MS-275, also known as Entinostat, is an inhibitor of histone deacetylases (HDACs) and preferentially inhibits HDAC1 over HDAC3. It does not inhibit HDAC8 (IC50 > 100 µM). It induces cyclin-dependent kinase inhibitor 1A (p21/CIP1/WAF1), slowing cell growth, differentiation, and tumor development in vivo. Recent studies suggest that MS-275 may be particularly useful as an antineoplastic agent when combined with other drugs like adriamycin, inhibitors of PARPs, or inhibitors of Hsp90.