Study of ACY-241 Alone and in Combination With Pomalidomide and Dexamethasone in Multiple Myeloma

Key Inclusion Criteria: * Must have a documented diagnosis of MM and have relapsed or relapsed-and-refractory disease. All patients must have relapsed after having achieved at least stable disease (SD) for at least 1 cycle of treatment to at least 1 prior regimen and then developed progressive disease (PD). Relapsed-and-refractory patients also have documented evidence of PD during or within 60 days of completing last treatment * Must have undergone prior treatment with at least 2 cycles of lenalidomide and at least 2 cycles of proteasome inhibitor unless not a candidate. * May have undergone prior treatment with pomalidomide if patient is not refractory to pomalidomide and has previously achieved a response of MR or better to pomalidomide. * Must have measurable disease (serum M-protein or urine M-protein). * Must have Eastern Cooperative Oncology Group (ECOG) Performance score of 0, 1, or 2. * Must be able to take low-dose aspirin, low molecular weight heparin, or other equivalent antithrombotic or anticoagulant daily as prophylactic anticoagulation. Key Exclusion Criteria: * Prior therapy with pomalidomide with best response of PD or SD. * Prior therapy with histone deacetylase (HDAC) inhibitor. * Any of the following laboratory abnormalities: Absolute neutrophil count(ANC) \< 1,000/µL, Platelet count \< 75,000/µL or \< 50,000/µL for patients in whom ≥ 50% of bone marrow nucleated cells are plasma cells, Hemoglobin \< 8 g/dL, Creatinine clearance \< 45 mL/min according to Cockcroft-Gault formula. If creatinine clearance calculated from the 24 hour urine sample is ≥ 45 mL/min, patient will qualify for the trial, Aspartate transaminase (AST) or Alanine transaminase (ALT) \> 3.0 × Upper Limited Normal (ULN), Serum total bilirubin \> 2.0 mg/dL or \> 3.0 × ULN for patients with hereditary benign hyperbilirubinaemia. * Hematologic growth factors are not allowed at screening or during the first cycle of phase 1a or 1b. * Nonsecretory myeloma or free light chain detected in serum only (ogliosecretory). * Hypersensitivity to thalidomide, lenalidomide, pomalidomide, or dexamethasone * Patients who received an allogeneic bone marrow or allogeneic peripheral blood stem cell transplant less than 12 months prior to initiation of study