Since none of the pan-HDACi evaluated in clinical trials up to date has been approved for the treatment of glioma, we planned to gain insight and dissect the role of the class I HDAC isoforms in glioma by the use of specific inhibitors 1–4, in comparison with the pan-HDACi 5 [11, 16, 28] as a reference. Here, HDAC9 is linked to central nervous system cancer.