Synergistic apoptosis of MCF-7 breast cancer cells by 2-methoxyestradiol and bis(ethyl)norspermine

2-Methoxyestradiol (2ME) is an estradiol metabolite with anti-tumor and anti-angiogenic properties. We studied the effect of 2ME on apoptosis of MCF-7 breast cancer cells and explored a combination therapy using 2ME and a polyamine analogue, bis(ethyl)norspermine (BE-3-3-3). Determination of viable cells on day 4 of treatment with 2ME/BE-3-3-3 combinations showed synergistic effects by Chou–Talalay analysis. APO-BRDU analysis showed that there was only 1.5 ± 0.5% apoptosis at 200 nM 2ME and 3.7 ± 1.7% in the presence of 2.5 μM BE-3-3-3. Combination of 200 nM 2ME and 2.5 μM BE-3-3-3 resulted in 52.2 ± 2.6% apoptosis. Up to 90% of the cells underwent apoptosis in the presence of 1000 nM 2ME and 2.5 μM BE-3-3-3. Combination treatments resulted in total disruption of microtubules and depletion of putrescine, spermidine and spermine. In addition, phosphorylation of Akt and nuclear localization of cyclin D1 were altered by 2ME/BE-3-3-3 combination. Our results suggest an important strategy to induce apoptosis of breast cancer cells, with potential applications in therapy.