G9a and Glp methylate lysine 373 in the tumor suppressor p53

Small molecule compounds targeting G9a/GLP: Recent advances and perspectives

As an important member of the histone methyltransferase family, G9a/GLP has been shown to be closely related to the occurrence and development of various diseases, such as tumors, fibrosis, and malaria. Selective small molecule inhibitors of G9a/GLP were first reported in 2007, and over the decade since then, more than 40 different types of G9a modulators have been developed. Classification by binding site includes s-adenosylmethionine (SAM)-competitive inhibitors and substrate-competitive inhibitors. According to the mechanism of action, these compounds can be divided into reversible inhibitors, irreversible inhibitors, dual inhibitors, degraders, etc. In this paper, we systematically reviewed the discovery methods, design strategies, structural optimization processes, binding modes, biological activity data, and pharmacokinetic properties of small molecules targeting G9a/GLP. This paper analyzed the challenges and opportunities in the development of small molecule compounds targeting G9a/GLP, aiming to offer valuable insights and perspectives for pharmaceutical researchers.

Epigenetic targets and their inhibitors in the treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a deadly lung disease characterized by fibroblast proliferation, excessive extracellular matrix buildup, inflammation, and tissue damage, resulting in respiratory failure and death. Recent studies suggest that impaired interactions among epithelial, mesenchymal, immune, and endothelial cells play a key role in IPF development. Advances in bioinformatics have also linked epigenetics, which bridges gene expression and environmental factors, to IPF. Despite the incomplete understanding of the pathogenic mechanisms underlying IPF, recent preclinical studies have identified several novel epigenetic therapeutic targets, including DNMT, EZH2, G9a/GLP, PRMT1/7, KDM6B, HDAC, CBP/p300, BRD4, METTL3, FTO, and ALKBH5, along with potential small-molecule inhibitors relevant for its treatment. This review explores the pathogenesis of IPF, emphasizing epigenetic therapeutic targets and potential small molecule drugs. It also analyzes the structure-activity relationships of these epigenetic drugs and summarizes their biological activities. The objective is to advance the development of innovative epigenetic therapies for IPF.

G9a an Epigenetic Therapeutic Strategy for Neurodegenerative Conditions: From Target Discovery to Clinical Trials

This review provides a comprehensive overview of the role of G9a/EHMT2, focusing on its structure and exploring the impact of its pharmacological and/or gene inhibition in various neurological diseases. In addition, we delve into the advancements in the design and synthesis of G9a/EHMT2 inhibitors, which hold promise not only as a treatment for neurodegeneration diseases but also for other conditions, such as cancer and malaria. Besides, we presented the discovery of dual therapeutic approaches based on G9a inhibition and different epigenetic enzymes like histone deacetylases, DNA methyltransferases, and other lysine methyltransferases. Hence, findings offer valuable insights into developing novel and promising therapeutic strategies targeting G9a/EHMT2 for managing these neurological conditions.

EHMT2 Suppresses ARRB1 Transcription and Activates the Hedgehog Signaling to Promote Malignant Phenotype and Stem Cell Property in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) represents the primary subtype of head and neck squamous cell carcinoma (HNSCC), characterized by a high morbidity and mortality rate. Although previous studies have established specific correlations between euchromatic histone lysine methyltransferase 2 (EHMT2), a histone lysine methyltransferase, and the malignant phenotype of OSCC cells, its biological functions in OSCC remain largely unknown. This study, grounded in bioinformatics predictions, aims to clarify the influence of EHMT2 on the malignant behavior of OSCC cells and delve into the underlying mechanisms. EHMT2 exhibited high expression in OSCC tissues and demonstrated an association with poor patient outcomes. Artificial EHMT2 silencing in OSCC cells, achieved through lentiviral vector infection, significantly inhibited colony formation, migration, invasion, and cell survival. Regarding the mechanism, EHMT2 was found to bind the promoter of arrestin beta 1 (ARRB1), thereby suppressing its transcription through H3K9me2 modification. ARRB1, in turn, was identified as a negative regulator of the Hedgehog pathway, leading to a reduction in the proteins GLI1 and PTCH1. Cancer stem cells (CSCs) were enriched through repeated sphere formation assays in two OSCC cell lines. EHMT2 was found to activate the Hedgehog pathway, thus promoting sphere formation, migration and invasion, survival, and tumorigenic activity of the OSCC-CSCs. Notably, these effects were counteracted by the additional overexpression of ARRB1. In conclusion, this study provides novel evidence suggesting that EHMT2 plays specific roles in enhancing stem cell properties in OSCC by modulating the ARRB1-Hedgehog signaling cascade.

NSD3 protein methylation and stabilization transforms human ES cells into variant state

Cultured human embryonic stem cells (hESCs) can develop genetic anomalies that increase their susceptibility to transformation. In this study, we characterized a variant hESC (vhESC) line and investigated the molecular mechanisms leading to the drift towards a transformed state. Our findings revealed that vhESCs up-regulate EMT-specific markers, accelerate wound healing, exhibit compromised lineage differentiation, and retain pluripotency gene expression in teratomas. Furthermore, we discovered an altered epigenomic landscape and overexpression of the lysine methyltransferases EHMT1, EHMT2, and NSD group of proteins in vhESCs. Remarkably, depleting NSD3 oncogene reversed the molecular and phenotypic changes in vhESCs. We identified a detailed mechanism where EHMT2 interacts and methylates NSD3 at lysine 477, stabilizing its protein levels in vhESCs. In addition, we showed that NSD3 levels are regulated by protein degradation in hESCs, and its stabilization leads to the emergence of the variant state. Overall, our study identify that misregulation of NSD3 in pluripotent stem cells, through methylation-mediated abrogation of its protein degradation, drives hESCs towards oncogenic transformation.

DNA Damage Stress Control Is a Truncated Large T Antigen and Euchromatic Histone Lysine Methyltransferase 2-Dependent Central Feature of Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is an aggressive skin cancer with a high mortality rate. Merkel cell polyomavirus causes 80% of MCCs, encoding the viral oncogenes small T and truncated large T (tLT) antigens. These proteins impair the RB1-dependent G1/S checkpoint blockade and subvert the host cell epigenome to promote cancer. Whole-proteome analysis and proximal interactomics identified a tLT-dependent deregulation of DNA damage response (DDR). Our investigation revealed, to our knowledge, a previously unreported interaction between tLT and the histone methyltransferase EHMT2. T antigen knockdown reduced DDR protein levels and increased the levels of the DNA damage marker γH2Ax. EHMT2 normally promotes H3K9 methylation and DDR signaling. Given that inhibition of EHMT2 did not significantly change the MCC cell proteome, tLT-EHMT2 interaction could affect the DDR. With tLT, we report that EHMT2 gained DNA damage repair proximal interactors. EHMT2 inhibition rescued proliferation in MCC cells depleted for their T antigens, suggesting impaired DDR and/or lack of checkpoint efficiency. Combined tLT and EHMT2 inhibition led to altered DDR, evidenced by multiple signaling alterations. In this study, we show that tLT hijacks multiple components of the DNA damage machinery to enhance tolerance to DNA damage in MCC cells, which could explain the genetic stability of these cancers.

