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Modulation of tamoxifen sensitivity by antisense Bcl-2 and trastuzumab in breast carcinoma cells
Article first published online: 13 APR 2005
Copyright © 2005 American Cancer Society
Volume 103, Issue 10, pages 2199–2207, 15 May 2005
How to Cite
Kim, R., Tanabe, K., Emi, M., Uchida, Y. and Toge, T. (2005), Modulation of tamoxifen sensitivity by antisense Bcl-2 and trastuzumab in breast carcinoma cells. Cancer, 103: 2199–2207. doi: 10.1002/cncr.21029
- Issue published online: 28 APR 2005
- Article first published online: 13 APR 2005
- Manuscript Accepted: 18 JAN 2005
- Manuscript Revised: 10 JAN 2005
- Manuscript Received: 30 AUG 2004
- breast carcinoma
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.
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.
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 μM (7.2-fold increase) and 0.5 μM (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 μM (1.3-fold) and 1.5 μM (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.
AS Bcl-2 appeared to be superior to trastuzumab with respect to regulating the signal-transduction pathways involved in breast carcinoma cells. Cancer 2005. © 2005 American Cancer Society.