Abstract B254: Targeted disruption of the EZH2-EED complex inhibits EZH2-dependent cancer.

Abstract

Abstract Enhancer of zeste homolog 2 (EZH2) is the histone lysine N-methyltransferase component of the Polycomb repressive complex 2 (PRC2), which, in conjunction with embryonic ectoderm development (EED) and suppressor of zeste 12 homolog(SUZ12), regulates cell lineage determination and homeostasis. Enzymatic hyperactivity of EZH2 has been linked to aberrant repression of tumor suppressor genes in diverse cancers. Here, we report the development of stabilized a-helix of EZH2 (SAH-EZH2) peptides that selectively inhibit H3 Lys27 trimethylation by dose-responsively disrupting the EZH2-EED complex and reducing EZH2 protein levels, a mechanism distinct from that reported for small-molecule EZH2 inhibitors targeting the enzyme catalytic domain. The essential α-helical domain of EZH2 (residues 40-68) that engages EED established the basis for designing hydrocarbon-stapled derivatives to disrupt the specific protein interaction. Non-natural amino acids with olefinic side chains were substituted at (i, i + 4) positions within the EZH2 α-helical sequence, followed by ruthenium-catalyzed olefin metathesis, to yield SAH-EZH2 peptides. Our lead, cell-permeable analog effectively targeted EED in situ, dissociated the EZH2-EED complex and impaired the function of PRC2, as reflected by reduction of the H3K27me3 and EZH2 protein levels, and increased expression of PRC2-regulated cell differentiation marker genes. In response to SAH-EZH2 treatment, murine MLL-AF9 leukemia cells, which are PRC2-dependent, manifested growth arrest and monocyte-macrophage differentiation, in accordance with the phenotypic consequences of shRNA-mediated reduction of EZH2 (or EED) or genetic ablation of Ezh2 (or Eed). In evaluating SAH-EZH2 activity alongside the small-molecule EZH2 inhibitor GSK126 in a series of B-cell lymphoma lines, we observed sequence-specific antiproliferative responses, transcriptional modulation, cellular specificity and a distinct mechanism of action for SAH-EZH2. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B254. Citation Format: Woojin Kim, Gregory H. Bird, Tobias Neff, Guoji Guo, Marc A. Kerenyi, Loren D. Walensky, Stuart H. Orkin. Targeted disruption of the EZH2-EED complex inhibits EZH2-dependent cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B254.