title: Tamoxifen long-term treatment in vitro alters the apoptotic response of MCF-7 breast cancer cells.
abstract: In this study, we examined alterations in the apoptotic response of tamoxifen (TAM)-resistant breast cancer cells. We used an in vitro selection approach for TAM resistance by means of long-term culture of MCF-7 breast cancer cells with increasing concentrations of TAM. The apoptotic response to TAM was determined by means of ELISA measurement of apoptotic DNA-histone complexes in cytoplasm and by Annexin-V staining. MCF-7(LT) cells isolated after 5 months of long-term treatment with TAM exhibited a significantly reduced apoptotic response to this drug, even if administered in high concentrations up to 20 microM. This reduced apoptotic response was also observed after treatment with the topoisomerase II inhibitor etoposide, a pro-apoptotic antineoplastic drug. Microarray experiments comparing the transcriptome of MCF-7(LT) and wild-type cells revealed both the down-regulated expression of several genes coding for pro-apoptotic proteins and the up-regulation of genes coding for apoptosis inhibitors. Further experiments to determine expression changes of the receptor tyrosine kinases HER2 and epidermal growth factor receptor did not reveal any alterations in MCF-7(LT) if compared to wild-type cells. Our findings suggest that long-term treatment with TAM in vitro does not necessarily change the expression of receptor tyrosine kinases, but can modulate the expression of apoptotic key genes impairing the apoptotic response of MCF-7 breast cancer cells.
authors.affiliation: Department of Obstetrics and Gynecology, University of Regensburg, Caritas Hospital St. Josef, Regensburg, Germany. treeck@wmail.com
authors.forename: Oliver
authors.initials: O
authors.lastname: Treeck
authors.forename: Rong
authors.initials: R
authors.lastname: Zhou
authors.forename: Klaus
authors.initials: K
authors.lastname: Diedrich
authors.forename: Olaf
authors.initials: O
authors.lastname: Ortmann
mesh_terms: D017304:Annexin A5 / Q000737:chemistry / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000473:pathology*; D004334:Drug Administration Schedule; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics; D004354:Drug Screening Assays, Antitumor; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D047629:Estrogen Receptor beta / Q000235:genetics / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology; D005858:Germany; D006657:Histones / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006824:Hybridization, Genetic; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D012313:RNA / Q000302:isolation & purification; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D013194:Staining and Labeling / Q000379:methods; D013629:Tamoxifen / Q000008:administration & dosage* / Q000493:pharmacokinetics; D013997:Time Factors; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000235:genetics
chemical_list: D017304:Annexin A5; D066246:ErbB Receptors; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005047:Etoposide; D006657:Histones; D012313:RNA; D018719:Erb-b2 Receptor Tyrosine Kinases; D013629:Tamoxifen