CASP9 and glioblastoma: We also demonstrated that the knockdown of p53 abrogated the expression of PUMA and the cleavage of caspase 9, caspase 3, and PARP in p53 wild-type GBM cells treated with TMZ+VPA (Figures 3C, D) and reversed the pro-apoptotic effect of VPA in TMZ treatment, indicating that VPA enhanced TMZ-induced cell apoptosis via p53–PUMA pathway activation.