53BP1 is a DNA damage response protein recruited to sites of double strand breaks through recognition of dimethylated lysine on histone 4 by its tandem Tudor domains. Like 53BP1, BRCA-1 plays a role in the regulation of DNA repair pathways, and BRCA-1 mutations have been strongly linked to breast and ovarian cancer. Interestingly, mice null for 53BP1 and BRCA-1 genes display minimal tumor formation, suggesting that the effects of deleterious BRCA-1 mutations could be prevented with potent 53BP1 small molecule antagonists. Herein, we describe a fragment screen that was used to identify compounds that bind to the 53BP1 Tudor domain and a chemoinformatic workflow to select near-neighbor analogues and establish structure activity relationships for these binders. The marked affinity improvements of the analogues over their parent fragments highlights the developability of these series and the utility of this approach in discovering novel hit compounds for 53BP1 and other methyl-lysine reader proteins.

Many common disease-causing mutations result in loss-of-function (LOF) of the proteins in which they occur. LOF mutations have proven recalcitrant to pharmacologic intervention, presenting a challenge for the development of targeted therapeutics. Polycomb repressive complex 2 (PRC2), which contains core subunits (EZH2, EED, and SUZ12), regulates gene activity by trimethylation of histone 3 lysine 27. The dysregulation of PRC2 catalytic activity by mutations has been implicated in cancer and other diseases. Among the mutations that cause PRC2 malfunction, an I363M LOF mutation of EED has been identified in myeloid disorders, where it prevents allosteric activation of EZH2 catalysis. We describe structure-based design and computational simulations of ligands created to ameliorate this LOF. Notably, these compounds selectively stimulate the catalytic activity of PRC2-EED-I363M over wildtype-PRC2. Overall, this work demonstrates the feasibility of developing targeted therapeutics for PRC2-EED-I363M that act as allosteric agonists, potentially correcting this LOF mutant phenotype.

Nat. Chem. Biol. 13, 389–395 (2017); published online 30 January 2017; corrected after print 14 June 2017 In the version of this article initially published, the keys for the graphs in Figure 5b–e incorrectly stated GDK126 instead of GSK126. The error has been corrected in the HTML and PDF versions of the article.

The function of EED within polycomb repressive complex 2 (PRC2) is mediated by a complex network of protein-protein interactions. Allosteric activation of PRC2 by binding of methylated proteins to the embryonic ectoderm development (EED) aromatic cage is essential for full catalytic activity, but details of this regulation are not fully understood. EED's recognition of the product of PRC2 activity, histone H3 lysine 27 trimethylation (H3K27me3), stimulates PRC2 methyltransferase activity at adjacent nucleosomes leading to H3K27me3 propagation and, ultimately, gene repression. By coupling combinatorial chemistry and structure-based design, we optimized a low-affinity methylated jumonji, AT-rich interactive domain 2 (Jarid2) peptide to a smaller, more potent peptidomimetic ligand (Kd = 1.14 ± 0.14 μM) of the aromatic cage of EED. Our strategy illustrates the effectiveness of applying combinatorial chemistry to achieve both ligand potency and property optimization. Furthermore, the resulting ligands, UNC5114 and UNC5115, demonstrate that targeted disruption of EED's reader function can lead to allosteric inhibition of PRC2 catalytic activity.