Diagnostic and Therapeutic MicroRNAs in Primary Myelofibrosis

Abstract

Primary myelofibrosis (PMF) is a pluripotent hematopoietic stem cell-derived malignancy, included in the heterogeneous group of myeloproliferative neoplasms (MPNs). PMF diagnosis is based on a composite assessment of clinical and laboratory data. The three major diagnostic criteria are: screening for driver mutations, exclusion of other conditions that can cause myelofibrosis, and bone marrow biopsy displaying megakaryocyte changes and fibrosis. PMF treatment options are only partially disease-modifying and consist mainly of symptom control. Recently, a new targeted therapy was introduced for PMF patients, JAK-STAT inhibitors (i.e. ruxolitinib). However, specific subgroups of patients do not benefit from the JAK-STAT inhibitors: (1) those who are carrying JAK2 mutations, but ruxolitinib does not reduce the spleen size; (2) triple negative patients (no JAK2, CALR, or MPL mutations); and (3) those who discontinue JAK-STAT therapy because of side effects. These subgroups are in need of new therapeutic approaches. Mature microRNAs (miRNAs) range from 16 to 28 nucleotides (nt) in length and regulate specific messenger RNAs at the post-transcriptional level. Numerous in vitro and in vivo studies have reported specific miRNAs, as well as complex miRNA networks, to be dysregulated in PMF. Several of these miRNAs were shown to be implicated in essential events of PMF pathophysiology: increase of bone marrow fibrosis, progression to acute myeloid leukemia, resistance to JAK-STAT inhibitors, and activation of differentiation of hematopoietic stem/progenitor cells into megakaryocytes. Hence, we propose miRNAs as a potential minimally invasive diagnostic tool for PMF and as therapeutic targets that could address the unmet medical needs of these patients.