title: cDNA transfection followed by the isolation of a MCF-7 breast cell line resistant to tamoxifen in vitro and in vivo.
abstract: A tamoxifen resistant cell line (clone 9) has been isolated from the tamoxifen sensitive, hormone responsive MCF-7 breast carcinoma cell line after transfection with mixed cDNA libraries, followed by tamoxifen selection in the presence of oestrogens. Transfection was confirmed by Southern analysis with vector probes. Clone 9 in several-fold more resistant to tamoxifen and other anti-oestrogens than wild type cells when cultured either as a monolayer or as colonies in soft agar but retains oestrogen receptors. Clone 9 was less responsive to 17-beta-oestradiol than were wild type MCF-7. In addition to showing in vitro tamoxifen resistance, clone 9 was also tamoxifen resistant in vivo when xenografted into the nude mouse. Culture medium conditioned by clone 9 cells stimulated quiescent cells of the same clone as well as wild type cells, whereas medium conditioned by wild type MCF-7 was inhibitory to both, suggesting that clone 9 may be secreting an autocrine growth factor. Clone 9 provides a novel model for further investigation of the mechanism of anti-oestrogen resistance that occurs without loss of oestrogen receptors. Preliminary results suggest that an autocrine growth stimulatory mechanism may be one pathway of such resistance.
authors.affiliation: Molecular Oncology Laboratory, Imperial Cancer Research Fund, University of Oxford, John Radcliffe Hospital, UK.
authors.forename: M
authors.initials: M
authors.lastname: Toi
authors.forename: A L
authors.initials: AL
authors.lastname: Harris
authors.forename: R
authors.initials: R
authors.lastname: Bicknell
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics*; D003001:Cloning, Molecular; D017077:Culture Media, Conditioned; D018076:DNA, Complementary; D004273:DNA, Neoplasm / Q000235:genetics*; D004274:DNA, Recombinant; D004351:Drug Resistance / Q000235:genetics*; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism; D005260:Female; D006133:Growth Substances / Q000502:physiology; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D053284:Polyunsaturated Alkamides; D011960:Receptors, Estrogen / Q000378:metabolism; D013629:Tamoxifen / Q000031:analogs & derivatives / Q000494:pharmacology* / Q000627:therapeutic use; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D014410:Tumor Stem Cell Assay
chemical_list: D017077:Culture Media, Conditioned; D018076:DNA, Complementary; D004273:DNA, Neoplasm; D004274:DNA, Recombinant; D004965:Estrogen Antagonists; D004967:Estrogens; D006133:Growth Substances; D053284:Polyunsaturated Alkamides; D011960:Receptors, Estrogen; D013629:Tamoxifen; C016601:afimoxifene; D004958:Estradiol; C051781:ICI 164384