The long-term survival rate of acute myeloid leukemia (AML) has been significantly prolonged due to the improvement of chemotherapeutic protocols and hemopoietic stem cell transplantation. However, about 20%-40% of the patients with refractory AML fail to achieve complete remission (CR) and approximately 50% of the CR patients will relapse eventually. 1-3 The refractoried and relapsed AML patients have very poor prognosis, therefore refractoriness and relapse are the major challenges for the chemotherapy of AML.