Phospho‐STAT5 and phospho‐Akt expression in chronic myeloproliferative neoplasms

Abstract

Summary The majority of Myeloproliferative Neoplasms (MPNs) are characterised by mutations in genes encoding molecules or receptors involved in cell signalling, the most common being the JAK2 V617F mutation. This mutation leads to ligand‐independent activation of downstream signalling pathways by constitutive phosphorylation. The signalling pathways affected include the Janus kinase‐signal transducers and activators of transcription (JAK‐STAT) and phosphotidylinositide‐3 kinase (PI3K) pathways, which regulate cell survival and apoptosis respectively. Monoclonal antibodies to phospho‐STAT5 and phospho‐Akt were generated and assessed by immunocytochemistry on bone marrow biopsies of MPN patients with JAK2 V617F, JAK2 exon 12, MPL exon 10 and KIT D816V mutations. JAK2 V617F mutation was associated with significantly increased levels of phosphorylated STAT5 and Akt in haemopoietic cells, most marked in megakaryocytes. In contrast, JAK2 exon 12 and MPL exon 10 mutations did not affect the level of phosphorylation. In systemic mastocytosis with KIT D618V mutation there was significantly increased expression of phosphorylated STAT5 and Akt in neoplastic mast cells although there was no change in the expression in other haemopoietic cells. JAK2 V617F is associated with upregulated phosphorylation of STAT5 and Akt in megakaryocytes, and to a lesser extent in other haemopoietic cells. Immunocytochemistry of bone marrow trephines for these phospho‐proteins can be used as a supplementary diagnostic test with a high negative predictive value.

Safety and efficacy of everolimus, a mTOR inhibitor, as single agent in a phase 1/2 study in patients with myelofibrosis

“…11 Increased phosphorylation of STAT5 and Akt was demonstrated by immunocytochemistry in the BM of patients with MPN. 12 Finally, RAD001 prevented in vitro cytokine-stimulated and cytokine-independent growth of primary MPN patients' cells, 14 overall providing a rationale for exploring the effectiveness of mTOR targeting in MPN treatment.…”

“…[6][7][8] A prominent feature of the pathogenesis of MF, as well as of MPN in general, is the direct or indirect activation of the JAK/STAT pathway by mutated proteins, 9 providing the rationale for the use of JAK2 inhibitors. 10 However, dysregulated activation of the PI3K/Akt and ERK downstream pathways in MPN cells has also been described, [11][12][13] and we recently reported that RAD001, a specific inhibitor of mammalian target of rapamycin (mTOR) signaling, prevented proliferation of MPN cell lines and primary cells 14 (C. Bogani, manuscript submitted, June 2011).…”

JAK2 inhibitors for myeloproliferative neoplasms: what is next?

“…V617F is associated with significantly increased levels of phospho-Akt in hematopoietic cells, 103,104 and multiple groups have shown synergism between JAK2 inhibitors and agents that interrupt the phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) axis in MPNs, both in vitro and in vivo. 105,106 Promising results were obtained with single-agent everolimus in patients with MF, particularly with regard to relief of MPN-associated symptoms.…”

Dual inhibition of Jak2 and STAT5 enhances killing of myeloproliferative neoplasia cells

“…1 --6 Based on findings of pre-clinical studies, we performed a phase I clinical study of WT1 peptide immunotherapy for patients with AML, myelodysplastic syndromes, breast or lung cancer, and were able to confirm the safety and clinical efficacy of this therapy. 7 In this report, we describe the long-term outcome for AML patients enrolled in this study.…”

“…4 Although small molecule Jak2 inhibitors are entering clinical trials, their ultimate efficacy is unclear. 5 In addition to the concern of insufficient inhibition of mutated Jak2 in vivo or the emergence of resistance through activation of complementary pathways, many MPNs contain other mutational events (for example, mutation in exon12 of Mpl, 6 or the KIT D618V mutation in patients with systemic mastocytosis 7 ), and thus are not sensitive to Jak inhibitors. Therefore, the development of inhibitors to common mediators of diverse signaling pathways in this disease is very desirable.…”