Metformin enhances antitumor action ofsodiumdichloroacetate against glioma C6.

Abstract

To investigate the anti-glioma activity of sodium dichloroacetate (DCA) and metformin (MTF) used in combination in vitro and in vivo. Cell survival, cell cycle, apoptosis, mitochondrial membrane potential (Δψm), ATP level, the glucose consumption rate, and lactate production rate were determined in vitro in cultured glioma C6cells. The antitumor action of agents in vivo was evaluated routinely by the prolongation of the life span of rats with transplanted intracerebral glioma C6and was confirmed by histological examination of tumor tissue. The half maximal inhibitory concentration (IC50) for DCA and MTF used separately was 79.2±2.1mM and 78.4±4.0mM, respectively, whereas IC50for DCA used in combination with 7.8mM MTF was 3.3fold lower (24.0±1.2mM, p < 0.05). The 1-day incubation of cells with DCA at a concentration close to IC50 (25mM), in combination with MTF at a concentration by order lower than IC50 (7.8mM), in contrast to their separate use, resulted in a decrease in the number of viable cells by 40% (p < 0.05); redistribution of the cells by the cell cycle phases toward decreased proportion of cells in the S-phase by 46% (p < 0.05) and an increased percentage of cells in the G0/G1phase by 24% (p < 0.05) compared to similar indices in the control. High proapoptotic activity of DCA in combination with MTF was supported by a significantly higher percentage of apoptotic cells in vitro than in the control (18.9±4.4% vs 5.7±1.3%, p < 0.05) and a high number of tumor cells with signs of apoptosis revealed during the histological examination of tumor pathomorphosis. The combined effect of DCA and MTF resulted in almost 4-fold decrease of the glucose consumption rate by glioma C6cells (0.23±0.05μmol/106cells/h vs 0.91 ± 0.12μmol/106cells/h, p < 0.05) compared to the corresponding parameters in the control, and 2-fold increased rate of lactate production (1.06 ± 0.03μmol/106cells/h vs 0.53 ± 0.03μmol/106cells/h, p < 0.05). At the same time, both Δψm and the level of intracellular ATP in the glioma C6cells treated with DCA and MTF, both separately and in combination, did not differ significantly from those indices in the control. In in vivo studies, the average life span of rats with intracranial transplanted glioma C6, treated with DCA in combination with MTF in a total dose of 1.1and 2.6g/kg body weight, respectively, was 50% higher (p < 0.001) than in the control group. In contrast, in the case of single-use (at a dose of 2.6g/kg), MTF increased the life span of tumor-bearing animals just by 19% (p < 0.01), whereas DCA alone (at a dose of 1.1g/kg) did not significantly change the survival time of rats. The obtained data indicate synergism of anti-glioma action of DCA and MTF in a case of their combined use both in vitro and in vivo and may be considered a starting point for the development of effective treatment regimens for malignant brain tumors based on the combined use of DCA and MTF.