Cell Kinetic Study of Tamoxifen Treated MCF-7 and MDA-MB 468 Breast Cancer Cell Lines

Apoptosis could be a major mechanism of antitumor effect of tamoxifen. Therefore this study is designed to characterize the kinetic behavior of tamoxifen-induced apoptosis in the estrogen receptor positive (ER+) and negative (ER-) cell lines, MCF-7 and MDA-MB-468. Frequency of cell death was examined by trypan blue and acridine orange staining. Annexin V-Fluorescein/PI was used in flow cytometry for distinguishing the dividing, apoptotic and necrotic cells and Hoechst 33258 staining was also applied to detect apoptotic changes in the nuclear morphology. The results showed that tamoxifen was able to induce apoptosis in both cell lines (χ2 test, P<0.05). In contrast to the MCF-7 cells, which responded to the low concentrations of tamoxifen (0.5-1μM), the treated MDA-MB-468 cells were affected at 20 μM (χ2 test, P<0.05). However, the kinetic data revealed that tamoxifen, at higher doses stimulates the ER+ cell proliferation. This is the first study showing these opposite effects in the kinetics of tamoxifen treated cells. Therefore it may serve as a guideline for the precautionary evaluation of suggested high doses of tamoxifen