Inhibitors of hydroperoxide metabolism enhance ascorbate-induced cytotoxicity

Abstract

Pharmacological ascorbate, via its oxidation, has been proposed as a pro-drug for the delivery of H₂O₂ to tumors. Pharmacological ascorbate decreases clonogenic survival of pancreatic cancer cells, which can be reversed by treatment with scavengers of H₂O₂. The goal of this study was to determine if inhibitors of intracellular hydroperoxide detoxification could enhance the cytotoxic effects of ascorbate. Human pancreatic cancer cells were treated with ascorbate alone or in combination with inhibitors of hydroperoxide removal including the glutathione disulfide reductase inhibitor 1,3 bis (2-chloroethyl)-1-nitrosurea (BCNU), siRNA targeted to glutathione disulfide reductase (siGR), and 2-deoxy-D-glucose (2DG), which inhibits glucose metabolism. Changes in the intracellular concentration of H₂O₂ were determined by analysis of the rate of aminotriazole-mediated inactivation of endogenous catalase activity. Pharmacological ascorbate increased intracellular H₂O₂ and depleted intracellular glutathione. When inhibitors of H₂O₂ metabolism were combined with pharmacological ascorbate the increase in intracellular H₂O₂ was amplified and cytotoxicity was enhanced. We conclude that inclusion of agents that inhibit cellular peroxide removal produced by pharmacological ascorbate leads to changes in the intracellular redox state resulting in enhanced cytotoxicity.

Keywords::

• hydrogen
• peroxide
• glutathione disulfide reductase
• catalase
• oxidative stress
• pancreatic cancer

Declaration of interest

The authors report no declarations of interest. The author alone are responsible for the content and writing of the paper.

This research was supported by NIH grant U01 CA166800, the Department of Veterans Affairs Medical Research Service, and the Susan L. Bader Foundation of Hope. TJvE had support from NIH P42 ES013661, Training Core; JRW had support from NIH T32CA078586 and NIH R01GM073929. The content is solely the responsibility of the authors and does not represent views of the Department of Veterans Affairs or the NIH.