Synergistic Effects of Resveratrol and Temozolomide Against Glioblastoma Cells: Underlying Mechanism and Therapeutic Implications

Purpose: Temozolomide (TMZ) is a commonly used anti-glioblastoma (GBM) drug. However, glioblastoma cells frequently show primal)/ and acquired resistance to TMZ. As a promising antiGBM candidate, resveratrol (Res) faces the similar problem as TMZ. Although resveratrol combined with TMZ (Res/TMZ) has been reported to be used to treat GBMs, it remains unclear whether this combination is broad-spectrum for all glioma cells until now, especially for GBM cells/cases with dual drug resistance. The study aimed to evaluate the synergistic effects of resveratrol and TMZ against GBMs and identify the underlying mechanisms. Materials and Methods: Drug sensitivities of rat RG-2, human LN-18 and LN-428 cell lines and effectiveness of Res/TMZ combinations were investigated via multiple experimental methods. O-6-methylguanine-DNA methyltransferase (MGMT) was observed by Western blotting and immunocytochemistry (ICC). Transducer and activator of transcription 3 (STAT3) signaling pathway and expression changes of STAT3-related gene were detected to explore the possible synergistic mechanism. Results: One hundred micromolar resveratrol and 500 mu M TMZ inhibited the growth of RG-2 cells and the low-dose combination (25 mu M/250 mu M) showed similar suppressive effects. LN-18 and, especially, LN-428 cells were neither sensitive to 100 mu M resveratrol nor to 500 mu M TMZ, while their growth was suppressed by combination of 75 mu M Res/750 mu M TMZ with the suppressive rates of 62.5% and 28.6% and apoptosis rates of 11.9% and 7.4%, respectively. Resveratrol had regulatory effect on the expression of MGMT and it could significantly down-regulate MGMT overexpression caused by TMZ. In addition, STAT3/Bcl2/survivin signaling pathway was also remarkably inhibited in Res/TMZ-treated GBM cells. Conclusion: Our results demonstrated synergistic effects of Res/TMZ on RG-2 cells and their bilaterally sensitizing effects to LN-18 and LN-428 cells. Frequent upregulation of MGMT and activation of STAT3 are the unfavorable factors for the treatment of GBMs and they may be the potential targets of Res/TMZ therapy.