BMS-911543 is a potent and selective JAK2 inhib itor. It displays potent anti-proliferative and pharmacodynamic effects in cell lines dependent upon JAK2 signaling, and has little activity in cell types dependent upon other pathways, such as JAK1 and JAK3. In addition, it displays anti-proliferative responses in colony growth assays using primary progenitor cells isolated from patients with JAK2(V617F)-positive myeloproliferative neoplasms (MPNs).