title: SRC drives growth of antiestrogen resistant breast cancer cell lines and is a marker for reduced benefit of tamoxifen treatment.
abstract: The underlying mechanisms leading to antiestrogen resistance in estrogen-receptor α (ER)-positive breast cancer is still poorly understood. The aim of this study was therefore to identify biomarkers and novel treatments for antiestrogen resistant breast cancer. We performed a kinase inhibitor screen on antiestrogen responsive T47D breast cancer cells and T47D-derived tamoxifen and fulvestrant resistant cell lines. We found that dasatinib, a broad-spectrum kinase inhibitor, inhibited growth of the antiestrogen resistant cells compared to parental T47D cells. Furthermore western blot analysis showed increased expression and phosphorylation of Src in the resistant cells and that dasatinib inhibited phosphorylation of Src and also signaling via Akt and Erk in all cell lines. Immunoprecipitation revealed Src: ER complexes only in the parental T47D cells. In fulvestrant resistant cells, Src formed complexes with the Human Epidermal growth factor Receptor (HER)1 and HER2. Neither HER receptors nor ER were co-precipitated with Src in the tamoxifen resistant cell lines. Compared to treatment with dasatinib alone, combined treatment with dasatinib and fulvestrant had a stronger inhibitory effect on tamoxifen resistant cell growth, whereas dasatinib in combination with tamoxifen had no additive inhibitory effect on fulvestrant resistant growth. When performing immunohistochemical staining on 268 primary tumors from breast cancer patients who had received tamoxifen as first line endocrine treatment, we found that membrane expression of Src in the tumor cells was significant associated with reduced disease-free and overall survival. In conclusion, Src was identified as target for treatment of antiestrogen resistant T47D breast cancer cells. For tamoxifen resistant T47D cells, combined treatment with dasatinib and fulvestrant was superior to treatment with dasatinib alone. Src located at the membrane has potential as a new biomarker for reduced benefit of tamoxifen.
authors.affiliation: Breast Cancer Group, Cell Death and Metabolism, Danish Cancer Society Research Center, Copenhagen, Denmark.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Larsen
authors.affiliation: Department of Pathology, Slagelse Hospital, Slagelse, Denmark.
authors.forename: Anne-Vibeke
authors.initials: AV
authors.lastname: Laenkholm
authors.affiliation: Statistics, Bioinformatics and Registry, Danish Cancer Society Research Center, Copenhagen, Denmark.
authors.forename: Anne Katrine
authors.initials: AK
authors.lastname: Duun-Henriksen
authors.affiliation: Department of Pathology, Odense University Hospital, Odense, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Bak
authors.affiliation: Breast Cancer Group, Cell Death and Metabolism, Danish Cancer Society Research Center, Copenhagen, Denmark.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Lykkesfeldt
authors.affiliation: Breast Cancer Group, Cell Death and Metabolism, Danish Cancer Society Research Center, Copenhagen, Denmark.
authors.forename: Tove
authors.initials: T
authors.lastname: Kirkegaard
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D014408:Biomarkers, Tumor / Q000378:metabolism*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology*; D045744:Cell Line, Tumor; D000069439:Dasatinib / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D005260:Female; D006801:Humans; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D013629:Tamoxifen / Q000627:therapeutic use*; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D014408:Biomarkers, Tumor; D020847:Estrogen Receptor Modulators; D047428:Protein Kinase Inhibitors; D013629:Tamoxifen; D019061:src-Family Kinases; D000069439:Dasatinib