The Emerging Roles of Aldehyde Dehydrogenase in Acute Myeloid Leukemia and Its Therapeutic Potential

Acute myeloid leukemia (AML) is a malignant disorder characterized by myeloid differentiation arrest and uncontrolled clonal expansion of abnormal myeloid progenitor cells. AML is the most common malignant bone marrow (BM) disease in adults and accounts for approximately 80% of adult leukemia cases. There has been little improvement in the treatment of patients with AML over the past decade. Cytogenetic and morphologic heterogeneity of AML and the difficulty in distinguishing leukemic stem cells (LSCs) from normal hematopoietic stem cells (HSCs) continue to be the major challenges in treating this malignancy. In recent years, intensive efforts have been made to explore novel potential markers for the efficient identification and characterization of leukemic stem cells. Aldehyde dehydrogenase (ALDH) is a potential target molecule that plays crucial roles in leukemic stem cell survival and multidrug resistance, mainly through its involvement in the detoxification of many endogenous and exogenous aldehydes. The selection and isolation of cancer stem cells based on high ALDH activity seem to be a useful approach in many human malignancies, especially leukemia. Moreover, it is worth mentioning that several previous studies have indicated that a high ALDH activity (classified as ALDHbr cells in flow cytometry) can act as an independent prognostic factor in several types of cancer. In the present review, we update and critically discuss the available data regarding the importance of ALDH activity in normal and leukemic stem cells and its potential diagnostic and therapeutic implications.