Multidrug resistance (MDR) is a common resistant mechanism of cancer cells to cytotoxic drugs in systemic therapy. MDR is characterized by increased expression of ATP-dependent drug exporting pumps which remove cytotoxic compounds from the cytosol. However, the mechanism whereby cancer cells rapidly respond to this increased ATP demand is not fully understood although the glycolytic nature of MDR phenotype has been evidenced repeatedly by previous reports. We thus hypothesized that flexibility and dependency on mitochondrial fuels would be altered in concert with the switch to glycolysis. In order to more accurate analyze glycolytic pathway, we newly developed an assay to improve glycolytic rate measurements by accounting for TCA-dependent CO2 contribution to extracellular acidification and to correlate Seahorse extracellular flux data with lactate production. In a comparison of glycolytic rates between MCF7 breast cancer cell line and its MDR variant MCF7/Dox using this new assay, we confirmed that in MCF7/Dox cells glycolysis rate under basal conditions is significantly increased compared to wild type cells. Furthermore, MCF7Dox presents a significant increase in compensatory glycolysis when mitochondrial ATP production is blocked. This metabolic profile switch is accompanied by a decreased dependency on glutamine to fuel mitochondrial respiration an increased tolerance of the MCF7/Dox cells to glutamine deprivation as compared to the MCF7 wild type. In contrast, dependency on glucose and fatty acids mitochondrial-oxidation was largely unchanged in MDR cells. Additionally, an increase in long chain fatty acid oxidation is observed when glucose and glutamine oxidation is blocked indicating that MDR cells has higher mitochondrial flexibility to compensate for inhibition of alternative fuels utilization although it preferentially uses glucose. Together these data demonstrate that acquisition of multidrug resistance in MCF7 cells fundamentally changes their metabolism from a glutamine-driven, oxidative phosphorylation dependent phenotype to a highly glycolytic and glucose-dependent phenotype. These findings have potential therapeutic relevance in the context of inhibition of specific mitochondrial fuel pathways to prevent therapy resistance.

Citation Format: Yoonseok Kam, Natalia Romero, Pamela Swain, Brian P. Dranka. Characterization of metabolic fuel dependency in multidrug resistant breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5432. doi:10.1158/1538-7445.AM2017-5432