Effects of Mifepristone and Tamoxifen on Calcium Modulation in DU-145 Prostate Cancer Cells

Abstract

Mifepristone (MIF) and Tamoxifen (TAM) have been used in the treatment of prostate cancer and breast cancer for more than a decade. MIF can induce apoptosis in both AR-positive and -negative prostate cancer cells. Because of its pleiotropic ligand-receptor properties, TAM exerts cytotoxic activity in estrogen (ER)-positive and various ER-negative cancer cells. However, the molecular mechanisms of these two substances are not yet clear. In the present work, we report that the cytotoxic effects of MIF and TAM are due to the modulation of intracellular Ca 2+ level in DU-145, androgen-insensitive cells. When the cells were treated with micromolar concentrations of either MIF or TAM, the growth and viability were significantly decreased in a dose-and time-dependent manner. The apoptosis induced by MIF or TAM was further proved and analyzed by confocal laser scanning microscopy (CLSM) and fluorescence-activated cell sorting (FACS). In the cells cultivated in a normal 1.5 mM Ca 2+ medium, both MIF and TAM also induced an increase of the intracellular Ca 2+ level in a dose-dependent fashion. Since a change in calcium level could not be found in cells of the Ca 2+ -free medium, the increase of intracellular Ca 2+ level might be due to an increase in extracellular calcium uptake. Our results show that the apoptotic effect was more prominent in TAM treatment compared to MIF treatment in DU-145 cells. The above findings might be due to the difference in the uppermost pathways of apoptosis induced by either MIF or TAM. When we checked the level of procaspase-8 activation, TAM showed minor level of activation, as opposed to MIF, which exerted strong activation. In both treatments, the levels of anti-apoptotic protein Bcl-2 decreased, and pro-apoptotic protein Bax level increased more than 2-fold. The activation of caspase-3, a key protease enzyme in the downstream pathway of apoptosis, was much higher in the cells treated with TAM, compared to the MIF treatment. The overall apoptotic activity shown in the present work was closely related to intracellular Ca 2+ concentration levels. Therefore, the cytotoxic activity induced by MIF and TAM might have been due to intracellular calcium modulation.