Mocetinostat (MGCD0103) is an HDAC inhibitor. It was shown to induce hyperacetylation of histones resulting in cancer cell selective apoptosis, and cause cell cycle blockade in various human cancer cell lines in a dose-dependent manner. Mocetinostat inhibites growth of human tumor xenografts in nude mice in a dose-dependent manner and its antitumor activity correlates with induction of histone acetylation in tumors.