PURPOSE: Triple-negative breast cancer (TNBC), and the basal-like TNBC subtype, accounts for ~20% of all breast cancer (BC) cases, and is particularly prevalent in younger patients of African-American and Hispanic descent. The importance of annexin A6 (AnxA6) as a tumor suppressor in various cancers has been widely investigated, but the mechanisms by which AnxA6-induced basal-like triple negative breast cancer progression remain largely unknown. Physiological changes such as hypoxia, metabolic acidosis, and oxidative stress in the tumor microenvironment (TME) during cancer progression endow cancer cells with malignant properties, ultimately leading to metastatic dissemination that remains the major cause of death in cancer patients. By linking the altered expression status of AnxA6, with changes in metabolic output of the tumor cells and the efficacy of the otherwise ineffective epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs), these metabolic vulnerabilities can be targeted to attenuate the growth and/or motility of this hard-to-treat breast cancer subtype. DESIGN METHODS: AnxA6-high (BT-549) and AnxA6-low (MDA-468) TNBC cell lines were cultured in hypoxic conditions (94%N2; 1%O2; 5%CO2; 37°C) using a Bactrox Hypoxia Chamber (Terra Universal Inc., Fullerton, CA). TNBC cells were treated with EGFR-TKI Lapatinib (Biovision Inc., Milpitas, CA).

RESULTS: We demonstrate that exposure of AnxA6-high (BT-549) and AnxA6-low (MDA-468) TNBC cell lines to acute hypoxia (1% O2; ≤24 hrs.) is associated with down-regulation of AnxA6 while chronic hypoxia (1% O2; >24 hrs.) led to a consistent up-regulation of AnxA6. AnxA6, FABP4, and HIF-1α downstream genes GLUT1 and PGK-1, mRNA levels were upregulated in chronic hypoxic conditions. AnxA6 metabolic studies reveal that contrary to AnxA6-high, down regulation of AnxA6 in TNBC cells increased lactate production, glucose consumption, and ATP-synthesis and lipid metabolism under hypoxia. In addition, chronic hypoxia sensitized TNBC cells to EGFR-TKIs. CONCLUSION: These data suggest that the transition from AnxA6-high to AnxA6-low may be dependent on hypoxia in the TME and consequently, TNBC cell survival and resistance to EGFR-targeted therapies.

Supported by NIH/NIGMS 1SC1CA211030 (AMS)

Citation Format: Stephen D. Williams, Amos M. Sakwe. Association between annexin-A6 expression and metabolic vulnerabilities of TNBC cells and their response to EGFR-tyrosine kinase inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5849.