Isoform-specific HDAC inhibitors have not yet entered clinical trials for glioblastoma, however, several small molecule inhibitors for HDAC6 have been developed and studied mostly in the context of neurodegenerative diseases.366–370 HDAC isoform-specific inhibitors may be less toxic with fewer off target effects and fewer severe adverse effects than pan-HDAC inhibitors. This evidence concerns the gene HDAC9 and neurodegenerative disease.