The antiepidermal growth factor receptor agent gefitinib (ZD1839/Iressa) improves antihormone response and prevents development of resistance in breast cancer in vitro

Endocrinology. 2003 Nov;144(11):5105-17. doi: 10.1210/en.2003-0705. Epub 2003 Aug 7.


Although many estrogen receptor-positive breast cancers initially respond to antihormones, responses are commonly incomplete with resistance ultimately emerging. Delineation of signaling mechanisms underlying these phenomena would allow development of therapies to improve antihormone response and compromise resistance. This in vitro investigation in MCF-7 breast cancer cells examines whether epidermal growth factor receptor (EGFR) signaling limits antiproliferative and proapoptotic activity of antihormones and ultimately supports development of resistance. It addresses whether the anti-EGFR agent gefitinib (ZD1839/Iressa; TKI: 1 mum) combined with the antihormones 4-hydroxytamoxifen (TAM: 0.1 mum) or fulvestrant (Faslodex; 0.1 mum) enhances growth inhibition and prevents resistance. TAM significantly suppressed MCF-7 growth over wk 2-5, reducing proliferation detected by immunocytochemistry and fluorescence-activated cell sorter cell cycle analysis. A modest apoptotic increase was observed by fluorescence-activated cell sorter and fluorescence microscopy, with incomplete bcl-2 suppression. EGFR induction occurred during TAM response, as measured by immunocytochemistry and Western blotting, with EGFR-positive, highly proliferative resistant growth subsequently emerging. Although TKI alone was ineffective on growth, TAM plus TKI cotreatment exhibited superior antigrowth activity vs. TAM, with no viable cells by wk 12. Cotreatment was more effective in inhibiting proliferation, promoting apoptosis, and eliminating bcl-2. Cotreatment blocked EGFR induction, markedly depleted ERK1/2 MAPK and protein kinase B phosphorylation, and prevented emergence of EGFR-positive resistance. Faslodex plus TKI cotreatment was also a superior antitumor strategy. Thus, increased EGFR evolves during treatment with antihormones, limiting their efficacy and promoting resistance. Gefitinib addition to antihormonal therapy could prove more effective in treating estrogen receptor-positive breast cancer and may combat development of resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Hormonal / pharmacology*
  • Apoptosis / drug effects
  • Breast Neoplasms / pathology*
  • Breast Neoplasms / physiopathology*
  • Cell Division / drug effects
  • Cell Line, Tumor
  • Drug Combinations
  • Drug Resistance / drug effects
  • Drug Synergism
  • Epidermal Growth Factor / antagonists & inhibitors*
  • ErbB Receptors / metabolism
  • ErbB Receptors / physiology
  • Estradiol / analogs & derivatives*
  • Estradiol / pharmacology*
  • Estrogen Antagonists / pharmacology*
  • Female
  • Fulvestrant
  • Gefitinib
  • Humans
  • Mitogen-Activated Protein Kinases / metabolism
  • Phosphorylation / drug effects
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • Quinazolines / pharmacology*
  • Signal Transduction / drug effects
  • Tamoxifen / analogs & derivatives*
  • Tamoxifen / pharmacology*


  • Antineoplastic Agents, Hormonal
  • Drug Combinations
  • Estrogen Antagonists
  • Proto-Oncogene Proteins
  • Quinazolines
  • Tamoxifen
  • afimoxifene
  • Fulvestrant
  • Estradiol
  • Epidermal Growth Factor
  • ErbB Receptors
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinases
  • Gefitinib