title: Compensatory increases in Her-2/neu activation in response to EGFR tyrosine kinase inhibition in colon cancer cell lines.
abstract: BACKGROUND
  Tyrosine kinase receptors of the ErbB family have become promising targets for anti-neoplastic drugs, but mechanisms of resistance are incompletely understood. To investigate such pathways, we applied a small-molecule, selective EGFR inhibitor, OSI-774, to three well-characterized colon cancer cell lines and studied the alterations of expression and activation of receptors in the erbB family.
  
  
  METHODS
  MTT assays were performed to determine the IC(50)s of GEO, FET, and HCT 116 human colorectal cancer cell lines treated with OSI-774. Plated cells were then exposed to either DMSO control or 7 microm of OSI-774 for treatment durations of 1, 3, 5, 7, 10, 14, 28, and 56 days. Cell lysates were evaluated by Western blotting, evaluating both total and phosphorylated levels of EGFR, Her-2/neu, and erbB-3.
  
  
  RESULTS
  IC(50) values for GEO, FET, and HCT 116 cell lines exposed to OSI-774 were 12.0, 16.0, and greater than 100 microm, respectively. In all treated cell lines, OSI-774 diminished EGFR activation but did not affect total expression compared with controls. In contrast, Her-2/neu activation was increased in all cell lines. These changes in EGFR and Her-2/neu were identified within 24 h but peaked later in the treatment cycle. ErbB-3 expression and activation did not follow a consistent pattern between cell lines.
  
  
  CONCLUSIONS
  Inhibition of EGFR led to increased activation of Her-2/neu. This result suggests a possible mechanism by which cells might escape the proapoptotic signals resulting from EGFR blockade. Our findings suggest concurrent inhibition of multiple members of the erbB family may yield stronger apoptotic responses than single receptor blockade alone.
authors.affiliation: Department of Surgery, Wilford Hall Medical Center, San Antonio, Texas, USA.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Learn
authors.forename: Naveen
authors.initials: N
authors.lastname: Krishnegowda
authors.forename: Jose
authors.initials: J
authors.lastname: Talamantez
authors.forename: Morton S
authors.initials: MS
authors.lastname: Kahlenberg
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000069347:Erlotinib Hydrochloride; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*
chemical_list: D066246:ErbB Receptors; D000069347:Erlotinib Hydrochloride; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases