Inclusion Criteria: - Men and women ≥18 years of age. - Karnofsky Performance Status (KPS) of ≥70%. - Life expectancy of ≥12 weeks. - Diagnosis of symptomatic MM with measurable disease, defined here as having at least one of the following: 1. Serum monoclonal protein (M-protein) ≥0.5 g/dL as determined by serum protein electrophoresis (SPEP) 2. Urine M-protein ≥200 mg/24 hrs 3. Serum free light chain (FLC) assay: involved FLC level ≥10 mg/dL (≥100 mg/L) provided serum FLC ratio is abnormal - Relapsed or relapsed and refractory MM after receiving at least 2 previous lines of therapy, 1 of which must be an immunomodulator. Relapsed myeloma is defined as the occurrence of any of the following after most recent treatment: 1. >25% increase in M-protein from the baseline levels; 2. reappearance of the M-protein that had become undetectable; or 3. increase in the size and number of lytic bone lesions recognized on radiographs (compression fractures per se do not constitute a relapse). Refractory myeloma (to most recent treatment) is defined as ≤25% response or progression during treatment or within 60 days after the completion of preceding treatment. Exclusion Criteria: - Polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome, osteosclerotic myeloma, or Crow-Fukase syndrome. - Plasma cell leukemia. - Primary amyloidosis. - Certain restrictions on prior treatments may apply. - ANC <0.75 x 10^9/L independent of Granulocyte colony-stimulating factor. - Platelets <50 x 10^9/L) independent of transfusion support. - AST or ALT ≥3.0 x upper limit of normal (ULN). - Total bilirubin >2.5 x ULN, unless due to Gilbert's syndrome. - Creatinine >2.5 mg/dL. - PT, INR, or aPTT >ULN. - Concomitant therapy with denosumab (bisphosphonate is allowed). - The subject has uncontrolled, significant intercurrent illness. - QTc >470 msec. - Unable to swallow capsules or disease significantly affecting gastrointestinal function, such as malabsorption syndrome, resection of the stomach or small bowel, or complete bowel obstruction. - Peripheral neuropathy Grade ≥2 on clinical examination within 14 days prior to enrollment.