Regulation of autophagy and cellular signaling through non-histone protein methylation

Autophagy is a highly conserved catabolic pathway that is precisely regulated and plays a significant role in maintaining cellular metabolic balance and intracellular homeostasis. Abnormal autophagy is directly linked to the development of various diseases, particularly immune disorders, neurodegenerative conditions, and tumors. The precise regulation of proteins is crucial for proper cellular function, and post-translational modifications (PTMs) are key epigenetic mechanisms in the regulation of numerous biological processes. Multiple proteins undergo PTMs that influence autophagy regulation. Methylation modifications on non-histone lysine and arginine residues have been identified as common PTMs critical to various life processes. This paper focused on the regulatory effects of non-histone methylation modifications on autophagy, summarizing related research on signaling pathways involved in autophagy-related non-histone methylation, and discussing current challenges and clinical significance. Our review concludes that non-histone methylation plays a pivotal role in the regulation of autophagy and its associated signaling pathways. Targeting non-histone methylation offers a promising strategy for therapeutic interventions in diseases related to autophagy dysfunction, such as cancer and neurodegenerative disorders. These findings provide a theoretical basis for the development of non-histone-methylation-targeted drugs for clinical use.

Cellular plasticity and non-small cell lung cancer: role of T and NK cell immune evasion and acquisition of resistance to immunotherapies

Lung cancer is a leading global cause of mortality, with non-small cell lung cancer (NSCLC) accounting for a significant portion of cases. Immune checkpoint inhibitors (ICIs) have transformed NSCLC treatment; however, many patients remain unresponsive. ICI resistance in NSCLC and its association with cellular plasticity, epithelial-mesenchymal transition (EMT), enhanced adaptability, invasiveness, and resistance is largely influenced by epigenetic changes, signaling pathways, tumor microenvironment, and associated immune cells, fibroblasts, and cytokines. Immunosuppressive cells, including M2 tumor-associated macrophages, myeloid-derived suppressor cells, and regulatory T cells, contribute to resistance by suppressing the immune response. This cellular plasticity is influenced when B cells, natural killer cells, and T cells are exhausted or inhibited by components of the tumor microenvironment. Conversely, diverse T cell, NK cell, and B cell subsets hold potential as predictive response markers particularly cytotoxic CD8+ T cells, effector memory T cells, activated T cells, tumor infiltrated NK cells, tertiary lymphoid structures, etc. influence treatment response. Identifying specific gene expressions and immunophenotypes within T cells may offer insights into early clinical responses to immunotherapy. ICI resistance in NSCLC is a multifaceted process shaped by tumor plasticity, the complex tumor microenvironment, and dynamic immune cell changes. Comprehensive analysis of these factors may lead to the identification of novel biomarkers and combination therapies to enhance ICI efficacy in NSCLC treatment.

G9a/GLP Modulators: Inhibitors to Degraders

Histone methylation, a crucial aspect of epigenetics, intricately involves specialized enzymes such as G9a, a histone methyltransferase (HMT) catalyzing the methylation of histone H3 lysine 9 (H3K9) and H3K27. Apart from histone modification, G9a regulates essential cellular processes such as deoxyribonucleic acid (DNA) replication, damage repair, and gene expression via modulating DNA methylation patterns. The dysregulation and overexpression of G9a are intricately linked to cancer initiation, progression, and metastasis, making it a compelling target for anticancer therapy. Moreover, aberrant levels of H3K9 dimethylation were identified in Alzheimer's disease (AD), broadening the scope of epigenetic implications across various pathologies. The quest for potent therapy has resulted in the identification of numerous G9a inhibitors/degraders, each demonstrating the potential to disrupt aberrant signaling pathways. This perspective provides valuable insights into the evolving potential and advancement of G9a modulators as promising candidates for treating a spectrum of diseases.

Emergent properties of the lysine methylome reveal regulatory roles via protein interactions and histone mimicry

AIMS

Epigenomics has significantly advanced through the incorporation of Systems Biology approaches. This study aims to investigate the human lysine methylome as a system, using a data-science approach to reveal its emergent properties, particularly focusing on histone mimicry and the broader implications of lysine methylation across the proteome.

METHODS

We employed a data-science-driven OMICS approach, leveraging high-dimensional proteomic data to study the lysine methylome. The analysis focused on identifying sequence-based recognition motifs of lysine methyltransferases and evaluating the prevalence and distribution of lysine methylation across the human proteome.

RESULTS

Our analysis revealed that lysine methylation impacts 15% of the known proteome, with a notable bias toward mono-methylation. We identified sequence-based recognition motifs of 13 lysine methyltransferases, highlighting candidates for histone mimicry. These findings suggest that the selective inhibition of individual lysine methyltransferases could have systemic effects rather than merely targeting histone methylation.

CONCLUSIONS

The lysine methylome has significant mechanistic value and should be considered in the design and testing of therapeutic strategies, particularly in precision oncology. The study underscores the importance of considering non-histone proteins involved in DNA damage and repair, cell signaling, metabolism, and cell cycle pathways when targeting lysine methyltransferases.

Lysine and arginine methylation of transcription factors

Post-translational modifications (PTMs) are implicated in many biological processes including receptor activation, signal transduction, transcriptional regulation and protein turnover. Lysine's side chain is particularly notable, as it can undergo methylation, acetylation, SUMOylation and ubiquitination. Methylation affects not only lysine but also arginine residues, both of which are implicated in epigenetic regulation. Beyond histone-tails as substrates, dynamic methylation of transcription factors has been described. The focus of this review is on these non-histone substrates providing a detailed discussion of what is currently known about methylation of hypoxia-inducible factor (HIF), P53, nuclear receptors (NRs) and RELA. The role of methylation in regulating protein stability and function by acting as docking sites for methyl-reader proteins and via their crosstalk with other PTMs is explored.

The Role of Methylation in Ferroptosis

Methylation modification is a crucial epigenetic alteration encompassing RNA methylation, DNA methylation, and histone methylation. Ferroptosis represents a newly discovered form of programmed cell death (PCD) in 2012, which is characterized by iron-dependent lipid peroxidation. The comprehensive investigation of ferroptosis is therefore imperative for a more profound comprehension of the pathological and pathophysiological mechanisms implicated in a wide array of diseases. Researches show that methylation modifications can exert either promotive or inhibitory effects on cell ferroptosis. Consequently, this review offers a comprehensive overview of the pivotal role played by methylation in ferroptosis, elucidating its associated factors and underlying mechanisms.

Epigenetics-targeted drugs: current paradigms and future challenges

Epigenetics governs a chromatin state regulatory system through five key mechanisms: DNA modification, histone modification, RNA modification, chromatin remodeling, and non-coding RNA regulation. These mechanisms and their associated enzymes convey genetic information independently of DNA base sequences, playing essential roles in organismal development and homeostasis. Conversely, disruptions in epigenetic landscapes critically influence the pathogenesis of various human diseases. This understanding has laid a robust theoretical groundwork for developing drugs that target epigenetics-modifying enzymes in pathological conditions. Over the past two decades, a growing array of small molecule drugs targeting epigenetic enzymes such as DNA methyltransferase, histone deacetylase, isocitrate dehydrogenase, and enhancer of zeste homolog 2, have been thoroughly investigated and implemented as therapeutic options, particularly in oncology. Additionally, numerous epigenetics-targeted drugs are undergoing clinical trials, offering promising prospects for clinical benefits. This review delineates the roles of epigenetics in physiological and pathological contexts and underscores pioneering studies on the discovery and clinical implementation of epigenetics-targeted drugs. These include inhibitors, agonists, degraders, and multitarget agents, aiming to identify practical challenges and promising avenues for future research. Ultimately, this review aims to deepen the understanding of epigenetics-oriented therapeutic strategies and their further application in clinical settings.

