Abstract 4372: Effects of high glucose and DCA on ROS production and viability of breast cancer cells with disrupted antioxidant systems
Authors: Buss Radek , Ellenbecker Collin , Minton Emily , Gray Lauren , Nolte Mona , Jaeke Aysiah , Feirer Russ 
Published: August 2019

A goal of this study was to determine if disruption of protective cellular antioxidant systems would sensitize cancer cells to dichloroacetate (DCA), a compound affecting mitochondrial metabolism (reversing the Warburg Effect). DCA shifts the metabolism of glucose back to mitochondrial oxidative phosphorylation, with subsequent production of reactive oxygen species (ROS) (Bonnet et al., 2007). While cancer cells consume large amounts of glucose to meet energy demands and provide substrates necessary for protein and nucleic acid biosynthesis, they utilize aerobic glycolytic pathways (Warburg metabolism) instead of oxidative phosphorylation. Glutathione (GSH) and thioredoxin (Trx) are among the antioxidants produced to protect cells from oxidative damage; oxidative stress occurs when the production of ROS overwhelms these systems. Biosynthesis of GSH and Trx were inhibited by treating cells with low levels of buthionine sulfoximine (BSO) and auranofin (AUR) to deplete GSH and Trx, respectively. Through its stimulation of ROS production, DCA should enhance the cytotoxic effects in cells with diminished antioxidant systems. A second goal was to investigate the effects of these compounds on cells grown in either low or high glucose media (1 g/L vs 4.5 g/L). Cells grown under high glucose conditions were expected to produce more ROS and exhibit greater sensitivity to the combination of DCA, BSO and AUR. The experiments were conducted using MDA-MB-231 and MCF-7, breast cancer cell lines with known differences in metabolism and responses to chemotherapeutic drugs.

BSO led to a dramatic decrease of GSH levels. AUR, at concentrations above 0.5 µM, significantly reduced cell viability when in combination with BSO. DCA alone reduced viability, but its effects were significantly enhanced when used in conjunction with BSO/AUR. Levels of ROS were quantified using a luminescence-based assay. In low glucose media, BSO/AUR and DCA had no effect on ROS production. In contrast, a high glucose environment led to elevated ROS production under all conditions, with the highest levels being induced by DCA in the cells having disrupted antioxidant systems. In the presence of BSO/AUR, MDA-MB-231 cells produced more ROS than MCF-7 cells. Overall, inhibition of antioxidant systems sensitized cells to DCA, increasing ROS and reducing viability.Previous studies have reported metabolic differences between cell lines (Gatenby and Gillies, 2004). MDA-MB-231 cells rely on aerobic glycolysis while MCF-7 cells are more reliant on mitochondrial oxidative phosphorylation. Therefore, MCF-7 cells have developed increased protection against ROS as compared to MDA-MB-231 cells (Theodossiou et al., 2017). These findings support the observed differences in response to BSO/AUR between the two cell lines. Paradoxically, MCF-7 cells were more sensitive to BSO/AUR than MDA-MB-231 cells in colony formation assays.

Citation Format: Radek Buss, Collin Ellenbecker, Emily Minton, Lauren Gray, Mona Nolte, Aysiah Jaeke, Russ Feirer. Effects of high glucose and DCA on ROS production and viability of breast cancer cells with disrupted antioxidant systems [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4372.