Abstract 376: γ-Tocotrienol negative modulation of the Warburg effect is mediated by the AMPK activation in malignant breast cancer cells

Abstract

Abstract Previous studies showed that γ-tocotrienol, a natural vitamin E derivative is associated with decrease in the rate of glycolysis in human mammary tumor cells. Therefore, studies were conducted to investigate the effects of γ-tocotrienol on key regulatory pathways of glucose metabolism in MCF-7 and MDA-MB-231 breast cancer cells. Unregulated proliferative capacity of cancer cells places huge metabolic load on cancer cells, which ultimately promotes the dysregulation of normal metabolic pathways. This dysregulation of energy metabolism manifests as a characteristic phenomenon called as the “Warburg effect”. The Warburg effect is an over-reliance on aerobic glycolysis by cancer cells to meet energy demand of proliferation. Akt has been reported as key regulator of Warburg effect in several tumors and is a known promoter of glycolysis. Additionally, 5'-AMP activated protein kinase (AMPK) is a known metabolic sensor that is activated when energy balance is disrupted in cells. In addition to their role in regulating cellular energy metabolism, Akt and AMPK also share several downstream targets like FoxO3a, a transcription factor. In the present study, protein expression using western blot and immunocytochemistry revealed that in human breast cancer cell lines MCF-7 and MDA-MB-231, γ-tocotrienol induced dose-dependent inhibition of Akt. This was associated with a rescue of Akt-induced inhibition of FoxO3a. In addition, γ-tocotrienol also induced a decrease in aerobic glycolysis as evidenced by a decrease in consumption of glucose and a decrease in glycolytic enzyme expression. Furthermore, results showed that γ-tocotrienol treatment induced activation of AMPK in breast cancer cells. Immunoprecipitation analysis also revealed a possible interaction between AMPK and FoxO3a in γ-tocotrienol treated cells. To study the effect of γ-tocotrienol-induced activation of AMPK on its downstream targets, microarray analysis was done using RT2-Profiler PCR array. The microarray revealed that γ-tocotrienol-induced AMPK activation resulted in downregulation of several genes that are critical regulators of aerobic glycolysis. In summary, results show that anticancer effects of γ-tocotrienol treatment are associated with significant inhibition in pro-Warburg signaling such as Akt activation, and a corresponding increase in activity of AMPK in human breast cancer cells. In addition, γ-tocotrienol reversal of Warburg effect is directly related to a reduction in the rate of glycolysis in these breast cancer cells. Finally, γ-tocotrienol-induced activation of AMPK signaling was found to significantly alter gene expression of various downstream targets of AMPK. These findings highlight the potential of vitamin E derivatives in targeting the metabolism of breast cancer cells. This work was supported in part by funds provided by the Louisiana Cancer Foundation. Citation Format: Venkatesh Dronamraju, Ibrahim G. Algayadh, Paul William Sylvester. γ-Tocotrienol negative modulation of the Warburg effect is mediated by the AMPK activation in malignant breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 376.