Abstract 1145: Overcoming chemoresistance and blocking metastasis in breast cancer by targeting HuR

Patients with metastatic breast cancer have a dismal 5-year survival rate of only 24%. Chemoresistance is another contributor to the high mortality of advanced breast cancer. The RNA-binding protein, Hu antigen R (HuR), is overexpressed at all stages of breast cancer development. Cytoplasmic HuR accumulation correlates with high-grade malignancy, poor distant disease-free survival and serves as a prognostic factor for poor clinical outcome in breast cancer. HuR promotes tumorigenesis by promoting mRNA stability and translation of proteins implicated in proliferation, survival, angiogenesis, invasion, and metastasis. HuR also modulates sensitivity of breast cancer cells to chemotherapy. Taken together, HuR is an emerging target for breast cancer therapy, especially metastatic breast cancer. Using shRNA and CRISPR technologies to modulate HuR expression in breast cancer cells, we found that cells with HuR KD/KO were less invasive and more sensitive to chemotherapy. In an effort to discover small molecules that disrupt the HuR-mRNA interaction and block HuR functions in breast cancer progression, metastasis and chemoresistance, high throughput screening (HTS) was carried out in several chemical libraries (~23,000 compounds) using fluorescence polarization (FP) assay, which identified several initial hits with sub-micromolar inhibitory constants (Ki). Those potential inhbitors were then validated by ALPHA assay (Amplified Luminescent Proximity Homogeneous Assay), confirmed by Surface Plasmon Resonance (SPR). In cell-based assays, top hit KH-3 and its optimized analogs, specifically shortened HuR target mRNA half-lifes and decreased the level of the encoded proteins. Moreover, those compounds inhibited invasion and restored chemosensitivity. qPCR arrays focusing on specific pathways revealed that HuR inhibitors potently upregulated metastatic suppressors and downregulated genes frequently overexpressed in lung metastases. In animal studies, KH-3 not only exhibited potent antitumor efficacy in orthotopic xenografts of breast cancer, but also efficiently blocked experimental metastasis. In conclusion, we identified potent and specific small molecule inhibitors of HuR-mRNA interaction for potential anti-metastatic therapy for breast cancer with HuR overexpression. Citation Format: Xiaoqing Wu, Rebecca Marquez, Shuang Han, Lan Lan, Dan A. Dixon, Jeffrey Aube, Danny R. Welch, Liang Xu. Overcoming chemoresistance and blocking metastasis in breast cancer by targeting HuR [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1145. doi:10.1158/1538-7445.AM2017-1145