Binding affinity of Entinostat (MS-275) against HDAC1 and HDAC2 is 282 nM and 156 nM, respectively. Effects of the HDAC inhibitor Entinostat (MS-275) have been examined in human leukemia and lymphoma cells (U937, HL-60, K562, and Jurkat) as well as in primary acute myelogenous leukemia blasts in relation to differentiation and apoptosis. MS-275 displays dose-dependent effects in each of the cell lines. When administered at a low concentration (e.g., 1 μM), MS-275 exhibits potent antiproliferative activity, inducing p21CIP1/WAF1-mediated growth arrest and expression of differentiation markers (CD11b) in U937 cells. Entinostat (MS-275) potently induces cell death, triggering apoptosis in ~70% of cells at 48 h.