title: Resistance to EGFR-TKI can be mediated through multiple signaling pathways converging upon cap-dependent translation in EGFR-wild type NSCLC.
abstract: BACKGROUND
  For the majority of patients with non-small-cell lung cancer (NSCLC), response to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) is suboptimal. In models of acquired resistance to EGFR-TKI, activation of Akt phosphorylation is frequently observed. Because Akt activation results in downstream initiation of cap-dependent protein translation, we hypothesized that a strategy of targeting cap-dependent translation in combination with erlotinib might enhance therapy.
  
  
  METHODS
  NSCLC cells that are wild type for EGFR were assayed for sensitivity to erlotinib. Serum-starved NSCLC cells were assayed for EGFR signaling and downstream pathway activation by immunoblot after stimulation with epidermal growth factor. EGFR signaling and signaling mediators of cap-dependent translation were assayed by immunoblot under serum-replete conditions 24 hours after treatment with erlotinib. Finally, combination treatment with erlotinib and two different cap-dependent translation inhibitors were done to assess the effect on cell viability.
  
  
  RESULTS
  EGFR signaling is coupled to activation of cap-dependent translation in EGFR wild-type cells. Erlotinib inhibits EGFR phosphorylation in EGFR-TKI resistant cells, however, results in activation of downstream signaling molecules including Akt and extracellular regulated kinase, ERK 1/2, resulting in maintenance of eukaryotic initiation factor 4F (eIF4F) activation. eIF4F cap-complex formation is maintained in erlotinib-resistant cells, but not in erlotinib-sensitive cells. Finally, using an antisense oligonucleotide against eukaryotic translation initiation factor 4E and a small-molecule inhibitor to disrupt eIF4F formation, we show that cap-dependent translation inhibition can enhance sensitivity to erlotinib.
  
  
  CONCLUSIONS
  The results of these studies support further clinical development of translation inhibitors for treatment of NSCLC in combination with erlotinib.
authors.affiliation: Department of Medicine, Division of Hematology, Oncology, and Transplantation, University of Minnesota Medical School, Minneapolis, MN 55455, USA. patel069@umn.edu
authors.forename: Manish R
authors.initials: MR
authors.lastname: Patel
authors.forename: Joe
authors.initials: J
authors.lastname: Jay-Dixon
authors.forename: Ahad A
authors.initials: AA
authors.lastname: Sadiq
authors.forename: Blake A
authors.initials: BA
authors.lastname: Jacobson
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kratzke
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D066246:ErbB Receptors / Q000235:genetics*; D000069347:Erlotinib Hydrochloride; D039562:Eukaryotic Initiation Factor-4F / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology; D012315:RNA Caps / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured
chemical_list: D039562:Eukaryotic Initiation Factor-4F; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D012315:RNA Caps; D000069347:Erlotinib Hydrochloride; C512478:EGFR protein, human; D066246:ErbB Receptors