Abstract
Thymidylate synthase (TYMS; EC 2.1.1.15) catalyzes the reductive methylation of 2ʹ-deoxyuridine-5ʹ-monophosphate (dUMP) by N5,N10-methyhlenetetrahydrofolate, forming dTMP for the maintenance of DNA replication and repair. Inhibitors of TYMS have been widely used in the treatment of neoplastic disease. A number of fluoropyrimidine and folate analogs have been developed that lead to inhibition of the enzyme, resulting in dTMP deficiency and cell death. In the current study, we have examined the role of oxidative stress in response to TYMS inhibitors. We observed that intracellular reactive oxygen species (ROS) concentrations are induced by these inhibitors and promote apoptosis. Activation of the enzyme NADPH oxidase (NOX), which catalyzes one-electron reduction of O2 to generate superoxide (O2●−), is a significant source of increased ROS levels in drug-treated cells. However, gene expression profiling revealed a number of other redox-related genes that may contribute to ROS generation. TYMS inhibitors also induce a protective response, including activation of the transcription factor nuclear factor E2-related factor 2 (NRF2), a critical mediator of defense against oxidative and electrophilic stress. Our results show that exposure to TYMS inhibitors induces oxidative stress that leads to cell death, while simultaneously generating a protective response that may underlie resistance against such death.
Footnotes
- Received April 23, 2015.
- Accepted October 5, 2015.
This work was supported by the National Cancer Institute [Grant CA44013]; and the National Institutes of Health Centers of Biomedical Research Excellence program of the National Institute of General Medical Sciences [Grant GM103336]. The Microarray Core Facility receives partial support from South Carolina IDeA Networks of Biomedical Research Excellence [Grant P20GM103499].
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- Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics
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