HDAC/Top-IN-1 is an orally active and pan HDAC/Top dual inhibitor with IC 50 s of 0.036 μM, 0.14 μM, 0.059 μM, 0.089 μM and 9.8 μM for HDAC1 , HDAC2 , HDAC3 , HDAC6 and HDAC8. HDAC/Top-IN-1 efficiently induces apoptosis with S cell-cycle arrest in HEL cells. HDAC/Top-IN-1 has exhibits excellent in vivo antitumor efficacy.