Abstract 1000: Estrogen receptor coactivator MED1 in breast tumorigenesis and therapeutic resistance

Abstract

Abstract Recent studies have established Mediator Subunit 1 (MED1) as a key ER transcriptional coactivator for in both normal mammary gland development and breast cancer. Significantly, the MED1 gene is located at the chromosome 17q12 region, also known as the HER2 amplicon, and co-amplifies with HER2 in almost all instances. Importantly, we found that MED1 serves as a key crosstalk point for the HER2 and ER pathways in anti-estrogen resistance of breast cancer. Significantly, MED1 expression highly correlates with poor disease-free survival of breast cancer patients; and most recent studies have discovered increased frequency of MED1 mutations in circulating tumor cells of human patients following anti-estrogen and anti-HER2 treatments. To determine the role of MED1 in HER2-driven tumorigenesis, we have crossed the MMTV-HER2 mammary tumor model with our established MED1 mutant knockin and newly generated MED1 mammary specific overexpression mouse models. Collectively, our studies revealed critical roles for MED1 in tumor progression, metastasis, cancer stem cell formation and therapeutic resistance in HER2-mediated mammary tumorigenesis. These studies not only for the first time reported key roles for a HER2 amplicon co-amplified gene in HER2-driven tumorigenesis but also support MED1 as a potential therapeutic target. To test that, we have assembled highly innovative RNA nanotechnology-based pRNA-HER2apt-siMED1 nanoparticles. We found these RNA nanoparticles have a very high Tm value, and is ultra-stable under RNase A, 8 M urea, serum and PBS conditions. Importantly, pRNA-HER2apt-siMED1 nanoparticles could specifically target HER2+ human breast cancer, efficiently deplete the expression of MED1 and decrease ER-mediated gene transcription both in vitro and in vivo. Most significantly, pRNA-HER2apt-siMED1 nanoparticles not only greatly reduce the growth, metastasis and cancer stem cell formation of HER2+ breast cancer, but are also able to overcome their therapeutic resistance. (This work is supported by Susan G. Komen for the Cure Foundation Career Catalyst Grant, American Cancer Society Research Scholar Grant and NIH/NCI Grant Number R01CA197865). Citation Format: Xiaoting Zhang. Estrogen receptor coactivator MED1 in breast tumorigenesis and therapeutic resistance [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 1000. doi:10.1158/1538-7445.AM2017-1000