Design and Synthesis of EZH2-Based PROTACs to Degrade the PRC2 Complex for Targeting the Noncatalytic Activity of EZH2

Pharmacological inhibition of EZH2 using a covalent inhibitor suppresses human ovarian cancer cell migration and invasion

Metastasis is the cause of poor prognosis in ovarian cancer (OC). Enhancer of Zeste homolog 2 (EZH2), a histone-lysine N-methyltransferase enzyme, promotes OC cell migration and invasion by regulating the expression of tissue inhibitor of metalloproteinase-2 (TIMP2) and matrix metalloproteinases-9 (MMP9). Hence, we speculated that EZH2-targeting therapy might suppress OC migration and invasion. In this study, the expression of EZH2, TIMP2, and MMP9 in OC tissues and cell lines was analyzed using The Cancer Genome Atlas (TCGA) database and western blotting, respectively. The effects of SKLB-03220, an EZH2 covalent inhibitor, on OC cell migration and invasion were investigated using wound-healing assays, Transwell assays, and immunohistochemistry. TCGA database analysis confirmed that the EZH2 and MMP9 mRNA expression was significantly higher in OC tissues, whereas TIMP2 expression was significantly lower than that in normal ovarian tissues. Moreover, EZH2 negatively correlated with TIMP2 and positively correlated with MMP9 expression. In addition to the anti-tumor activity of SKLB-03220 in a PA-1 xenograft model, immunohistochemistry results showed that SKLB-03220 markedly increased the expression of TIMP2 and decreased the expression of MMP9. Additionally, wound-healing and Transwell assays showed that SKLB-03220 significantly inhibited the migration and invasion of both A2780 and PA-1 cells in a concentration-dependent manner. SKLB-03220 inhibited H3K27me3 and MMP9 expression and increased TIMP2 expression in PA-1 cells. Taken together, these results indicate that the EZH2 covalent inhibitor SKLB-03220 inhibits metastasis of OC cells by upregulating TIMP2 and downregulating MMP9, and could thus serve as a therapeutic agent for OC.

Exposure to the extremely low-frequency electromagnetic field induces changes in the epigenetic regulation of gene expression in the endometrium

Increasing technological development results in more sources of the extremely low-frequency electromagnetic field (ELF-EMF), which is recognized as an environmental risk factor. The results of the past study indicate that the ELF-EMF can affect the level of DNA methylation. The study aimed to determine whether the ELF-EMF induces changes in epigenetic regulation of gene expression in the endometrium of pigs during the peri-implantation period. Endometrial slices (100 ± 5 mg) collected on days 15-16 of pregnancy were exposed in vitro to the ELF-EMF at a frequency of 50 Hz for 2 h of treatment duration. To determine the impact of the ELF-EMF on elements of epigenetic regulations involved in DNA methylation, histone modification, and microRNA biogenesis in the endometrium, the DNMT1 and DNMT3a; EZH2, UHRF1, and MBD1; DICER1 and DGCR8 mRNA transcript and protein abundance were analyzed using Real-Time PCR and Western blot, respectively. Moreover, EED and SUZ12 mRNA transcript, global DNA methylation, and the activity of histone deacetylase (HDAC) were analyzed. The changes in the abundance of DNMT1 and DNMT3a, EZH2 mRNA transcript and protein, EED and SUZ12 mRNA transcript, global DNA methylation level, HDAC activity, and the abundance of proteins involved in microRNA biogenesis evoked by the ELF-EMF in the endometrium were observed. The ELF-EMF possesses the potential to alter epigenetic regulation of gene expression in the porcine endometrium. Observed alterations may be the reason for changes in the transcriptomic profile of the endometrium exposed to the ELF-EMF which in turn may disrupt biological processes in the uterus during peri-implantation.

Discovery of a novel, highly potent EZH2 PROTAC degrader for targeting non-canonical oncogenic functions of EZH2

Aberrant expression of EZH2, the main catalytic subunit of PRC2, has been implicated in numerous cancers, including leukemia, breast, and prostate. Recent studies have highlighted non-catalytic oncogenic functions of EZH2, which EZH2 catalytic inhibitors cannot attenuate. Therefore, proteolysis-targeting chimera (PROTAC) degraders have been explored as an alternative therapeutic approach to suppress both canonical and non-canonical oncogenic activity. Here we present MS8847, a novel, highly potent EZH2 PROTAC degrader that recruits the E3 ligase von Hippel-Lindau (VHL). MS8847 degrades EZH2 in a concentration-, time-, and ubiquitin-proteasome system (UPS)-dependent manner. Notably, MS8847 induces superior EZH2 degradation and anti-proliferative effects in MLL-rearranged (MLL-r) acute myeloid leukemia (AML) cells compared to previously published EZH2 PROTAC degraders. Moreover, MS8847 degrades EZH2 and inhibits cell growth in triple-negative breast cancer (TNBC) cell lines, displays efficacy in a 3D TNBC in vitro model, and has a pharmacokinetic (PK) profile suitable for in vivo efficacy studies. Overall, MS8847 is a valuable chemical tool for the biomedical community to investigate canonical and non-canonical oncogenic functions of EZH2.

Regulation of EZH2 protein stability: new mechanisms, roles in tumorigenesis, and roads to the clinic

The importance of EZH2 as a key methyltransferase has been well documented theoretically. Practically, the first EZH2 inhibitor Tazemetostat (EPZ6438), was approved by FDA in 2020 and is used in clinic. However, for most solid tumors it is not as effective as desired and the scope of clinical indications is limited, suggesting that targeting its enzymatic activity may not be sufficient. Recent technologies focusing on the degradation of EZH2 protein have drawn attention due to their potential robust effects. This review focuses on the molecular mechanisms that regulate EZH2 protein stability via post-translational modifications (PTMs), mainly including ubiquitination, phosphorylation, and acetylation. In addition, we discuss recent advancements of multiple proteolysis targeting chimeras (PROTACs) strategies and the latest degraders that can downregulate EZH2 protein. We aim to highlight future directions to expand the application of novel EZH2 inhibitors by targeting both EZH2 enzymatic activity and protein stability.

