title: mTOR inhibitors alone and in combination with JAK2 inhibitors effectively inhibit cells of myeloproliferative neoplasms.
abstract: BACKGROUND
  Dysregulated signaling of the JAK/STAT pathway is a common feature of chronic myeloproliferative neoplasms (MPN), usually associated with JAK2V617F mutation. Recent clinical trials with JAK2 inhibitors showed significant improvements in splenomegaly and constitutional symptoms in patients with myelofibrosis but meaningful molecular responses were not documented. Accordingly, there remains a need for exploring new treatment strategies of MPN. A potential additional target for treatment is represented by the PI3K/AKT/mammalian target of rapamycin (mTOR) pathway that has been found constitutively activated in MPN cells; proof-of-evidence of efficacy of the mTOR inhibitor RAD001 has been obtained recently in a Phase I/II trial in patients with myelofibrosis. The aim of the study was to characterize the effects in vitro of mTOR inhibitors, used alone and in combination with JAK2 inhibitors, against MPN cells.
  
  
  RESULTS
  Mouse and human JAK2V617F mutated cell lines and primary hematopoietic progenitors from MPN patients were challenged with an allosteric (RAD001) and an ATP-competitive (PP242) mTOR inhibitor and two JAK2 inhibitors (AZD1480 and ruxolitinib). mTOR inhibitors effectively reduced proliferation and colony formation of cell lines through a slowed cell division mediated by changes in cell cycle transition to the S-phase. mTOR inhibitors also impaired the proliferation and prevented colony formation from MPN hematopoietic progenitors at doses significantly lower than healthy controls. JAK2 inhibitors produced similar antiproliferative effects in MPN cell lines and primary cells but were more potent inducers of apoptosis, as also supported by differential effects on cyclinD1, PIM1 and BcLxL expression levels. Co-treatment of mTOR inhibitor with JAK2 inhibitor resulted in synergistic activity against the proliferation of JAK2V617F mutated cell lines and significantly reduced erythropoietin-independent colony growth in patients with polycythemia vera.
  
  
  CONCLUSIONS
  These findings support mTOR inhibitors as novel potential drugs for the treatment of MPN and advocate for clinical trials exploiting the combination of mTOR and JAK2 inhibitor.
authors: Department of Medical and Surgical Care, Section of Hematology, University of Florence, Florence, Italy.
authors: Costanza
authors: C
authors: Bogani
authors: Niccolò
authors: N
authors: Bartalucci
authors: Serena
authors: S
authors: Martinelli
authors: Lorenzo
authors: L
authors: Tozzi
authors: Paola
authors: P
authors: Guglielmelli
authors: Alberto
authors: A
authors: Bosi
authors: Alessandro M
authors: AM
authors: Vannucchi
mesh_terms: D000818:Animals; D018952:Antigens, CD34 / Q000378:metabolism; D016022:Case-Control Studies; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D003114:Colony-Forming Units Assay; D004357:Drug Synergism; D000068338:Everolimus; D006412:Hematopoietic Stem Cells / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D053614:Janus Kinase 2 / Q000037:antagonists & inhibitors* / Q000235:genetics; D051379:Mice; D009154:Mutation; D009196:Myeloproliferative Disorders / Q000201:enzymology* / Q000235:genetics; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011687:Purines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*
chemical_list: C545606:AZD 1480; D018952:Antigens, CD34; D007211:Indoles; D047428:Protein Kinase Inhibitors; D011687:Purines; D011720:Pyrazoles; D011743:Pyrimidines; D000068338:Everolimus; D053614:Janus Kinase 2; D058570:TOR Serine-Threonine Kinases; C572919:PP242; D020123:Sirolimus
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