Glucose Influences the Response of Glioblastoma Cells to Temozolomide and Dexamethasone

Abstract

Objective: Current research indicates that weakness of glucose metabolism plays an important role in silencing of invasiveness and growth of hypoxic tumors such as GBM. Moreover, there are indications that DXM, frequently used in treatment, may support GBM energy metabolism and provoke its recurrence.

Methods: We carried out in vitro experiments on the commercial T98G cell line and two primary GBM lines (HROG02, HROG17) treated with TMZ and/or DXM in physiological oxygen conditions for GBM (2.5% oxygen) and for comparison, in standard laboratory conditions (20% oxygen). The influence of different glucose levels on selected malignancy features of GBM cells-cellular viability and division, dynamic of cell culture changes, colony formation and concentration of InsR have been elevated.

Results: Under 2.5% oxygen and high glucose concentration, an attenuated cytotoxic effect of TMZ and intensification of malignancy features in all glioblastoma cell lines exposed to DXM was seen. Furthermore, preliminary retrospective analysis to assess the correlation between serum glucose levels and Ki-67 expression in surgical specimens derived from patients with GBM (IV) treated with radio-chemotherapy and prophylactic DXM therapy was performed.

Conclusion: The data suggest a link between the in vitro study results and clinical data. High glucose can influence on GBM progression through the promotion of the following parameters: cell viability, dispersal, InsR expression and cell proliferation (Ki-67). However, this problem needs more studies and explain the mechanism of action studied drugs.

Keywords: adjuvant treatment in brain cancer; brain tumor; chemotherapy in brain cancer; glioblastoma; glucose in cancer.

Figure 1.

(A and B) Effect of TMZ, DXM and combination of TMZ+DXM on viability of T98G cells cultured in medium containing different glucose concentrations (0.6 g/L; 1 g/L; 4.5 g/L) in 2.5% physiological hypoxia (A) and 20% oxygen (standard laboratory conditions) (B). Each bar represents the mean ± SEM of at least three independent experiments. Values were analyzed by one-way ANOVA, followed by Tukey post hoc test, *P < .05 vs control (untreated cells). Correlation between groups was tested by calculating the correlation coefficient (Pearson’s test).

Figure 2.

(A and B) Cell divisions of T98G cells exposed to TMZ, DXM and combination of TMZ+DXM cultured in different glucose concentrations (0.6 g/L; 1 g/L; 4.5 g/L) in 2.5% (A) and 20% oxygen (B). Each bar represents the mean ± SEM of at least three independent experiments. Values were analyzed by one-way ANOVA, followed by Tukey post hoc test, *P < .05 vs control-TMZ, DXM, combination of TMZ+DXM. Correlation between groups was tested by calculating the correlation coefficient (Pearson’s test).

Figure 3.

InsR expression in T98G cells exposed to: TMZ, DXM and combination of TMZ+DXM. Glioblastoma cells were cultured in medium containing different glucose concentration (0.6 g/L; 1 g/L; 4.5 g/L) in 2.5% oxygen and 20% oxygen. Data are represented as means ± SEM of triplicate samples. ^*P < .05 vs. control (untreated cells). Each bar represents the mean ± SEM of at least three independent experiments. Values were analyzed by one-way ANOVA, followed by Tukey post hoc test, *P < .0 5 vs control (untreated cells). Correlation between groups was tested by calculating the correlation coefficient (Pearson’s test).

Figure 4.

Microphotographs presenting three GBM cell lines cultured in medium containing different glucose concentration: 0.6 g/L (A–D); 1 g/L (E–H); 4.5 g/L (I–L) and exposed to: DXM (B, F, J), TMZ (C, G, K) or combination of DXM+TMZ (D, H, L); A, E, I—T98G control group of cells not exposed to drugs. A—T98G cells cultured in 2.5% (physiologic conditions for GBM) and 20% oxygen (B) (standard laboratory conditions) C—Cells of primary line HROG02 cultured in 2.5% and 20% oxygen (D) E—Cells of primary line HROG17 cultured in 2.5% oxygen and 20% (F) Analyses were conducted using the Juli cell analyzer (magnification ×20). No convolution was carried out on the pictures.

Figure 5.

Correlation between blood glucose levels and the Ki-67 index in patients. Patients were classified into 3 categories according to glucose concentration and Ki-67 expression. The subgroups were compared using the long-rank test. Analysis were performed using Spearman’s correlation coefficient and Mann-Whitney test. All differences were considered statistically significant at the level of P < .05.