Overview of epigenetic degraders based on PROTAC, molecular glue, and hydrophobic tagging technologies

Epigenetic pathways play a critical role in the initiation, progression, and metastasis of cancer. Over the past few decades, significant progress has been made in the development of targeted epigenetic modulators (e.g., inhibitors). However, epigenetic inhibitors have faced multiple challenges, including limited clinical efficacy, toxicities, lack of subtype selectivity, and drug resistance. As a result, the design of new epigenetic modulators (e.g., degraders) such as PROTACs, molecular glue, and hydrophobic tagging (HyT) degraders has garnered significant attention from both academia and pharmaceutical industry, and numerous epigenetic degraders have been discovered in the past decade. In this review, we aim to provide an in-depth illustration of new degrading strategies (2017-2023) targeting epigenetic proteins for cancer therapy, focusing on the rational design, pharmacodynamics, pharmacokinetics, clinical status, and crystal structure information of these degraders. Importantly, we also provide deep insights into the potential challenges and corresponding remedies of this approach to drug design and development. Overall, we hope this review will offer a better mechanistic understanding and serve as a useful guide for the development of emerging epigenetic-targeting degraders.

Design, synthesis, and evaluation of VHL-based EZH2 degraders for breast cancer

EZH2 (enhancer of zeste homolog 2) is one of the most important histone methyltransferases (HMTs), and overexpression of EZH2 can lead to proliferation, migration and angiogenesis of tumor cells. But most of EZH2 inhibitors are only effective against some hematologic malignancies and have poor efficacy against solid tumors. Here, we report the design, synthesis, and evaluation of highly potent proteolysis targeting chimeric (PROTACs) small molecules targeting EZH2. We developed a potent and effective EZH2 degrader P4, which effectively induced EZH2 protein degradation and inhibited breast cancer cell growth. Further studies showed that P4 can significantly decrease the degree of H3K27me3 in MDA-MB-231 cell line, induce apoptosis and G0/G1 phase arrest in Pfeiffer and MDA-MB-231 cell lines. Therefore, P4 is a potential anticancer molecule for breast cancer treatment.

Discovery of a PROTAC degrader for METTL3-METTL14 complex

N6-methyladenosine (m6A) methylation is the most abundant type of RNA modification that is mainly catalyzed by the METTL3-METTL14 methyltransferase complex. This complex has been linked to multiple cancers and is considered a promising therapeutic target for acute myeloid leukemia (AML). However, only a few METTL3 inhibitors targeting the catalytic activity were developed recently. Here, we present the discovery of WD6305 as the potent and selective proteolysis-targeting chimera (PROTAC) degrader of METTL3-METTL14 complex. WD6305 suppresses m6A modification and the proliferation of AML cells, and promotes apoptosis much more effectively than its parent inhibitor. WD6305 also affects a variety of signaling pathways related to the development and proliferation of AML. Collectively, our study reveals PROTAC degradation of METTL3-METTL14 complex as a potential anti-leukemic strategy and provides desirable chemical tool for further understanding METTL3-METTL14 protein functions.

Small molecules targeting selected histone methyltransferases (HMTs) for cancer treatment: Current progress and novel strategies

Histone methyltransferases (HMTs) play a critical role in gene post-translational regulation and diverse physiological processes, and are implicated in a plethora of human diseases, especially cancer. Increasing evidences demonstrate that HMTs may serve as a potential therapeutic target for cancer treatment. Thus, the development of HMTs inhibitor have been pursued with steadily increasing interest over the past decade. However, the disadvantages such as insufficient clinical efficacy, moderate selectivity, and propensity for acquired resistance have hindered the development of conventional HMT inhibitors. New technologies and methods are imperative to enhance the anticancer activity of HMT inhibitors. In this review, we first review the structure and biological functions of the several essential HMTs, such as EZH2, G9a, PRMT5, and DOT1L. The internal relationship between these HMTs and cancer is also expounded. Next, we mainly focus on the latest progress in the development of HMT modulators encompassing dual-target inhibitors, targeted protein degraders and covalent inhibitors from perspectives such as rational design, pharmacodynamics, pharmacokinetics, and clinical status. Lastly, we also discuss the challenges and future directions for HMT-based drug discovery for cancer therapy.

Conformationally constrained potent inhibitors for enhancer of zeste homolog 2 (EZH2)

The enhancer of zeste homolog 2 (EZH2) plays the role of the main catalytic subunit of polycomb repressive complex 2 (PRC2) that catalyzes the methylation of histone H3 lysine 27 (H3K27). Overexpression or mutation of EZH2 has been observed in many types of hematologic malignancies and solid tumors, such as myeloma, lymphoma, prostate, breast, kidney, and lung cancers. EZH2 has been demonstrated as a promising therapeutic target for the treatment of tumors. Based on the structure of 1 (EPZ-6438), a series of novel conformationally constrained derivatives were designed and synthesized aiming to improve the EZH2 inhibition activity, especially for mutated EZH2. Structure and activity relationship (SAR) exploration and optimization at both enzymatic and cellular levels led to the discovery of 28. In vitro, 28 displayed potent EZH2 inhibition activity with an IC50 value of 0.95 nM, which is comparable to EPZ-6438 (1). 28 exhibited high anti-proliferation activity against different lymphoma cell lines including WSU-DLCL2, Pfeiffer and Karpas-422 (IC50 = 2.36, 1.73, and 1.82 nM, respectively). In vivo, 28 showed acceptable pharmacokinetic characteristics (oral bioavailability F = 36.9%) and better efficacy than 1 in both Pfeiffer and Karpas-422 xenograft mouse models, suggesting that it can be further developed as a potential therapeutic candidate for EZH2-associated cancers.

Discovery of dihydropyridinone derivative as a covalent EZH2 degrader

EZH2 is overexpressed in multiple types of cancer and high expression level of EZH2 correlates with poor prognosis. Besides the regulation of H3K27 trimethylation, EZH2 itself regulates its downstream proteins in a PRC2- and methylation-independent way. Starting from an approved EZH2 inhibitor EPZ-6438, we used covalent drug design and medicinal chemistry approaches to discover a novel covalent EZH2 degrader 38, which forms a covalent bond with EZH2 Cys663 and showed strong biochemical activities against EZH2 WT and mutants. Compound 38 exhibited potent antiproliferation effects against both B-cell lymphoma and TNBC cell lines by reducing the levels of H3K27me3 and EZH2. The mass spectrometry, washout and competition experiments confirmed the covalent binding of 38 to EZH2. This study demonstrates that covalent EZH2 degraders could provide an opportunity for the development of promising new drug candidates.