From regulation to deregulation of p53 in hematologic malignancies: implications for diagnosis, prognosis and therapy

The p53 protein, encoded by the TP53 gene, serves as a critical tumor suppressor, playing a vital role in maintaining genomic stability and regulating cellular responses to stress. Dysregulation of p53 is frequently observed in hematological malignancies, significantly impacting disease progression and patient outcomes. This review aims to examine the regulatory mechanisms of p53, the implications of TP53 mutations in various hematological cancers, and emerging therapeutic strategies targeting p53. We conducted a comprehensive literature review to synthesize recent findings related to p53's multifaceted role in hematologic cancers, focusing on its regulatory pathways and therapeutic potential. TP53 mutations in hematological malignancies often lead to treatment resistance and poor prognosis. Current therapeutic strategies, including p53 reactivation and gene therapy, show promise in improving treatment outcomes. Understanding the intricacies of p53 regulation and the consequences of its mutations is essential for developing effective diagnostic and therapeutic strategies in hematological malignancies, ultimately enhancing patient care and survival.

A cytoplasmic form of EHMT1N methylates viral proteins to enable inclusion body maturation and efficient viral replication

Protein lysine methyltransferases (PKMTs) methylate histone and non-histone proteins to regulate biological outcomes such as development and disease including viral infection. While PKMTs have been extensively studied for modulating the antiviral responses via host gene regulation, their role in methylation of proteins encoded by viruses and its impact on host-pathogen interactions remain poorly understood. In this study, we discovered distinct nucleo-cytoplasmic form of euchromatic histone methyltransferase 1 (EHMT1N/C), a PKMT, that phase separates into viral inclusion bodies (IBs) upon cytoplasmic RNA-virus infection (Sendai Virus). EHMT1N/C interacts with cytoplasmic EHMT2 and methylates SeV-Nucleoprotein upon infection. Elevated nucleoprotein methylation during infection correlated with coalescence of small IBs into large mature platforms for efficient replication. Inhibition of EHMT activity by pharmacological inhibitors or genetic depletion of EHMT1N/C reduced the size of IBs with a concomitant reduction in replication. Additionally, we also found that EHMT1 condensation is not restricted to SeV alone but was also seen upon pathogenic RNA viral infections caused by Chandipura and Dengue virus. Collectively, our work elucidates a new mechanism by which cytoplasmic EHMT1 acts as proviral host factor to regulate host-pathogen interaction.

Targeting LSD1 in cancer: Molecular elucidation and recent advances

Histones are the main components of chromatin, functioning as an instructive scaffold to maintain chromosome structure and regulate gene expression. The dysregulation of histone modification is associated with various pathological processes, especially cancer initiation and development, and histone methylation plays a critical role. However, the specific mechanisms and potential therapeutic targets of histone methylation in cancer are not elucidated. Lys-specific demethylase 1A (LSD1) was the first identified demethylase that specifically removes methyl groups from histone 3 at lysine 4 or lysine 9, acting as a repressor or activator of gene expression. Recent studies have shown that LSD1 promotes cancer progression in multiple epigenetic regulation or non-epigenetic manners. Notably, LSD1 dysfunction is correlated with repressive cancer immunity. Many LSD1 inhibitors have been developed and clinical trials are exploring their efficacy in monotherapy, or combined with other therapies. In this review, we summarize the oncogenic mechanisms of LSD1 and the current applications of LSD1 inhibitors. We highlight that LSD1 is a promising target for cancer treatment. This review will provide the latest theoretical references for further understanding the research progress of oncology and epigenetics, deepening the updated appreciation of epigenetics in cancer.

Lysine methylation modifications in tumor immunomodulation and immunotherapy: regulatory mechanisms and perspectives

Lysine methylation is a crucial post-translational modification (PTM) that significantly impacts gene expression regulation. This modification not only influences cancer development directly but also has significant implications for the immune system. Lysine methylation modulates immune cell functions and shapes the anti-tumor immune response, highlighting its dual role in both tumor progression and immune regulation. In this review, we provide a comprehensive overview of the intrinsic role of lysine methylation in the activation and function of immune cells, detailing how these modifications affect cellular processes and signaling pathways. We delve into the mechanisms by which lysine methylation contributes to tumor immune evasion, allowing cancer cells to escape immune surveillance and thrive. Furthermore, we discuss the therapeutic potential of targeting lysine methylation in cancer immunotherapy. Emerging strategies, such as immune checkpoint inhibitors (ICIs) and chimeric antigen receptor T-cell (CAR-T) therapy, are being explored for their efficacy in modulating lysine methylation to enhance anti-tumor immune responses. By targeting these modifications, we can potentially improve the effectiveness of existing treatments and develop novel therapeutic approaches to combat cancer more effectively.

GLP and G9a histone methyltransferases as potential therapeutic targets for lymphoid neoplasms

Histone methyltransferases (HMTs) are enzymes that regulate histone methylation and play an important role in controlling transcription by altering the chromatin structure. Aberrant activation of HMTs has been widely reported in certain types of neoplastic cells. Among them, G9a/EHMT2 and GLP/EHMT1 are crucial for H3K9 methylation, and their dysregulation has been associated with tumor initiation and progression in different types of cancer. More recently, it has been shown that G9a and GLP appear to play a critical role in several lymphoid hematologic malignancies. Importantly, the key roles played by both enzymes in various diseases made them attractive targets for drug development. In fact, in recent years, several groups have tried to develop small molecule inhibitors targeting their epigenetic activities as potential anticancer therapeutic tools. In this review, we discuss the physiological role of GLP and G9a, their oncogenic functions in hematologic malignancies of the lymphoid lineage, and the therapeutic potential of epigenetic drugs targeting G9a/GLP for cancer treatment.

Forkhead box O1 in metabolic dysfunction-associated fatty liver disease: molecular mechanisms and drug research

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a chronic liver disease that progresses from hepatic steatosis to non-alcoholic steatohepatitis, cirrhosis, and liver cancer, posing a huge burden on human health. Existing research has confirmed that forkhead box O1 (FOXO1), as a member of the FOXO transcription factor family, is upregulated in MAFLD. Its activity is closely related to nuclear-cytoplasmic shuttling and various post-translational modifications including phosphorylation, acetylation, and methylation. FOXO1 mediates the progression of MAFLD by regulating glucose metabolism, lipid metabolism, insulin resistance, oxidative stress, hepatic fibrosis, hepatocyte autophagy, apoptosis, and immune inflammation. This article elaborates on the regulatory role of FOXO1 in MAFLD, providing a summary and new insights for the current status of drug research and targeted therapies for MAFLD.

Mining the Dynamical Properties of Substrate and FAD Binding Pockets of LSD1: Hints for New Inhibitor Design Direction

Lysine-specific demethylase 1 (LSD1), a highly sophisticated epigenetic regulator, orchestrates a range of critical cellular processes, holding promising therapeutic potential for treating diverse diseases. However, the clinical research progress targeting LSD1 is very slow. After 20 years of research, only one small-molecule drug, BEA-17, targeting the degradation of LSD1 and CoREST has been approved by the U.S. Food and Drug Administration. The primary reason for this may be the lack of abundant structural data regarding its intricate functions. To gain a deeper understanding of its conformational dynamics and guide the drug design process, we conducted molecular dynamics simulations to explore the conformational states of LSD1 in the apo state and under the influence of cofactors of flavin adenine dinucleotide (FAD) and CoREST. Our results showed that, across all states, the substrate binding pocket exhibited high flexibility, whereas the FAD binding pocket remained more stable. These distinct dynamical properties are essential for LSD1's ability to bind various substrates while maintaining efficient demethylation activity. Both pockets can be enlarged by merging with adjacent pockets, although only the substrate binding pocket can shrink into smaller pockets. These new pocket shapes can inform inhibitor design, particularly for selectively FAD-competitive inhibitors of LSD1, given the presence of numerous FAD-dependent enzymes in the human body. More interestingly, in the absence of FAD binding, the united substrate and FAD binding pocket are partitioned by the conserved residue of Tyr761, offering valuable insights for the design of inhibitors that disrupt the crucial steric role of Tyr761 and the redox role of FAD. Additionally, we identified pockets that positively or negatively correlate with the substrate and FAD binding pockets, which can be exploited for the design of allosteric or concurrent inhibitors. Our results reveal the intricate dynamical properties of LSD1 as well as multiple novel conformational states, which deepen our understanding of its sophisticated functions and aid in the rational design of new inhibitors.

