Chemical Probes for the Lysine Methyltransferases EZH2 and G9a: Design, Development, and Application

In eukaryotic genomes, DNA is wrapped around histone proteins to form repeating units known as nucleosomes, which are further condensed into chromosomes. This high level of structure creates a barrier to transcription, which is maintained or reversed via modifications to the N-terminal tails of histone proteins. Histone lysine methyltransferases catalyze the mono-, di-, and/or trimethylation of lysine residues within histone tails; the methylation state of histone tails has profound effects on transcription. For example, polycomb repressive complex 2 (PRC2) is responsible for regulating the methylation status of histone 3 lysine 27 (H3K27) via the catalytic subunit EZH1 or EZH2, and the lysine methyltransferase G9a catalyzes mono- and dimethylation of histone 3 lysine 9 (H3K9). These methyltransferases are of great interest, because trimethylation of H3K27 and dimethylation of H3K9 are transcriptionally repressive marks that play a key role in the progression of many diseases. Chemical probes that selectively inhibit the methyltransferase of interest are valuable tools to drive further understanding of the biological function of these proteins and assess their potential as therapeutic targets. Here we describe the design, development, and application of chemical probes and tools for both EZH1 and EZH2 (UNC1999), and G9a (UNC0965). UNC1999 was the first orally bioavailable chemical probe of EZH1 and EZH2. This discovery led to the design of a biotinylated tool (UNC2399), which allows for selective chemiprecipitation of EZH1 and EZH2 from cellular lysates. UNC1999 is also the most panactive EZH1 and EZH2 chemical probe to date. We exploited this feature to demonstrate the potential therapeutic application of small molecule inhibition of both EZH1 and EZH2 in MLL-rearranged leukemia. Lastly, we detail the in vitro and ex vivo use of a biotinylated G9a inhibitor (UNC0965) in a chemical-based chromatin immunoprecipitation (chem-ChIP) assay for studying G9a chromatin occupancy.Doctor of Philosoph

Targeting EZH2 and PRC2 dependence as novel anticancer therapy

Distinctive patterns of chromatin modification control gene expression and define cellular identity during development and cell differentiation. Polycomb repressive complex 2 (PRC2), the sole mammalian enzymatic complex capable of establishing gene-repressive high-degree methylation of histone H3 at lysine 27 (H3K27), plays crucial roles in regulation of normal and malignant hematopoiesis. Recently, increasing evidence has indicated that recurrent gain-of-function mutation and overexpression of EZH2, the catalytic subunit of PRC2, drive and promote malignant transformation such as B-cell lymphomagenesis, providing a rationale for PRC2 inhibition as a novel anticancer strategy. Here, we summarize the recently developed strategies for inhibition of PRC2, which include a series of highly specific, highly potent, small-molecule inhibitors of EZH2 and EZH1, an EZH2-related methyltransferase. PRC2 establishes functional crosstalk with numerous epigenetic machineries during dynamic regulation of gene transcription. Perturbation of such functional crosstalk caused by genetic events observed in various hematologic cancers, such as inactivation of SNF5 and somatic mutation of UTX, confers PRC2 dependence, thus rendering an increased sensitivity to PRC2 inhibition. We discuss our current understanding of EZH2 somatic mutations frequently found in B-cell lymphomas and recurrent mutations in various other epigenetic regulators as novel molecular predictors and determinants of PRC2 sensitivity. As recent advances have indicated a critical developmental or tumor-suppressive role for PRC2 and EZH2 in various tissue types, we discuss concerns over potentially toxic or even adverse effects associated with EZH2/1 inhibition in certain biological contexts or on cancer genetic background. Collectively, inhibition of PRC2 catalytic activity has emerged as a promising therapeutic intervention for the precise treatment of a range of genetically defined hematologic malignancies and can be potentially applied to a broader spectrum of human cancers that bear similar genetic and epigenetic characteristics. Published by Elsevier Inc. on behalf of ISEH - International Society for Experimental Hematology

A chemical tool for chemiprecipitation of the lysine methyltransferase, G9a, in vitro and in vivo

Here we report the design, synthesis, and biochemical characterization of a new chemical tool, UNC0965. UNC0965 is a biotinylated version of our previously reported G9a chemical probe, UNC0638. Importantly, UNC0965 maintains high in vitro potency and is cell penetrant. The biotinylated tag of UNC0965 enables chemiprecipitation of G9a from whole cell lysates. Further, the cell penetrance of UNC0965 allowed us to explore the localization of G9a on chromatin both in vitro and in vivo

