Lung Cancer Therapy Targeting Histone Methylation: Opportunities and Challenges.
ABSTRACT: Lung cancer is one of the most common malignancies. In spite of the progress made in past decades, further studies to improve current therapy for lung cancer are required. Dynamically controlled by methyltransferases and demethylases, methylation of lysine and arginine residues on histone proteins regulates chromatin organization and thereby gene transcription. Aberrant alterations of histone methylation have been demonstrated to be associated with the progress of multiple cancers including lung cancer. Inhibitors of methyltransferases and demethylases have exhibited anti-tumor activities in lung cancer, and multiple lead candidates are under clinical trials. Here, we summarize how histone methylation functions in lung cancer, highlighting most recent progresses in small molecular inhibitors for lung cancer treatment.
Project description:Lysine methylation is one of the most prominent histone posttranslational modifications that regulate chromatin structure. Changes in histone lysine methylation status have been observed during cancer formation, which is thought to be a consequence of the dysregulation of histone lysine methyltransferases or the opposing demethylases. KDM4/JMJD2 proteins are demethylases that target histone H3 on lysines 9 and 36 and histone H1.4 on lysine 26. This protein family consists of three ~130-kDa proteins (KDM4A-C) and KDM4D/JMJD2D, which is half the size, lacks the double PHD and Tudor domains that are epigenome readers and present in the other KDM4 proteins, and has a different substrate specificity. Various studies have shown that KDM4A/JMJD2A, KDM4B/JMJD2B, and/or KDM4C/JMJD2C are overexpressed in breast, colorectal, lung, prostate, and other tumors and are required for efficient cancer cell growth. In part, this may be due to their ability to modulate transcription factors such as the androgen and estrogen receptor. Thus, KDM4 proteins present themselves as novel potential drug targets. Accordingly, multiple attempts are under way to develop KDM4 inhibitors, which could complement the existing arsenal of epigenetic drugs that are currently limited to DNA methyltransferases and histone deacetylases.
Project description:Histone methylation represents one of the most critical epigenetic events in DNA function regulation in eukaryotic organisms. Classic molecular biology and genetics tools provide significant knowledge about mechanisms and physiological roles of histone methyltransferases and demethylases in various cellular processes. In addition to this stream line, development and application of chemistry and chemistry-related techniques are increasingly involved in biological study, and offer information otherwise difficult to obtain by standard molecular biology methods. Herein, we review recent achievements and progress in developing and applying chemical and biochemical approaches in the study of histone methylation, including chromatin immunoprecipitation, chemical ligation, mass spectrometry, biochemical methylation and demethylation assays, and inhibitor development. These technological advances allow histone methylation to be studied from genome-wide level to molecular and atomic levels. With ChIP technology, information can be obtained about precise mapping of histone methylation patterns at specific promoters, genes, or other genomic regions. MS is particularly useful in detecting and analyzing methylation marks in histone and nonhistone protein substrates. Chemical approaches that permit site-specific incorporation of methyl groups into histone proteins greatly facilitate the investigation of biological impacts of methylation at individual modification sites. Discovery and design of selective organic inhibitors of histone methyltransferases and demethylases provide chemical probes to interrogate methylation-mediated cellular pathways. Overall, these chemistry-related technological advances have greatly improved our understanding of the biological functions of histone methylation in normal physiology and diseased states, and also are of great potential to translate basic epigenetics research into diagnostic and therapeutic applications in the clinic.
Project description:Reversible histone methylation has emerged in the last few years as an important mechanism of epigenetic regulation. Histone methyltransferases and demethylases have been identified as contributing factors in the development of several diseases, especially cancer. Therefore, they have been postulated to be new drug targets with high therapeutic potential. Here, we review histone demethylases with a special focus on their potential role in oncology drug discovery. We present an overview over the different classes of enzymes, their biochemistry, selected data on their role in physiology and already available inhibitors.
