A Trial to Evaluate Two Schedules of MS275 in Combination With 5AC in Elderly Patients With Acute Myeloid Leukemia (AML)

1. To estimate the major response rate (complete and partial responses by the International Working Group (IWG) response criteria) in patients with AML who are \>= 60 years old and unable to tolerate or decline cytotoxic chemotherapy or patients who have relapsed despite one prior regimen and are treated with (a) 5AC 50mg/m2 subcutaneously/intravenously for 10 days on days 1 - 10 of a 28 day cycle given in combination with entinostat 8 mg (flat dose) administered orally on days 3 and10 of each cycle or (b) the same regimen of 5AC with entinostat given on days 10 and 17. 2. To estimate the overall response rate (complete, partial, and hematologic improvement- major by IWG criteria) following treatment with two different dose schedules of 5-Azacytidine and entinostat in patients with AML \>= 60 years old who are unable to tolerate or decline cytotoxic chemotherapy or those who have relapsed despite one prior regimen. The secondary objectives of the study are: 1. To identify changes in gene promoter methylation and gene expression in response to combination therapy with 5AC and entinostat and compare the dynamics and kinetics of these alterations in promoter methylation and gene re-expression in the two different dosing schedules. 2. To evaluate the effect of entinostat on the induction of hyperacetylation of histones from peripheral blood and/or bone marrow samples. 3. To evaluate changes in DNA damage in response to combination therapy using gammaH2AX determination by western blotting. 4. To evaluate immune parameters after exposure to 5AC and entinostat when given at either dosing schedule and to evaluate these in relation to clinical outcomes. 5. To evaluate duration of response.