HDAC-IN-49 is a potent unselective HDAC ( HDAC ) inhibitor with IC 50 s of 13 nM, 14 nM, 21 nM, 1880 nM, and 10 nM for HDAC1 , HDAC2 , HDAC3 , HDAC4 , and HDAC6. HDAC-IN-49 demonstrates prominent antileukemic activity with low cytotoxic activity toward healthy cells.