Although potent HDAC8 inhibitors have beenreported, most of themshowed modest selectivity over other HDAC isoforms and had limitedantiproliferative activities in various cancer models.21−25 This indicates the need for novel modalities to increase the HDAC8inhibitory potency and also raises interest in targeting its nonenzymaticfunctions. This evidence concerns the gene HDAC9 and cancer.