Data from Androgen Receptor Supports an Anchorage-Independent, Cancer Stem Cell-like Population in Triple-Negative Breast Cancer

Preclinical and early clinical trials indicate that up to 50% of triple-negative breast cancers (TNBC) express androgen receptor (AR) and are potentially responsive to antiandrogens. However, the function of AR in TNBC and the mechanisms by which AR-targeted therapy reduces tumor burden are largely unknown. We hypothesized that AR maintains a cancer stem cell (CSC)-like tumor-initiating population and serves as an antiapoptotic factor, facilitating anchorage independence and metastasis. AR levels increased in TNBC cells grown in forced suspension culture compared with those in attached conditions, and cells that expressed AR resisted detachment-induced apoptosis. Culturing TNBC cells in suspension increased the CSC-like population, an effect reversed by AR inhibition. Pretreatment with enzalutamide (Enza) decreased the tumor-initiating capacity of TNBC cells and reduced tumor volume and viability when administered simultaneously or subsequent to the chemotherapeutic paclitaxel; simultaneous treatment more effectively suppressed tumor recurrence. Overall, our findings suggest that AR-targeted therapies may enhance the efficacy of chemotherapy even in TNBCs with low AR expression by targeting a CSC-like cell population with anchorage independence and invasive potential. Cancer Res; 77(13); 3455–66. ©2017 AACR.