Document Type

Thesis

Date of Degree

Spring 2016

Degree Name

MS (Master of Science)

Degree In

Pharmacology

First Advisor

Joseph Cullen

Second Advisor

Dawn Quelle

Abstract

Compared to normal cells, cancer cells tend to have higher concentrations of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) due to an accelerated cellular metabolism. The high ROS content leaves cancer cells increasingly susceptible to oxidative stress-induced cell death. This susceptibility can be manipulated in selective cancer therapy by further increasing production of ROS or inhibiting peroxide removal systems or a combination of the two.

Pharmacological ascorbate (high-dose intravenous ascorbate) has been shown to sensitize pancreatic cancer to ionizing radiation (IR) by increasing production of ROS such as H2O2. Glutathione reductase (GR) and thioredoxin reductase (TrxR) are both important enzymes in peroxide removal systems. GR and TrxR function to recycle key electron donors in the cellular removal of H2O2. We hypothesized that inhibiting the peroxide removal systems via inhibition of GR and TrxR would enhance ascorbate-induced cytotoxicity in pancreatic cancer cells.

Inhibition of TrxR activity enhanced ascorbate-induced cytotoxicity in MIA PaCa-2 pancreatic cancer cells. Additionally, knockdown of GR protein expression in combination with pharmacological ascorbate treatment increased MIA PaCa-2 pancreatic cancer cell sensitivity to IR. In MIA PaCa-2 and 403 F1 patient-derived pancreatic cancer cells, inhibition of both TrxR and GR activity combined with pharmacological ascorbate enhanced radiosensitivity. However, this effect was not seen in 339 patient-derived pancreatic cancer cells treated with the same dose of ascorbate. In conclusion, inhibition of TrxR activity, GR activity, or both enhances radiosensitivity and ascorbate-induced cytotoxicity in some, but not all, pancreatic cancer cell lines. Treatments combining ascorbate with inhibition of H2O2 removal may be an effective strategy for treatment of pancreatic adenocarcinoma.

Public Abstract

Pancreatic adenocarcinoma is the fourth leading cause of cancer deaths in the United States. Surgical resection of the primary tumor is currently the only treatment with curative potential. Adjuvant treatments have thus far not been shown to significantly improve long-term survival. Compared to normal cells, cancer cells have increased reactive oxygen species (ROS) levels because of their accelerated metabolism. The high ROS content of cancer cells leaves them even more susceptible to oxidative stress-induced cell death. This particular trait can be manipulated in selective cancer therapy. Glutathione reductase (GR) and thioredoxin reductase (TrxR) are important enzymes in peroxide removal systems that function to recycle key electron donors in the cellular removal of hydrogen peroxide (H2O2). Intravenous (pharmacological) ascorbate produces high plasma concentrations that are cytotoxic to tumor cells. Ascorbate auto-oxidation generates H2O2. Likewise, radiation therapy is known to increase levels of ROS, including H2O2. We hypothesized that inhibiting the peroxide removal systems via inhibition of GR and TrxR will enhance ascorbate-induced cytotoxicity in pancreatic cancer cells. Here, we show that inhibition of TrxR activity, GR activity, or both enhances radiosensitivity and ascorbate-induced cytotoxicity in MIA PaCa-2 and 403 F1 pancreatic cancer cell lines, but not in 339 pancreatic cancer cells. Therapies combining ascorbate with inhibition of H2O2 removal have the potential to be an effective strategy in treatment of pancreatic adenocarcinoma.

Keywords

publicabstract, ascorbate, Free Radical and Radiation Biology, pancreatic cancer, peroxide removal, Pharmacology, ROS

Pages

v, 17

Bibliography

17

Copyright

Copyright 2016 Hannah Van Beek

Included in

Pharmacology Commons

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