Ezh2 Methyltransferase Regulates Disseminating Tumor Cells In Breast Cancer Metastasis

Triple negative breast cancer (TNBC, ER-, PR-, HER2-) exhibits the worst outcome due to higher rates of metastasis compared to non TNBC subtypes. Despite this clinical significance, there is a conspicuous lack of FDA approved molecularly targeted anti-metastatic therapies for TNBC. The enhancer of zeste homolog 2 (EZH2), a catalytic core subunit of the Polycomb repressive complex 2 (PRC2) with histone methyltransferase (HMT) activity is associated with the worst clinical outcome in breast cancer patients. Using a combination of genetic and pharmacological approaches, we show that EZH2 HMT blockade did not impact primary tumor growth, but significantly reduced distal metastases. Metastasis suppression was associated with a marked reduction of tumor-initiating cells (TICs) in primary tumor, circulating tumor cells (CTCs) in the blood and impaired lung colonization. Using a SOX2/OCT4 promoter reporter system, we identified EZH2-sensitive metastatic cells with GATA3 low luminal progenitor phenotypes in the primary tumor, and EZH2 HMT blockade restored GATA3 expression, promoted differentiation of luminal progenitors and impaired metastasis. These key preliminary findings have led to the hypothesis that EZH2 promotes metastasis, and that inhibition of EZH2 HMT may constitute a viable anti-metastatic approach. We will also discuss the potential of EZH2 inhibition in combination with chemotherapy as an effective strategy against TNBC metastasis. Citation Format: Shira Yomtoubian, Seongho Ryu, Sharrell Lee, Geoff Markowitz, Dingcheng Gao, Vivek Mittal. EZH2 methyltransferase regulates disseminating tumor cells in breast cancer metastasis [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 5078. doi:10.1158/1538-7445.AM2017-5078