Dual oxidase-induced sustained generation of hydrogen peroxide contributes to pharmacologic ascorbate-induced cytotoxicity

Abstract

Pharmacologic ascorbate treatment (P-AscH-, high-dose, intravenous vitamin C) results in a transient short-term increase in the flux of hydrogen peroxide that is preferentially cytotoxic to cancer cells versus normal cells. This study examines whether an increase in hydrogen peroxide is sustained posttreatment and potential mechanisms involved in this process. Cellular bioenergetic profiling following treatment with P-AscH- was examined in tumorigenic and nontumorigenic cells. P-AscH- resulted in sustained increases in the rate of cellular oxygen consumption (OCR) and reactive oxygen species (ROS) in tumor cells, with no changes in nontumorigenic cells. Sources for this increase in ROS and OCR were DUOX 1 and 2, which are silenced in pancreatic ductal adenocarcinoma, but upregulated with P-AscH- treatment. An inducible catalase system, to test causality for the role of hydrogen peroxide, reversed the P-AscH-–induced increases in DUOX, whereas DUOX inhibition partially rescued P-AscH-–induced toxicity. In addition, DUOX was significantly downregulated in pancreatic cancer specimens compared with normal pancreas tissues. Together, these results suggest that P-AscH-–induced toxicity may be enhanced by late metabolic shifts in tumor cells, resulting in a feed-forward mechanism for generation of hydrogen peroxide and induction of metabolic stress through enhanced DUOX expression and rate of oxygen consumption.