DOI

10.17077/etd.ke1ezy2m

Document Type

Dissertation

Date of Degree

Spring 2017

Access Restrictions

Access restricted until 07/13/2019

Degree Name

PhD (Doctor of Philosophy)

Degree In

Free Radical and Radiation Biology

First Advisor

Goswami, Prabhat C.

First Committee Member

Spitz, Douglas R.

Second Committee Member

Buettner, Garry R.

Third Committee Member

Domann, Frederick E.

Fourth Committee Member

Cullen, Joseph J.

Abstract

Combination radiation and chemotherapy are commonly used to treat locoregionally advanced head and neck squamous cell carcinoma. Aggressive dosing of these therapies is significantly hampered by side effects due to normal tissue toxicity. Selenium represents an adjuvant that selectively sensitizes cancer cells to therapy, potentially by inducing lipid peroxidation (LPO). This study investigated whether one such selenium compound, methylseleninic acid (MSA), induces LPO and radiation sensitivity in HNSCC cells. Results from BODIPY C11 oxidation and ferric thiocyanate assay revealed that MSA induced LPO in HNSCC cells rapidly and persistently. Cell counts and propidium iodide viability assays showed that MSA was more toxic to HNSCC cells than other related selenium compounds, and this toxicity was abrogated by treatment with α-tocopherol, an LPO inhibitor. MSA was also found to sensitize HNSCC cells to radiation by clonogenic assay. The addition of MSA to a cell-free solution of glutathione (GSH) resulted in an increase in oxygen consumption as measured by Clark electrode, suggesting the formation of reactive oxygen species. Intracellular GSH in HNSCC was depleted following MSA treatment. Supplementation of the intracellular GSH pool with N-acetylcysteine (NAC) rendered the cells more sensitive to MSA. Results from this study identify MSA as an inducer of LPO, and reveal its capability to sensitize HNSCC to radiation. MSA may represent a potent adjuvant to combination therapy in HNSCC.

Public Abstract

The success of treating cancer is frequently limited by damage to non-cancerous cells. Selenium is an essential micronutrient that sensitizes cancer cells to therapy while protecting normal cells. The manner in which this sensitization occurs is not well understood. However, selenium can be delivered in many forms, which tend to exhibit different effects.

This study investigated one particular selenium compound, methylseleninic acid (MSA), and how it impacts head and neck squamous cell carcinoma (HNSCC) cells. Results indicate that MSA can initiate a toxic chain reaction, referred to as lipid peroxidation (LPO). Inhibiting this chain reaction protected cancer cells from MSA-induced toxicity. MSA was found to be more toxic to HNSCC cells than similar selenium compounds, and it also rendered them more sensitive to radiation. MSA also depleted the cancer cells of glutathione, an essential cellular antioxidant. However, replenishing the glutathione pool in the cancer cells resulted in greater sensitivity to MSA rather than protection. Combining glutathione and MSA in the absence of cells resulted in an increased rate of disappearance of oxygen, which suggests the formation of reactive oxygen species, many of which are capable of inducing LPO.

Overall, this research suggests that selenium, and MSA in particular, is a promising addition to current therapy options for cancer patients. Sensitizing cancer cells to radiation helps to improve cure rates, while reducing debilitating side effects. More work is needed to better understand how MSA affects normal cells, to ensure that it doesn’t sensitize them as well.

Keywords

Aging, Cancer, Lipid peroxidation, Radiation, Selenium

Pages

xiii, 101 pages

Bibliography

Includes bibliographical references (pages 86-101).

Copyright

Copyright © 2017 John Thomas Lafin

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