HDAC6 and glioblastoma: Our previous study has demonstrated that azaindolylsulfonamide (MPT0B291), a histone deacetylase (HDAC) inhibitor selective for HDAC6 (IC50 ≈ 0.0052 μM) [10, 11], induces cellular senescence in stem-like GBM cells and prolongs the survival of mice-bearing temozolomide (TMZ)-resistant xenografts through downregulation of Sp1 and its targeted genes associated with drug resistance [10].