Background/Objectives: Glycolysis and mitochondrial oxidative phosphorylation are the two major metabolic pathways for cellular ATP production. The metabolic plasticity displayed by cancer cells allows them to effectively shift between each of these pathways as a means of adapting to various growth conditions, thus ensuring their survival, proliferation and disease progression. Metabolic plasticity also provides cancer cells with the ability to circumvent many traditional monotherapies aimed at only one or the other of the major ATP-producing pathways. The purpose of this study was to determine the effectiveness of a dual treatment strategy aimed simultaneously at both pathways of ATP production in human breast cancer cells. It was hypothesized that concurrent exposure of these cells to the mitochondria-targeting chemotherapeutic agent, elesclomol, in combination with either of two glycolytic inhibitors, 2-deoxy-D-glucose or 3-bromopyruvate, would yield greater in vitro anticancer effects than those observed for any of the compounds used as a single agent. Methods: Cytotoxicity and clonogenic assays were employed to assess the survival and proliferation of MCF7 and MDA-MB-231 human breast adenocarcinoma cells exposed to the compounds alone and in combination. Results: The data obtained show that the cancer-cell-killing and antiproliferative effects of the dual treatment were significantly enhanced compared to those observed for any of the compounds alone. Conclusions: The results of this study are important in that they suggest the possibility of a novel and effective chemotherapeutic strategy for breast cancer cell killing.

This study investigated the cellular and mitochondrial toxicities of the pentacyclic triterpenoid and plant-specialized metabolite ursolic acid (UA) in human breast adenocarcinoma cell lines. Cell viability and clonogenic assays showed that UA induced potent cytotoxic and antiproliferative effects in MDA-MB-231 and MCF7 cells. Confocal images of living cells showed that UA caused a depolarization of the mitochondrial membrane potential and spectrophotometric measurement of electron transport chain enzyme activity in isolated organelles showed that UA induced a dose-dependent decrease in mitochondrial succinate-cytochrome reductase activity. These results demonstrate a direct, site-specific inhibitory effect of UA on mitochondrial bioenergetic function. Furthermore, the efficacy of a drug combination aimed concurrently at both major pathways of ATP production in breast cancer cells was investigated. The data show that when MDA-MB-231 and MCF7 cells were treated with UA in combination with either 2-deoxy-D-glucose or 3-bromopyruvate, two inhibitors of glycolysis, the resulting cytotoxicity was greater than that induced by any of the compounds used independently. The results of this study are important in that they demonstrate direct mitochondrial targets of UA and suggest the possibility of using this natural, plant-derived metabolite in combination with glycolytic inhibitors as a novel and effective dual treatment strategy for breast cancer cell killing.