Allosteric Modulators of Polycomb Repressive 2 Gene Repression as Potential Therapeutics for the Development of Novel Epigenetic Cancer Therapies

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Novel and effective anticancer therapies are still of great need since they hold the potential for lower mortality rates, reoccurrence and better quality of life for patients. Cancer is a genetic disease, but its development also involves multiple epigenetic alterations. Epigenetics regulates transcription by modulating chromatin architecture through different mechanisms. Hence, dysregulation of such mechanisms can result in aberrant gene expression or silencing, which in turn can lead to carcinogenesis. One of the most relevant epigenetic modifications is the methylation of lysine 27 at histone 3 (H3K27), a broadly known repressive histone mark. H3K27 methylation is incorporated by the polycomb repressive complex 2 (PRC2), a multimeric protein complex formed by four core components: EZH2, EED, SUZ12 and RbAp46/48, all of which are essential for its catalytic activity. Overexpression of PRC2 proteins, particularly of EZH2, results in hyperactivation of the complex and high levels of H3K27m3, which are associated to a myriad of human cancers. Several PRC2 inhibitors have been discovered to date, some which are currently in clinical development. These compounds target either the catalytic SET domain of EZH2 or EED allosterically. Although they have delivered some promising results, recent reports indicate that extended dosing with them leads to secondary EZH2 mutants that become resistant to treatment. Hence, novel inhibitors of PRC2 function are of great interest, since such compounds could offer an alternative solution to address the above-mentioned resistant profiles. Recently, our laboratory has reported the discovery of a potent, cell permeable stapled peptide, GN-ZW11, as a potent and selective inhibitor of H3K27me3 in renal carcinoma cells. This compound was designed to target the SANT2 domain in EZH2, and thus it may well be the first-in class EZH2 allosteric inhibitor described to date. The current proposal aims to expand our preliminary studies with GN-ZW11 by carrying out, first, structural-activity relationship studies to understand the molecular determinants of its binding, as well as to gather valuable data for the design of GN-ZW11 analogs with improved potency and stability. Secondly, we propose to carry out further biological assays in metastatic renal carcinoma cells to better understand the mechanism of action of GN-ZW11 and to evaluate its therapeutic potential for the treatment of clear cell renal cell carcinoma. Finally, we plan on expanding our preliminary studies to other cancer cell lines in which PRC2 proteins have been found overexpressed and to investigate the impact of PRC2 inhibition by GN-ZW11 in vivo, by measuring its ability to induce tumor regression in mouse xenografts models. In summary, the proposed research project will result in the preparation and validation of a new family of allosteric inhibitors of PRC2 function. We expect that the knowledge gained from these studies will help to improve our overall understanding surrounding the role of EZH2 in oncology, and will also guide the identification of targeted chemotherapeutics for treating humans in the future.