Targeting reversible post-translational modifications with PROTACs: a focus on enzymes modifying protein lysine and arginine residues

PROTACs represent an emerging field in medicinal chemistry, which has already led to the development of compounds that reached clinical studies. Posttranslational modifications contribute to the complexity of proteomes, with 2846 disease-associated sites. PROTAC field is very advanced in targeting kinases, while its use for enzymes mediating posttranslational modifications of the basic amino acid residues, started to be developed recently. Therefore, we bring together this less popular class of PROTACs, targeting lysine acetyltransferases/deacetylases, lysine and arginine methyltransferases, ADP-ribosyltransferases, E3 ligases, and ubiquitin-specific proteases. We put special emphasis on structural aspects of PROTAC elements to facilitate the lengthy experimental endeavours directed towards developing PROTACs. We will cover the period from the inception of the field, 2017, to April 2023.

Redirecting the specificity of tripartite motif containing-21 scaffolds using a novel discovery and design approach

Hijacking the ubiquitin proteasome system to elicit targeted protein degradation (TPD) has emerged as a promising therapeutic strategy to target and destroy intracellular proteins at the post-translational level. Small molecule-based TPD approaches, such as proteolysis-targeting chimeras (PROTACs) and molecular glues, have shown potential, with several agents currently in clinical trials. Biological PROTACs (bioPROTACs), which are engineered fusion proteins comprised of a target-binding domain and an E3 ubiquitin ligase, have emerged as a complementary approach for TPD. Here, we describe a new method for the evolution and design of bioPROTACs. Specifically, engineered binding scaffolds based on the third fibronectin type III domain of human tenascin-C (Tn3) were installed into the E3 ligase tripartite motif containing-21 (TRIM21) to redirect its degradation specificity. This was achieved via selection of naïve yeast-displayed Tn3 libraries against two different oncogenic proteins associated with B-cell lymphomas, mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) and embryonic ectoderm development protein (EED), and replacing the native substrate-binding domain of TRIM21 with our evolved Tn3 domains. The resulting TRIM21-Tn3 fusion proteins retained the binding properties of the Tn3 as well as the E3 ligase activity of TRIM21. Moreover, we demonstrated that TRIM21-Tn3 fusion proteins efficiently degraded their respective target proteins through the ubiquitin proteasome system in cellular models. We explored the effects of binding domain avidity and E3 ligase utilization to gain insight into the requirements for effective bioPROTAC design. Overall, this study presents a versatile engineering approach that could be used to design and engineer TRIM21-based bioPROTACs against therapeutic targets.

Design, synthesis and evaluation of EZH2-based PROTACs targeting PRC2 complex in lymphoma

EZH2 is a member of PcG and can induce the occurrence of cancer when it is highly expressed. As an EZH2 inhibitor, Tazemetostat (EPZ6438) can inhibit the methylation catalytic activity of EZH2. However, many studies have shown that inhibition of EZH2 alone does not efficiently block tumor development. Therefore, in this study, proteolytic targeting chimera technology was employed to enhance the antiproliferative potency of EPZ6438 by degrading the oncogenic activity of EZH2. Several PROTACs have been synthesized by combining EPZ6438 with four E3 ligase ligands based on VHL, CRBN, MDM2, and cIAP E3 ligase systems. In our study, compound E-3P-MDM2 is the most active PROTAC molecule. It degraded EZH2 of the SU-DHL-6 cells in a concentration and dose-dependent manner and also degraded both EED and SUZ12 protein without affecting their mRNA levels, then significantly inhibited the expression of H3K27me3. The in vitro antiproliferative activity of E-3P-MDM2 was much stronger than that of EPZ6438.

Recent advances in developing degraders & inhibitors of lysine methyltransferases

Over the last several decades, there has been continued interest in developing novel therapeutic approaches targeting protein lysine methyltransferases (PKMTs). Along with PKMT inhibitors, targeted protein degradation (TPD) has emerged as a promising strategy to attenuate aberrant PKMT activity. Particularly, proteolysis targeting chimeras (PROTACs) effectively eliminate PKMTs of interest, suppressing all enzymatic and non-enzymatic functions. PROTACs and other TPD approaches add new depth to PKMT research and novel therapeutics discovery. This review focuses on recent advances in PKMT degrader and inhibitor development over the last several years.

3D based generative PROTAC linker design with reinforcement learning

Proteolysis targeting chimera (PROTAC), has emerged as an effective modality to selectively degrade disease-related proteins by harnessing the ubiquitin-proteasome system. Due to PROTACs' hetero-bifunctional characteristics, in which a linker joins a warhead binding to a protein of interest (POI), conferring specificity and a E3-ligand binding to an E3 ubiquitin ligase, this could trigger the ubiquitination and transportation of POI to the proteasome, followed by degradation. The rational PROTAC linker design is challenging due to its relatively large molecular weight and the complexity of maintaining the binding mode of warhead and E3-ligand in the binding pockets of counterpart. Conventional linker generation method can only generate linkers in either 1D SMILES or 2D graph, without taking into account the information of ternary structures. Here we propose a novel 3D linker generative model PROTAC-INVENT which can not only generate SMILES of PROTAC but also its 3D putative binding conformation coupled with the target protein and the E3 ligase. The model is trained jointly with the RL approach to bias the generation of PROTAC structures toward pre-defined 2D and 3D based properties. Examples were provided to demonstrate the utility of the model for generating reasonable 3D conformation of PROTACs. On the other hand, our results show that the associated workflow for 3D PROTAC conformation generation can also be used as an efficient docking protocol for PROTACs.

Dual Targeting of EZH2 Degradation and EGFR/HER2 Inhibition for Enhanced Efficacy against Burkitt's Lymphoma

EZH2, a histone methyltransferase, contributes significantly to cancer cell survival and proliferation. Although various EZH2 inhibitors have demonstrated promise in treating lymphoma, they have not fully managed to curb lymphoma cell proliferation despite effective reduction of the H3K27me3 mark. We used MS1943, an EZH2 selective degrader, which successfully diminishes EZH2 levels in lymphoma cells. Additionally, lapatinib, a dual inhibitor of the epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) tyrosine kinases, targets a receptor protein that regulates cell growth and division. The overexpression of this protein is often observed in lymphoma cells. Our study aims to combine these two therapeutic targets to stimulate apoptosis pathways and potentially suppress Burkitt's lymphoma cell survival and proliferation in a complementary and synergistic manner. We observed that a combination of MS1943 and lapatinib induced apoptosis in Daudi cells and caused cell cycle arrest at the S and G2/M phases in both Ramos and Daudi cells. This strategy, using a combination of MS1943 and lapatinib, presents a promising therapeutic approach for treating lymphoma and potentially Burkitt's lymphoma.

