Transcriptional and Proteomic Changes Associated with the Sensitivity and Resistance to JAK2 Inhibitors: Implications for the Treatment of BCR-ABL (-) Myeloproliferative Neoplasms (MPNs)

Myeloproliferative neoplasms (MPNs) are hematological malignancies characterized by the uncontrolled growth of myeloid-derived cells, including erythrocytes, platelets and/or granulocytes. Dysregulated JAK2 signaling has been implicated in the pathogenesis of these MPNs. Several activating mutations within the JAK2 signaling axis have been identified in MPN patients. Most notably, a somatic activating mutation in the pseudokinase domain of JAK2 (JAK2V617F) leading to constitutive activation of JAK2 was identified in a subset of MPN patients (Baxter et al., 2005; James et al., 2005; Kralovics et al., 2005; & Levine et al., 2005). Moreover, activating mutations that occur upstream of JAK2 at the growth factor receptor level have also been reported in MPN patients. In particular, an activating mutation in the thrombopoietin receptor (c-MPL/Tpo), MPLW515L, which also causes spontaneous activation of JAK2, was recently identified in MPN patients (Pikman et al, 2006). Finally, expression of JAK2V617F or MPLW515L mutations promotes a MPN-like phenotype in animal models, reinforcing the causal role of altered JAK2 signaling in the pathogenesis of these MPNs (Bumm et al., 2006 & Wernig et al., 2006).;This dissertation will summarize my results regarding the functional characterization of a novel and highly selective JAK2 inhibitor, BMS-911543. We have investigated the impact of BMS-911543 in cell lines which are reliant upon mutant JAK2V617F or mutant c-MPL/TPO-R (MPLW515L) for their survival and proliferation. We have demonstrated that in JAK2V617F and MPLW515L dependent models, BMS911543 is anti-proliferative and that these growth inhibitory effects are due to induction of apoptosis and modulation of cell cycle progression. I went on to identify a unique molecular signature that is associated with JAK2 inhibition and includes modulation of known JAK-STAT target genes such as SOCS1 and PIM1 but also introduces a subset of STAT1-dependent genes not previously reported to be regulated by JAK2 inhibition. Lastly, we generated BMS-911543 resistant cells to identify mechanism (s) of acquired resistance that may develop upon continued exposure to JAK2 inhibitors. Differential gene expression patterns were observed between resistant and sensitive cells suggesting that resistant cells may preferentially activate a distinct subset of genes to circumvent the anti-proliferative effects of JAK2 inhibition.