Molecular mechanism of drug induced apoptosis and chemoresistance in estrogen receptor alpha +/- breast cancer cell lines: mcf-7 and mda-mb-231

Official URL: http://192.168.1.20/record=b1427169 (Table of Contents)

It was recently shown that inhibition or downregulation of Bcl-2 represents a new therapeutic approach to by-pass chemoresistance mechanism in cancer cells. Therefore, we explored the potential of this approach in breast cancer cells; MCF-7 (drug-sensitive; p53 wild type) and MDA-MB-231 (drug-insensitive; p53 mutant). Cisplatin and paclitaxel induced apoptosis in a dose-dependent manner in both cell lines. Furthermore, silencing of Bcl-2 remarkably increased cisplatin and paclitaxel induced apoptosis. Dose dependent induction of apoptosis by cisplatin and paclitaxel was enhanced by the pre-treatment of these cells with HA14-1, a Bcl-2 inhibitor. Although the effect of cisplatin on cell death was significant in MCF-7 and MDA-MB- 231, paclitaxel was less potent only in MDA-MB-231 cells. To further understand the distinct role of drugs in breast cancer cells which were pre-treated with HA14-1, changes in mitochondrial membrane potential, caspase activation, and Bcl-2 family protein levels, generation of reactive oxygen species and lipid peroxidation were studied. The apoptotic effect of cisplatin with or without HA14- 1 pre-treatment was shown to be caspase-dependent in both cell lines. While proapoptotic Bcl-2 proteins (Bax, Puma, Bad) were found to be up-regulated, Bcl-2 and Bcl-xL were down-regulated when cells were pre-treated with HA14-1 followed by cisplatin or paclitaxel. MCF-7 and MDA-MB-231 cells overexpressing Bcl-2 displayed different responses upon drug-treatment. Although cisplatin could still induce apoptosis in Bcl-2 overexpressing MCF-7 cells by promoting pro-apoptotic Bcl-2 family members, Bcl-2 overexpression abrogated paclitaxel induced apoptosis in MCF-7 and MDA-MB-231 breast cancer cells, respectively. In conclusion, our findings suggest two important implications for understanding cisplatin and paclitaxel induced apoptosis mechanism and the potential role of Bcl-2 in this apoptotic pathway. First, the potentiating effect of Bcl-2 inhibitor (HA14-1) is drug and cell type specific and may not only depend on the inhibition of Bcl-2. Importantly, alteration of other pro-apoptotic or anti-apoptotic Bcl-2 family members may dictate the apoptotic response when HA14-1 is combined with chemotherapeutic drugs. Second, cisplatin activated a p53- regulated pro-apoptotic pathway to overcome Bcl-2 mediated resistance. These insights may be useful for the development of novel treatments for cancer cells overexpressing anti-apoptotic Bcl-2 proteins.