title: A molecular model for the mechanism of acquired tamoxifen resistance in breast cancer.
abstract: OBJECTIVE
  Oestrogen (E2)-stimulated growth re-emerges after a c-Src inhibitor blocking E2-induced apoptosis. A resulting cell line, MCF-7:PF, is selected with features of functional oestrogen receptor (ER) and over-expression of insulin-like growth factor-1 receptor beta (IGF-1Rβ). We addressed the question of whether the selective ER modulator (SERM), 4-hydroxytamoxifen (4-OHT) or other SERMs could target ER to prevent E2-stimulated growth in MCF-7:PF cells.
  
  
  METHODS
  Protein levels of receptors and signalling pathways were examined by immunoblotting. Expression of mRNA was measured through real-time RT-PCR. Recruitment of ER or nuclear receptor coactivator 3 (SRC3) to the promoter of ER-target gene was detected by chromatin-immunoprecipitation (ChIP).
  
  
  RESULTS
  4-OHT and other SERMs stimulated cell growth in an ER-dependent manner. However, unlike E2, 4-OHT suppressed classical ER-target genes as does the pure antioestrogen ICI 182,780 (ICI). ChIP assay indicated that 4-OHT did not recruit ER or SRC3 to the promoter of ER-target gene, pS2. Paradoxically, 4-OHT reduced total IGF-1Rβ but increased phosphorylation of IGF-1Rβ. Mechanistic studies revealed that 4-OHT functioned as an agonist to enhance the non-genomic activity of ER and activate focal adhesion molecules to further increase phosphorylation of IGF-1Rβ. Disruption of membrane-associated signalling, IGF-1R and focal adhesion kinase (FAK), completely abolished 4-OHT-stimulated cell growth.
  
  
  CONCLUSIONS
  This study is the first to recapitulate a cellular model in vitro of acquired tamoxifen resistance developed in athymic mice in vivo. Importantly, it provides a rationale that membrane-associated pathways may be valuable therapeutic targets for tamoxifen resistant patients in clinic.
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington DC 20057, United States.
authors.forename: Ping
authors.initials: P
authors.lastname: Fan
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington DC 20057, United States.
authors.forename: Fadeke A
authors.initials: FA
authors.lastname: Agboke
authors.affiliation: Cancer and Cell Biology Division, The Translational Genomics Research Institute, Phoenix, AZ 85004, United States.
authors.forename: Heather E
authors.initials: HE
authors.lastname: Cunliffe
authors.affiliation: Cancer and Cell Biology Division, The Translational Genomics Research Institute, Phoenix, AZ 85004, United States.
authors.forename: Pilar
authors.initials: P
authors.lastname: Ramos
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington DC 20057, United States. Electronic address: vcj2@georgetown.edu.
authors.forename: V Craig
authors.initials: VC
authors.lastname: Jordan
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D020847:Estrogen Receptor Modulators / Q000627:therapeutic use; D004967:Estrogens / Q000737:chemistry; D005260:Female; D006801:Humans; D061986:MCF-7 Cells; D010766:Phosphorylation; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D020845:Selective Estrogen Receptor Modulators / Q000627:therapeutic use; D015398:Signal Transduction; D013629:Tamoxifen / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000627:therapeutic use
chemical_list: D020847:Estrogen Receptor Modulators; D004967:Estrogens; D011960:Receptors, Estrogen; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; C016601:afimoxifene; D017526:Receptor, IGF Type 1
keywords: Focal adhesion molecules; Insulin-like growth factor-1 receptor beta (IGF-1Rβ); Non-genomic pathway; Resistance; Selective oestrogen receptor modulator (SERM)