A. Patient-derived bone marrow mononuclear cells were cultured in semisolid medium in the presence of increasing doses of A46, with or without thrombopoietin (TPO). At the end of 14 days, the numbers of megakaryocyte colony-forming units (CFU-Megs) were counted and plotted as a function of treatment condition. Each condition was measured in duplicate. *p < 0.05 with respect to 0 μM A46 (−TPO), #p < 0.05 with respect to 0 μM A46 (+TPO), and §p < 0.05 (+ TPO) vs. (−TPO). B and C. Bone marrow aspirates obtained from either Jak2-WT or Jak2-V617F transgenic mice were treated with 0, 2.5, or 25 μM A46 for 24 hours, ex vivo. The drug was then washed away and the cells were cultured in drug-free semi-solid medium for an additional 5 days. The numbers of erythroid burst-forming units (BFU-E) in each sample were then plotted as a function of genotype. Each point was measured in duplicate. *, p<0.05 vs. − EPO 0 μM control;, p<0.05 vs. + EPO 0 μM control; #, p<0.05 vs. − EPO, within same drug treatment group.