G9a in Cancer: Mechanisms, Therapeutic Advancements, and Clinical Implications

G9a, also named EHMT2, is a histone 3 lysine 9 (H3K9) methyltransferase responsible for catalyzing H3K9 mono- and dimethylation (H3K9me1 and H3K9me2). G9a contributes to various aspects of embryonic development and tissue differentiation through epigenetic regulation. Furthermore, the aberrant expression of G9a is frequently observed in various tumors, particularly in prostate cancer, where it contributes to cancer pathogenesis and progression. This review highlights the critical role of G9a in multiple cancer-related processes, such as epigenetic dysregulation, tumor suppressor gene silencing, cancer lineage plasticity, hypoxia adaption, and cancer progression. Despite the increased research on G9a in prostate cancer, there are still significant gaps, particularly in understanding its interactions within the tumor microenvironment and its broader epigenetic effects. Furthermore, this review discusses the recent advancements in G9a inhibitors, including the development of dual-target inhibitors that target G9a along with other epigenetic factors such as EZH2 and HDAC. It aims to bring together the existing knowledge, identify gaps in the current research, and suggest future directions for research and treatment strategies.

Discovery of the First-in-Class G9a/GLP PROTAC Degrader

Aberrantly expressed lysine methyltransferases G9a and GLP, which catalyze mono- and dimethylation of histone H3 lysine 9 (H3K9), have been implicated in numerous cancers. Recent studies have uncovered both catalytic and noncatalytic oncogenic functions of G9a/GLP. As such, G9a/GLP catalytic inhibitors have displayed limited anticancer activity. Here, we report the discovery of the first-in-class G9a/GLP proteolysis targeting chimera (PROTAC) degrader 10 (MS8709), as a potential anticancer therapeutic. 10 induces G9a/GLP degradation in a concentration-, time-, and ubiquitin-proteasome system (UPS)-dependent manner. Futhermore, 10 does not alter the mRNA expression of G9a/GLP and is selective for G9a/GLP over other methyltransferases. Moreover, 10 displays superior cell growth inhibition to the parent G9a/GLP inhibitor UNC0642 in prostate, leukemia, and lung cancer cells and has suitable mouse pharmacokinetic properties for in vivo efficacy studies. Overall, 10 is a valuable chemical biology tool to further investigate the functions of G9a/GLP and a potential therapeutic for treating G9a/GLP-dependent cancers.

Integration of ligand and structure-based pharmacophore screening for the identification of novel natural leads against Euchromatic histone lysine methyltransferase 2 (EHMT2/G9a)

Herein, we report a blended ligand and structure-based pharmacophore screening approach to identify new natural leads against the Protein Lysine Methyltransferase 2 (EHMT2/G9a). The EHMT2/G9a has been associated with Cancer, Alzheimer's, and aging and is considered an emerging drug target having no clinically passed inhibitor. Purposefully, we developed the ligand-based pharmacophore (Pharmacophore-L) based on the common features of known inhibitors and the structure-based pharmacophore (Pharmacophore-S) based on the interaction profile of available crystal structures. The Pharmacophore-L and Pharmacophore-S were subjected to multiple tiers of validations and utilized in combination for the screening of total 741543 compounds coming from multiple databases. Additional layers of stringency were applied in the screening process to test drug-likeness (using Lipinski's rule, Veber's rule, SMARTS and ADMET filtration), to rule out any toxicity (TOPKAT analysis). The interaction profiles, stabilities, and comparative analysis against the reference were carried out by flexible docking, MD simulation, and MM-GBSA analysis, which finally led to three leads as potential inhibitors of G9a.Communicated by Ramaswamy H. Sarma.

Molecular and functional anticancer effects of GLP/G9a inhibition by UNC0646 in MeWo melanoma cells

In recent years, histone methyltransferases (HMTs) have emerged as important therapeutic targets in cancer due to their oncogenic role. Herein, we used the GLP/G9a inhibitor UNC0646 to assess whether the inhibition of such HMTs could induce cell death in MeWo melanoma cells. Furthermore, we investigated the cellular and molecular mechanisms involved in the observed cell death events. Finally, we performed a functional genomics analysis of 480 melanoma samples to characterize G9a/GLP involvement in melanoma. Interestingly, after UNC0646 treatment, MeWo cells underwent apoptosis, followed by loss of mitochondrial membrane potential and the generation of reactive oxygen species (ROS). Furthermore, MeWo cells treated with UNC0646 showed cell cycle arrest and inhibition of proliferation. At the molecular level, UNC0646 treatment increased the transcriptional levels of CDK1 and BAX, and decreased BCL-2 mRNA levels. Finally, we performed a functional enrichment analysis, which demonstrated that dozens of biological pathways were enriched in melanoma samples according to GLP and G9a expression, including apoptosis and necrosis. Taken together, our data show that inhibition of GLP/G9a using UNC0646 exerts anticancer effects on melanoma cells by controlling their proliferation and inducing apoptosis.

Discovery of the First-in-class G9a/GLP PROTAC Degrader

Aberrantly expressed lysine methyltransferases G9a and GLP, which catalyze mono- and di-methylation of histone H3 lysine 9 (H3K9), have been implicated in numerous cancers. Recent studies have uncovered both catalytic and non-catalytic oncogenic functions of G9a/GLP. As such, G9a/GLP catalytic inhibitors have displayed limited anticancer activity. Here, we report the discovery of the first-in-class G9a/GLP proteolysis targeting chimera (PROTAC) degrader, 10 (MS8709), as a potential anticancer therapeutic. 10 induces G9a/GLP degradation in a concentration-, time, and ubiquitin-proteasome system (UPS)-dependent manner, does not alter the mRNA expression of G9a/GLP and is selective for G9a/GLP over other methyltransferases. Moreover, 10 displays superior cell growth inhibition to the parent G9a/GLP inhibitor UNC0642 in prostate, leukemia, and lung cancer cells and has suitable mouse pharmacokinetic properties for in vivo efficacy studies. Overall, 10 is a valuable chemical biology tool to further investigate the functions of G9a/GLP and a potential therapeutic for treating G9a/GLP-dependent cancers.

Uncovering New Conformational States of the Substrate Binding Pocket of LSD1 Potential for Inhibitor Design via Funnel Metadynamics

Lysine-specific demethylase 1 (LSD1) is a promising therapeutic target for cancer therapy. So far, over 80 crystal structures of LSD1 in different complex states have been deposited in the Protein Data Bank, which are valuable resources for performing structure-based drug design. However, among all of the crystal structures of LSD1, the substrate binding pocket, which is the most efficient druggable site for designing LSD1 inhibitors at present, is very similar no matter whether LSD1 is in the apo or any holo forms, which is inconsistent with its versatile demethylase functions. To investigate whether the substrate binding pocket is rigid or exhibits other representative conformations different from the crystal conformations that are feasible for designing new LSD1 inhibitors, we performed funnel metadynamics simulations to study the conformation dynamics of LSD1 in the binding process of two effective LSD1 inhibitors (CC-90011 and 6X0, CC-90011 undergoing clinical trials). Our results showed that the entrance of the substrate binding pocket is very flexible. Two representative entrance conformations of LSD1 counting against binding with the substrate of histone H3 were detected, which may be used for structure-based LSD1 inhibitor design. Besides, alternative optimal binding modes and prebinding modes for both inhibitors were also detected, which depicted that the key interactions changed along with the binding process. Our results should provide great help for LSD1 inhibitor design.