An Orally Bioavailable Chemical Probe of the Lysine Methyltransferases EZH2 and EZH1

EZH2 or EZH1 is the catalytic subunit of the polycomb repressive complex 2 that catalyzes methylation of histone H3 lysine 27 (H3K27). The trimethylation of H3K27 (H3K27me3) is a transcriptionally repressive post-translational modification. Overexpression of EZH2 and hypertrimethylation of H3K27 have been implicated in a number of cancers. Several selective inhibitors of EZH2 have been reported recently. Herein we disclose UNC1999, the first orally bioavailable inhibitor that has high in vitro potency for wild-type and mutant EZH2 as well as EZH1, a closely related H3K27 methyltransferase that shares 96% sequence identity with EZH2 in their respective catalytic domains. UNC1999 was highly selective for EZH2 and EZH1 over a broad range of epigenetic and non-epigenetic targets, competitive with the cofactor SAM, and non-competitive with the peptide substrate. This inhibitor potently reduced H3K27me3 levels in cells and selectively killed diffused large B cell lymphoma cell lines harboring the EZH2Y641N mutant. Importantly, UNC1999 was orally bioavailable in mice, making this inhibitor a valuable tool for investigating the role of EZH2 and EZH1 in chronic animal studies. We also designed and synthesized UNC2400, a close analog of UNC1999 with >1,000-fold lower potency than UNC1999 as a negative control for cell-based studies. Finally, we created a biotin-tagged UNC1999 (UNC2399) which enriched EZH2 in pull-down studies, and a UNC1999 – dye conjugate (UNC2239) for co-localization studies with EZH2 in live cells. Taken together, these compounds represent a set of useful tools for the biomedical community to investigate the role of EZH2 and EZH1 in health and disease

Combining Cloud-Based Free Energy Calculations, Synthetically Aware Enumerations and Goal-Directed Generative Machine Learning for Rapid Large-Scale Chemical Exploration and Optimization

The hit identification process usually involves the profiling of millions to more recently billions of compounds either via traditional experimental high throughput screens (HTS) or computational virtual high throughput screens (vHTS). We have previously demonstrated that by coupling reaction-based enumeration, active learning and free energy calculations, a similarly large-scale exploration of chemical space can be extended to the hit-to-lead process. In this work, we augment that approach by coupling large scale enumeration and cloud-based FEP profiling with goal-directed generative machine learning, which results in a higher enrichment of potent ideas compared to large scale enumeration alone, while simultaneously staying within the bounds of a predefined drug-like property space. We are able to achieve this by building the molecular distribution for generative machine learning from the PathFinder rules-based enumeration and optimizing for a weighted sum QSAR based multi-parameter optimization function. We examine the utility of this combined approach by designing potent inhibitors of cyclin-dependent kinase 2 (CDK2) and demonstrate a coupled workflow that can: (1) provide a 6.4 fold enrichment improvement in identifying 50 50 <100 nM. The reported data suggest combining both reaction-based and generative machine learning for ideation results in a higher enrichment of potent compounds over previously described approaches, and can rapidly accelerate the discovery of novel chemical matter within a predefined potency and property space.<br /

Reaction-based Enumeration, Active Learning, and Free Energy Calculations to Rapidly Explore Synthetically Tractable Chemical Space and Optimize Potency of Cyclin Dependent Kinase 2 Inhibitors

We report a new computational technique, PathFinder, that uses retrosynthetic analysis followed by combinatorial synthesis to generate novel compounds in synthetically accessible chemical space. Coupling PathFinder with active learning and cloud-based free energy calculations allows for large-scale potency predictions of compounds on a timescale that impacts drug discovery. The process is further accelerated by using a combination of population-based statistics and active learning techniques. Using this approach, we rapidly optimized R-groups and core hops for inhibitors of cyclin-dependent kinase 2. We explored greater than 300 thousand ideas and identified 35 ligands with diverse commercially available R-groups and a predicted IC50 50 < 100 nM. The rapid turnaround time, and scale of chemical exploration, suggests that this is a useful approach to accelerate the discovery of novel chemical matter in drug discovery campaigns

Structure–Activity Relationship Studies for Enhancer of Zeste Homologue 2 (EZH2) and Enhancer of Zeste Homologue 1 (EZH1) Inhibitors

