Abstract P1-13-08: Inhibition of RNA binding protein HuR function sensitizes the TNBC to chemotherapy
Authors: Wei Lanjing , Zhang Qi , Zhong Cuncong , Aubé Jeffrey , Welch Danny R. , Wu Xiaoqing , Xu Liang 
Published: March 2023

Abstract
The 5-year relative survival rate for triple-negative breast cancer (TNBC) is 77%, which is notably lower than 90%, the overall survival rate for breast cancer. The primary systemic treatment for TNBC remains to be chemotherapy. However, patients frequently develop resistance to conventional chemotherapy, greatly compromising the anti-tumor effects of chemodrugs. Therefore, this study is aimed to enhance the effects of chemotherapy. The RNA-binding protein Hu antigen R (HuR) plays an important role in chemotherapy resistance. HuR post-transcriptionally regulates the stability of the target mRNA by binding to the U- or AU-rich elements (ARE) mainly in the 3’ untranslated region (UTR) of mRNA. In most cases, the binding stabilizes mRNA, thereby enhancing the translation of the encoded protein, many of which are implicated in multiple cancer hallmarks, including chemoresistance. The overexpression of HuR, and accumulated cytoplasmic expression, are reported to be related to chemoresistance in many types of cancer cells. We hypothesized that inhibition of HuR function by disrupting its interaction with mRNA can accelerate the decay of mRNA and thus reduce the translation of proteins contributing to chemoresistance. Previously, our lab reported a small molecule HuR inhibitor, KH-3, which potently inhibits HuR function by disrupting the HuR-mRNA interactions. To test our hypothesis, we utilized KH-3 as a tool compound to assess whether HuR inhibition enhances the efficacy of chemotherapy for TNBC cells. We generated a cell sub-line (231-TR) derived from the human TNBC cell line MDA-MB-231 with acquired resistance against docetaxel (TXT). Compared with the parental cell line, 231-TR exhibited similar sensitivity to KH-3 in the MTT-based cytotoxicity assay and the colony formation assay. The in vitro and in vivo combination of KH-3 and TXT synergized in inhibiting cell proliferation and tumor growth of multiple TNBC cell lines. Regarding mechanisms of action, the apoptosis pathway was downregulated and the Wnt signaling pathway was upregulated in 231-TR cells. KH-3 treatment downregulated β-Catenin, involved in promoting cell proliferation, in a time and dose-dependent manner. KH-3 was also identified to induce apoptosis cell death via inhibiting the anti-apoptotic protein BCL2. The cell cycle analysis revealed that KH-3 treatment caused the S phase accumulation. Therefore, the cell proliferation inhibition by KH-3 results from a combination of apoptosis and cell cycle arrest. Furtherly, KH-3 restored the effects of docetaxel in inducing apoptotic cell death in 231-TR cells. Together, this study provides a new strategy to overcome chemotherapy resistance in TNBC cells by functional inhibiting HuR.
Citation Format: Lanjing Wei, Qi Zhang, Cuncong Zhong, Jeffrey Aubé, Danny R. Welch, Xiaoqing Wu, Liang Xu. Inhibition of RNA binding protein HuR function sensitizes the TNBC to chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-13-08.