Lysine demethylase 3A promotes chondrogenic differentiation of aged human dental pulp stem cells

BACKGROUND/PURPOSE

Aging severely impairs the beneficial effects of human dental pulp stem cells (hDPSCs) on cartilage regeneration. Lysine demethylase 3A (KDM3A) is involved in regulating mesenchymal stem cells (MSCs) senescence and bone aging. In this study, we investigated the role of KDM3A in hDPSCs aging and whether KDM3A could rejuvenate aged hDPSCs to enhance their chondrogenic differentiation capacity.

MATERIALS AND METHODS

The cellular aging of hDPSCs was evaluated by senescence-associated β-galactosidase (SA-β-gal) staining. Protein levels were determined using Western blot analysis. KDM3A was overexpressed in aged hDPSCs by lentivirus infection. Quantitative reverse-transcription polymerase chain reaction (RT-qPCR) were used to determine the mRNA levels of stemness markers. Toluidine blue staining was used to evaluate the effect of KDM3A overexpression on the chondrogenic differentiation of aged hDPSCs.

RESULTS

hDPSCs at passage 12 or treated with etoposide exhibited augmented cellular senescence as evidenced by increased SA-β-gal activity. KDM3A was significantly increased during senescence of hDPSCs. Overexpression of KDM3A did not affect the stemness properties but significantly promoted the chondrogenic differentiation of aged hDPSCs.

CONCLUSION

Our findings indicate that KDM3A plays an important role in the maintenance of the chondrogenic differentiation capacity of aged hDPSCs and suggest that therapies targeting KDM3A may be a novel strategy to rejuvenate aged hDPSCs.

Discovery of novel G9a/GLP covalent inhibitors for the treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) has become a serious threat to women's health. Research on epigenetic drugs is gradually deepening and is expected to provide new options for the treatment of TNBC. G9a/GLP has been shown to play an important role in the development of a variety of tumors, including TNBC. Most reported G9a/GLP inhibitors are reversible inhibitors, and covalent inhibitors with novel mechanisms of action are expected to offer unique advantages. In this study, we designed a series of novel G9a/GLP covalent inhibitors using a structure-based drug design strategy. Compound 7c (ZZM-1220) exhibited potent enzyme inhibitory activity and anti-TNBC proliferative activity. Our biochemical studies showed that ZZM-1220 could covalently bind to G9a/GLP and inhibit H3K9me2 in cells. It could significantly induce apoptosis of TNBC cells and block the cell cycle in the G2/M phase. It is worth noting that ZZM-1220 continuously inhibited the growth of cancer cells and the expression of H3K9me2 after washing out. These data suggested that ZZM-1220 could be used as a promising lead compound for the development of G9a/GLP covalent inhibitors for the treatment of TNBC.

Tumor-suppressive functions of protein lysine methyltransferases

Protein lysine methyltransferases (PKMTs) play crucial roles in histone and nonhistone modifications, and their dysregulation has been linked to the development and progression of cancer. While the majority of studies have focused on the oncogenic functions of PKMTs, extensive evidence has indicated that these enzymes also play roles in tumor suppression by regulating the stability of p53 and β-catenin, promoting α-tubulin-mediated genomic stability, and regulating the transcription of oncogenes and tumor suppressors. Despite their contradictory roles in tumorigenesis, many PKMTs have been identified as potential therapeutic targets for cancer treatment. However, PKMT inhibitors may have unintended negative effects depending on the specific cancer type and target enzyme. Therefore, this review aims to comprehensively summarize the tumor-suppressive effects of PKMTs and to provide new insights into the development of anticancer drugs targeting PKMTs.

Writers and readers of H3K9me2 form distinct protein networks during the cell cycle that include candidates for H3K9 mimicry

Histone H3 lysine 9 methylation (H3K9me), which is written by the Euchromatic Histone Lysine Methyltransferases EHMT1 and EHMT2 and read by the heterochromatin protein 1 (HP1) chromobox (CBX) protein family, is dysregulated in many types of cancers. Approaches to inhibit regulators of this pathway are currently being evaluated for therapeutic purposes. Thus, knowledge of the complexes supporting the function of these writers and readers during the process of cell proliferation is critical for our understanding of their role in carcinogenesis. Here, we immunopurified each of these proteins and used mass spectrometry to define their associated non-histone proteins, individually and at two different phases of the cell cycle, namely G1/S and G2/M. Our findings identify novel binding proteins for these writers and readers, as well as corroborate known interactors, to show the formation of distinct protein complex networks in a cell cycle phase-specific manner. Furthermore, there is an organizational switch between cell cycle phases for interactions among specific writer-reader pairs. Through a multi-tiered bioinformatics-based approach, we reveal that many interacting proteins exhibit histone mimicry, based on an H3K9-like linear motif. Gene ontology analyses, pathway enrichment, and network reconstruction inferred that these comprehensive EHMT and CBX-associated interacting protein networks participate in various functions, including transcription, DNA repair, splicing, and membrane disassembly. Combined, our data reveals novel complexes that provide insight into key functions of cell cycle-associated epigenomic processes that are highly relevant for better understanding these chromatin-modifying proteins during cell cycle and carcinogenesis.

Histone and DNA Methylation as Epigenetic Regulators of DNA Damage Repair in Gastric Cancer and Emerging Therapeutic Opportunities

Gastric cancer (GC), one of the most common malignancies worldwide, is a heterogeneous disease developing from the accumulation of genetic and epigenetic changes. One of the most critical epigenetic alterations in GC is DNA and histone methylation, which affects multiple processes in the cell nucleus, including gene expression and DNA damage repair (DDR). Indeed, the aberrant expression of histone methyltransferases and demethylases influences chromatin accessibility to the DNA repair machinery; moreover, overexpression of DNA methyltransferases results in promoter hypermethylation, which can suppress the transcription of genes involved in DNA repair. Several DDR mechanisms have been recognized so far, with homologous recombination (HR) being the main pathway involved in the repair of double-strand breaks. An increasing number of defective HR genes are emerging in GC, resulting in the identification of important determinants of therapeutic response to DDR inhibitors. This review describes how both histone and DNA methylation affect DDR in the context of GC and discusses how alterations in DDR can help identify new molecular targets to devise more effective therapeutic strategies for GC, with a particular focus on HR-deficient tumors.

Distinct functions of EHMT1 and EHMT2 in cancer chemotherapy and immunotherapy

EHTM1 (GLP) and EHMT2 (G9a) are closely related protein lysine methyltransferases often thought to function together as a heterodimer to methylate histone H3 and non-histone substrates in diverse cellular processes including transcriptional regulation, genome methylation, and DNA repair. Here we show that EHMT1/2 inhibitors cause ATM-mediated slowdown of replication fork progression, accumulation of single-stranded replication gaps, emergence of cytosolic DNA, and increased expression of STING. EHMT1/2 inhibition strongly potentiates the efficacy of alkylating chemotherapy and anti-PD-1 immunotherapy in mouse models of tripe negative breast cancer. The effects on DNA replication and alkylating agent sensitivity are largely caused by the loss of EHMT1-mediated methylation of LIG1, whereas the elevated STING expression and remarkable response to immunotherapy appear mainly elicited by the loss of EHMT2 activity. Depletion of UHRF1, a protein known to be associated with EHMT1/2 and LIG1, also induces STING expression, and depletion of either EHMT2 or UHRF1 leads to demethylation of specific CpG sites in the STING1 promoter, suggestive of a distinct EHMT2-UHRF1 axis that regulates DNA methylation and gene transcription. These results highlight distinct functions of the two EHMT paralogs and provide enlightening paradigms and corresponding molecular basis for combination therapies involving alkylating agents and immune checkpoint inhibitors.