Targeting EZH2 in SMARCB1-deficient sarcomas: Advances and opportunities to potentiate the efficacy of EZH2 inhibitors

Soft tissue sarcomas (STSs) are rare mesechymal malignancies characterized by distintive molecular, histological and clinical features. Many STSs are considered as predominatly epigenetic diseases due to underlying chromatin deregulation. Discovery of deregulated functional antagonism between the chromatin remodeling BRG1/BRM-associated (BAFs) and the histone modifying Polycomb repressor complexes (PRCs) has provided novel actionable targets. In epithelioid sarcoma (ES), extracranial, extrarenal malignant rhabdoid tumors (eMRTs) and synovial sarcoma (SS), the total or partial loss of the BAF core subunit SMARCB1, driven by different alterations, is associated with PRC2 deregulation and dependency on its enzymatic subunit, EZH2. In these SMARCB1-deficient STSs, aberrant EZH2 expression and/or activity emerged as a druggable vulnerability. Although preclinical investigation supported EZH2 targeting as a promising therapeutic option, clinical studies demonstrated a variable response to EZH2 inhibitors. Actually, whereas the clinical benefit recorded in ES patients prompted the FDA approval of the EZH2 inhibitor tazemetostat, the modest and sporadic responses observed in eMRT and SS patients highlighted the need to deepen mechanistic as well as pharmacological investigations to improve drug effectiveness. We summarize the current knowledge of different mechanisms driving SMARCB1 deficiency and EZH2 deregulation in ES, eMRT and SS along with preclinical and clinical studies of EZH2-targeting agents. Possible implication of the PRC2- and enzymatic-independent functions of EZH2 and of its homolog, EZH1, in the response to anti-EZH2 agents will be discussed together with combinatorial strategies under investigation to improve the efficacy of EZH2 targeting in these tumors.

Chemically induced degradation of epigenetic targets

Proteolysis-targeting chimeras (PROTACs) are heterobifunctional small molecules that induce the ternary complex formation between a protein-of-interest (POI) and an E3 ligase, leading to targeted polyubiquitination and degradation of the POI. Particularly, PROTACs have the distinct advantage of targeting both canonical and noncanonical functions of epigenetic targets over traditional inhibitors, which typically target canonical functions only, resulting in greater therapeutic efficacy. In this review, we methodically analyze published PROTAC degraders of epigenetic writer, reader, and eraser proteins and their in vitro and in vivo effects. We highlight the mechanism of action of these degraders and their advantages in targeting both canonical and noncanonical functions of epigenetic targets in the context of cancer treatment. Furthermore, we present a future outlook for this exciting field. Overall, pharmacological degradation of epigenetic targets has emerged as an effective and attractive strategy to thwart cancer progression and growth.

Recent advances in EZH2-based dual inhibitors in the treatment of cancers

The enhancer of zeste homolog 2 (EZH2) protein is the catalytic subunit of one of the histone methyltransferases. EZH2 catalyzes the trimethylation of lysine 27 of histone H3 (H3K27me3) and further alters downstream target levels. EZH2 is upregulated in cancer tissues, wherein its levels correlate strongly with cancer genesis, progression, metastasis, and invasion. Consequently, it has emerged as a novel anticancer therapeutic target. Nonetheless, developing EZH2 inhibitors (EZH2i) has encountered numerous difficulties, such as pre-clinical drug resistance and poor therapeutic effect. The EZH2i synergistically suppresses cancers when used in combination with additional antitumor drugs, such as PARP inhibitors, HDAC inhibitors, BRD4 inhibitors, EZH1 inhibitors, and EHMT2 inhibitors. Typically, the use of dual inhibitors of two different targets mediated by one individual molecule has been recognized as the preferred approach for overcoming the limitations of EZH2 monotherapy. The present review discusses the theoretical basis for designing EZH2-based dual-target inhibitors, and also describes some in vitro and in vivo analysis results.

Targeted Degradation of PRC1 Components, BMI1 and RING1B, via a Novel Protein Complex Degrader Strategy

Polycomb repressive complex 1 (PRC1) is an essential epigenetic regulator that mainly controls histone H2A Lys119 mono-ubiquitination (H2AK119ub). B cell-specific Moloney murine leukemia virus Integration site 1 (BMI1) and really interesting new gene 1B (RING1B) are PRC1 core components and play critical roles in the development of various cancers. However, therapeutic agents targeting PRC1 are very limited. In this study, MS147, the first degrader of PRC1 core components, BMI1 and RING1B, is discovered via a novel protein complex degradation strategy that utilizes the target protein's interacting partner protein (embryonic ectoderm development (EED)). MS147, which comprises an EED small-molecule binder linked to a ligand of the E3 ligase von Hippel-Lindau (VHL), degrades BMI1/RING1B in an EED-, VHL-, ubiquitination-, and time-dependent manner. MS147 preferentially degrades BMI1/RING1B over polycomb repressive complex 2 (PRC2) core components. Consequently, MS147 effectively reduces H2AK119ub, but not histone H3 Lys27 tri-methylation (H3K27me3), which is catalyzed by PRC2. Furthermore, MS147 effectively inhibits the proliferation of cancer cell lines that are insensitive to PRC2 inhibitors/degraders. Overall, this study provides a novel BMI1/RING1B degrader, which is a useful chemical tool to further investigate the roles of PRC1 in cancer, and a novel protein complex degradation strategy, which can potentially expand the degradable human proteome.

