Mocetinostat is an orally administered histone deacetylase (HDAC) inhibitor. Azacitidine is a hypomethylating agent (HMA) used to treat MDS. In this study, patients with intermediate- or high-risk MDS will receive treatment with mocetinostat and azacitidine to evaluate the safety of the study treatment. Safety assessments will include echocardiograms, electrocardiograms and routine safety laboratory studies (hematology and serum chemistry). In addition, clinical response to treatment will be monitored using bone marrow aspirates or biopsies, and other routine methods.