EZH2 or EZH1 (enhancer of zeste homologue 2 or 1) is the catalytic subunit of polycomb repressive complex 2 (PRC2) that catalyzes methylation of histone H3 lysine 27 (H3K27). PRC2 hyperactivity and/or hypertrimethylation of H3K27 are associated with numerous human cancers, therefore inhibition of PRC2 complex has emerged as a promising therapeutic approach. Recent studies have shown that EZH2 and EZH1 are not functionally redundant and inhibition of both EZH2 and EZH1 is necessary to block the progression of certain cancers such as mixed-lineage leukemia (MLL)-rearranged leukemias. Despite the significant advances in discovery of EZH2 inhibitors, there has not been a systematic structure–activity relationship (SAR) study to investigate the selectivity between EZH2 and EZH1 inhibition. Here, we report our SAR studies that focus on modifications to various regions of the EZH2/1 inhibitor UNC1999 (<b>5</b>) to investigate the impact of the structural changes on EZH2 and EZH1 inhibition and selectivity

An Orally Bioavailable Chemical Probe of the Lysine Methyltransferases EZH2 and EZH1

EZH2 or EZH1 is the catalytic subunit of the polycomb repressive complex 2 that catalyzes methylation of histone H3 lysine 27 (H3K27). The trimethylation of H3K27 (H3K27me3) is a transcriptionally repressive post-translational modification. Overexpression of EZH2 and hypertrimethylation of H3K27 have been implicated in a number of cancers. Several selective inhibitors of EZH2 have been reported recently. Herein we disclose UNC1999, the first orally bioavailable inhibitor that has high <i>in vitro</i> potency for wild-type and mutant EZH2 as well as EZH1, a closely related H3K27 methyltransferase that shares 96% sequence identity with EZH2 in their respective catalytic domains. UNC1999 was highly selective for EZH2 and EZH1 over a broad range of epigenetic and non-epigenetic targets, competitive with the cofactor SAM and non-competitive with the peptide substrate. This inhibitor potently reduced H3K27me3 levels in cells and selectively killed diffused large B cell lymphoma cell lines harboring the EZH2^Y641N mutant. Importantly, UNC1999 was orally bioavailable in mice, making this inhibitor a valuable tool for investigating the role of EZH2 and EZH1 in chronic animal studies. We also designed and synthesized UNC2400, a close analogue of UNC1999 with potency >1,000-fold lower than that of UNC1999 as a negative control for cell-based studies. Finally, we created a biotin-tagged UNC1999 (UNC2399), which enriched EZH2 in pull-down studies, and a UNC1999–dye conjugate (UNC2239) for co-localization studies with EZH2 in live cells. Taken together, these compounds represent a set of useful tools for the biomedical community to investigate the role of EZH2 and EZH1 in health and disease

Targeting EZH2 and PRC2 dependence as novel anticancer therapy

Distinctive patterns of chromatin modification control gene expression and define cellular identity during development and cell differentiation. Polycomb repressive complex 2 (PRC2), the sole mammalian enzymatic complex capable of establishing gene-repressive high-degree methylation of histone H3 at lysine 27 (H3K27), plays crucial roles in regulation of normal and malignant hematopoiesis. Recently, increasing evidence has indicated that recurrent gain-of-function mutation and overexpression of EZH2, the catalytic subunit of PRC2, drive and promote malignant transformation such as B-cell lymphomagenesis, providing a rationale for PRC2 inhibition as a novel anticancer strategy. Here, we summarize the recently developed strategies for inhibition of PRC2, which include a series of highly specific, highly potent, small-molecule inhibitors of EZH2 and EZH1, an EZH2-related methyltransferase. PRC2 establishes functional crosstalk with numerous epigenetic machineries during dynamic regulation of gene transcription. Perturbation of such functional crosstalk caused by genetic events observed in various hematologic cancers, such as inactivation of SNF5 and somatic mutation of UTX, confers PRC2 dependence, thus rendering an increased sensitivity to PRC2 inhibition. We discuss our current understanding of EZH2 somatic mutations frequently found in B-cell lymphomas and recurrent mutations in various other epigenetic regulators as novel molecular predictors and determinants of PRC2 sensitivity. As recent advances have indicated a critical developmental or tumor-suppressive role for PRC2 and EZH2 in various tissue types, we discuss concerns over potentially toxic or even adverse effects associated with EZH2/1 inhibition in certain biological contexts or on cancer genetic background. Collectively, inhibition of PRC2 catalytic activity has emerged as a promising therapeutic intervention for the precise treatment of a range of genetically defined hematologic malignancies and can be potentially applied to a broader spectrum of human cancers that bear similar genetic and epigenetic characteristics. Published by Elsevier Inc. on behalf of ISEH - International Society for Experimental Hematology