Pharmacological inhibition of EZH2 by ZLD1039 suppresses tumor growth and pulmonary metastasis in melanoma cells in vitro and in vivo

The incidence and mortality rate of malignant melanoma are increasing worldwide. Metastasis reduces the efficacy of current melanoma therapies and leads to poor prognosis for patients. EZH2 is a methyltransferase that promotes the proliferation, metastasis, and drug resistance of tumor cells by regulating transcriptional activity. EZH2 inhibitors could be effective in melanoma therapies. Herein, we aimed to investigate whether the pharmacological inhibition of EZH2 by ZLD1039, a potent and selective S-adenosyl-l-methionine-EZH2 inhibitor, suppresses tumor growth and pulmonary metastasis in melanoma cells. Results showed that ZLD1039 selectively reduced H3K27 methylation in melanoma cells by inhibiting EZH2 methyltransferase activity. Additionally, ZLD1039 exerted excellent antiproliferative effects on melanoma cells in 2D and 3D culture systems. Administration of ZLD1039 (100 mg/kg) by oral gavage caused antitumor effects in the A375 subcutaneous xenograft mouse model. RNA sequencing and GSEA revealed that the ZLD1039-treated tumors exhibited changes in the gene sets enriched from the "Cell Cycle" and "Oxidative Phosphorylation", whereas the "ECM receptor interaction" gene set had a negative enrichment score. Mechanistically, ZLD1039 induced G0/G1 phase arrest by upregulating p16 and p27 and inhibiting the functions of the cyclin D1/CDK6 and cyclin E/CDK2 complexes. Moreover, ZLD1039 induced apoptosis in melanoma cells via the mitochondrial reactive oxygen species apoptotic pathway, consistent with the changes in transcriptional signatures. ZLD1039 also exhibited excellent antimetastatic effects on melanoma cells in vitro and in vivo. Our data highlight that ZLD1039 may be effective against melanoma growth and pulmonary metastasis and thus could serve as a therapeutic agent for melanoma.

Discovery of Norbornene as a Novel Hydrophobic Tag Applied in Protein Degradation

Hydrophobic tagging (HyT) is a potential therapeutic strategy for targeted protein degradation (TPD). Norbornene was discovered as an unprecedented hydrophobic tag in this study and was used to degrade the anaplastic lymphoma kinase (ALK) fusion protein by linking it to ALK inhibitors. The most promising degrader, Hyt-9, potently reduced ALK levels through Hsp70 and the ubiquitin-proteasome system (UPS) in vitro without compensatory upregulation of ALK. Furthermore, Hyt-9 exhibited a significant tumor-inhibiting effect in vivo with moderate oral bioavailability. More importantly, norbornene can also be used to degrade the intractable enhancer of zeste homolog 2 (EZH2) when tagged with the EZH2 inhibitor tazemetostat. Thus, the discovery of novel hydrophobic norbornene tags shows promise for the future development of TPD technology.

PROTAC Linkerology Leads to an Optimized Bivalent Chemical Degrader of Polycomb Repressive Complex 2 (PRC2) Components

Bivalent chemical degraders, otherwise known as proteolysis-targeting chimeras (PROTACs), have proven to be an efficient strategy for targeting overexpressed or mutated proteins in cancer. PROTACs provide an alternative approach to small-molecule inhibitors, which are restricted by occupancy-driven pharmacology, often resulting in acquired inhibitor resistance via compensatory increases in protein expression. Despite the advantages of bivalent chemical degraders, they often have suboptimal physicochemical properties and optimization for efficient degradation remains highly unpredictable. Herein, we report the development of a potent EED-targeted PRC2 degrader, UNC7700. UNC7700 contains a unique cis-cyclobutane linker and potently degrades PRC2 components EED (DC50 = 111 nM; Dmax = 84%), EZH2WT/EZH2Y641N (DC50 = 275 nM; Dmax = 86%), and to a lesser extent SUZ12 (Dmax = 44%) after 24 h in a diffuse large B-cell lymphoma DB cell line. Characterization of UNC7700 and related compounds for ternary complex formation and cellular permeability to provide a rationale for the observed improvement in degradation efficiency remained challenging. Importantly, UNC7700 dramatically reduces H3K27me3 levels and is anti-proliferative in DB cells (EC50 = 0.79 ± 0.53 μM).

Dissecting and targeting noncanonical functions of EZH2 in multiple myeloma via an EZH2 degrader

Multiple myeloma (MM) is the second most common hematological malignancy with poor prognosis. Enhancer of zeste homolog 2 (EZH2) is the enzymatic subunit of polycomb repressive complex 2 (PRC2), which catalyzes trimethylation of histone H3 lysine 27 (H3K27me3) for transcriptional repression. EZH2 have been implicated in numerous hematological malignancies, including MM. However, noncanonical functions of EZH2 in MM tumorigenesis are not well understood. Here, we uncovered a noncanonical function of EZH2 in MM malignancy. In addition to the PRC2-mediated and H3K27me3-dependent canonical function, EZH2 interacts with cMyc and co-localizes with gene activation-related markers, promoting MM tumorigenesis in a PRC2- and H3K27me3-independent manner. Both canonical EZH2-PRC2 and noncanonical EZH2-cMyc complexes can be effectively depleted in MM cells by MS177, an EZH2 degrader we reported previously, leading to profound activation of EZH2-PRC2-associated genes and simultaneous suppression of EZH2-cMyc oncogenic nodes. The MS177-induced degradation of both canonical EZH2-PRC2 and noncanonical EZH2-cMyc complexes also reactivated immune response genes in MM cells. Phenotypically, targeting of EZH2's both canonical and noncanonical functions by MS177 effectively suppressed the proliferation of MM cells both in vitro and in vivo. Collectively, this study uncovers a new noncanonical function of EZH2 in MM tumorigenesis and provides a novel therapeutic strategy, pharmacological degradation of EZH2, for treating EZH2-dependent MM.

Design, Synthesis, and Biological Evaluation of a Potent Dual EZH2-BRD4 Inhibitor for the Treatment of Some Solid Tumors

Enhancer of zeste homolog 2 (EZH2) mediates the trimethylation of histone 3 lysine 27 (H3K27) to promote gene silencing. Inhibition of EZH2 is a viable strategy for cancer treatment; however, only a small subset of hematological malignancies are sensitive to small-molecule EZH2 inhibitors. EZH2 inhibitors cause H3K27 acetylation in most solid tumors, leading to drug resistance. Bromodomain-containing protein 4 (BRD4) inhibitors were reported to enhance the sensitivity of solid tumors to EZH2 inhibitors. Thus, we designed and evaluated a series of dual EZH2-BRD4 inhibitors. ZLD-2, the most promising compound, exhibited potent inhibitory activity against EZH2 and BRD4. Compared to the EZH2 inhibitor GSK126, ZLD-2 displayed potent antiproliferation activity against breast, lung, bladder, and pancreatic cancer cells. In vivo, ZLD-2 exhibited antitumor activity in a BxPC-3 mouse xenograft model, whereas GSK126 promoted tumor growth. Thus, ZLD-2 may be a lead compound for treating solid tumors.

