Abstract P1-07-07: Targeting reversal of epithelial-mesenchymal transition through FOXM1 inhibition in breast cancer cells
Authors: Arora R , Tan M , Yates CC , Dean-Colomb W 
Published: August 2014

Purpose: Triple-negative breast cancer (TNBC), representing up to 20% of all breast cancer cases, is a highly diverse group of cancer that is associated with an aggressive phenotype, with affected patients having a poorer prognosis. Its treatment has been challenging due to its heterogeneity and the absence of well-defined molecular targets.

Epithelial-to-mesenchymal transition (EMT) is one of the hallmarks of aggressive breast cancers and is associated with increased metastatic potential. TNBCs have been shown to exhibit elevated EMT. Thus, reversal of EMT has been identified as a viable target in the treatment of aggressive breast cancers.

FOXM1 is an oncogenic transcription factor of the Forkhead family and it has a well-defined role in cell proliferation and cell-cycle progression. FOXM1 has been reported to be over-expressed in breast cancer. In prostate cancer, FOXM1 overexpression has been linked to increase EMT. We have previously shown that targeting NF-kB with panepoxydone (PP), an NF-kB inhibitor isolated from Lentinus crinitus (an edible mushroom), has significant antitumor activity against breast cancer cells with a resultant decrease in cell migration and invasion and induction of apoptosis. We have further identified that the FOXM1 promoter has a binding site for NF-kB. Thus, in this study, we investigated whether PP-induced inhibition of breast cancer cell growth could be attributed to FoxM1 activity and EMT reversal.

Experimental Design: The estrogen receptor positive (MCF-7) and three different triple negative (MDA-MB-231, MDA-MB-453, and MDA-MB-468) breast cancer cell lines were selected to observe the effect of PP on FOXM1and EMT markers.

Results: In the current study, we investigated whether panepoxydone- induced inhibition of breast cancer cell growth could be attributed to FoxM1activity and EMT reversal. Breast cancer cells were treated with increasing concentrations of PP and proteins collected after 24 hrs. Panepoxydone treatment significantly reduced FOXM1 expression in MCF-7 and MDA-MB-231 (1.7 and 2.4-fold, respectively, p &lt; 0.05) but not in MDAMB-453 and MDAMB-468 cells when analyzed through western blot analysis. Furthermore, we showed that treatment with PP resulted in alteration of EMT-associated proteins with a significant increase in E-cadherin in all the cell lines (ranging from 1.8 to 4.2-fold, p &lt; 0.05) and a decrease in mesenchymal markers vimentin and zeb1 in the MDA-MB-231 cells (2.5 and 2-fold respectively, p &lt; 0.05).

To further elucidate the relationship between FOXM1 on EMT reversal, we then silenced FOXM1 in MDA-MB-231 cells and evaluated its effect on the EMT-associated markers. Again we noted upregulation of E cadherin (3.5-fold, p&lt; 0.01) and down-regulation of vimentin (4.5-fold, p &lt;0.01) in FOXM1, which was very similar to what was observed in the PP-treated MDA-MB-231 cells.

Conclusion: These studies show, for the first time, the role of FOXM1 in EMT reversal in breast cancer cells. Furthermore, it shows that use of an NF-kB inhibitor, such as panepoxydone, may be helpful in elucidating the relationship between these two transcriptional factors, in the reversal of the EMT phenotype in aggressive breast cancer cells.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-07-07.