Inhibition of EZH2 Catalytic Activity Selectively Targets a Metastatic Subpopulation in Triple-Negative Breast Cancer

Epigenetic changes are increasingly being appreciated as key events in breast cancer progression. However, breast cancer subtype-specific epigenetic regulation remains poorly investigated. Here we report that EZH2 is a leading candidate of epigenetic modulators associated with the TNBC subtype and that it predicts poor overall survival in TNBC patients. We demonstrate that specific pharmacological or genetic inhibition of EZH2 catalytic activity impairs distant metastasis. We further define a specific EZH2(high) population with enhanced invasion, mammosphere formation, and metastatic potential that exhibits marked sensitivity to EZH2 inhibition. Mechanistically, EZH2 inhibition differentiates EZH2(high) basal cells to a luminal-like phenotype by derepressing GATA3 and renders them sensitive to endocrine therapy. Furthermore, dissection of human TNBC heterogeneity shows that EZH2(high) basal-like 1 and mesenchymal subtypes have exquisite sensitivity to EZH2 inhibition compared with the EZH2(low) luminal androgen receptor subtype. These preclinical findings provide a rationale for clinical development of EZH2 as a targeted therapy against TNBC metastasis.