Objective To investigate the radiobiological effects of VPA-BSANPs on C6 and U87 glioma cells in vitro.Methods C6 and U87 glioma cells were treated with different concentrations of VPA and VPA-BSANPs for 12 h and 24 h,and MTT assay was used to determine cell viability.C6 and U87 cells were treated with different concentrations of VPA and VPA-BSANPs conbined with X-ray irradiation (0,2,4,6,and 8 Gy),and colony formation assay was used to determine plating efficiency (PE).C6 and U87 glioma cells were treated with different concentrations of VPA and VPA-BSANPs for 12 h,followed by X-ray irradiation (0,4,and 8 Gy),and flow cytometry using Annexin V-FITC/PI staining was used to examine cell apoptosis.Western blot was used to evaluate the effects of VPA and VPA-BSANPs on radiation-induced apoptosis protein expression.One-way ANOVA was used for comparison of means with homogeneity of variance between multiple groups,and the t-test was used for comparison of means between two groups.Results Without irradiation,VPA and VPA-BSANPs had no significant inhibitory effects on the proliferation of C6 and U87 cells (P=0.328,0.920).The PE of cells treated with VPA-BSANPs combined with irradiation was significantly lower than that of cells treated with VPA combined with irradiation (P=0.000).In C6 and U87 cells,VPA-BSANPs combined with irradiation increased the expression of p53 and Bax (P =0.000,0.000 and P =0.010,0.002),but reduced the expression of Bcl-2 (P =0.008,0.000).Active caspase-3 fragments were only found in the cells treated with VPA-BSANPs combined with irradiation and VPA combined with irradiation,but were less in the former cells than in the latter cells (P=0.004).The active fragments of peroxisome proliferator-activated receptor were only found in the cells treated with VPA-BSANPs combined with irradiation.Conclusions VPA-BSANPs can increase the radiosensitivity of C6 and U87 glioma cells in vitro,possibly by promoting the apoptosis of tumor cells induced by radiation.