Endocrine Abstracts

IntroductionAromatase Inhibitors (AI) are standard therapy for hormone receptor positive breast cancers in post-menopausal patients. Unfortunately, resistance is common and previous studies from our lab suggest that the altered steroid environment may be a driver. Using label-free mass spectrometry we set out to explore the unique androgen receptor (AR) interactome that supervenes in AI resistant breast cancer and associated hyper-androgenic environment.

Methods: AR expression was evaluated in a primary breast cancer tissue-microarray (n=844) with nuclear and cytoplasmic localization quantified. LC-MS/MS analysis was utilized to identify proteins interacting with the AR in AI resistant cells in the presence of androgen excess. Validation was carried out by co-immunoprecipitation and imaging analysis. Live-cell imaging, Seahorse MitoStress Assays and flow cytometry were used to quantify changes in mitochondria and cell metabolism arising in AI resistant models post exposure to A4.

Results: Utilising digital pathology we evaluated the localisation of the androgen receptor (AR) protein in a large cohort of breast cancer specimens (n=844) and show that abundant cytoplasmic AR protein associated with poor survival only in the post-menopausal cohort and most significantly in the therapy refractory Luminal B subtype (p=0.0085). Exploration of the AR protein interactome via LC-MS/MS in AI resistant cell line models identified protein partners previously linked with castrate resistant prostate cancer (beta-catenin) and proteins associated with adaptive metabolic response and estrogen receptor repression (SLIRP, IGFBP5). Seahorse analysis confirmed A4 exposure causes a metabolic shift in AI resistant cells, increasing glycolysis.

Discussion: The findings of this study highlight novel non-genomic AR protein interactions that could aid our understanding of the role played by androgens in metabolic health and the development of endocrine-resistance in specific breast cancer subtypes.