title: Epidermal growth factor receptor coexpression modulates susceptibility to Herceptin in HER2/neu overexpressing breast cancer cells via specific erbB-receptor interaction and activation.
abstract: BACKGROUND
  Growth factors and Herceptin specifically and differentially modulate cell proliferation of tumor cells. However, the mechanism of action on erbB-receptor level is incompletely understood. We evaluated Herceptin's capacity to modulate erbB-receptor activation and interaction on the cell surface level and thereby potentially impair cell proliferation of HER2/neu (c-erbB2) overexpressing breast cancer cells, both in the presence and absence of relevant growth factors.
  
  
  METHODS
  BT474 and SK-BR-3 breast cancer cell lines were treated with Epidermal Growth Factor (EGF), Heregulin, and with Herceptin in different combinations. Kinetics of cell proliferation were evaluated flow cytometrically based on BrdU-labeling. Fluorescence Resonance Energy Transfer, ELISAs and phosphorylation site specific Western Blotting was performed to investigate erbB-receptor interaction and activation.
  
  
  RESULTS
  EGF induced EGFR/EGFR and EGFR/c-erbB2 interactions correlate with stimulation of cell proliferation in BT474 cells. Both homo- and heterodimerization are considerably less pronounced in SK-BR-3 cells and heterointeraction is additionally reduced by EGF treatment, causing inhibition of cell proliferation. Heregulin stimulates cell proliferation extensively in both cell lines. Herceptin drives BT474 cells more efficiently into quiescence than it does with SK-BR-3 cells and thereby blocks cell cycle progress. In SK-BR-3 Herceptin treatment causes c-erbB2 phosphorylation of Y877 and Y1248, EGF induces Y877 and Y1112 phosphorylation. The Y1112 phosphorylation site, activated by EGF in SK-BR-3 cell, is bypassed in BT474. In addition the inhibitory capacity of Herceptin on BT474 and SK-BR-3 cell proliferation depends on the presence and absence of growth factors to a various extent.
  
  
  CONCLUSIONS
  The growth inhibitory effect of Herceptin on c-erbB2 overexpressing breast cancer cells is considerably modulated by EGFR coexpression and consequently EGFR/c-erbB2 homo- and heterointeractions, as well as the presence or absence of growth factors. C-erbB2 overexpression alone is insufficient to predict the impact of growth factors and antibodies on cell proliferation. The optimization and specification of therapeutic approaches based on erbB-receptor targeting requires to account for EGFR coexpression as well as the potential presence of erbB-receptor relevant growth factors.
authors.affiliation: Institute of Pathology, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Diermeier
authors.forename: Gábor
authors.initials: G
authors.lastname: Horváth
authors.forename: Ruth
authors.initials: R
authors.lastname: Knuechel-Clarke
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Hofstaedter
authors.forename: János
authors.initials: J
authors.lastname: Szöllosi
authors.forename: Gero
authors.initials: G
authors.lastname: Brockhoff
mesh_terms: D000911:Antibodies, Monoclonal / Q000378:metabolism* / Q000494:pharmacology / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D002277:Carcinoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D004357:Drug Synergism; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006131:Growth Inhibitors / Q000378:metabolism / Q000494:pharmacology / Q000627:therapeutic use; D006801:Humans; D020890:Neuregulin-1 / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D000068878:Trastuzumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D006131:Growth Inhibitors; D020890:Neuregulin-1; D018719:Erb-b2 Receptor Tyrosine Kinases; D011956:Receptors, Cell Surface; D000068878:Trastuzumab