Ricolinostat (ACY-1215, Rocilinostat) is a selective HDAC6 inhibitor with IC50 of 5 nM in a cell-free assay. It is >10-fold more selective for HDAC6 than HDAC1/2/3 (class I HDACs) with slight activity against HDAC8, minimal activity against HDAC4/5/7/9/11, Sirtuin1, and Sirtuin2. Ricolinostat (ACY-1215) suppresses cell proliferation and promotes apoptosis. Phase 2.