PCI-24781 (also known as CRA-024781) is a novel, broad spectrum inhibitor of HDACs that shows antitumor activity in vitro. PCI-24781 primarily targets HDAC1 (Ki = 7 nM). It also exhibits modest potenty toward HDACs 2, 3, 6, and 10 and greater than 40-fold selectivity against HDAC8.