Eltrombopag is used for treating thrombocytopenia (abnormally low platelet levels in blood). The drug stimulates thrombopoietin receptors on immature hematopoietic progenitor cells in the bone marrow, leading to increased platelet production. In a study published online on September 12 in Science Translational Medicine, Britta Will, Ph.D., and Ulrich Steidl, M.D., Ph.D., describe a previously unknown molecular mechanism by which eltrombopag stimulates immature hematopoietic stem cells (HSC) to produce multilineage progenitor cells (i.e., capable of differentiating into many different types of blood cells). The authors found that eltrombopag chelates (binds) iron inside immature HSCs, leading to a transient reduction in intracellular iron levels which, in turn, stimulates stem cell self-renewal. This iron chelation-dependent mechanism of eltrombopag could be clinically important for preserving healthy levels of HSCs under stressful conditions such as chemotherapy or irradiation. Dr. Will is an assistant professor of medicine and of cell biology at Einstein. Dr. Steidl is the Diane and Arthur B. Belfer Faculty Scholar in Cancer Research, director of the Stem Cell Isolation and Xenotransplantation Facility and a professor of cell biology and of medicine at Einstein and associate chair for translational research in oncology at Montefiore.