Curcumin and Radiotherapy Exert Synergistic Anti-Glioma Effect In Vitro

Abstract

Curcumin, a bioactive polyphenol, is known to have anticancer properties. In this study, the effectiveness of curcumin pretreatment as a strategy for radio-sensitizing glioblastoma cell lines was explored. For this, U87 and T98 cells were treated with curcumin, exposed to 2 Gy or 4 Gy of irradiation, and the combined effect was compared to the antiproliferative effect of each agent when given individually. Cell viability and proliferation were evaluated with the trypan blue exclusion assay and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The synergistic effects of the combination treatment were analyzed with CompuSyn software. To examine how the co-treatment affected different phases of cell-cycle progression, a cell-cycle analysis via flow cytometry was performed. Treatment with curcumin and radiation significantly reduced cell viability in both U87 and T98 cell lines. The combination treatment arrested both cell lines at the G2/M phase to a higher extent than radiation or curcumin treatment alone. The synergistic effect of curcumin when combined with temozolomide resulted in increased tumor cell death. Our results demonstrate for the first time that low doses of curcumin and irradiation exhibit a strong synergistic anti-proliferative effect on glioblastoma cells in vitro. Therefore, this combination may represent an innovative and promising strategy for the treatment of glioblastoma, and further studies are needed to fully understand the molecular mechanism underlying this effect.

Keywords: curcumin; glioblastoma cells; radiation.

Figure 1

Structure of curcumin. It was drawn using ChemSpider, an online free chemical structure database.

Figure 2

Cytotoxic effect of curcumin on glioblastoma cell lines U87 and T98 at 72 h. Values shown are the means and standard deviations from three independent experiments and are normalized to non-treated cells (p < 0.05 vs. control). The IC50 values were determined using the non-linear regression analysis model of GraphPad Prism Version 8.

Figure 3

Morphological changes in U87 (a) and T98 (b) cell populations after treatment with crystal violet staining (0.2% Crystal Violet) (Scale bars = 50 μm). Images were recorded at 10× magnification. Cells were seeded in 6-well plates and 24 h later exposed to increasing curcumin concentrations. Crystal violet solution was added 48 h later and the cells were incubated at room temperature for 2–3 min. The excess crystal violet was removed, and plates were washed twice and left overnight to dry.

Figure 4

Graphical presentations obtained from the CompuSyn Report for the curcumin and radiation combination in U87 cells. (a) Dose–effect curve; (b) combination index plot.

Figure 5

Graphical presentations obtained from the CompuSyn Report for the curcumin and radiation combination in T98 cells. (a) Dose–effect curve; (b) combination index plot.

Figure 6

Dose reduction plots for the combination of curcumin and radiation at different experimental points for U87 (a) and T98 (b) cells. DRI >1 shows favorable dose reduction of both factors.

Figure 7

Histogram representation of cell-cycle distribution in U87 cells after treatment with increasing curcumin concentrations. Cells (10⁴) were seeded in 24-well plates and after 24 h were exposed to different curcumin concentrations; 2 h later, the plates were irradiated with 2 Gy. After 72 h, the cells were stained with propidium iodide and the DNA content was observed.

Figure 8

Histogram representation of cell-cycle distribution in T98 cells after treatment with increasing curcumin concentrations. Following the same procedure, the cells were stained with propidium iodide at 72 h, and the DNA content was observed. Curcumin and radiation co-treatment induced G2/M arrest in glioblastoma cells.

Figure 9

Cytotoxic effect of temozolomide on glioblastoma cell line U87. The IC50 value for temozolomide was calculated at 80 μΜ with an R² = 0.9814.

Figure 10

Graphical presentations obtained from the CompuSyn Report for the curcumin and temozolomide combination in U87 cells. (a) Combination index plot; (b) dose–reduction plot.

Figure 11

Lethal concentration determination.