title: Effect of methotrexate on JAK/STAT pathway activation in myeloproliferative neoplasms.
abstract: BACKGROUND
  The myeloproliferative neoplasms are a group of haematological malignancies characterised by pathological activation of the JAK/STAT (Janus kinase and signal transducer and activator of transcription) intracellular signalling pathway. 50-95% of patients have an acquired mutation (JAK2V617F) causing constitutive activation of JAK2. Our aim was to find new treatments for myeloproliferative neoplasms by identifying compounds that suppress JAK/STAT pathway activation.
  
  
  METHODS
  We used a luciferase-based transcriptional assay in the low complexity Drosophila model system to screen a library of 2000 small molecules for modulators of JAK/STAT pathway activation. Screen hits were validated with western blotting in the HDLM-2 Hodgkin's lymphoma cell line. The HEL cell line, in which constitutive JAK/STAT pathway activation is caused by JAK2V617F, was used to determine the relevance of screen hits for treatment of myeloproliferative neoplasms.
  
  
  RESULTS
  Methotrexate and the chemically similar drug aminopterin were independently identified as strong inhibitors of the Drosophila JAK/STAT pathway, an effect conserved to human cells. Methotrexate did not affect protein phosphorylation in other intracellular signalling pathways. Methotrexate caused significant suppression of JAK/STAT activation in HEL cells at a concentration equivalent to that seen in patients taking low-dose oral methotrexate (p≤0·001).
  
  
  CONCLUSIONS
  Our results suggest that methotrexate is a promising treatment for myeloproliferative neoplasms that could be translated into clinical trials after assessment in primary cells. These results are particularly relevant in myelofibrosis. Inhibitors of JAK1/2 improve symptoms and prolong life in myelofibrosis, but their use is limited by cost. Other existing therapies for myelofibrosis appear no more effective than placebo. Methotrexate might bring the benefits of JAK/STAT pathway inhibition at a lower cost.
  
  
  BACKGROUND
  Cancer Research UK, Yorkshire Cancer Research, UK Medical Research Council, Wellcome Trust, EU Framework Cancer Pathways.
authors: Sheffield Cancer Research Centre, University of Sheffield, Sheffield, UK. Electronic address: mdp12sjt@sheffield.ac.uk.
authors: Sally
authors: S
authors: Thomas
authors: Bateson Centre, Department of Biomedical Science, University of Sheffield, Sheffield, UK.
authors: Katherine
authors: K
authors: Fisher
authors: Department of Haematology, Royal Hallamshire Hospital, Sheffield, UK.
authors: John
authors: J
authors: Snowden
authors: Academic Unit of Clinical Oncology, University of Sheffield, Sheffield, UK; Sheffield Experimental Cancer Medicine Centre, Weston Park Hospital, Sheffield, UK.
authors: Sarah
authors: S
authors: Danson
authors: Sheffield RNAi Screening Facility, Department of Biomedical Science, University of Sheffield, Sheffield, UK.
authors: Stephen
authors: S
authors: Brown
authors: Bateson Centre, Department of Biomedical Science, University of Sheffield, Sheffield, UK.
authors: Martin
authors: M
authors: Zeidler