title: Estrogen Receptor β as a Therapeutic Target in Breast Cancer Stem Cells.
abstract: Breast cancer cells with tumor-initiating capabilities (BSCs) are considered to maintain tumor growth and govern metastasis. Hence, targeting BSCs will be crucial to achieve successful treatment of breast cancer.
  
  
  
  We characterized mammospheres derived from more than 40 cancer patients and two breast cancer cell lines for the expression of estrogen receptors (ERs) and stem cell markers. Mammosphere formation and proliferation assays were performed on cells from 19 cancer patients and five healthy individuals after incubation with ER-subtype selective ligands. Transcriptional analysis was performed to identify pathways activated in ERβ-stimulated mammospheres and verified using in vitro experiments. Xenograft models (n = 4 or 5 per group) were used to study the role of ERs during tumorigenesis.
  
  
  
  We identified an absence of ERα but upregulation of ERβ in BSCs associated with phenotypic stem cell markers and responsible for the proliferative role of estrogens. Knockdown of ERβ caused a reduction of mammosphere formation in cell lines and in patient-derived cancer cells (40.7%, 26.8%, and 39.1%, respectively). Gene set enrichment analysis identified glycolysis-related pathways (false discovery rate < 0.001) upregulated in ERβ-activated mammospheres. We observed that tamoxifen or fulvestrant alone was insufficient to block proliferation of patient-derived BSCs while this could be accomplished by a selective inhibitor of ERβ (PHTPP; 53.7% in luminal and 45.5% in triple-negative breast cancers). Furthermore, PHTPP reduced tumor initiation in two patient-derived xenografts (75.9% and 59.1% reduction in tumor volume, respectively) and potentiated tamoxifen-mediated inhibition of tumor growth in MCF7 xenografts.
  
  
  
  We identify ERβ as a mediator of estrogen action in BSCs and a novel target for endocrine therapy.
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden.|Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Ran
authors.initials: R
authors.lastname: Ma
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden.|Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Govindasamy-Muralidharan
authors.initials: GM
authors.lastname: Karthik
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden.|Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.
authors.forename: John
authors.initials: J
authors.lastname: Lövrot
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden.|Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.|Department of Pathology and Cytology, Karolinska University Laboratory, Stockholm, Sweden.
authors.forename: Felix
authors.initials: F
authors.lastname: Haglund
authors.affiliation: Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.|Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden.
authors.forename: Gustaf
authors.initials: G
authors.lastname: Rosin
authors.affiliation: Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, Houston, TX, USA.
authors.forename: Anne
authors.initials: A
authors.lastname: Katchy
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden.|Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden.|Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Lisa
authors.initials: L
authors.lastname: Viberg
authors.affiliation: Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.|Department of Breast and Endocrine Surgery, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Frisell
authors.affiliation: Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden.|Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, Houston, TX, USA.|Science for Life Laboratory, Department of Proteomics, KTH, Royal Institute of Technology, Stockholm, Sweden.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Williams
authors.affiliation: Department of Medical and Health Sciences, Department of Medicine and Health, Linköping University, Linköping, Sweden.
authors.forename: Stig
authors.initials: S
authors.lastname: Linder
authors.affiliation: Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.|Department of Breast and Endocrine Surgery, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Irma
authors.initials: I
authors.lastname: Fredriksson
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden.|Cancer Center Karolinska, Karolinska Institutet, Stockholm, Sweden.|Department of Pathology and Cytology, Karolinska University Laboratory, Stockholm, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Hartman
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002277:Carcinoma / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D047629:Estrogen Receptor beta / Q000037:antagonists & inhibitors* / Q000235:genetics*; D005260:Female; D000077267:Fulvestrant; D055785:Gene Knockdown Techniques; D006019:Glycolysis; D006801:Humans; D061986:MCF-7 Cells; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D014411:Neoplastic Stem Cells / Q000187:drug effects; D010641:Phenotype; D011720:Pyrazoles / Q000008:administration & dosage / Q000494:pharmacology*; D011743:Pyrimidines / Q000008:administration & dosage / Q000494:pharmacology*; D018874:Spheroids, Cellular / Q000187:drug effects / Q000378:metabolism*; D013629:Tamoxifen / Q000008:administration & dosage / Q000494:pharmacology; D064726:Triple Negative Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D047368:Tumor Burden; D015854:Up-Regulation
chemical_list: C556295:4-(2-phenyl-5,7-bis(trifluoromethyl)pyrazolo(1,5-a)pyrimidin-3-yl)phenol; D047629:Estrogen Receptor beta; D011720:Pyrazoles; D011743:Pyrimidines; D013629:Tamoxifen; D000077267:Fulvestrant; D004958:Estradiol