PROTACs in Epigenetic Cancer Therapy: Current Status and Future Opportunities

The epigenetic regulation of gene functions has been proven to be strongly associated with the development and progression of cancer. Reprogramming the cancer epigenome landscape is one of the most promising target therapies in both treatments and in reversing drug resistance. Proteolytic targeted chimeras (PROTACs) are an emerging therapeutic modality for selective degradation via the native ubiquitin-proteasome system. Rapid advances in PROTACs have facilitated the exploration of targeting epigenetic proteins, a lot of PROTAC degraders have already been designed in the field of epigenetic cancer therapy, and PROTACs targeting epigenetic proteins can better exploit target druggability and improve the mechanistic understanding of the epigenetic regulation of cancer. Thus, this review focuses on the progress made in the development of PROTAC degraders and PROTAC drugs targeting epigenetics in cancer and discusses challenges and future opportunities for the field.

Discovery of IHMT-337 as a potent irreversible EZH2 inhibitor targeting CDK4 transcription for malignancies

Enhancer of zeste homolog 2 (EZH2), an enzymatic subunit of PRC2 complex, plays an important role in tumor development and progression through its catalytic and noncatalytic activities. Overexpression or gain-of-function mutations of EZH2 have been significantly associated with tumor cell proliferation of triple-negative breast cancer (TNBC) and diffuse large B-cell lymphoma (DLBCL). As a result, it has gained interest as a potential therapeutic target. The currently available EZH2 inhibitors, such as EPZ6438 and GSK126, are of benefit for clinical using or reached clinical trials. However, certain cancers are resistant to these enzymatic inhibitors due to its noncatalytic or transcriptional activity through modulating nonhistone proteins. Thus, it may be more effective to synergistically degrade EZH2 in addition to enzymatic inhibition. Here, through a rational design and chemical screening, we discovered a new irreversible EZH2 inhibitor, IHMT-337, which covalently bounds to and degrades EZH2 via the E3 ligase CHIP-mediated ubiquitination pathway. Moreover, we revealed that IHMT-337 affects cell cycle progression in TNBC cells through targeting transcriptional regulating of CDK4, a novel PRC2 complex- and enzymatic activity-independent function of EZH2. More significantly, our compound inhibits both DLBCL and TNBC cell proliferation in different preclinical models in vitro and in vivo. Taken together, our findings demonstrate that in addition to enzymatic inhibition, destroying of EZH2 by IHMT-337 could be a promising therapeutic strategy for TNBC and other malignancies that are independent of EZH2 enzymatic activity.

Progress of small molecules for targeted protein degradation: PROTACs and other technologies

Recent years have witnessed the rapid development of targeted protein degradation (TPD), especially proteolysis targeting chimeras. These degraders have manifested many advantages over small molecule inhibitors. To date, a huge number of degraders have been excavated against over 70 disease-related targets. In particular, degraders against estrogen receptor and androgen receptor have crowded into phase II clinical trial. TPD technologies largely expand the scope of druggable targets, and provide powerful tools for addressing intractable problems that can not be tackled by traditional small molecule inhibitors. In this review, we mainly focus on the structures and biological activities of small molecule degraders as well as the elucidation of mechanisms of emerging TPD technologies. We also propose the challenges that exist in the TPD field at present.

Polycomb Repressive Complex 2 in Oncology

Dynamic regulation of the chromatin state by Polycomb Repressive Complex 2 (PRC2) provides an important mean for epigenetic gene control that can profoundly influence normal development and cell lineage specification. PRC2 and PRC2-induced methylation of histone H3 lysine 27 (H3K27) are critically involved in a wide range of DNA-templated processes, which at least include transcriptional repression and gene imprinting, organization of three-dimensional chromatin structure, DNA replication and DNA damage response and repair. PRC2-based genome regulation often goes wrong in diseases, notably cancer. This chapter discusses about different modes-of-action through which PRC2 and EZH2, a catalytic subunit of PRC2, mediate (epi)genomic and transcriptomic regulation. We will also discuss about how alteration or mutation of the PRC2 core or axillary component promotes oncogenesis, how post-translational modification regulates functionality of EZH2 and PRC2, and how PRC2 and other epigenetic pathways crosstalk. Lastly, we will briefly touch on advances in targeting EZH2 and PRC2 dependence as cancer therapeutics.

Bridged Proteolysis Targeting Chimera (PROTAC) Enables Degradation of Undruggable Targets

Proteolysis Targeting Chimeras (PROTACs) are attractive therapeutic modalities for degrading disease-causing proteins. While many PROTACs have been developed for numerous protein targets, current small-molecule PROTAC approaches cannot target undruggable proteins that do not have small-molecule binders. Here, we present a novel PROTAC approach, termed bridged PROTAC, which utilizes a small-molecule binder of the target protein's binding partner to recruit the protein complex into close proximity with an E3 ubiquitin ligase to target undruggable proteins. Applying this bridged PROTAC strategy, we discovered MS28, the first-in-class degrader of cyclin D1, which lacks a small-molecule binder. MS28 effectively degrades cyclin D1, with faster degradation kinetics and superior degradation efficiency than CDK4/6, through recruiting the CDK4/6-cyclin D1 complex to the von Hippel-Lindau E3 ligase. MS28 also suppressed the proliferation of cancer cells more effectively than CDK4/6 inhibitors and degraders. Altogether, the bridged PROTAC strategy could provide a generalizable platform for targeting undruggable proteins.

Noncanonical EZH2 drives retinoic acid resistance of variant acute promyelocytic leukemias

Cancer cell heterogeneity is a major driver of therapy resistance. To characterize resistant cells and their vulnerabilities, we studied the PLZF-RARA variant of acute promyelocytic leukemia, resistant to retinoic acid (RA), using single-cell multiomics. We uncovered transcriptional and chromatin heterogeneity in leukemia cells. We identified a subset of cells resistant to RA with proliferation, DNA replication, and repair signatures that depend on a fine-tuned E2F transcriptional network targeting the epigenetic regulator enhancer of zeste homolog 2 (EZH2). Epigenomic and functional analyses validated the driver role of EZH2 in RA resistance. Targeting pan-EZH2 activities (canonical/noncanonical) was necessary to eliminate leukemia relapse-initiating cells, which underlies a dependency of resistant cells on an EZH2 noncanonical activity and the necessity to degrade EZH2 to overcome resistance. Our study provides critical insights into the mechanisms of RA resistance that allow us to eliminate treatment-resistant leukemia cells by targeting EZH2, thus highlighting a potential targeted therapy approach. Beyond RA resistance and acute promyelocytic leukemia context, our study also demonstrates the power of single-cell multiomics to identify, characterize, and clear therapy-resistant cells.

