Decitabine, Arsenic Trioxide and Ascorbic Acid for Myelodysplastic Syndromes and Acute Myeloid Leukemia

Inclusion Criteria: 1. MDS (either de novo or secondary) fitting any of the FAB classifications or AML defined by FAB classification criteria. Patients with \< 5% bone marrow blasts must also meet one of the following criteria: 1. Symptomatic anemia with either hemoglobin \<10.0 g/dL or requiring red blood cell (RBC) transfusion 2. Thrombocytopenia with a history of two or more platelet counts \< 50,000 / µL or a significant hemorrhage requiring platelet transfusions, or 3. Neutropenia with two or more absolute neutrophil counts \< 1,000 /µL. AML patients must also have a WBC \< 10,000µL and meet one of the following two criteria: 1. Age greater than or equal to 60 years 2. Relapsed AML and are not a candidate for cytotoxic chemotherapy. 2. ECOG performance status of 0-2. 3. Must give written informed consent indicating their awareness of the investigational nature of this study and its potential hazards. 4. Adequate renal and hepatic function (creatinine \< 1.5x institutional upper limit of normal, total bilirubin ≤ 1.5x institutional upper limit of normal, AST and ALT ≤ 2x institutional upper limit of normal). 5. Serum potassium \> 4.0 mEq/L, serum magnesium \> 1.8 mg/dL. 6. Life expectancy of at least 16 weeks. 7. Women of childbearing age must have a negative serum pregnancy test prior to initiating therapy. 8. Sexually active women of childbearing potential must use effective birth control during the trial and for at least two months following the trial. 9. Men must be willing to avoid fathering a new child while receiving therapy with decitabine. 10. Greater than or equal to 18 years, no upper age limit 11. Individuals who are candidates for hematopoietic stem cell transplantation and who meet all other study criteria may participate in the study and receive intravenous decitabine in combination with arsenic trioxide and Ascorbic acid as a treatment prior to transplantation. Exclusion Criteria: 1. Known central nervous system (CNS) leukemia. 2. Previously received greater than or equal to 5 cycles of azacitidine (Vidaza®, Pharmion Corp., Boulder, CO) or decitabine (Dacogen®, MGI Pharma Inc. Bloomington, MN). 3. QTc \> 460 msec. 4. Known or suspected hypersensitivity to decitabine, arsenic or ascorbic acid. 5. Receiving any other investigational agents within 30 days of first dose of study drug. 6. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, congestive heart failure of NYHA class 3 or 4, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situation that would limit compliance with study requirements. 7. Known positive serology for HIV. 8. Had radiotherapy within 14 days prior to study enrollment. 9. Known presence of hepatic tumors. 10. \< 18 years of age 11. Exclude women who are pregnant or breast feeding. 12. Known history of glucose-6-phosphate deficiency (G6PD). 13. Currently taking a Class Ia or Class III antiarrhythmic or other medication causally associated with prolonging QTc. 14. Use of aspirin with platelet counts \< 50,000/µl.