Epigenetic dysregulation is a common feature of most cancers, often occurring directly through alteration of epigenetic machinery. Over the last several years, a new generation of drugs directed at ...epigenetic modulators have entered clinical development, and results from these trials are now being disclosed. Unlike first-generation epigenetic therapies, these new agents are selective, and many are targeted to proteins which are mutated or translocated in cancer. This review will provide a summary of the epigenetic modulatory agents currently in clinical development and discuss the opportunities and challenges in their development. As these drugs advance in the clinic, drug discovery has continued with a focus on both novel and existing epigenetic targets. We will provide an overview of these efforts and the strategies being employed.
Chronic exposure to inducers of DNA base oxidation and single and double strand breaks contribute to tumorigenesis. In addition to the genetic changes caused by this DNA damage, such tumors often ...contain epigenetically silenced genes with aberrant promoter region CpG island DNA hypermethylation. We herein explore the relationships between such DNA damage and epigenetic gene silencing using an experimental model in which we induce a defined double strand break in an exogenous promoter construct of the E-cadherin CpG island, which is frequently aberrantly DNA hypermethylated in epithelial cancers. Following the onset of repair of the break, we observe recruitment to the site of damage of key proteins involved in establishing and maintaining transcriptional repression, namely SIRT1, EZH2, DNMT1, and DNMT3B, and the appearance of the silencing histone modifications, hypoacetyl H4K16, H3K9me2 and me3, and H3K27me3. Although in most cells selected after the break, DNA repair occurs faithfully with preservation of activity of the promoter, a small percentage of the plated cells demonstrate induction of heritable silencing. The chromatin around the break site in such a silent clone is enriched for most of the above silent chromatin proteins and histone marks, and the region harbors the appearance of increasing DNA methylation in the CpG island of the promoter. During the acute break, SIRT1 appears to be required for the transient recruitment of DNMT3B and subsequent methylation of the promoter in the silent clones. Taken together, our data suggest that normal repair of a DNA break can occasionally cause heritable silencing of a CpG island-containing promoter by recruitment of proteins involved in silencing. Furthermore, with contribution of the stress-related protein SIRT1, the break can lead to the onset of aberrant CpG island DNA methylation, which is frequently associated with tight gene silencing in cancer.
Non-genetic drug resistance is increasingly recognised in various cancers. Molecular insights into this process are lacking and it is unknown whether stable non-genetic resistance can be overcome. ...Using single cell RNA-sequencing of paired drug naïve and resistant AML patient samples and cellular barcoding in a unique mouse model of non-genetic resistance, here we demonstrate that transcriptional plasticity drives stable epigenetic resistance. With a CRISPR-Cas9 screen we identify regulators of enhancer function as important modulators of the resistant cell state. We show that inhibition of Lsd1 (Kdm1a) is able to overcome stable epigenetic resistance by facilitating the binding of the pioneer factor, Pu.1 and cofactor, Irf8, to nucleate new enhancers that regulate the expression of key survival genes. This enhancer switching results in the re-distribution of transcriptional co-activators, including Brd4, and provides the opportunity to disable their activity and overcome epigenetic resistance. Together these findings highlight key principles to help counteract non-genetic drug resistance.
Drugs that modify the epigenome are powerful tools for treating cancer, but these drugs often have pleiotropic effects, and identifying patients who will benefit from them remains a major clinical ...challenge. Here we show that medulloblastomas driven by the transcription factor Gfi1 are exquisitely dependent on the enzyme lysine demethylase 1 (Kdm1a/Lsd1). We demonstrate that Lsd1 physically associates with Gfi1, and that these proteins cooperate to inhibit genes involved in neuronal commitment and differentiation. We also show that Lsd1 is essential for Gfi1-mediated transformation: Gfi1 proteins that cannot recruit Lsd1 are unable to drive tumorigenesis, and genetic ablation of Lsd1 markedly impairs tumor growth in vivo. Finally, pharmacological inhibitors of Lsd1 potently inhibit growth of Gfi1-driven tumors. These studies provide important insight into the mechanisms by which Gfi1 contributes to tumorigenesis, and identify Lsd1 inhibitors as promising therapeutic agents for Gfi1-driven medulloblastoma.
Targeting Histone Methylation in Cancer McCabe, Michael T; Mohammad, Helai P; Barbash, Olena ...
The cancer journal (Sudbury, Mass.),
2017 Sep/Oct, Letnik:
23, Številka:
5
Journal Article
Recenzirano
Most, if not all, human cancers exhibit altered epigenetic signatures that promote aberrant gene expression that contributes to cellular transformation. Historically, attempts to pharmacologically ...intervene in this process have focused on DNA methylation and histone acetylation. More recently, genome-wide studies have identified histone and chromatin regulators as one of the most frequently dysregulated functional classes in a wide range of cancer types. These findings have provided numerous potential therapeutic targets including many that affect histone methylation. These include histone lysine methyltransferases such as enhancer of zeste homolog 2 and DOT1L, protein arginine methyltransferases such as protein arginine methyltransferase 5, and histone lysine demethylases such as lysine-specific demethylase 1. This review presents the rationale for targeting histone methylation in oncology and provides an update on a few key targets that are being investigated in the clinic.
