title: Biochemical studies of apoptosis induced by tamoxifen in estrogen receptor positive and negative breast cancer cell lines.
abstract: OBJECTIVE
  Tamoxifen has been reported to show an efficacy in the treatment of breast cancer. Apoptosis could be a major mechanism of its antitumor effect. Therefore, this study has been designed to investigate the biochemical mechanisms of tamoxifen-induced apoptosis in both ER(+) MCF-7 and ER(-) MDA-MB468 breast cancer cell lines.
  
  
  METHODS
  Trypan blue dye exclusion test, Annexin V-Fluorescein/PI flow cytometry, MTT assay and Hoechst 33258 staining were used to detect cytotoxicity and apoptosis. The activation of caspase-3 was assayed by colorimetric assay kit. Bcl-2 and Bax proteins were estimated by western immunoblotting method.
  
  
  RESULTS
  Tamoxifen induced apoptosis in both cell lines (chi-square test, p < 0.05). Unlike the MCF-7 cells, which responded to the low concentration (1 microM), the treated MDA-MB468 cells have mainly been affected at a higher dose (20 microM) at which a significant increase was also obtained in the caspase-3 activity (chi-square test, p < 0.05). Interestingly, tamoxifen at doses higher than 2.5 microM increased cell proliferation in the MCF-7 cells. The levels of Bcl-2 and Bax remained unchanged.
  
  
  CONCLUSIONS
  Since tamoxifen has induced apoptosis in both cell lines by different mechanisms, it might be concluded that there exists ER(+) and ER(-) pathways for the induction of apoptosis.
authors.affiliation: Clinical Biochemistry Department, School of Medical Science, Tarbiat Modarres University, Tehran, Iran.
authors.forename: Siamak
authors.initials: S
authors.lastname: Salami
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Karami-Tehrani
mesh_terms: D017304:Annexin A5; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D006690:Bisbenzimidazole; D001943:Breast Neoplasms; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D005260:Female; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D006801:Humans; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011960:Receptors, Estrogen / Q000096:biosynthesis*; D013629:Tamoxifen / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein
chemical_list: D017304:Annexin A5; D018931:Antineoplastic Agents, Hormonal; C494826:BAX protein, human; D061945:Caspase Inhibitors; D005456:Fluorescent Dyes; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011960:Receptors, Estrogen; D051028:bcl-2-Associated X Protein; D013629:Tamoxifen; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D006690:Bisbenzimidazole