“…2,8,9 One of these, a nonpeptidyl, hydrazone class small molecule, named Eltrombopag (E; SB-497115), was recently approved by the Food and Drug Administration for use in adult chronic idiopathic thrombocytopenic purpura patients. 10,11 Because Mpl and/or Tpo is expressed by many malignant hematopoietic cell types, [12][13][14] concern that Mpl agonists might exacerbate a leukemia patient's disease is appropriate. We investigated this issue using primary human leukemia cells and a prototype nonpeptidyl, hydrazone class, Mpl agonist, SB-559457 (SB; Figure 1A) whose in vitro megakaryocytopoietic properties are virtually indistinguishable from rhTpo (5M SB ϭ 100 ng/mL; 2.8M rhTpo).…”