The nontoxic natural compound Curcumin exerts anti-proliferative, anti-migratory, and anti-invasive properties against malignant gliomas

Abstract

Background: New drugs are constantly sought after to improve the survival of patients with malignant gliomas. The ideal substance would selectively target tumor cells without eliciting toxic side effects. Here, we report on the anti-proliferative, anti-migratory, and anti-invasive properties of the natural, nontoxic compound Curcumin observed in five human glioblastoma (GBM) cell lines in vitro.

Methods: We used monolayer wound healing assays, modified Boyden chamber trans-well assays, and cell growth assays to quantify cell migration, invasion, and proliferation in the absence or presence of Curcumin at various concentrations. Levels of the transcription factor phospho-STAT3, a potential target of Curcumin, were determined by sandwich-ELISA. Subsequent effects on transcription of genes regulating the cell cycle were analyzed by quantitative real-time PCR. Effects on apoptosis were determined by caspase assays.

Results: Curcumin potently inhibited GBM cell proliferation as well as migration and invasion in all cell lines contingent on dose. Simultaneously, levels of the biologically active phospho-STAT3 were decreased and correlated with reduced transcription of the cell cycle regulating gene c-Myc and proliferation marking Ki-67, pointing to a potential mechanism by which Curcumin slows tumor growth.

Conclusions: Curcumin is part of the diet of millions of people every day and is without known toxic side effects. Our data show that Curcumin bears anti-proliferative, anti-migratory, and anti-invasive properties against GBM cells in vitro. These results warrant further in vivo analyses and indicate a potential role of Curcumin in the treatment of malignant gliomas.

Figures

Figure 1

Cell proliferation. A. Line graphs showing representative growth curves of human GBM cells when treated with or without Curcumin at various concentrations (10 μM, 20 μM, or 50 μM, respectively). B. Bar graphs showing dose-dependency of cell viability when treated with Curcumin (0, 10 μM, 20 μM, or 50 μM, respectively) after 72 h. Data are from three independent experiments. Controls are set at 100%. Statistically significant differences compared to controls are marked by asterisks (* P < 0.05, ** P < 0.01, *** P < 0.001). Unless indicated by n.s., differences between groups are statistically significant (P < 0.05 or less). C. Bar graphs showing decrease in genomic transcription of c-Myc after treatment with Curcumin (0, 10 μM, 20 μM, or 50 μM, respectively) for 2 h. Data are from three independent experiments. Controls are set at 100%. An asterisk indicates differences that are statistically significant compared to controls. D. Bar graphs showing decrease in genomic transcription of Ki-67 after treatment with Curcumin (0, 10 μM, 20 μM, or 50 μM, respectively) for 24 h. Data are from three independent experiments. Controls are set at 100%. An asterisk indicates differences that are statistically significant compared to controls. E. Bar graphs showing effect of treatment with Curcumin (0, 10 μM, 20 μM, or 50 μM, respectively) for 24 h on caspase 3-like activity. Data are from three independent experiments. Staurosporine (STS) treated cells served as a positive control for induction of apoptosis. An asterisk indicates differences that are statistically significant compared to untreated cells.

Figure 2

Cell migration/invasion and STAT3 levels. A. Bar graphs showing a dose-dependent reduction of intracellular levels of phosphorylated STAT3 by Curcumin (0, 10 μM, 20 μM, or 50 μM, respectively) determined by ELISA. Data are from four independent experiments. An asterisk indicates differences that are statistically significant compared to controls. B. Bar graphs showing restoration of phosphorylated STAT3 levels in MZ-256 cells following treatment with Curcumin (0, 10, 20, 50 μM) for 2 h as determined by sandwich ELISA. In cells treated with 10 or 20 μM, normal levels are restored after 12 h, and they further increase after 24 h. Phosphorylated STAT3 levels remain low for up to 24 h in cells treated with 50 μM Curcumin. When in contrast cells are treated with Curcumin continuously for 24 h, phosphorylated STAT3 levels remain low. Data are from three independent experiments. An asterisk indicates differences that are statistically significant compared to controls. C. Bar graphs showing a dose-dependent reduction of GBM cell motility by Curcumin (0, 10 μM, or 20 μM, respectively) determined by wound healing assays. Data are from three independent experiments. An asterisk indicates differences that are statistically significant compared to controls. D. Bar graphs showing a dose-dependent reduction of the invasive capability of GBM cells by Curcumin (0, 10 μM, 20 μM, or 50 μM, respectively) determined by modified Boyden chamber assays. Data are from three independent experiments. An asterisk indicates differences that are statistically significant compared to controls.