Data from Chronic Myelogenous Leukemia– Initiating Cells Require Polycomb Group Protein EZH2

Abstract

<div>Abstract<p>Tyrosine kinase inhibitors (TKI) have revolutionized chronic myelogenous leukemia (CML) management. Disease eradication, however, is hampered by innate resistance of leukemia-initiating cells (LIC) to TKI-induced killing, which also provides the basis for subsequent emergence of TKI-resistant mutants. We report that EZH2, the catalytic subunit of Polycomb Repressive Complex 2 (PRC2), is overexpressed in CML LICs and required for colony formation and survival and cell-cycle progression of CML cell lines. A critical role for EZH2 is supported by genetic studies in a mouse CML model. Inactivation of <i>Ezh2</i> in conventional conditional mice and through CRISPR/Cas9-mediated gene editing prevents initiation and maintenance of disease and survival of LICs, irrespective of BCR–ABL1 mutational status, and extends survival. Expression of the EZH2 homolog EZH1 is reduced in EZH2-deficient CML LICs, creating a scenario resembling complete loss of PRC2. EZH2 dependence of CML LICs raises prospects for improved therapy of TKI-resistant CML and/or eradication of disease by addition of EZH2 inhibitors.</p><p><b>Significance:</b> This work defines EZH2 as a selective vulnerability for CML cells and their LICs, regardless of BCR–ABL1 mutational status. Our findings provide an experimental rationale for improving disease eradication through judicious use of EZH2 inhibitors within the context of standard-of-care TKI therapy. <i>Cancer Discov; 6(11); 1237–47. ©2016 AACR.</i></p><p><i>See related article by Scott et al., p. 1248</i>.</p><p><i>This article is highlighted in the In This Issue feature, p. 1197</i></p></div>