Mocetinostat, also known as MGCD0103 or MG0103, is an isotype-selective inhibitor of human histone deacetylases (HDAC), a family of enzymes involved in epigenetic regulation of gene transcription as well as cell proliferation, death and motility. Mocetinostat potently inhibits HDAC class I (HDAC1, HDAC2, and HDAC3) and class IV (HDAC11), with values of inhibition constant IC50 of 0.15 μmol/L, 0.29 μmol/L, 1.66 μmol/L, and 0.59 μmol/L respectively, rather than HDAC class II. Mocetinostat exerts anti-tumor activity against a broad range of human cancer cells through HDAC inhibition, in which it induces histone hyperacetylation and apoptosis and causes cell cycle blockade in a dose-dependent manner.