One of the biggest gaps in our knowledge about epigenomes is how their interplay with cellular signaling influences development, adult cellular differentiation and disease.
Lysine specific demethylase 1 (LSD1) is a histone modifying enzyme that suppresses gene expression through demethylation of lysine 4 on histone H3. The anti-tumor activity of GSK2879552 and GSK-LSD1, ...potent, selective irreversible inactivators of LSD1, has previously been described. Inhibition of LSD1 results in a cytostatic growth inhibitory effect in a range of acute myeloid leukemia cell lines. To enhance the therapeutic potential of LSD1 inhibition in this disease setting, a combination of LSD1 inhibition and all-
retinoic acid was explored. All-
retinoic acid is currently approved for use in acute promyelocytic leukemia in which it promotes differentiation of abnormal blast cells into normal white blood cells. Combined treatment with all-
retinoic acid and GSK2879552 results in synergistic effects on cell proliferation, markers of differentiation, and, most importantly, cytotoxicity. Ultimately the combination potential for LSD1 inhibition and ATRA will require validation in acute myeloid leukemia patients, and clinical studies to assess this are currently underway.
SMYD3 is a lysine methyltransferase overexpressed in colorectal, breast, prostate, and hepatocellular tumors, and has been implicated as an oncogene in human malignancies. Methylation of MEKK2 by ...SMYD3 is important for regulation of the MEK/ERK pathway, suggesting the possibility of selectively targeting SMYD3 in RAS-driven cancers. Structural and kinetic characterization of SMYD3 was undertaken leading to a co-crystal structure of SMYD3 with a MEKK2-peptide substrate bound, and the observation that SMYD3 follows a partially processive mechanism. These insights allowed for the design of GSK2807, a potent and selective, SAM-competitive inhibitor of SMYD3 (Ki = 14 nM). A high-resolution crystal structure reveals that GSK2807 bridges the gap between the SAM-binding pocket and the substrate lysine tunnel of SMYD3. Taken together, our data demonstrate that small-molecule inhibitors of SMYD3 can be designed to prevent methylation of MEKK2 and these could have potential use as anticancer therapeutics.
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•Structure-based design of a bisubstrate analog inhibitor of SMYD3•Previously unreported co-crystal structure of SMYD3 with a peptide substrate bound•Methylation of MEKK2 was determined to be partially processive•SMYD3 inhibitors have potential as anticancer therapeutic agents
Van Aller et al. describe the structure-based design of a potent, selective SMYD3 inhibitor, a bisubstrate analog reaching into both substrate pockets. Guided by a MEKK2-peptide co-crystal structure, their work highlights the opportunity to design modulators of RAS-driven tumor pathways through inhibition of SMYD3.
Arginine methylation has been recognized as a post-translational modification with pleiotropic effects that span from regulation of transcription to metabolic processes that contribute to aberrant ...cell proliferation and tumorigenesis. This has brought significant attention to the development of therapeutic strategies aimed at blocking the activity of protein arginine methyltransferases (PRMTs), which catalyze the formation of various methylated arginine products on a wide variety of cellular substrates. GSK3368715 is a small molecule inhibitor of type I PRMTs currently in clinical development. Here, we evaluate the effect of type I PRMT inhibition on arginine methylation in normal human peripheral blood mononuclear cells and utilize a broad proteomic approach to identify type I PRMT substrates. This work identified heterogenous nuclear ribonucleoprotein A1 (hnRNP-A1) as a pharmacodynamic biomarker of type I PRMT inhibition. Utilizing targeted mass spectrometry (MS), methods were developed to detect and quantitate changes in methylation of specific arginine residues on hnRNP-A1. This resulted in the development and validation of novel MS and immune assays useful for the assessment of GSK3368715 induced pharmacodynamic effects in blood and tumors that can be applied to GSK3368715 clinical trials.
Disruption of epigenetic regulation is a hallmark of acute myeloid leukemia (AML), but epigenetic therapy is complicated by the complexity of the epigenome. Herein, we developed a long-term primary ...AML
platform to determine whether targeting different epigenetic layers with 5-azacytidine and LSD1 inhibitors would yield improved efficacy. This combination was most effective in
AML, where it extinguished leukemia stem cells and particularly induced genes with both LSD1-bound enhancers and cytosine-methylated promoters. Functional studies indicated that derepression of genes such as
contributes to drug efficacy. Mechanistically, combination therapy increased enhancer-promoter looping and chromatin-activating marks at the
locus. CRISPRi of the LSD1-bound enhancer in patient-derived
AML was associated with dampening of therapeutic
induction.
knockdown in human hematopoietic stem/progenitor cells induced loss of enhancer 5-hydroxymethylation and facilitated LSD1-mediated enhancer inactivation. Our data provide a basis for rational targeting of cooperating aberrant promoter and enhancer epigenetic marks driven by mutant epigenetic modifiers. SIGNIFICANCE: Somatic mutations of genes encoding epigenetic modifiers are a hallmark of AML and potentially disrupt many components of the epigenome. Our study targets two different epigenetic layers at promoters and enhancers that cooperate to aberrant gene silencing, downstream of the actions of a mutant epigenetic regulator.
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