Study of SX-682 Alone and in Combination With Oral or Intravenous Decitabine in Subjects With Myelodysplastic Syndrome

Inclusion Criteria: * Diagnosis of MDS by World Health Organization criteria, and either 1. International Prognostic Scoring System (IPSS) low risk or intermediate-1 risk patients without 5q deletion: i. Dose escalation portion: failed prior treatment with at least 4 cycles started of a hypomethylating agent (HMA; azacitidine or decitabine) defined as no response to treatment, loss of response at any time point, or progressive disease/intolerance to therapy. ii. Dose expansion portion: failed prior treatment defined as no response to treatment with at least 4 cycles started of HMA, loss of response at any time point, or progressive disease/intolerance to therapy ("HMA failure"); or no prior treatment with HMA ("HMA naive"). 2. IPSS low risk or intermediate-1 risk patients with 5q deletion: i. Dose escalation portion: failed prior treatment with at least 4 cycles started of lenalidomide and 4 cycles of hypomethylating agent (azacitidine or decitabine) defined as no response to treatment, loss of response at any time point, or progressive disease/intolerance to therapy. ii. Dose expansion portion: same as non-del(5q) lower risk cohort + requirement of failed prior treatment with lenalidomide defined as no response to treatment with at least 4 cycles started of lenalidomide, loss of response at any time point, or progressive disease/intolerance to therapy. 3. IPSS intermediate-2 risk or high risk patients: HMA failure or HMA naïve as defined above. * Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 2 * Screening laboratory values: 1. Renal glomerular filtration rate (GFR) ≥ 30 ml/min; 2. Aspartate aminotransferase (AST) / Alanine aminotransferase (ALT) ≤ 3.0 times upper limit of normal; 3. Bilirubin \< 1.5 times upper limit of normal; 4. No history of HIV being HIV positive; 5. No active Hepatitis B or Hepatitis C infection. * Life expectancy ≥ 12 weeks. * Women of childbearing potential (WOCBP) must use study specified contraception. * WOCBP demonstrate negative pregnancy test. * Not breastfeeding. * Men sexually active must use study specified contraception. Exclusion Criteria: * Use of chemotherapeutic agents or experimental agents for MDS within 14 days of the first day of study drug treatment. * Use of erythroid stimulating agents, Granulocyte-colony stimulating factor (G-CSF), or Granulocyte-macrophage colony-stimulating factor (GM-CSF) within 14 days of the first day of study drug treatment, or during the study. * Mean triplicate heart rate-corrected QT interval (QTc) \> 500 msec. * Any of the following cardiac abnormalities: 1. QT interval \> 480 msec corrected using Fridericia's formula; 2. Risk factors for Torsade de Pointes; 3. Use of medication that prolongs the QT interval with the exception of drugs that are considered absolutely essential for the care of the subject; 4. Myocardial infarction ≤ 6 months prior to first day of study drug treatment; 5. Unstable angina pectoris or serious uncontrolled cardiac arrhythmia. * Any serious or uncontrolled medical disorder. * Prior malignancy within the previous 2 years except for local cancers that have been cured; or patients who have been adequately treated and have low risk of reoccurrence. * Subjects with a condition requiring systemic treatment with either corticosteroids (\> 10 mg daily prednisone equivalents) or other immunosuppressive medications within 14 days of study drug administration. Inhaled or topical steroids, and adrenal replacement doses \> 10 mg daily prednisone equivalents are permitted in the absence of active autoimmune disease. * Use of other investigational drugs within 30 days of study drug administration. * Major surgery within 4 weeks of study drug administration. * Live-virus vaccination within 30 days of study drug administration. * Allergy to study drug component.