Summary. The use of inhibitors of energy metabolism of malignant cells is a new promising trend in the treatment of cancer patients, based on one of the unique features of the malignant cell, namely the dominance of glycolysis over oxidative phosphorylation, even in the presence of oxygen, the so-called Warburg effect. Aim: To study time-dependent cytotoxicity of sodium dichloroacetate (DCA) and metformin (MTF) against metastatic tumor cells and action of these agents on tumor cell migration. Materials and Methods: In the study low metastatic LLC/R9 variant of Lewis lung carcinoma was used. The number of living cells in the cytotoxic test was evaluated using sulforhodamine B after 1, 2 and 3 days of cell incubation in vitro. The parameters of the sensitivity of tumor cells to the action of DCA and MTF in vitro were calculated using nonlinear and linear regression of experimental data. The effect of DCA and MTF on cellular motility in vitro was evaluated using a Boyden chamber by calculation of the number of cells that migrated to the bottom side of the filter within 3 days of incubation. The statistical analysis of the data was carried out with the use of descriptive methods, Student’s t-criterion, nonlinear, and linear regression analysis. Results: IC50 of DCA was found to be equal to 50.8 ± 7.6 mM at the first day of incubation with LLC/R9 cells and decreased by 1.9 (p < 0.05) and 2.1 (p < 0.05) times at the 2nd and 3rd days, respectively. Despite the almost identical ІC50 at the 2nd and 3rd days, an increase in the incubation period of cells with DCA for up to 3 days increased the C0 parameter, which reflects the maximum concentration of the agent that does not exhibit cytotoxic effects, by 93% (p < 0.05) compared to this at the 2nd day (16.2 ± 1.4 mM vs 8.4 ± 1.0 mM, correspondently). Unlike DCA, the LLC/R9 cell population was not homogeneous by the sensitivity to the action of MTF; at least at the 3rd day, an appearance of MTF-resistant subpopulation was observed, accounting for 35% of all cells. IC50 of MTF was equal to 12.1 ± 0.6 mM, and unlike DCA, this index progressively decreased at the 2nd and 3rd days by 1.4 (p < 0.05) and 9.3 times (p < 0.05) respectively. Action of DCA at a concentration of 25 mM alone and in combination with MTF at the concentrations of 0.1 mM and 0.7 mM resulted in an increase in cell migration by 65% (p < 0.05), 63% (p < 0.05) and 78.5% (p < 0.05), respectively. There was no significant effect of MTF on the tumor cell migration. Conclusions: The sensitivity of the metastatic Lewis lung carcinoma cells to the action of the modifiers of the energy metabolism increased significantly with an increase in the incubation period, apparently, primarily due to the shortage of nutrient substrates and, in particular, glucose, indicating the relevance of their combined use as well as with other agents, which promote the deficiency of glucose in the tumor microenvironment.
Summary. It is known that the arsenal of chemotherapeutic agents for the treatment of malignant brain tumors is quite limited, which causes the high relevance of research aimed at finding new effective antitumor regimens, including the use of energy metabolism modifiers. Aim: To investigate the anti-glioma activity of sodium dichloroacetate (DCA) and metformin (MTF) used in combination in vitro and in vivo. Materials and Methods: 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 C6 cells. The antitumor action of agents in vivo was evaluated routinely by the prolongation of the life span of rats with transplanted intracerebral glioma C6 and was confirmed by histological examination of tumor tissue. Results: The half maximal inhibitory concentration (IC50) for DCA and MTF used separately was 79.2 ± 2.1 mM and 78.4 ± 4.0 mM, respectively, whereas IC50 for DCA used in combination with 7.8 mM MTF was 3.3 fold lower (24.0 ± 1.2 mM, p < 0.05). The 1-day incubation of cells with DCA at a concentration close to IC50 (25 mM), in combination with MTF at a concentration by order lower than IC50 (7.8 mM), 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/G1 phase 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 C6 cells (0.23 ± 0.05 μmol/106 cells/h vs 0.91 ± 0.12 μmol/106 cells/h, p < 0.05) compared to the corresponding parameters in the control, and 2-fold increased rate of lactate production (1.06 ± 0.03 μmol/106 cells/h vs 0.53 ± 0.03 μmol/106 cells/h, p < 0.05). At the same time, both Δψm and the level of intracellular ATP in the glioma C6 cells 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 1.1 and 2.6 g/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 2.6 g/kg), MTF increased the life span of tumor-bearing animals just by 19% (p < 0.01), whereas DCA alone (at a dose of 1.1 g/kg) did not significantly change the survival time of rats. Conclusions: 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.
