title: Response to mTOR inhibition: activity of eIF4E predicts sensitivity in cell lines and acquired changes in eIF4E regulation in breast cancer.
abstract: BACKGROUND
  Inhibitors of the kinase mTOR, such as rapamycin and everolimus, have been used as cancer therapeutics with limited success since some tumours are resistant. Efforts to establish predictive markers to allow selection of patients with tumours likely to respond have centred on determining phosphorylation states of mTOR or its targets 4E-BP1 and S6K in cancer cells. In an alternative approach we estimated eIF4E activity, a key effector of mTOR function, and tested the hypothesis that eIF4E activity predicts sensitivity to mTOR inhibition in cell lines and in breast tumours.
  
  
  RESULTS
  We found a greater than three fold difference in sensitivity of representative colon, lung and breast cell lines to rapamycin. Using an assay to quantify influences of eIF4E on the translational efficiency specified by structured 5'UTRs, we showed that this estimate of eIF4E activity was a significant predictor of rapamycin sensitivity, with higher eIF4E activities indicative of enhanced sensitivity. Surprisingly, non-transformed cell lines were not less sensitive to rapamycin and did not have lower eIF4E activities than cancer lines, suggesting the mTOR/4E-BP1/eIF4E axis is deregulated in these non-transformed cells. In the context of clinical breast cancers, we estimated eIF4E activity by analysing expression of eIF4E and its functional regulators within tumour cells and combining these scores to reflect inhibitory and activating influences on eIF4E. Estimates of eIF4E activity in cancer biopsies taken at diagnosis did not predict sensitivity to 11-14 days of pre-operative everolimus treatment, as assessed by change in tumour cell proliferation from diagnosis to surgical excision. However, higher pre-treatment eIF4E activity was significantly associated with dramatic post-treatment changes in expression of eIF4E and 4E-binding proteins, suggesting that eIF4E is further deregulated in these tumours in response to mTOR inhibition.
  
  
  CONCLUSIONS
  Estimates of eIF4E activity predict sensitivity to mTOR inhibition in cell lines but breast tumours with high estimated eIF4E activity gain changes in eIF4E regulation in order to enhance resistance.
authors.affiliation: Leeds Institute of Molecular Medicine, St, James's University Hospital, Leeds University, UK.
authors.forename: Sampoorna
authors.initials: S
authors.lastname: Satheesha
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Cookson
authors.forename: Louise J
authors.initials: LJ
authors.lastname: Coleman
authors.forename: Nicola
authors.initials: N
authors.lastname: Ingram
authors.forename: Brijesh
authors.initials: B
authors.lastname: Madhok
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Hanby
authors.forename: Charlotte A B
authors.initials: CA
authors.lastname: Suleman
authors.forename: Vicky S
authors.initials: VS
authors.lastname: Sabine
authors.forename: E Jane
authors.initials: EJ
authors.lastname: Macaskill
authors.forename: John M S
authors.initials: JM
authors.lastname: Bartlett
authors.forename: J Michael
authors.initials: JM
authors.lastname: Dixon
authors.forename: Jim N
authors.initials: JN
authors.lastname: McElwaine
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Hughes
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D039561:Eukaryotic Initiation Factor-4E / Q000235:genetics / Q000378:metabolism*; D000068338:Everolimus; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011300:Preoperative Care; D014176:Protein Biosynthesis / Q000187:drug effects; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D046509:Tissue Culture Techniques
chemical_list: D020121:5' Untranslated Regions; D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D039561:Eukaryotic Initiation Factor-4E; D010750:Phosphoproteins; D000068338:Everolimus; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus