EPO and myeloproliferative disorder: In the presence of EPO, ZT55 inhibited the burst forming unit-erythroid (BFU-E) growth of clonogenic progenitors with IC50 ranging from 19.47 to 35.43 μM for MPN-patient donors and 60 μM for healthy donors, indicating an increased sensitivity to JAK2 inhibition compared with normal healthy volunteers (Fig. 6b).