Project description:Protein methylation, a post-translational modification (PTM), is observed in a wide variety of cell types from prokaryotes to eukaryotes. With recent and rapid advancements in epigenetic research, the importance of protein methylation has been highlighted. The methylation of histone proteins that contributes to the epigenetic histone code is not only dynamic but is also finely controlled by histone methyltransferases and demethylases, which are essential for the transcriptional regulation of genes. In addition, many nonhistone proteins are methylated, and these modifications govern a variety of cellular functions, including RNA processing, translation, signal transduction, DNA damage response, and the cell cycle. Recently, the importance of protein arginine methylation, especially in cell cycle regulation and DNA repair processes, has been noted. Since the dysregulation of protein arginine methylation is closely associated with cancer development, protein arginine methyltransferases (PRMTs) have garnered significant interest as novel targets for anticancer drug development. Indeed, several PRMT inhibitors are in phase 1/2 clinical trials. In this review, we discuss the biological functions of PRMTs in cancer and the current development status of PRMT inhibitors in cancer therapy.
Project description:During the last decade, we saw an explosion of studies investigating the role of lysine methylation/demethylation of histones and non-histone proteins, such as p53, NF-kappaB, and E2F1. These 'Ying-Yang' post-translational modifications are important to fine-tuning the activity of these proteins. Lysine methylation and demethylation are catalyzed by protein lysine methyltransferases (PKMTs) and protein lysine demethylases (PKDMs). PKMTs, PKDMs, and their substrates have been shown to play important roles in cancers. Although the underlying mechanisms of tumorigenesis are still largely unknown, growing evidence is starting to link aberrant regulation of methylation to tumorigenesis. This review focuses on summarizing the recent progress in understanding of the function of protein lysine methylation, and in the discovery of small molecule inhibitors for PKMTs and PKDMs. We also discuss the potential and the caveats of targeting protein lysine methylation for the treatment of cancer.
Project description:Cancer-testis antigens (CTA), such as NY-ESO-1, MAGE-A1, and MAGE-A3, are immunogenic proteins encoded by genes, which are normally expressed only in male germ cells but are activated by ill-defined epigenetic mechanisms in human tumors, including lung cancers. Previously, we reported induction of these CTAs in cancer cells, but not normal cells, by DNA-demethylating agents and histone deacetylase inhibitors using clinically achievable exposure conditions. In the present study, we evaluated chromatin alterations associated with repression/activation of cancer-testis genes in lung cancer cells to further develop gene-induction regimens for cancer immunotherapy. Repression of NY-ESO-1, MAGE-A1, and MAGE-A3 coincided with DNA hypermethylation, recruitment, and binding of polycomb-group proteins, and histone heterochromatin modifications within the promoters of these genes. Derepression coincided with DNA demethylation, dissociation of polycomb proteins, and presence of euchromatin marks within the respective promoters. Short hairpin RNAs were used to inhibit several histone methyltransferases (KMT) and histone demethylases (KDM) that mediate histone methylation and repress gene expression. Knockdown of KMT6, KDM1, or KDM5B markedly enhanced deoxyazacytidine (DAC)-mediated activation of these cancer-testis genes in lung cancer cells. DZNep, a pharmacologic inhibitor of KMT6 expression, recapitulated the effects of KMT6 knockdown. Following DAC-DZNep exposure, lung cancer cells were specifically recognized and lysed by allogeneic lymphocytes expressing recombinant T-cell receptors recognizing NY-ESO-1 and MAGE-A3. Combining DNA-demethylating agents with compounds, such as DZNep, that modulate histone lysine methylation may provide a novel epigenetic strategy to augment cancer-testis gene expression as an adjunct to adoptive cancer immunotherapy.
