Limited Efficacy of BMS-911543 in a Murine Model of JAK2^V617F Myeloproliferative Neoplasm

Activation of JAK2, frequently as a result of the JAK2^V617F mutation, is a characteristic feature of the classical myeloproliferative neoplasms (MPN) polycythemia vera, essential thrombocythemia and myelofibrosis and thought to be responsible for the constitutional symptoms associated with these diseases. BMS-911543 is a JAK2 selective inhibitor that induces apoptosis in JAK2-dependent cell lines and inhibits the growth of CD34⁺ progenitor cells from patients with V617F⁺ MPN. To explore the clinical potential of this inhibitor, we tested BMS-911543 in a murine retroviral transduction – transplantation model of JAK2^V617F MPN. Treatment was initiated at two dose levels (3 mg/kg and 10 mg/kg) when the hematocrit exceeded 70%. Following the first week, white blood cell counts were reduced to normal in the high dose group and were maintained well below the vehicle-treated mice throughout the study. However, BMS-911543 had no effect on red cell parameters. After 42 days of treatment, the proportion of JAK2^V617F - positive cells in hematopoietic tissues was identical to controls or slightly increased compared to controls. Plasma concentrations of IL-6, IL-15, and TNFα were elevated in MPN mice and reduced in the high dose treatment group, while other cytokines were unchanged. Collectively, these results show that BMS-911543 has limited activity in this murine model of JAK2^V617F – driven MPN and suggest that targeting JAK2 alone may be insufficient to achieve effective disease control.