title: Epidermal growth factor receptor activity determines response of colorectal cancer cells to gefitinib alone and in combination with chemotherapy.
abstract: OBJECTIVE
  Up to now, there have been no established predictive markers for response to epidermal growth factor receptor (EGFR/HER1/erbB1) inhibitors alone and in combination with chemotherapy in colorectal cancer. To identify markers that predict response to EGFR-based chemotherapy regimens, we analyzed the response of human colorectal cancer cell lines to the EGFR-tyrosine kinase inhibitor, gefitinib (Iressa, AstraZeneca, Wilmington, DE), as a single agent and in combination with oxaliplatin and 5-fluorouracil (5-FU).
  
  
  METHODS
  Cell viability was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and crystal violet cell viability assays and analyzed by ANOVA. Apoptosis was measured by flow cytometry, poly(ADP-ribose) polymerase, and caspase 3 cleavage. EGFR protein phosphorylation was detected by Western blotting.
  
  
  RESULTS
  Cell lines displaying high constitutive EGFR phosphorylation (a surrogate marker for EGFR activity) were more sensitive to gefitinib. Furthermore, in cell lines exhibiting low constitutive EGFR phosphorylation, an antagonistic interaction between gefitinib and oxaliplatin was observed, whereas in cell lines with high basal EGFR phosphorylation, the interaction was synergistic. In addition, oxaliplatin treatment increased EGFR phosphorylation in those cell lines in which oxaliplatin and gefitinib were synergistic but down-regulated EGFR phosphorylation in those lines in which oxaliplatin and gefitinib were antagonistic. In contrast to oxaliplatin, 5-FU treatment increased EGFR phosphorylation in all cell lines and this correlated with synergistic decreases in cell viability when 5-FU was combined with gefitinib.
  
  
  CONCLUSIONS
  These results suggest that phospho-EGFR levels determine the sensitivity of colorectal cancer cells to gefitinib alone and that chemotherapy-mediated changes in phospho-EGFR levels determine the nature of interaction between gefitinib and chemotherapy.
authors.affiliation: Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, North Ireland.
authors.forename: Sandra
authors.initials: S
authors.lastname: Van Schaeybroeck
authors.forename: Anthi
authors.initials: A
authors.lastname: Karaiskou-McCaul
authors.forename: Donal
authors.initials: D
authors.lastname: Kelly
authors.forename: Daniel
authors.initials: D
authors.lastname: Longley
authors.forename: Leeona
authors.initials: L
authors.lastname: Galligan
authors.forename: Eric
authors.initials: E
authors.lastname: Van Cutsem
authors.forename: Patrick
authors.initials: P
authors.lastname: Johnston
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D004336:Drug Antagonism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D005472:Fluorouracil / Q000494:pharmacology; D000077156:Gefitinib; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D009944:Organoplatinum Compounds / Q000494:pharmacology; D000077150:Oxaliplatin; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D000970:Antineoplastic Agents; D009944:Organoplatinum Compounds; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D012333:RNA, Messenger; D000077150:Oxaliplatin; D066246:ErbB Receptors; D000077156:Gefitinib; D005472:Fluorouracil