3D QSAR pharmacophore based lead identification of G9a lysine methyltransferase towards epigenetic therapeutics

The G9a, Lysine Methyltransferase that methylates the histone 3 lysine 9 (H3K9) of the nucleosome, is an excellent epigenetic target having no clinically passed inhibitor currently owing to adverse in vivo ADMET toxicities. In this work, we have carried out detailed computational investigations to find novel and safer lead against the target using advanced 3 D QSAR pharmacophore screening of databases containing more than 400000 entrees of natural compounds. The screening was conducted at different levels at increasing stringencies by employing pharmacophore mapping, druglikenesses and interaction profiles of the selected to identify potential hit compounds. The potential hits were further screened by advanced flexible docking, ADME and toxicity analysis to eight hit compounds. Based on the comparative analysis of the hits with the reference inhibitor, we identified one lead inhibitor against the G9a, having better binding efficacy and a safer ADMET profile than the reference inhibitor. Finally, the results were further verified using robust molecular dynamics simulation and MM-GBSA binding energy calculation. The natural compounds are generally considered benign due to their long human uses and this is the first attempt of in silico screening of a large natural compound library against G9a to our best knowledge. Therefore, the finding of this study may add value towards the development of epigenetic therapeutics against the G9a.Communicated by Ramaswamy H. Sarma.

Activity Guided Azide-methyllysine Photo-trapping for Substrate Profiling of Lysine Demethylases

Reversible post-translational modifications (PTMs) are key to establishing protein-protein and protein-nucleic acid interactions that govern a majority of the signaling pathways in cells. Sequence-specific PTMs are catalyzed by transferases, and their removal is carried out by a class of reverse-acting enzymes termed "detransferases". Currently available chemoproteomic approaches have been valuable in characterizing substrates of transferases. However, proteome-wide cataloging of the substrates of detransferases is challenging, mostly due to the loss of the epitope, rendering immunoprecipitation and activity-based methods ineffective. Herein, we develop a general chemoproteomic strategy called crosslinking-assisted substrate identification (CASI) for systematic characterization of cellular targets of detransferases and successfully apply it to lysine demethylases (KDMs) which catalyze the removal of methyl groups from lysine sidechain in histones to modulate gene transcription. By setting up a targeted azido-methylamino photo-reaction deep inside the active site of KDM4, engineered to carry p-azido phenylalanine, we reveal a novel "demethylome" that has escaped the traditional methods. The proteomic survey led to the identification of a battery of nonhistone substrates of KDM4, extending the biological footprint of KDM4 beyond its canonical functions in gene transcription. A notable finding of KDM4A-mediated demethylation of an evolutionarily conserved lysine residue in eukaryotic translational initiation factor argues for a much broader role of KDM4A in ribosomal processes. CASI, representing a substantive departure from earlier approaches by shifting focus from simple peptide-based probes to employing full-length photo-activatable demethylases, is poised to be applied to >400 human detransferases, many of which have remained poorly understood due to the lack of knowledge about their cellular targets.

Demethylation of EHMT1/GLP Protein Reprograms Its Transcriptional Activity and Promotes Prostate Cancer Progression

Epigenetic reprogramming, mediated by genomic alterations and dysregulation of histone reader and writer proteins, plays a critical role in driving prostate cancer progression and treatment resistance. However, the specific function and regulation of EHMT1 (also known as GLP) and EHMT2 (also known as G9A), well-known histone 3 lysine 9 methyltransferases, in prostate cancer progression remain poorly understood. Through comprehensive investigations, we discovered that both EHMT1 and EHMT2 proteins have the ability to activate oncogenic transcription programs in prostate cancer cells. Silencing EHMT1/2 or targeting their enzymatic activity with small-molecule inhibitors can markedly decrease prostate cancer cell proliferation and metastasis in vitro and in vivo. In-depth analysis of posttranslational modifications of EHMT1 protein revealed the presence of methylation at lysine 450 and 451 residues in multiple prostate cancer models. Notably, we found that lysine 450 can be demethylated by LSD1. Strikingly, concurrent demethylation of both lysine residues resulted in a rapid and profound expansion of EHMT1's chromatin binding capacity, enabling EHMT1 to reprogram the transcription networks in prostate cancer cells and activate oncogenic signaling pathways. Overall, our studies provide valuable molecular insights into the activity and function of EHMT proteins during prostate cancer progression. Moreover, we propose that the dual-lysine demethylation of EHMT1 acts as a critical molecular switch, triggering the induction of oncogenic transcriptional reprogramming in prostate cancer cells. These findings highlight the potential of targeting EHMT1/2 and their demethylation processes as promising therapeutic strategies for combating prostate cancer progression and overcoming treatment resistance.

Significance

In this study, we demonstrate that EHMT1 and EHMT2 proteins drive prostate cancer development by transcriptionally activating multiple oncogenic pathways. Mechanistically, the chromatin binding of EHMT1 is significantly expanded through demethylation of both lysine 450 and 451 residues, which can serve as a critical molecular switch to induce oncogenic transcriptional reprogramming in prostate cancer cells.

Lysine 68 Methylation-Dependent SOX9 Stability Control Modulates Chondrogenic Differentiation in Dental Pulp Stem Cells

Dental pulp stem cells (DPSCs), characterized by easy availability, multi-lineage differentiation ability, and high proliferation ability, are ideal seed cells for cartilage tissue engineering. However, the epigenetic mechanism underlying chondrogenesis in DPSCs remains elusive. Herein, it is demonstrated that KDM3A and G9A, an antagonistic pair of histone-modifying enzymes, bidirectionally regulate the chondrogenic differentiation of DPSCs by controlling SOX9 (sex-determining region Y-type high-mobility group box protein 9) degradation through lysine methylation. Transcriptomics analysis reveals that KDM3A is significantly upregulated during the chondrogenic differentiation of DPSCs. In vitro and in vivo functional analyses further indicate that KDM3A promotes chondrogenesis in DPSCs by boosting the SOX9 protein level, while G9A hinders the chondrogenic differentiation of DPSCs by reducing the SOX9 protein level. Furthermore, mechanistic studies indicate that KDM3A attenuates the ubiquitination of SOX9 by demethylating lysine (K) 68 residue, which in turn enhances SOX9 stability. Reciprocally, G9A facilitates SOX9 degradation by methylating K68 residue to increase the ubiquitination of SOX9. Meanwhile, BIX-01294 as a highly specific G9A inhibitor significantly induces the chondrogenic differentiation of DPSCs. These findings provide a theoretical basis to ameliorate the clinical use of DPSCs in cartilage tissue-engineering therapies.

Discovery of SDS-347 as a specific peptide competitive inhibitor of G9a with promising anti-cancer potential

BACKGROUND

G9a is a histone H3K9 methyltransferase enzyme found highly upregulated in many cancers. H3 binds to the rigid I-SET domain and the cofactor, S-adenosyl methionine, binds to the flexible post-SET domain of G9a. Inhibition of G9a is known to inhibit the growth of cancer cell-lines.

METHODS

Recombinant G9a and H3 were used to develop radioisotope-based inhibitor screening assay. The identified inhibitor was evaluated for isoform selectivity. The mode of enzymatic inhibition was studied by enzymatic assays and bioinformatics. Anti-proliferative activity of the inhibitor was studied in cancer cell lines by utilizing MTT assay. The mechanism of cell death was studied by western blotting and microscopy.

RESULTS

We developed a robust G9a inhibitor screening assay that led to the discovery of SDS-347 as a potent G9a inhibitor with IC₅₀ of 3.06 μM. It was shown to reduce the levels of H3K9me2 in cell-based assay. The inhibitor was found to be peptide competitive and highly specific as it did not show any significant inhibition of other histone methyltransferases and DNA methyltransferase. Docking studies showed that SDS-347 could form direct bonding interaction with Asp1088 of the peptide-binding site. SDS-347 showed anti-proliferative effect against various cancer cell lines especially the K562 cells. Our data suggested that SDS-347 mediated antiproliferative action via ROS generation, induction of autophagy and apoptosis.

