TP53 and glioblastoma: Therefore, we summarized the results revealing that low-dose and long-term treatment with SAHA in GBM spheroids induces p53 phosphorylation at Ser33 causing an increase in cell cycle checkpoint activation (Fig. 6), but SAHA in high-dose and short-term treatment induces p53 phosphorylation at Ser15 leading to p53-dependent apoptosis in U87MG spheroids, and even induces p53-independent apoptosis in U373MG spheroids (Fig. 6).