Non-canonical AR activity facilitates endocrine resistance in breast cancer

Kee Ming Chia, Heloisa Milioli, Neil Portman, Geraldine Laven-Law, Rhiannon Coulson, Aliza Yong, Davendra Segara, Andrew Parker, Catherine E. Caldon, Niantao Deng, Alexander Swarbrick, Wayne D. Tilley, Theresa E. Hickey, Elgene Lim

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

The role of androgen receptor (AR) in endocrine-resistant breast cancer is controversial and clinical trials targeting AR with an AR antagonist (e.g., enzalutamide) have been initiated. Here, we investigated the consequence of AR antagonism using in vitro and in vivo models of endocrine resistance. AR antagonism in MCF7-derived tamoxifen-resistant (TamR) and long-term estrogen-deprived breast cancer cell lines were achieved using siRNA-mediated knockdown or pharmacological inhibition with enzalutamide. The efficacy of enzalutamide was further assessed in vivo in an estrogen-independent endocrine-resistant patient-derived xenograft (PDX) model. Knockdown of AR inhibited the growth of the endocrine-resistant cell line models. Microarray gene expression profiling of the TamR cells following AR knockdown revealed perturbations in proliferative signaling pathways upregulated in endocrine resistance. AR loss also increased some canonical ER signaling events and restored sensitivity of TamR cells to tamoxifen. In contrast, enzalutamide did not recapitulate the effect of AR knockdown in vitro, even though it inhibited canonical AR signaling, which suggests that it is the non-canonical AR activity that facilitated endocrine resistance. Enzalutamide had demonstrable efficacy in inhibiting AR activity in vivo but did not affect the growth of the endocrine-resistant PDX model. Our findings implicate non-canonical AR activity in facilitating an endocrine-resistant phenotype in breast cancer. Unlike canonical AR signaling which is inhibited by enzalutamide, non-canonical AR activity is not effectively antagonized by enzalutamide, and this has important implications in the design of future AR-targeted clinical trials in endocrine-resistant breast cancer.

Original languageEnglish
Pages (from-to)251-264
Number of pages14
JournalEndocrine-Related Cancer
Volume26
Issue number2
DOIs
Publication statusPublished - Feb 2019
Externally publishedYes

Keywords

  • Ar
  • Breast cancer
  • Endocrine resistance
  • Enzalutamide
  • PDX

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