Abstract P2-09-05: The potent anti-androgen enzalutamide demonstrates broad anti-tumour activity across all androgen receptor-positive triple-negative breast cancer subtypes

Abstract

Abstract Background: Up to 30% of triple-negative breast cancers (TNBC) show expression of the androgen receptor (AR) and may therefore be candidates for AR-targeted therapy. Molecular profiling of TNBC has identified the luminal AR (LAR) subset, which shares many aspects of ER-positive luminal cancers but is resistant to ER-targeted therapy. LAR cancers highly express the AR, are heavily enriched in hormone-regulated pathways and demonstrate tumour growth in response to androgen stimulation that can be inhibited by the mixed AR agonist/antagonist bicalutamide. The objective of this study was to investigate the role of AR signalling in TNBC in more detail and to evaluate the potential of the second generation anti-androgen Enzalutamide in this setting relative to bicalutamide. Methods: A panel of 13 TNBC breast cancer cell lines was selected, representing different molecular subtypes of TNBC (including 4 LAR cell lines). Baseline AR expression was determined using qPCR (Taqman) and Western-Blot (Antibody, Santa Cruz Biotechnology). The effects of enzalutamide and bicalumatide on cell proliferation and survival were determined using MTT assays with and without DHT stimulation. Comprehensive molecular profiling (including Illumina Human HT-12 v4 whole genome mRNA and Illumina Human 450K methylation microarrays) was applied before and after enzalutamide treatment to define the molecular signature associated with sensitivity to enzalutamide therapy. All statistical calculations and IC50 doses were calculated using Prism v6.0 (GraphPad). Results: A wide range of AR expression was confirmed across the cell line panel defining 3 groups with complete lack of AR expression, low/moderate AR expressions levels, or very high expression in the LAR subtype (with up to 100-fold greater AR expression compared to other TNBC subtypes). Enzalutamide demonstrated broad anti-tumour activity across all AR+ TNBC subtypes (but not in AR-negative subtypes), with IC50 values being similar in LAR and non-LAR cell lines. Treatment with enzalutamide resulted in more effective growth inhibition and a broader range of activity compared to bicalutamide. Data on molecular profiles of enzalutamide sensitivity will be presented at the meeting. Conclusion: AR inhibition is a promising therapeutic strategy for both LAR and non-LAR AR-expressing TNBC. The potent anti-androgen enzalutamide shows broad activity across all AR+ TNBC subtypes and warrants further clinical evaluation. A phase 2 study of enzalutamide in AR+ TNBC has been initiated. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-09-05.