Enzalutamide Overcomes Dihydrotestosterone-Induced Chemoresistance in Triple- Negative Breast Cancer Cells via Apoptosis.

BACKGROUND: Triple-negative breast cancer is challenging to treat due to its heterogeneity and lack of therapeutic targets. Hence, systemic chemotherapy is still the mainstay in TNBC treatment. Unfortunately, patients commonly develop chemoresistance. Androgen signalling through its receptor is an essential player in breast cancer, where it has been shown to confer chemoresistance to TNBC cells. OBJECTIVE: The objective of the study was to elucidate the mechanistic effects of enzalutamide in the chemoresponse of TNBC cells to doxorubicin through the apoptosis pathway. METHODS: MDA-MB-231 and MDA-MB-453 cells were used as model systems of TNBC. Cell viability and apoptosis were investigated upon treatment of cells with doxorubicin in the presence of dihydrotestosterone (DHT) and/or enzalutamide. Caspase 3/7 activity and TUNEL assays were performed to assess the induction of apoptosis. The expression of apoptosis-regulatory genes was assayed by qPCR for the detection of expression changes. RESULTS: Enzalutamide decreased the viability of MDA-MB-231 and MDA-MB- 453 cells and reduced DHT-induced chemoresistance of both cell lines. It also increased the chemosensitivity towards doxorubicin in MDA-MB-231 cells. Increasing DNA degradation and caspase 3/7 activity were concomitant with these outcomes. Moreover, enzalutamide downregulated the expression of the anti-apoptosis genes, mcl1 and bcl2, in MDA-MB-231 cells, while increasing the expression of the pro-apoptotic gene bid. On the other hand, DHT upregulated the expression of the anti-apoptosis genes, mcl1 and bcl2, in both cell lines. CONCLUSION: DHT increased the expression of the anti-apoptosis genes mcl1 and bcl2 in the TNBC cells, presumably leading to cell survival via the prevention of doxorubicin-induced apoptosis. On the other hand, enzalutamide may sensitize the cells to doxorubicin through downregulation of the bid/bcl2/mcl1 axis that normally activates the executive caspases, caspase 3/7. The activities of the latter enzymes were apparent in DNA degradation at the late stages of apoptosis.

The Association of RGS2 and Slug in the Androgen-induced Acquisition of Mesenchymal Features of Breast MDA-MB-453 Cancer Cells.

BACKGROUND: Epithelial-mesenchymal transition (EMT) of tumor cells is a prerequisite to cancer cell invasion and metastasis. This process involves a network of molecular alterations. Androgen receptor (AR) plays an important role in the biology of breast cancers, particularly those dependent on AR expression like luminal AR (LAR) breast cancer subtype. We have recently reported that the AR agonist, dihydrotestosterone (DHT), induces a mesenchymal transition of MDA-MB-453 cells, concomitant with transcriptional up-regulation of Slug and regulator of G protein signaling 2 (RGS2). OBJECTIVE: The role of Slug and RGS2 in mediating the DHT-induced effects in these cells was investigated. METHODS: MDA-MB-453 cells were used as a model system of LAR breast cancer. Immunofluorescence was used to examine cell morphology and protein localization. Protein expression was analyzed by immunoblotting. Protein localization was confirmed by cell fractionation followed by immunoblotting. Protein-protein interaction was confirmed by co-immunoprecipitation followed by immunoblotting. Transwell membranes were used to assess cell migration. Transfection of cells with siRNA molecules that target Slug and RGS2 mRNA was utilized to delineate the modes of action of these two molecules. RESULTS: Treatment of MDA-MB-453 cells with DHT induced the expression of both proteins. In addition, AR-Slug, AR-RGS2, and Slug-RGS2 interactions were observed shortly after AR activation. Knocking down Slug abrogated the basal, but not the DHT-induced, cell migration and blocked DHT-induced mesenchymal transition. On the other hand, RGS2 knocked-down cells had an increased level of Slug protein and assumed mesenchymal cell morphology with induced migration, and the addition of DHT further elongated cell morphology and stimulated their migration. Inhibition of AR or ß-catenin reverted the RGS2 knocked-down cells to the epithelial phenotype, but only inhibition of AR blocked their DHT-induced migration. CONCLUSIONS: These results suggest the involvement of RGS2 and Slug in a complex molecular network regulating the DHT-induced mesenchymal features in MDA-MB-453 cells. The study may offer a better understanding of the biological role of AR in breast cancer toward devising AR-based therapeutic strategies.

