HDAC9 and glioblastoma: Nowadays, inhibitors of histone methyltransferases have not yet reached the clinical trial stage, however, various HDAC inhibitors, including valproic acid have been approved by the FDA and are tested against different types of malignancies, including glioblastoma (Weller et al., 2011; Berendsen et al., 2012; Krauze et al., 2015).