γ-Tocotrienol Suppression of the Warburg Effect Is Mediated by AMPK Activation in Human Breast Cancer Cells

Abstract

Cancer cell metabolism is characterized by aerobic glycolysis or the “Warburg effect”. Enhanced Akt signaling is associated with activation of various downstream enzymes involved in the glycolytic process, whereas activation of 5′-AMP-activated kinase (AMPK) acts to terminate energy expending mechanisms and decrease glycolytic enzyme expression. Studies were conducted to determine if the anticancer effects of γ-tocotrienol, are mediated through a suppression in aerobic glycolysis. Results show that treatment with 0–7 μM γ-tocotrienol throughout a 4-day culture period resulted in a dose-responsive increase in AMPK activation, and corresponding decrease in Akt activity in human MCF-7 and MDA-MB-231 breast cancer cells. γ-Tocotrienol treatment was also found to induce a dose-responsive decrease in phosphorylated-Fox03 (inactivated), a transcription factor that acts to inhibit in the levels of glycolytic enzyme, and this decrease was associated with a reduction in glycolytic enzyme levels and activity, as well as glucose consumption in these cells. PCR microarray analysis shows that γ-tocotrienol treatment decreases the expression of genes associate with metabolic signaling and glycolysis in MCF-7 and MDA-MB-231 breast cancer cells. In summary, these findings demonstrate that the anticancer effects of γ-tocotrienol are mediated, at least in part, by a suppression in the Warburg effect.

Acknowledgments

The authors would like to thank the First Tech International Ltd. for providing γ-tocotrienol for use in these studies. The authors also thank Dr. Karen P. Briski for her generous assistance and use of the laser confocal microscope and the BioRad-icycler.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Author’s Contribution to the Paper

Venkateshwara Dronamraju: Provided substantial contribution to the conception and design of nearly all experiments performed in the study, acquisition of the data and analysis and interpretation of the data. He also wrote the first draft of the paper and final approval of the version of the paper to be published. Baher A. Ibrahim: Provided substantial contribution on designing and interpretation of the microarray experiments. He also played an important role in editing the Materials and Methods and Results Sections associated with the microarray experiments. Baher also gave final approval of the version of the paper to be published. Karen P. Briski: Provided substantial contribution on designing and interpretation of the microarray experiments and immunocytochemistry experiments, as well as contributing to editing the sections in the paper related to microarray and immunocytochemistry experimentation. She also gave final approval of the version of the paper to be published. Paul W. Sylvester: Provided substantial contribution to conception and design, as well as data analysis and interpretation. He also played a primary role in drafting and revising the paper critically for important intellectual content. Dr. Sylvester also gave final approval of the version to be published.

Additional information

Funding

This work was supported in part by funds provided by the Louisiana Cancer Foundation.