title: ZD1839, a specific epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, induces the formation of inactive EGFR/HER2 and EGFR/HER3 heterodimers and prevents heregulin signaling in HER2-overexpressing breast cancer cells.
abstract: OBJECTIVE
  ZD1839 is a tyrosine kinase inhibitor of the epidermal growth factor receptor (EGFR) that has shown clinical activity against EGFR-expressing tumors. Our aim was to explore the effects of ZD1839 in breast cancer cell lines expressing different levels of EGFR and the closely related HER2 receptor.
  
  
  METHODS
  We studied the growth-inhibitory effects of ZD1839 in a series of breast carcinoma cell lines. In HER2-overexpressing BT-474 breast cancer cells, we studied the effects of ZD1839 on cell growth and heterodimerization of receptors under basal and ligand-stimulated conditions.
  
  
  RESULTS
  ZD1839 was an equally potent inhibitor of growth in breast cancer cells expressing high levels of EGFR and HER2. In BT-474 breast cancer cells, ZD1839 abolished EGF- and heregulin-induced activation of ErbB receptors and downstream signaling molecules. Because ZD1839 does not inhibit the HER2 tyrosine kinase in vitro, and because heregulin is a ligand that activates HER2 by binding to HER3 and HER4 but does not bind to the EGFR, our findings suggested that ZD1839 interfered with HER2 function in intact cells. Searching for mechanisms, we report that ZD1839 induces the formation of inactive unphosphorylated EGFR/HER2 and EGFR/HER3 heterodimers. Furthermore, ZD1839 completely abolishes basal and heregulin-induced formation of active phosphorylated HER2/HER3 heterodimers.
  
  
  CONCLUSIONS
  ZD1839 inhibits the growth of HER2-overexpressing breast cancer cells, possibly by sequestration of HER2 and HER3 receptors in an inactive heterodimer configuration with the EGFR. Our findings suggest that there is a strong rationale to conduct clinical trials of ZD1839 in patients with HER2-overexpressing breast tumors.
authors.affiliation: Laboratory of Oncology Research, Medical Oncology Service, Vall d'Hebron University Hospital, Barcelona 08035, Spain.
authors.forename: Judit
authors.initials: J
authors.lastname: Anido
authors.forename: Pablo
authors.initials: P
authors.lastname: Matar
authors.forename: Joan
authors.initials: J
authors.lastname: Albanell
authors.forename: Marta
authors.initials: M
authors.lastname: Guzmán
authors.forename: Federico
authors.initials: F
authors.lastname: Rojo
authors.forename: Joaquin
authors.initials: J
authors.lastname: Arribas
authors.forename: Steve
authors.initials: S
authors.lastname: Averbuch
authors.forename: Jose
authors.initials: J
authors.lastname: Baselga
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism; D002455:Cell Division; D045744:Cell Line, Tumor; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate; D000077156:Gefitinib; D006801:Humans; D008024:Ligands; D008954:Models, Biological; D020890:Neuregulin-1 / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011799:Quinazolines / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D020893:Receptor, ErbB-3 / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D000970:Antineoplastic Agents; D066246:ErbB Receptors; D016650:Fluorescein-5-isothiocyanate; D000077156:Gefitinib; D008024:Ligands; D020890:Neuregulin-1; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3