Project description:BACKGROUND:Small molecule modulators of epigenetic processes are currently sought as basic probes for biochemical mechanisms, and as starting points for development of therapeutic agents. N(?)-Methylation of lysine residues on histone tails is one of a number of post-translational modifications that together enable transcriptional regulation. Histone lysine demethylases antagonize the action of histone methyltransferases in a site- and methylation state-specific manner. N(?)-Methyllysine demethylases that use 2-oxoglutarate as co-factor are associated with diverse human diseases, including cancer, inflammation and X-linked mental retardation; they are proposed as targets for the therapeutic modulation of transcription. There are few reports on the identification of templates that are amenable to development as potent inhibitors in vivo and large diverse collections have yet to be exploited for the discovery of demethylase inhibitors. PRINCIPAL FINDINGS:High-throughput screening of a ?236,000-member collection of diverse molecules arrayed as dilution series was used to identify inhibitors of the JMJD2 (KDM4) family of 2-oxoglutarate-dependent histone demethylases. Initial screening hits were prioritized by a combination of cheminformatics, counterscreening using a coupled assay enzyme, and orthogonal confirmatory detection of inhibition by mass spectrometric assays. Follow-up studies were carried out on one of the series identified, 8-hydroxyquinolines, which were shown by crystallographic analyses to inhibit by binding to the active site Fe(II) and to modulate demethylation at the H3K9 locus in a cell-based assay. CONCLUSIONS:These studies demonstrate that diverse compound screening can yield novel inhibitors of 2OG dependent histone demethylases and provide starting points for the development of potent and selective agents to interrogate epigenetic regulation.
Project description:The term epigenetics is defined as heritable changes in gene expression that are not due to alterations of the DNA sequence. In the last years, it has become more and more evident that dysregulated epigenetic regulatory processes have a central role in cancer onset and progression. In contrast to DNA mutations, epigenetic modifications are reversible and, hence, suitable for pharmacological interventions. Reversible histone methylation is an important process within epigenetic regulation, and the investigation of its role in cancer has led to the identification of lysine methyltransferases and demethylases as promising targets for new anticancer drugs. In this review, we describe those enzymes and their inhibitors that have already reached the first stages of clinical trials in cancer therapy, namely the histone methyltransferases DOT1L and EZH2 as well as the demethylase LSD1.
Project description:As a leading cause of cancer deaths worldwide, colorectal cancer (CRC) results from accumulation of both genetic and epigenetic alterations. Disruption of epigenetic regulation in CRC, particularly aberrant histone methylation mediated by histone methyltransferases (HMTs) and demethylases (HDMs), have drawn increasing interest in recent years. In this paper, we aim to review the roles of histone methylation and associated enzymes in the pathogenesis of CRC, and the development of small-molecule modulators to regulate histone methylation for treating CRC. Multiple levels of evidence suggest that aberrant histone methylations play important roles in CRC. More than 20 histone-methylation enzymes are found to be clinically relevant to CRC, including 17 oncoproteins and 8 tumor suppressors. Inhibitors of EZH2 and DOT1L have demonstrated promising therapeutic effects in preclinical CRC treatment. Potent and selective chemical probes of histone-methylation enzymes are required for validation of their functional roles in carcinogenesis and clinical translations as CRC therapies. With EZH2 inhibitor EPZ-6438 entering into phase I/II trials for advanced solid tumors, histone methylation is emerging as a promising target for CRC.
Project description:Histone proteins constitute the core component of the nucleosome, the basic unit of chromatin. Chemical modifications of histone proteins affect their interaction with genomic DNA, the accessibility of recognized proteins, and the recruitment of enzymatic complexes to activate or diminish specific transcriptional programs to modulate cellular response to extracellular stimuli or insults. Methylation of histone proteins was demonstrated 50 years ago; however, the biological significance of each methylated residue and the integration between these histone markers are still under intensive investigation. Methylation of histone H3 on lysine 27 (H3K27) is frequently found in the heterochromatin and conceives a repressive marker that is linked with gene silencing. The identification of enzymes that add or erase the methyl group of H3K27 provides novel insights as to how this histone marker is dynamically controlled under different circumstances. Here we summarize the methyltransferases and demethylases involved in the methylation of H3K27 and show the new evidence by which the H3K27 methylation can be established via an alternative mechanism. Finally, the progress of drug development targeting H3K27 methylation-modifying enzymes and their potential application in cancer therapy are discussed.