Modulation of tamoxifen sensitivity by antisense Bcl-2 and trastuzumab in breast carcinoma cells.
BACKGROUND
Because the overexpression of HER-2 and Bcl-2 is associated with resistance to tamoxifen (TAM), the authors examined the effect of antisense (AS) Bcl-2 on sensitivity to TAM compared with the effect of trastuzumab on sensitivity to TAM in breast carcinoma cell lines.


METHODS
Drug sensitivity was assessed in vitro using a [3-4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay with the breast carcinoma cell lines ZR-75-1, MDA-MB-453, and BT-474. AS Bcl-2 18-mer phosphorothioate oligonucleotide was applied. Apoptotic cell death was assessed with the terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick-end labeling method, and gene expression was evaluated with Western blot analysis.


RESULTS
The expression of Bcl-2 was identified in ZR-75-1 and BT-474 cells and, to a lesser extent, in MDA-MB-453 cells. Overexpression of HER-2 was identified in BT-474 cells, and moderate expression was identified in MDA-MB-453 and ZR-75-1 cells. Combination treatment with trastuzumab or AS Bcl-2 enhanced TAM sensitivity in ZR-75-1 cells, which showed 50% inhibitory concentration (IC50) values of 0.9 microM (7.2-fold increase) and 0.5 microM (13.0-fold), respectively. Combination treatment with trastuzumab or AS Bcl-2 slightly enhanced TAM sensitivity of BT-474 cells, with IC50 values of 3.0 microM (1.3-fold) and 1.5 microM (2.6-fold), respectively. The sensitivity of MDA-MB-453 cells to TAM was not enhanced by combination with trastuzumab or AS Bcl-2. Modulation of TAM sensitivity by AS Bcl-2 was superior to modulation by trastuzumab in HER-2-expressing and Bcl-2-expressing breast carcinoma cells. Enhanced sensitivity in combination with AS Bcl-2 was associated with down-regulation of Bcl-2 and pAkt, which was correlated with the induction of Bax and caspase-3, leading to apoptosis.


CONCLUSIONS
AS Bcl-2 appeared to be superior to trastuzumab with respect to regulating the signal-transduction pathways involved in breast carcinoma cells.
Kim
Ryungsa
R
International Radiation Information Center, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan. rkim@hiroshima-u.ac.jp
Tanabe
Kazuaki
K
Emi
Manabu
M
Uchida
Yoko
Y
Toge
Tetsuya
T
D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D016375:Antisense Elements (Genetics) / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D002277:Carcinoma / Q000188:drug therapy* / Q000473:pathology; D053148:Caspase 3; D020169:Caspases / Q000187:drug effects; D045744:Cell Line, Tumor; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004792:Enzyme Precursors / Q000187:drug effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D020287:In Situ Nick-End Labeling; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000627:therapeutic use*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000627:therapeutic use*; D015398:Signal Transduction / Q000187:drug effects; D013629:Tamoxifen / Q000627:therapeutic use*; D000068878:Trastuzumab; D051028:bcl-2-Associated X Protein
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D018931:Antineoplastic Agents, Hormonal; D016375:Antisense Elements (Genetics); D053148:Caspase 3; D020169:Caspases; D004792:Enzyme Precursors; D019253:Proto-Oncogene Proteins c-bcl-2; D018719:Erb-b2 Receptor Tyrosine Kinases; D013629:Tamoxifen; D000068878:Trastuzumab; D051028:bcl-2-Associated X Protein; C494826:BAX protein, human; C505407:CASP3 protein, human