Triple negative breast cancer (TNBC) has a poor prognosis and, by definition, lacks estrogen receptor and progesterone receptor expression as well as HER2 amplification and thus is unresponsive to targeted HER2 or endocrine therapy. Although TNBC lacks expression of hormone receptors commonly associated with breast cancer, androgen receptor (AR) protein is expressed in 12-32% of TNBC. AR is a well characterized driver of prostate cancer that is effectively targeted with FDA-approved antagonists. The goal of the proposed study is to determine the function of AR in TNBC and whether AR antagonists used to treat prostate cancer may be effective in AR+ TNBC. Based on the preliminary data outlined in this proposal, we have generated a working model of AR action in TNBC in which AR acts as a transcription factor to regulate key genes, including amphiregulin (AREG). Transcription of these genes allows AR to mediate proliferation, migration and invasion and maintain a cancer stem cell (CSC) population. We hypothesize that inhibiting AR will prevent these functions and impede tumor growth and invasion.
The aims of this proposal are to determine how AR influences proliferation, invasion and cancer stem cell maintenance (Aim 1) and to determine if AR inhibition will decrease tumor growth, initiation and metastasis in preclinical animal models (Aim 2).
In Aim 1, the mechanism of AR function in TNBC will be determined by assessing transcriptional regulation of critical genes, performing phenotype rescue experiments and evaluating CSC populations.
Aim 2 will be assessed using TNBC xenograft models treated with an AR antagonist. Completion of the proposed studies will determine if and how AR supports tumor progression in AR+ TNBC and guide the rational use of anti-androgen therapy to improve patient outcome. Together, these studies will serve to guide the development of a new, molecularly- targeted therapy in this aggressive breast cancer subtype with limited therapeutic options.

Public Health Relevance

Triple negative breast cancer has a poor prognosis and lacks estrogen receptor, progesterone receptor and HER2 amplification and thus does not respond to targeted HER2 or endocrine therapies. However, up to a third of triple negative breast cancers express androgen receptor protein (AR) and our preliminary data suggest that AR+ TNBC critically depends on AR. Just as prostate cancers critically depend on AR and often respond to treatment with AR antagonists, AR+ TNBC may also be reliant on AR for traits that contribute to tumor survival and progression, and may benefit from treatment with AR antagonists.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1)
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Mcguirl, Michele
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University of Colorado Denver
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Barton, Valerie N; Christenson, Jessica L; Gordon, Michael A et al. (2017) Androgen Receptor Supports an Anchorage-Independent, Cancer Stem Cell-like Population in Triple-Negative Breast Cancer. Cancer Res 77:3455-3466
Barton, Valerie N; D'Amato, Nicholas C; Gordon, Michael A et al. (2015) Multiple molecular subtypes of triple-negative breast cancer critically rely on androgen receptor and respond to enzalutamide in vivo. Mol Cancer Ther 14:769-78
Barton, Valerie N; D'Amato, Nicholas C; Gordon, Michael A et al. (2015) Androgen Receptor Biology in Triple Negative Breast Cancer: a Case for Classification as AR+ or Quadruple Negative Disease. Horm Cancer 6:206-13