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Myelodysplastic syndromes (MDS) include a heterogeneous group of acquired hematopoietic malignancies characterized by ineffective hematopoiesis, peripheral cytopenias, and a varying propensity for progression to acute myeloid leukemia. Patients with higher risk MDS have dismal outcomes and treatment options are very limited. Aside from allogeneic hematopoietic cell transplantation, the only potentially curative treatment, DNA methyltransferase inhibitors (DNMTIs) are the only intervention that prolongs overall survival in patients with higher risk MDS. The clinical use of DNMTIs in MDS was one of the earliest successful attempts at epigenetic reprogramming of cancer. In this review, we discuss the clinical use of DNMTIs in MDS highlighting the current challenges and controversies and future directions of research needed to explore the full therapeutic potential of these agents.

Myelodysplastic syndromes (MDS) include a heterogeneous group of acquired hematopoietic malignancies characterized by ineffective hematopoiesis, peripheral cytopenias, and a varying propensity for progression to acute myeloid leukemia. The clinical heterogeneity in MDS is a reflection of its molecular heterogeneity. Better understanding of aberrant epigenetics, dysregulation of immune responses, and del(5q) MDS has provided the rationale for well-established treatments in MDS. Further understanding of abnormal signal transduction and aberrant apoptosis pathways has led to development of new rational therapies that are in advanced phases of clinical translation. This review seeks to describe recent developments in our understanding of the pathogenesis of MDS and the potential therapeutic implications of these observations.

Since the discovery of the activating V617F mutation in Janus kinase 2 (JAK2), a number of pharmacologic inhibitors of JAK2 have entered clinical trials for patients with myelofibrosis. However, ruxolitinib, approved in 2011, remains the only one currently available for treatment of myelofibrosis, with many others having been discontinued for toxicity, and considerable uncertainty surrounding the future of those still in development. Areas covered: The available clinical data on pacritinib and momelotinib, the two agents in the most advanced phases of clinical testing in myelofibrosis, are examined in detail. NS-018 and INCB039110, selective inhibitors of JAK2 and JAK1, respectively, are also discussed. Finally, the JAK2 inhibitors no longer in clinical development are summarized in tabular form. Expert opinion: The different agents evaluated clearly differ in their kinomes, toxicity profiles and potential for myelosuppression. If approved, the JAK2-specific non-myelosuppressive inhibitor pacritinib could fulfill a major unmet need, that of patients with significant cytopenias. However, toxicity concerns persist. The data from the pivotal trials of momelotinib do not support its approval, although improvement of anemia is an important benefit. Selective JAK1 inhibition alone is unlikely to succeed in myelofibrosis. In these circumstances, rational ruxolitinib-based combinations may represent the best way forward.