HDAC3/6-IN-2 (compound 15) is a potent HDAC6 and HDAC3 inhibitor, with IC 50 values of 0.368 and 0.635 μM, respectively. HDAC3/6-IN-2 shows antitumor activity, and induces cancer cell apoptosis. HDAC3/6-IN-2 decreases the levels of HDAC6 and HDAC3 , associated with upregulation of acetylated H3 and α-tubulin.