Abstract 1784: Functional characteristics of chemotherapy-resistance in triple negative breast cancer

Abstract Background: Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer-related death among women worldwide. Triple negative breast cancer (TNBC) is an aggressive subtype representing 15-20% of all breast cancers. TNBC often ends with a poor clinical outcome due to high histological grade and recurrence rates with few treatment options. Chemotherapy remains the standard of care for TNBC treatment, but unfortunately, patients frequently develop resistance, and alternative treatment strategies for chemoresistant disease remain a major unmet need. ERβ, a second form of the estrogen receptor, is known to be expressed in approximately 20-30% of TNBC, and ligand-mediated activation of ERβ elicits potent anti-cancer effects in chemosensitive TNBC. However, the utility of ERβ in the chemoresistant setting remains unclear. Materials and methods: To study the mechanistic basis of chemoresistance in TNBC cells and identify alternative treatment approaches for chemotherapy-resistant disease, doxorubicin-resistant (Doxo-R) and paclitaxel-resistant (Taxol-R) cell lines were generated using MDA-MB-231 cells. A Doxycycline (dox) inducible expression system was used to overexpress ERβ in these cells. RNA sequencing and transcription factor (TF) activation profiling was performed to glean a comprehensive mechanistic insight into mechanisms of resistance and the functions of ERβ, and the efficacy of ERβ targeted therapies, were assessed. Results: Doxo-R and Taxol-R cells exhibited a 3- and 12-fold decrease in sensitivity to their respective chemotherapeutic agents. Doxo-R cells were more sensitive to paclitaxel while Taxol-R cells exhibited no changes in sensitivity to doxorubicin. Expression of ERβ had no impact on the IC50s for either chemotherapy drug. Taxol-R cells exhibited a significantly increased number of cells in the S phase. Proliferation assays revealed that ERβ targeting agents, including estradiol (E2) and the ERβ-specific agonist LY500307 (LY), led to substantial inhibition of cell proliferation, migration, and invasion when ERβ was expressed. We identified a large spectrum of genes expression changes that were acquired in Doxo-R and Taxol-R cells. These changes included 91 kinases genes in Doxo-R cells and 164 in Taxol-R cells. TF activation profiling indicated that eight and four TFs were activated more than 2-fold, including NRF1, WT1, and SATB1 in both Doxo-R and Taxol-R cells. Conclusions: Doxo-R and Taxol-R TNBC cell lines were successfully established and serve as a good model for studying the mechanisms of chemotherapy resistance and screening effective agents to reverse or treat chemoresistant disease. As in the sensitive setting, ERβ targeted therapies may represent an alternative treatment for TNBC patients with chemorefractory ERβ+ disease, a possibility that is currently being explored through a phase II clinical trial (NCT03941730). Citation Format: Xiyin Wang, Michael J. Emch, John R. Hawse. Functional characteristics of chemotherapy-resistance in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1784.