Involvement of ß-catenin in Androgen-induced Mesenchymal Transition of Breast MDA-MB-453 Cancer Cells.

Purpose The cellular and molecular dynamics of DHT-induced EMT in MDA-MB-453 cells were investigated.Methods:PCR arrays were used to examine the expression of EMT-regulatory genes. Immunoblotting was used to detect protein levels and confirm protein-protein interaction following immunoprecipitation. Immunofluorescence was used to observe rearrangement of the actin cytoskeleton and cell morphology. Cell migration was assessed by transwell assayResults: Change of cell morphology was concomitant with increased cell migration after treating cells with DHT. Exposure of cells to DHT for one hour was sufficient to induce changes in cell morphology and actin cytoskeleton after 72 hours indicating altered gene expression. A long-term lasting nuclear translocation of AR was observed after a short exposure of cells to DHT. Investigating the expression of 84 EMT-related genes revealed down-expression of ß-catenin, N-cadherin, and TCF-4 and increased expression of Slug, all of which were confirmed at the protein level. Yet, not only early interaction of AR and ß-catenin was observed following AR activation, inhibition of ß-catenin blocked DHT-induced mesenchymal transition and migration. Wnt signaling was found to be partially important in DHT-induced morphological alteration. The mesenchymal transition of cells could be induced by treating cells with an inhibitor of glycogen synthase kinase-3ß, an enzyme that inhibits ß-catenin; this morphological transition could be reversed by antagonizing AR suggesting that AR functions downstream of ß-catenin.Conclusions: These results suggest that MDA-MB-453 cells undergo partial EMT induced by DHT, ß-catenin is critical for this phenotypic change, and AR probably reciprocally mediates the mesenchymal transition of these cells upon activation of GSK-3 ß.

Androgen downregulates desmocollin-2 in association with induction of mesenchymal transition of breast MDA-MB-453 cancer cells.

Desmosomes are cellular structures that are critical in cell-cell adhesion and in maintaining tissue architecture. Changes in the expression of desmocollin-2 (DSC2) have been noted during tumor progression into an invasive phenotype and as cells undergo epithelial-mesenchymal transition. We have previously reported that breast MDA-MB-453 cancer cells, a luminal androgen receptor (AR) model of triple-negative breast cancer, acquire mesenchymal features when treated with the AR agonist, dihydrotestosterone (DHT). We have therefore investigated androgen regulation of the expression and cellular localization of DSC2 in MDA-MB-453 cells. Treatment of the cells with DHT resulted in a dose-dependent reduction in DSC2 protein levels and dispersion of its membrane localization concomitant with AR- and ß-catenin-mediated mesenchymal transition of cells. A significant correlation was revealed between decreased expression of AR and increased expression of DSC2 in patient samples. In addition, whereas lower expression of AR was associated with a reduced overall and recurrence-free survival of breast cancer patients, higher expression of DSC2 was found in invasive breast tumors than in normal breast cells and was correlated with lower patient survival. Upon knocking down DSC2, the cells became elongated, mesenchymal-like, and slightly, but insignificantly, more migratory. The addition of DHT further stimulated cell elongation and migration. DSC2 siRNA-transfected cells reverted to a normal epithelial morphology upon inhibition of ß-catenin. These results highlight the role of DSC2 in maintaining the epithelial morphology of MDA-MB-453 cells and the negative regulation of the desmosomal protein by DHT during stimulation of the androgen-induced, ß-catenin-mediated mesenchymal transition of the cells.