Dose Escalation of OXi4503 as Single Agent and Combination With Cytarabine w/Subsequent Ph 2 Cohorts for AML and MDS

Inclusion Criteria: 1. Provide informed consent 2. ≥ 18 years of age 3. Phase 1 (dose escalation) subjects must have either: * AML that has failed to achieve complete remission or morphologic complete remission or * MDS - Marrow blasts must be \> 5% and disease failed at least 1 prior hypomethylating agent 4. Phase 2 (expansion) subjects must have either MDS or relapsed/refractory AML 5. Eastern Cooperative Oncology Group performance status 0, 1, or 2 6. Total bilirubin ≤ 2 7. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels ≤ 2.5 times upper limit of normal (ULN) 8. Serum creatinine \< 2.5 times ULN 9. Prothrombin time (PT)/international normalized ratio and (PTT) in normal range ± 25% 10. Women of child-bearing potential 11. Males with female partners of child-bearing potential must agree to use physician-approved contraceptive methods Exclusion Criteria: 1. Acute promyelocytic leukemia 2. Absolute peripheral blood myeloblast count greater than 20,000/mm3 3. Uncontrolled hypertension 4. History of congenital long QT syndrome or torsades de pointes 5. Pathologic bradycardia or heart block 6. Prolonged baseline QTc 7. Hiistory of ventricular arrhythmia 8. Myocardial infarction and/or new ST elevation 9. Any history of hemorrhagic stroke 10. Symptomatic congestive heart failure 11. Major hemorrhagic event within 28 days 12. Suggestive central nervous system involvement with leukemia 13. Any open wound 14. Pregnant and nursing subjects are excluded 15. Treatment with any anticancer therapy 16. Treatment with colchicine is excluded. 17. Psychiatric disorders that would interfere with consent