131 - Inhibition of Peroxide Removal Enhances Pharmacological Ascorbate and Ionizing Radiation-Induced Cytotoxicity of Pancreatic Ductal Adenocarcinoma

Abstract

Pancreatic ductal adenocarcinoma (PDA) is the third leading cause of cancer deaths with a poor 5 year survival rate of only 8.2%. PDA cells produce high levels of reactive oxygen species (ROS) compared to normal cells, thereby increasing their susceptibility to oxidative stress-induced cell death. Therefore, targeting pathways that are essential in peroxide removal, such as the enzymes glutathione reductase and thioredoxin reductase, could be utilized as a tool for cancer therapy to further disrupt a cancer cells ability to overcome excess ROS. Pharmacological ascorbate is a pro-oxidant that has been shown to enhance cytotoxicity and radio-sensitize several cancer types through an H2O2-mediated mechanism. The objective of this study was to examine the effects of pharmacological ascorbate on PDA cells as an adjuvant to radiation therapy in addition to therapies that inhibit peroxide removal including auranofin (inhibits thioredoxin reductase) and 2-deoxyglucose or glucose deprivation (inhibits regeneration of NADPH). Human PDA cell lines AsPC-1 and MiaPaCa-2 were evaluated for clonogenic survival after treatment with either auranofin (500 nM), 2-deoxyglucose (25 mM), or glucose deprivation for 24 hrs, in combination with irradiation (1-2 Gy) and pharmacological ascorbate (1-2 mM) for 1 hr. Auranofin was shown to inhibit thioredoxin reductase activity, sensitize PDA cells to pharmacological ascorbate treatment and significantly reduce clonogenic cell survival by an additional 50% or 36% for MiaPaca-2 cells (P≤ 0.0001) and 29% or 39% for AsPC-1 cells (P≤ 0.01-0.0001) at 1 and 2 Gy, respectively. Inclusion of 2-deoxyglucose reduced clonogenic cell survival by an additional 20% or 9.5% for MiaPaCa-2 cells (P≤ 0.001-0.01) and 23% or 8% for AsPC-1 cells (P≤ 0.01-0.0001) at 1 and 2 Gy, respectively. Glucose deprivation enhanced cytotoxicity of MiaPaca-2 cells by an additional 40% or 29% (P≤ 0.0001) at 1 and 2 Gy, respectively. Inhibition of peroxide removal sensitizes PDA cells to irradiation and pharmacological ascorbate cytotoxicity. Therapies incorporating these strategies have the potential to be effective for the treatment of PDA.