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