Abstract 1783: JNK/MDR1 confers chemo-resistance in breast cancer cells carrying estrogen receptor activating mutations

Abstract

Abstract Background: Endocrine therapy is the mainstay treatment for estrogen receptor-α (ER) positive breast cancer (BC) patients. However, all metastatic BC patients develop resistance, which in nearly 40% of patients is due to activating mutations, mostly Y537S and D538G, in the ligand-binding domain (LBD). Tumors harboring these mutations are more aggressive and the patients' prognosis is worse. We hypothesized that refractory response to further treatment lines, i.e, chemotherapy, partially accounts for the worse prognosis. Hence, our goal was to study whether LBD-ER BC cells are resistant to chemotherapy and reveal the mechanism of action. Methods: We used MCF-7 cells stably expressing WT-ER, Y537S or D538G-ER mutations. Cell proliferation and viability were determined using MTT, methylene blue and colony assays. We evaluated apoptosis by monitoring cleaved-PARP and flow cytometry using Annexin/7AAD staining. MDR1 expression was studied using qRT-PCR and western-blot. JNK/c-Jun pathway was studied by pJNK and cJun expressions, cJun transcriptional activity, ChIP assay and pharmacological inhibition. Results: LBD-ER cells exhibited higher proliferation and viability and exerted less apoptosis compared to WT-ER cells following treatment with paclitaxel, doxorubicin, and 5-FU. MDR1 expression and JNK pathway activity was higher in D538G cells compared to both WT-ER and Y537S cells. Importantly, inhibition of the JNK pathway, using SP600125 and BI-78D3, lead to decreased MDR1 expression, increased cleaved PARP, and decreased viability in the D538G cells. In addition, our results revealed that JNK increased c-Jun binding activity of the MDR1 gene in the D538G mutated cells. Conclusions: These results indicate that LBD-ER cells confer resistance to chemotherapy. The mechanisms leading to it are diverse, and we found that in D538G increased JNK pathway activation resulted in elevated MDR1 expression and chemo-resistance. This paves the way to therapies aiming at inhibition the JNK pathway in order to restore chemo-resistance. This study also highlights the marked differences between these seemingly similar mutations, strengthening the necessity to adopt a personalized treatment approach for BC patients who developed endocrine resistance. Citation Format: Marwa Taya, Keren Merenbakh-Lamin, Tami Rubinek, Ido Wolf. JNK/MDR1 confers chemo-resistance in breast cancer cells carrying estrogen receptor activating mutations [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 1783.