CONCLUSION

Overall, the findings of the current study include development of a new G9a inhibitor screening assay and identification of SDS-347, as a novel, peptide competitive and highly specific G9a inhibitor with promising anticancer potential.

Structure-Based Design and Characterization of the Highly Potent and Selective Covalent Inhibitors Targeting the Lysine Methyltransferases G9a/GLP

Protein lysine methyltransferases G9a and GLP, which catalyze mono- and di-methylation of histone H3K9 and nonhistone proteins, play important roles in diverse cellular processes. Overexpression or dysregulation of G9a and GLP has been identified in various types of cancer. Here, we report the discovery of a highly potent and selective covalent inhibitor 27 of G9a/GLP via the structure-based drug design approach following structure-activity relationship exploration and cellular potency optimization. Mass spectrometry assays and washout experiments confirmed its covalent inhibition mechanism. Compound 27 displayed improved potency in inhibiting the proliferation and colony formation of PANC-1 and MDA-MB-231 cell lines and exhibited enhanced potency in reducing the levels of H3K9me2 in cells compared to noncovalent inhibitor 26. In vivo, 27 showed significant antitumor efficacy in the PANC-1 xenograft model with good safety. These results clearly indicate that 27 is a highly potent and selective covalent inhibitor of G9a/GLP.

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.

TNFα Effects on Adipocytes Are Influenced by the Presence of Lysine Methyltransferases, G9a (EHMT2) and GLP (EHMT1)

Impaired adipocyte function contributes to systemic metabolic dysregulation, and altered fat mass or function increases the risk of Type 2 diabetes. EHMTs 1 and 2 (euchromatic histone lysine methyltransferases 1 and 2), also known as the G9a-like protein (GLP) and G9a, respectively, catalyze the mono- and di-methylation of histone 3 lysine 9 (H3K9) and also methylate nonhistone substrates; in addition, they can act as transcriptional coactivators independent of their methyltransferase activity. These enzymes are known to contribute to adipocyte development and function, and in vivo data indicate a role for G9a and GLP in metabolic disease states; however, the mechanisms involved in the cell-autonomous functions of G9a and GLP in adipocytes are largely unknown. Tumor necrosis factor alpha (TNFα) is a proinflammatory cytokine typically induced in adipose tissue in conditions of insulin resistance and Type 2 diabetes. Using an siRNA approach, we have determined that the loss of G9a and GLP enhances TNFα-induced lipolysis and inflammatory gene expression in adipocytes. Furthermore, we show that G9a and GLP are present in a protein complex with nuclear factor kappa B (NF-κB) in TNFα-treated adipocytes. These novel observations provide mechanistic insights into the association between adipocyte G9a and GLP expression and systemic metabolic health.

Discovery of Novel Substrate-Competitive Lysine Methyltransferase G9a Inhibitors as Anticancer Agents

Identification of structurally novel inhibitors of lysine methyltransferase G9a has been a subject of intense research in cancer epigenetics. Starting with the high-throughput screening (HTS) hit rac-10a obtained from the chemical library of the University of Tokyo Drug Discovery Initiative, the structure-activity relationship of the unique substrate-competitive inhibitors was established with the help of X-ray crystallography and fragment molecular orbital (FMO) calculations for the ligand-protein interaction. Further optimization of the in vitro characteristics and drug metabolism and pharmacokinetics (DMPK) properties led to the identification of 26j (RK-701), which is a structurally distinct potent inhibitor of G9a/GLP (IC50 = 27/53 nM). Compound 26j exhibited remarkable selectivity against other related methyltransferases, dose-dependent attenuation of cellular H3K9me2 levels, and tumor growth inhibition in MOLT-4 cells in vitro. Moreover, compound 26j showed inhibition of tumor initiation and growth in a carcinogen-induced hepatocellular carcinoma (HCC) in vivo mouse model without overt acute toxicity.

Discovery of cysteine-targeting covalent histone methyltransferase inhibitors

Post-translational methylation of histone lysine or arginine residues by histone methyltransferases (HMTs) plays crucial roles in gene regulation and diverse physiological processes and is implicated in a plethora of human diseases, especially cancer. Therefore, histone methyltransferases have been increasingly recognized as potential therapeutic targets. Consequently, the discovery and development of histone methyltransferase inhibitors have been pursued with steadily increasing interest over the past decade. However, the disadvantages of limited clinical efficacy, moderate selectivity, and propensity for acquired resistance have hindered the development of HMTs inhibitors. Targeted covalent modification represents a proven strategy for kinase drug development and has gained increasing attention in HMTs drug discovery. In this review, we focus on the discovery, characterization, and biological applications of covalent inhibitors for HMTs with emphasis on advancements in the field. In addition, we identify the challenges and future directions in this fast-growing research area of drug discovery.

The Four Homeostasis Knights: In Balance upon Post-Translational Modifications

A cancer outcome is a multifactorial event that comes from both exogenous injuries and an endogenous predisposing background. The healthy state is guaranteed by the fine-tuning of genes controlling cell proliferation, differentiation, and development, whose alteration induces cellular behavioral changes finally leading to cancer. The function of proteins in cells and tissues is controlled at both the transcriptional and translational level, and the mechanism allowing them to carry out their functions is not only a matter of level. A major challenge to the cell is to guarantee that proteins are made, folded, assembled and delivered to function properly, like and even more than other proteins when referring to oncogenes and onco-suppressors products. Over genetic, epigenetic, transcriptional, and translational control, protein synthesis depends on additional steps of regulation. Post-translational modifications are reversible and dynamic processes that allow the cell to rapidly modulate protein amounts and function. Among them, ubiquitination and ubiquitin-like modifications modulate the stability and control the activity of most of the proteins that manage cell cycle, immune responses, apoptosis, and senescence. The crosstalk between ubiquitination and ubiquitin-like modifications and post-translational modifications is a keystone to quickly update the activation state of many proteins responsible for the orchestration of cell metabolism. In this light, the correct activity of post-translational machinery is essential to prevent the development of cancer. Here we summarize the main post-translational modifications engaged in controlling the activity of the principal oncogenes and tumor suppressors genes involved in the development of most human cancers.

De novo methylation of histone H3K23 by the methyltransferases EHMT1/GLP and EHMT2/G9a

Epigenetic modifications to histone proteins serve an important role in regulating permissive and repressive chromatin states, but despite the identification of many histone PTMs and their perceived role, the epigenetic writers responsible for generating these chromatin signatures are not fully characterized. Here, we report that the canonical histone H3K9 methyltransferases EHMT1/GLP and EHMT2/G9a are capable of catalyzing methylation of histone H3 lysine 23 (H3K23). Our data show that while both enzymes can mono- and di-methylate H3K23, only EHMT1/GLP can tri-methylate H3K23. We also show that pharmacologic inhibition or genetic ablation of EHMT1/GLP and/or EHMT2/G9a leads to decreased H3K23 methylation in mammalian cells. Taken together, this work identifies H3K23 as a new direct methylation target of EHMT1/GLP and EHMT2/G9a, and highlights the differential activity of these enzymes on H3K23 as a substrate.

Current perspectives on interethnic variability in multiple myeloma: Single cell technology, population pharmacogenetics and molecular signal transduction

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This review discusses the emerging single cell technologies and applications in Multiple myeloma (MM), population pharmacogenetics of MM, resistance to chemotherapy, genetic determinants of drug-induced toxicity, molecular signal transduction.