Background: Anticancer action of sodium dichloroacetate (DCA) could be related to its ability to activate oxidative phosphorylation leading to enhanced generation of reactive oxygen species and induction of apoptosis. On the other hand, activation of oxidative phosphorylation could promote tumor cell survival, in particular, via increased ATP synthesis. Such ambiguous effects of DCA could influence its anticancer effectiveness, depending on biological properties of a tumor, schedule of DCA administration and its dosage. The aim of the study was to analyze anticancer effect of DCA against glioma С6 in rats under conditions of different schedules of its administration and various dosages. Materials and Methods: The study was carried out in Wistar rats with intracerebrally transplanted glioma С6 cells. Therapy with DCA was performed as follows: daily for 6 days starting from the second day after tumor cell transplantation (schedule І) or 7th day (schedule ІІ) at a dose of 1.0 g/kg, or daily for 13 days starting from the second day at doses of 1.0; 1.5 or 4.5 g/kg (schedule ІІІ). An influence of hypoxia on anticancer effect of DCA was studied using hypoxic chambers where oxygen content was maintained at a level of 12.5–13% for 3 h after DCA administration to glioma С6 bearing rats. The state of mitochondrial electron transport chain components in tumor cells was studied using electron paramagnetic resonance. Results: It has been shown that therapy with DCA using schedule I resulted in 15% decrease of animals life span (LS; р < 0.05), while the use of schedule II had no effect on this index. Prolonged administration of DCA (schedule ІІІ) resulted in significant antitumor effect and increased LS of rats by 25.5% (p < 0.05). Under hypoxic conditions, treatment with DCA resulted in a significant increase of animal LS by 15–22%. Dosage of DCA had a moderate effect of its anticancer action. Maximal effect, an increase of LS by 34.5% (p < 0.05) was detected at a dose of 1.5 g/kg. It has been shown that anticancer activity of DCA under all studied conditions is not related to its influence on a functional state of tumor cell mitochondria. Conclusion: Anticancer effect of DCA significantly depends on a schedule of its administration; being administered at equal total dose, but dependent on the schedule DCA could cause ambiguous effects varying from tumor growth stimulation to significant anticancer activity. Under hypoxic conditions, anticancer efficacy of DCA against glioma С6 is significantly enhanced.
Background: The efficacy of antimetabolic therapy of malignant neoplasms could not be explained solely by the direct mechanisms of action of such energy metabolism inhibitors as sodium dichloroacetate (DCA) and metformin (MTF). The indirect effects of DCA and MTF on the organs and tissues, which could play significant role in the antitumor activity of these agents, have not been thoroughly explored. Aim: To investigate the effect of MTF, DCA and their combination on the survival of rats with C6 glioma and major haematological and biochemical blood parameters. Materials and Methods: DCA and MTF were administered orally to inbred female rats for 11 days starting from the second day after tumor cell transplantation at a total dose of 1.1 and 2.6 g/kg, respectively. When combined treatment was used, MTF was administered 3 hours after the administration of DCA. The content of lactate and pyruvate in blood plasma was determined on the ChemWell® 2910 (Combi) automatic analyzer. Blood parameters were determined using the Particle Counter PCE210 automatic hematology analyzer. Results: The administration of DCA did not significantly affect the life span of rats with C6 glioma. Duration of life of rats, which were administered with MTF only, was significantly higher (by 19.1%, p < 0.01). Combined administration of DCA + MTF prolonged life span of animals with glioma by 50% (p < 0.001). The positive result of antitumor activity of MTF alone and in combination with DCA correlated with a decrease in the mean platelet volume/platelet count (MPV/PLT) ratio by 75.0% (p < 0.05) compared with tumor control. In addition, the expressed antitumor effect of combination therapy with DCA and MTF was associated with a decrease (p < 0.05) in glucose and lactate levels in blood plasma of rats with C6 glioma by 10% and 41.4%, respectively, compared to tumor control. Analysis of blood parameters showed that the growth of C6 glioma was accompanied by the development of leukopenia, anemia and thrombocytopenia. The introduction of DCA caused the correction of manifestations of anemia and leukopenia, but did not affect the level of platelets in the blood of animals with glioma. MTF alone and in combination with DCA positively influenced the number of white blood cells and caused complete thrombocytopenia correction, increasing platelet count by more than 200% (p < 0.001). Conclusion: The ability of MTF either used alone or in combination with DCA to influence the development of C6 glioma which is manifested in an increase in the lifespan of rats has been revealed. The most pronounced antitumor effect was recorded against the background of the combined use of these agents, which may be due to their ability to lower the levels of lactate and glucose in the blood of tumorbearing rats. It is proved that MTF both in monotherapy and in combination with DCA provides correction of anemia and thrombocytopenia, which arise at the background of glioma C6 growth.
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