Targeting micro-environmental pathways by PROTACs as a therapeutic strategy

Tumor microenvironment (TME) composes of multiple cell types and non-cellular components, which supports the proliferation, metastasis and immune surveillance evasion of tumor cells, as well as accounts for the resistance to therapies. Therefore, therapeutic strategies using small molecule inhibitors (SMIs) and antibodies to block potential targets in TME are practical for cancer treatment. Targeted protein degradation using PROteolysis-TArgeting Chimera (PROTAC) technic has several advantages over traditional SMIs and antibodies, including overcoming drug resistance. Thus many PROTACs are currently under development for cancer treatment. In this review, we summarize the recent progress of PROTAC development that target TME pathways and propose the potential direction of future PROTAC technique to advance as novel cancer treatment options.

Combined inhibition of PARP and EZH2 for cancer treatment: Current status, opportunities, and challenges

Tumors with BRCA1/2 mutations or homologous recombination repair defects are sensitive to PARP inhibitors through the mechanism of synthetic lethality. Several PARP inhibitors are currently approved for ovarian, breast and pancreatic cancer in clinical practice. However, more than 40% of patients with BRCA1/2 mutations are insensitive to PARP inhibitors, which has aroused attention to the mechanism of PARP resistance and sensitization schemes. PARP inhibitor resistance is related to homologous recombination repair, stability of DNA replication forks, PARylation and epigenetic modification. Studies on epigenetics have become the hotspots of research on PARP inhibitor resistance. As an important epigenetic regulator of transcription mediated by histone methylation, EZH2 interacts with PARP through DNA homologous recombination, DNA replication, posttranslational modification, tumor immunity and other aspects. EZH2 inhibitors have been just shifting from the bench to the bedside, but the combination scheme in cancer therapy has not been fully explored yet. Recently, a revolutionary drug design combining PARP inhibitors and EZH2 inhibitors based on PROTAC techniques has shed light on the resolution of PARP inhibitor resistance. This review summarizes the interactions between EZH2 and PARP, suggests the potential PARP inhibitor sensitization effect of EZH2 inhibitors, and further discusses the potential populations that benefit from the combination of EZH2 inhibitors and PARP inhibitors.

Novel Design Strategies to Enhance the Efficiency of Proteolysis Targeting Chimeras

Despite the success of drug discovery over the past decades, many potential drug targets still remain intractable for small molecule modulation. The development of proteolysis targeting chimeras (PROTACs) that trigger degradation of the target proteins provides a conceptually novel approach to address drug targets that remained previously elusive. Currently, the main challenge of PROTAC development is the identification of efficient, tissue- and cell-selective PROTAC molecules with good drug-likeness and favorable safety profiles. This review focuses on strategies to enhance the effectiveness and selectivity of PROTACs. We provide a comprehensive summary of recently reported PROTAC design strategies and discuss the advantages and disadvantages of these strategies. Future perspectives for PROTAC design will also be discussed.

Chemistries of bifunctional PROTAC degraders

Proteolysis targeting chimeras (PROTACs) technology is a novel and promising therapeutic strategy using small molecules to induce ubiquitin-dependent degradation of proteins. It has received extensive attention from both academia and industry as it can potentially access previously inaccessible targets. However, the design and optimization of PROTACs present big challenges for researchers, and the general strategy for its development and optimization is a lot of trial and error based on experience. This review highlights the important advances in this rapidly growing field and critical limitations of the traditional trial-and-error approach to developing PROTACs by analyzing numerous representative examples of PROTACs development. We summarize and analyze the general principles and strategies for PROTACs design and optimization from the perspective of chemical structure design, and propose potential future pathways to facilitate the development of PROTACs.

Discovery of Small-Molecule Degraders of the CDK9-Cyclin T1 Complex for Targeting Transcriptional Addiction in Prostate Cancer

Aberrant hyperactivation of cyclins results in carcinogenesis and therapy resistance in cancers. Direct degradation of the specific cyclin or cyclin-dependent kinase (CDK)-cyclin complex by small-molecule degraders remains a great challenge. Here, we applied the first application of hydrophobic tagging to induce degradation of CDK9-cyclin T1 heterodimer, which is required to keep productive transcription of oncogenes in cancers. LL-K9-3 was identified as a potent small-molecule degrader of CDK9-cyclin T1. Quantitative and time-resolved proteome profiling exhibited LL-K9-3 induced selective and synchronous degradation of CDK9 and cyclin T1. The expressions of androgen receptor (AR) and cMyc were reduced by LL-K9-3 in 22RV1 cells. LL-K9-3 exhibited enhanced anti-proliferative and pro-apoptotic effects compared with its parental CDK9 inhibitor SNS032 and suppressed downstream signaling of CDK9 and AR more effectively than SNS032. Moreover, LL-K9-3 inhibited AR and Myc-driven oncogenic transcriptional programs and exerted stronger inhibitory effects on several intrinsic target genes of AR than the monomeric CDK9 PROTAC (Thal-SNS032).

Chemical biology and pharmacology of histone lysine methylation inhibitors

Histone lysine methylation is a post-translational modification that plays a key role in the epigenetic regulation of a broad spectrum of biological processes. Moreover, the dysregulation of histone lysine methyltransferases (KMTs) has been implicated in the pathogenesis of several diseases particularly cancer. Due to their pathobiological importance, KMTs have garnered immense attention over the last decade as attractive therapeutic targets. These endeavors have culminated in tens of chemical probes that have been used to interrogate many aspects of histone lysine methylation. Besides, over a dozen inhibitors have been advanced to clinical trials, including the EZH2 inhibitor tazemetostat approved for the treatment of follicular lymphoma and advanced epithelioid sarcoma. In this Review, we highlight the chemical biology and pharmacology of KMT inhibitors and targeted protein degraders focusing on the clinical development of EZH1/2, DOT1L, Menin-MLL, and WDR5-MLL inhibitors. We also briefly discuss the pharmacologic targeting of other KMTs.

