Relapsed and refractory hematologic malignancies have poor responses to standard therapy and are associated with a poor prognosis. For example, relapsed acute myeloid leukemia (AML) is a highly aggressive and resistant disease, particularly when associated with first complete response (CR) duration of less than 12 months. Thus, there is an urgent need for new agents in relapsed and refractory hematologic malignancies such as acute leukemia. In elderly patients, where the tolerance of aggressive induction therapy is often poor and curative options such as bone marrow transplantation HSCT are not available, the need for effective non-aggressive drug regimens for AML is even greater.