test our hypotheses with the following two Specific Aims: 1. Determine if ascorbate selectively induces radio-sensitization of human pancreatic cancer cells (vs. normal cells) in vitro via the flux of H2O2 generated from metal ion catalyzed auto-oxidation of ascorbate. 2. Determine if ascorbate selectively induces radio-sensitization of human pancreatic cancer cells in vivo. If we can rigorously demonstrate that the radiosensitization mediated by pharmacological ascorbate induces preferential oxidative stress and subsequent cytotoxicity in human pancreatic cancer cells, then the results of this application will provide a foundation for the rational design of a combined modality cancer therapy that is highly responsive to the RFA PA-09-167 from NCCAM entitled "Developmental Projects in Complementary Approaches to Cancer Care". PUBLIC HEALTH RELEVANCE: Intravenous ascorbate produces high plasma concentrations in the range that is cytotoxic to pancreatic tumor cells. Pharmacological ascorbate has been hypothesized to be a pro-drug for formation of hydrogen peroxide (H2O2). Our proposal investigates mechanisms to enhance radiosensitivity of human pancreatic cancer cells by the flux of H2O2 generated by treatment with pharmacological ascorbate.