Targeting Triple-Negative Breast Cancer by a Novel Proteolysis Targeting Chimera Degrader of Enhancer of Zeste Homolog 2

Enhancer of zeste homolog 2 (EZH2), a catalytic subunit of polycomb repressive complex 2 (PRC2), is overexpressed in triple-negative breast cancer (TNBC), correlating with poor prognosis. However, EZH2 catalytic inhibitors are ineffective in suppressing the growth of TNBC cells that are dependent on EZH2. Knockdown of EZH2 inhibits the proliferation of these cells, suggesting that EZH2 protein overexpression but not its catalytic activity is critical for driving TNBC progression. Several proteolysis targeting chimera (PROTAC) degraders of EZH2, including the von Hippel-Lindau (VHL)-recruiting PROTAC YM281, have been reported. However, the effects of these EZH2 PROTACs in TNBC cells were not investigated. Here, we report the discovery and characterization of a novel, potent, and selective EZH2 PROTAC degrader, MS8815 (compound 16), which induced robust EZH2 degradation in a concentration-, time-, and proteasome-dependent manner in TNBC cells. Importantly, 16 effectively suppressed the cell growth in multiple TNBC cell lines and primary patient TNBC cells.

PROTACs: great opportunities for academia and industry (an update from 2020 to 2021)

PROteolysis TArgeting Chimeras (PROTACs) technology is a new protein-degradation strategy that has emerged in recent years. It uses bifunctional small molecules to induce the ubiquitination and degradation of target proteins through the ubiquitin–proteasome system. PROTACs can not only be used as potential clinical treatments for diseases such as cancer, immune disorders, viral infections, and neurodegenerative diseases, but also provide unique chemical knockdown tools for biological research in a catalytic, reversible, and rapid manner. In 2019, our group published a review article “PROTACs: great opportunities for academia and industry” in the journal, summarizing the representative compounds of PROTACs reported before the end of 2019. In the past 2 years, the entire field of protein degradation has experienced rapid development, including not only a large increase in the number of research papers on protein-degradation technology but also a rapid increase in the number of small-molecule degraders that have entered the clinical and will enter the clinical stage. In addition to PROTAC and molecular glue technology, other new degradation technologies are also developing rapidly. In this article, we mainly summarize and review the representative PROTACs of related targets published in 2020–2021 to present to researchers the exciting developments in the field of protein degradation. The problems that need to be solved in this field will also be briefly introduced.

Discovery of precision targeting EZH2 degraders for triple-negative breast cancer

EZH2 is usually overexpressed in TNBC and other tumors, which has a great influence on the occurrence, development and prognosis of tumors. However, current EZH2 inhibitors, including Tazemetostat and GSK126, affect the methyl catalytic capacity of EZH2 and have little effect on the tumorigenic activity of EZH2 itself, resulting in poor efficacy against most solid tumors. Herein, we designed and optimized proteolytic targeting chimeras (PROTACs) precision targeting EZH2. The most active PROTAC molecule U3i has a high affinity for PRC2 complex (K_D = 16.19 nM) and show good inhibitory effects on MDA-MB-231 (IC₅₀ = 0.57 μM) and MDA-MB-468 (IC₅₀ = 0.38 μM) cells. Compared with that of the GSK126, the growth inhibitory activities of U3i against these two TNBC cells increased by approximately 20- and 30-fold. Further studies showed that U3i can degrade PRC2 complex in TNBC cells, induce apoptosis, and cause little damage to normal cells. Therefore, U3i is a potential anticancer molecule for TNBC treatment.

Targeting epigenetic modulators using PROTAC degraders: Current status and future perspective

Epigenetic modulators perform critical functions in gene expression for rapid adaption to external stimuli and are prevalent in all higher-order organisms. The establishment of a link between dysregulation of epigenetic processes and disease pathogenesis, particularly in cancer, has led to much interest in identifying drug targets. This prompted the development of small molecule inhibitors, primarily in haematological malignancies. While there have been epigenetic-targeting drugs to receive FDA approval for the treatment of cancers, many suffer from limited applicability, toxicity and the onset of drug resistance, as our understanding of the biology remains incomplete. The recent advent of genome-wide RNAi and CRISPR screens has shed new light on loss of specific proteins causing vulnerabilities of specific cancer types, highlighting the potential for exploiting synthetic lethality as a therapeutic approach. However, small molecule inhibitors have largely been unable to recapitulate phenotypic effects observed using genome-wide knockdown approaches. This mechanistic disconnect and gap are set to be addressed by targeted protein degradation. Degraders such as PROTACs targeting epigenetic proteins recapitulate CRISPR mediated genetic knockdown at the post-translational level and therefore can better exploit target druggability. Here, we review the current landscape of epigenetic drug discovery, the rationale behind and progress made in the development of PROTAC degraders, and look at future perspectives for the field.

Exploring Methods of Targeting Histone Methyltransferases and Their Applications in Cancer Therapeutics

Histone methyltransferases (HMTs) are enzymes that catalyze the methylation of lysine or arginine residues of histone proteins, a key post-translational modification (PTM). Aberrant expression or activity of these enzymes can lead to abnormal histone methylation of cancer-related genes and thus promote tumorigenesis. Histone methyltransferases have been implicated in chemotherapeutic resistance and immune stimulation, making these enzymes potential therapeutic targets of interest, and chemically targeting these proteins provides an avenue for novel drug development in cancer therapy. This Review aims to discuss the evolution of chemical approaches that have emerged in the past five years to design probes targeting these enzymes, including inhibition through noncovalent inhibitors, covalent inhibitors, and targeted protein degradation through proteolysis targeting chimeras (PROTACs). This Review also highlights how these compounds have been used to study the myriad of HMT functions in cancer progression and treatment response. The recent advancement of some of these drugs into human clinical investigation and even to regulatory approval highlights HMTs as a promising class of targets for chemical intervention and novel therapy development.

Lysine methyltransferase inhibitors: where we are now

Protein lysine methyltransferases constitute a large family of epigenetic writers that catalyse the transfer of a methyl group from the cofactor S-adenosyl-l-methionine to histone- and non-histone-specific substrates. Alterations in the expression and activity of these proteins have been linked to the genesis and progress of several diseases, including cancer, neurological disorders, and growing defects, hence they represent interesting targets for new therapeutic approaches. Over the past two decades, the identification of modulators of lysine methyltransferases has increased tremendously, clarifying the role of these proteins in different physio-pathological states. The aim of this review is to furnish an updated outlook about the protein lysine methyltransferases disclosed modulators, reporting their potency, their mechanism of action and their eventual use in clinical and preclinical studies.