title: An oestrogen-dependent model of breast cancer created by transformation of normal human mammary epithelial cells.
abstract: BACKGROUND
  About 70% of breast cancers express oestrogen receptor alpha (ESR1/ERalpha) and are oestrogen-dependent for growth. In contrast with the highly proliferative nature of ERalpha-positive tumour cells, ERalpha-positive cells in normal breast tissue rarely proliferate. Because ERalpha expression is rapidly lost when normal human mammary epithelial cells (HMECs) are grown in vitro, breast cancer models derived from HMECs are ERalpha-negative. Currently only tumour cell lines are available to model ERalpha-positive disease. To create an ERalpha-positive breast cancer model, we have forced normal HMECs derived from reduction mammoplasty tissue to express ERalpha in combination with other relevant breast cancer genes.
  
  
  METHODS
  Candidate genes were selected based on breast cancer microarray data and cloned into lentiviral vectors. Primary HMECs prepared from reduction mammoplasty tissue were infected with lentiviral particles. Infected HMECs were characterised by Western blotting, immunofluorescence microscopy, microarray analysis, growth curves, karyotyping and SNP chip analysis. The tumorigenicity of the modified HMECs was tested after orthotopic injection into the inguinal mammary glands of NOD/SCID mice. Cells were marked with a fluorescent protein to allow visualisation in the fat pad. The growth of the graft was analysed by fluorescence microscopy of the mammary glands and pathological analysis of stained tissue sections. Oestrogen dependence of tumour growth was assessed by treatment with the oestrogen antagonist fulvestrant.
  
  
  RESULTS
  Microarray analysis of ERalpha-positive tumours reveals that they commonly overexpress the Polycomb-group gene BMI1. Lentiviral transduction with ERalpha, BMI1, TERT and MYC allows primary HMECs to be expanded in vitro in an oestrogen-dependent manner. Orthotopic xenografting of these cells into the mammary glands of NOD/SCID mice results in the formation of ERalpha-positive tumours that metastasise to multiple organs. The cells remain wild type for TP53, diploid and genetically stable. In vivo tumour growth and in vitro proliferation of cells explanted from tumours are dependent on oestrogen.
  
  
  CONCLUSIONS
  We have created a genetically defined model of ERalpha-positive human breast cancer based on normal HMECs that has the potential to model human oestrogen-dependent breast cancer in a mouse and enables the study of mechanisms involved in tumorigenesis and metastasis.
authors.affiliation: NCCR Molecular Oncology, Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland.
authors.forename: Stephan
authors.initials: S
authors.lastname: Duss
authors.forename: Sylvie
authors.initials: S
authors.lastname: André
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Nicoulaz
authors.forename: Maryse
authors.initials: M
authors.lastname: Fiche
authors.forename: Hervé
authors.initials: H
authors.lastname: Bonnefoi
authors.forename: Cathrin
authors.initials: C
authors.lastname: Brisken
authors.forename: Richard D
authors.initials: RD
authors.lastname: Iggo
mesh_terms: D001940:Breast / Q000166:cytology*; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology; D018929:Cell Culture Techniques; D002471:Cell Transformation, Neoplastic; D004847:Epithelial Cells / Q000166:cytology* / Q000473:pathology; D047628:Estrogen Receptor alpha / Q000235:genetics; D004967:Estrogens / Q000502:physiology*; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000473:pathology; D005822:Genetic Vectors; D006801:Humans; D007621:Karyotyping; D016086:Lentivirus / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis
chemical_list: D047628:Estrogen Receptor alpha; D004967:Estrogens