Histone deacetylase inhibitor, valproic acid, radiosensitizes the C6 glioma cell line in vitro

Valproic acid (VPA) is a well-tolerated drug that is used to treat seizure disorders and that has recently been shown to inhibit histone deacetylase. The present study investigated the effects of VPA on the radiosensitization of the rat C6 glioma cell line in vitro. To select an appropriate treatment concentration and time, MTT and flow cytometry assays were performed to measure the inhibitory effects of VPA at various concentrations and incubation time-points. The radiosensitizing effect of VPA was determined using clonogenic experiments. VPA- and radiation-induced C6 apoptosis was analyzed using quantitative polymerase chain reaction and western blot analysis. Cell proliferation was significantly inhibited by VPA in a time- and dose-dependent manner (P<0.05). VPA enhanced radiation-induced C6 cell death and there was clear inhibition of clonogenic formation [sensitizer enhancement ratio (SER), 1.30]. This effect was closely associated with the concentration of VPA. VPA treatment decreased the mRNA and protein levels of Bcl-2, whereas increased changes were detected with Bax. At a concentration of 0.5 mmol/l, VPA had a low toxicity and enhanced the radiosensitization of the C6 cells. VPA may radiosensitize glioma cells by inhibiting cellular proliferation and inducing apoptosis by regulating apoptosis-related molecular changes.