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The role(s) of epigenetics and noncoding RNAs including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) that influence the risk and severity of MM are also discussed.

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It is understood that ethnic component acts as a driver of variable response to chemotherapy in different sub-populations globally.

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This review augments our understanding of genetic variability in ‘myelomagenesis’ and drug-induced toxicity, myeloma microenvironment at the molecular and cellular level, and developing precision medicine strategies to combat this malignancy.

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The emerging single cell technologies hold great promise for enhancing our understanding of MM tumor heterogeneity and clonal diversity.

Multiple myeloma (MM) is an aggressive cancer characterised by malignancy of the plasma cells and a rising global incidence. The gold standard for optimum response is aggressive chemotherapy followed by autologous stem cell transplantation (ASCT). However, majority of the patients are above 60 years and this presents the clinician with complications such as ineligibility for ASCT, frailty, drug-induced toxicity and differential/partial response to treatment. The latter is partly driven by heterogenous genotypes of the disease in different subpopulations. In this review, we discuss emerging single cell technologies and applications in MM, population pharmacogenetics of MM, resistance to chemotherapy, genetic determinants of drug-induced toxicity, molecular signal transduction, as well as the role(s) played by epigenetics and noncoding RNAs including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) that influence the risk and severity of the disease. Taken together, our discussions further our understanding of genetic variability in ‘myelomagenesis’ and drug-induced toxicity, augment our understanding of the myeloma microenvironment at the molecular and cellular level and provide a basis for developing precision medicine strategies to combat this malignancy.

The Histone Demethylase HR Suppresses Breast Cancer Development through Enhanced CELF2 Tumor Suppressor Activity

The hairless (HR) gene encodes a transcription factor with histone demethylase activity that is essential for development and tissue homeostasis. Previous studies suggest that mutational inactivation of HR promotes tumorigenesis. To investigate HR mutations in breast cancer, we performed targeted next-generation sequencing using DNA isolated from primary breast cancer tissues. We identified HR somatic mutations in approximately 15% of the patient cohort (n = 85), compared with 23% for BRCA2, 13% for GATA3, 7% for BRCA1, and 3% for PTEN in the same patient cohort. We also found an average 23% HR copy number loss in breast cancers. In support of HR's antitumor functions, HR reconstitution in HR-deficient human breast cancer cells significantly suppressed tumor growth in orthotopic xenograft mouse models. We further demonstrated that HR's antitumor activity was at least partly mediated by transcriptional activation of CELF2, a tumor suppressor with RNA-binding activity. Consistent with HR's histone demethylase activity, pharmacologic inhibition of histone methylation suppressed HR-deficient breast cancer cell proliferation, migration and tumor growth. Taken together, we identified HR as a novel tumor suppressor that is frequently mutated in breast cancer. We also showed that pharmacologic inhibition of histone methylation is effective in suppressing HR-deficient breast tumor growth and progression.

The crucial role of epigenetic regulation in breast cancer anti-estrogen resistance: Current findings and future perspectives

Breast cancer (BC) cell de-sensitization to Tamoxifen (TAM) or other selective estrogen receptor (ER) modulators (SERM) is a complex process associated with BC heterogeneity and the transformation of ER signalling. The most influential resistance-related mechanisms include modifications in ER expression and gene regulation patterns. During TAM/SERM treatment, epigenetic mechanisms can effectively silence ER expression and facilitate the development of endocrine resistance. ER status is efficiently regulated by specific epigenetic tools including hypermethylation of CpG islands within ER promoters, increased histone deacetylase activity in the ER promoter, and/or translational repression by miRNAs. Over-methylation of the ER α gene (ESR1) promoter by DNA methyltransferases was associated with poor prognosis and indicated the development of resistance. Moreover, BC progression and spreading were marked by transformed chromatin remodelling, post-translational histone modifications, and expression of specific miRNAs and/or long non-coding RNAs. Therefore, targeted inhibition of histone acetyltransferases (e.g. MYST3), deacetylases (e.g. HDAC1), and/or demethylases (e.g. lysine-specific demethylase LSD1) was shown to recover and increase BC sensitivity to anti-estrogens. Indicated as a powerful molecular instrument, the administration of epigenetic drugs can regain ER expression along with the activation of tumour suppressor genes, which can in turn prevent selection of resistant cells and cancer stem cell survival. This review examines recent advances in the epigenetic regulation of endocrine drug resistance and evaluates novel anti-resistance strategies. Underlying molecular mechanisms of epigenetic regulation will be discussed, emphasising the utilization of epigenetic enzymes and their inhibitors to re-program irresponsive BCs.

Identification of an Epi-metabolic dependency on EHMT2/G9a in T-cell acute lymphoblastic leukemia

Genomic studies have identified recurrent somatic alterations in genes involved in DNA methylation and post-translational histone modifications in acute lymphoblastic leukemia (ALL), suggesting new opportunities for therapeutic interventions. In this study, we identified G9a/EHMT2 as a potential target in T-ALL through the intersection of epigenome-centered shRNA and chemical screens. We subsequently validated G9a with low-throughput CRISPR-Cas9-based studies targeting the catalytic G9a SET-domain and the testing of G9a chemical inhibitors in vitro, 3D, and in vivo T-ALL models. Mechanistically we determined that G9a repression promotes lysosomal biogenesis and autophagic degradation associated with the suppression of sestrin2 (SESN2) and inhibition of glycogen synthase kinase-3 (GSK-3), suggesting that in T-ALL glycolytic dependent pathways are at least in part under epigenetic control. Thus, targeting G9a represents a strategy to exhaust the metabolic requirement of T-ALL cells.

Histone Lysine Methylation Modification and Its Role in Vascular Calcification

Histone methylation is an epigenetic change mediated by histone methyltransferase, and has been connected to the beginning and progression of several diseases. The most common ailments that affect the elderly are cardiovascular and cerebrovascular disorders. They are the leading causes of death, and their incidence is linked to vascular calcification (VC). The key mechanism of VC is the transformation of vascular smooth muscle cells (VSMCs) into osteoblast-like phenotypes, which is a highly adjustable process involving a variety of complex pathophysiological processes, such as metabolic abnormalities, apoptosis, oxidative stress and signalling pathways. Many researchers have investigated the mechanism of VC and related targets for the prevention and treatment of cardiovascular and cerebrovascular diseases. Their findings revealed that histone lysine methylation modification may play a key role in the various stages of VC. As a result, a thorough examination of the role and mechanism of lysine methylation modification in physiological and pathological states is critical, not only for identifying specific molecular markers of VC and new therapeutic targets, but also for directing the development of new related drugs. Finally, we provide this review to discover the association between histone methylation modification and VC, as well as diverse approaches with which to investigate the pathophysiology of VC and prospective treatment possibilities.

Potential Therapeutics Targeting Upstream Regulators and Interactors of EHMT1/2

Euchromatin histone lysine methyltransferases (EHMTs) are epigenetic regulators responsible for silencing gene transcription by catalyzing H3K9 dimethylation. Dysregulation of EHMT1/2 has been reported in multiple cancers and is associated with poor clinical outcomes. Although substantial insights have been gleaned into the downstream targets and pathways regulated by EHMT1/2, few studies have uncovered mechanisms responsible for their dysregulated expression. Moreover, EHMT1/2 interacting partners, which can influence their function and, therefore, the expression of target genes, have not been extensively explored. As none of the currently available EHMT inhibitors have made it past clinical trials, understanding upstream regulators and EHMT protein complexes may provide unique insights into novel therapeutic avenues in EHMT-overexpressing cancers. Here, we review our current understanding of the regulators and interacting partners of EHMTs. We also discuss available therapeutic drugs that target the upstream regulators and binding partners of EHMTs and could potentially modulate EHMT function in cancer progression.