EHMT1 and EHMT2 inhibition induces fetal hemoglobin expression

A molecular glue degrader of the WIZ transcription factor for fetal hemoglobin induction

Sickle cell disease (SCD) is a prevalent, life-threatening condition attributable to a heritable mutation in β-hemoglobin. Therapeutic induction of fetal hemoglobin (HbF) can ameliorate disease complications and has been intently pursued. However, safe and effective small-molecule inducers of HbF remain elusive. We report the discovery of dWIZ-1 and dWIZ-2, molecular glue degraders of the WIZ transcription factor that robustly induce HbF in erythroblasts. Phenotypic screening of a cereblon (CRBN)-biased chemical library revealed WIZ as a previously unknown repressor of HbF. WIZ degradation is mediated by recruitment of WIZ(ZF7) to CRBN by dWIZ-1, as resolved by crystallography of the ternary complex. Pharmacological degradation of WIZ was well tolerated and induced HbF in humanized mice and cynomolgus monkeys. These findings establish WIZ degradation as a globally accessible therapeutic strategy for SCD.

Ehmt2 inactivation in pancreatic epithelial cells shapes the transcriptional landscape and inflammation response of the whole pancreas

Introduction: The Euchromatic Histone Methyl Transferase Protein 2 (EHMT2), also known as G9a, deposits transcriptionally repressive chromatin marks that play pivotal roles in the maturation and homeostasis of multiple organs. Recently, we have shown that Ehmt2 inactivation in the mouse pancreas alters growth and immune gene expression networks, antagonizing Kras-mediated pancreatic cancer initiation and promotion. Here, we elucidate the essential role of Ehmt2 in maintaining a transcriptional landscape that protects organs from inflammation. Methods: Comparative RNA-seq studies between normal postnatal and young adult pancreatic tissue from Ehmt2 conditional knockout animals (Ehmt2 fl/fl ) targeted to the exocrine pancreatic epithelial cells (Pdx1-Cre and P48 Cre/+ ), reveal alterations in gene expression networks in the whole organ related to injury-inflammation-repair, suggesting an increased predisposition to damage. Thus, we induced an inflammation repair response in the Ehmt2 fl/fl pancreas and used a data science-based approach to integrate RNA-seq-derived pathways and networks, deconvolution digital cytology, and spatial transcriptomics. We also analyzed the tissue response to damage at the morphological, biochemical, and molecular pathology levels. Results and discussion: The Ehmt2 fl/fl pancreas displays an enhanced injury-inflammation-repair response, offering insights into fundamental molecular and cellular mechanisms involved in this process. More importantly, these data show that conditional Ehmt2 inactivation in exocrine cells reprograms the local environment to recruit mesenchymal and immunological cells needed to mount an increased inflammatory response. Mechanistically, this response is an enhanced injury-inflammation-repair reaction with a small contribution of specific Ehmt2-regulated transcripts. Thus, this new knowledge extends the mechanisms underlying the role of the Ehmt2-mediated pathway in suppressing pancreatic cancer initiation and modulating inflammatory pancreatic diseases.

The Discovery of Selective Protein Arginine Methyltransferase 5 Inhibitors in the Management of β-Thalassemia through Computational Methods

β-Thalassemia is an inherited genetic disorder associated with β-globin chain synthesis, which ultimately becomes anemia. Adenosine-2,3-dialdehyde, by inhibiting arginine methyl transferase 5 (PRMT5), can induce fetal hemoglobin (HbF) levels. Hence, the materialization of PRMT5 inhibitors is considered a promising therapy in the management of β-thalassemia. This study conducted a virtual screening of certain compounds similar to 5'-deoxy-5'methyladenosine (3XV) using the PubChem database. The top 10 compounds were chosen based on the best docking scores, while their interactions with the PRMT5 active site were analyzed. Further, the top two compounds demonstrating the lowest binding energy were subjected to drug-likeness analysis and pharmacokinetic property predictions, followed by molecular dynamics simulation studies. Based on the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) score and molecular interactions, (3R,4S)-2-(6-aminopurin-9-yl)-5-[(4-ethylcyclohexyl)sulfanylmethyl]oxolane-3,4-diol (TOP1) and 2-(6-Aminopurin-9-yl)-5-[(6-aminopurin-9-yl)methylsulfanylmethyl]oxolane-3,4-diol (TOP2) were identified as potential hit compounds, while TOP1 exhibited higher binding affinity and stabler binding capabilities than TOP2 during molecular dynamics simulation (MDS) analysis. Taken together, the outcomes of our study could aid researchers in identifying promising PRMT5 inhibitors. Moreover, further investigations through in vivo and in vitro experiments would unquestionably confirm that this compound could be employed as a therapeutic drug in the management of β-thalassemia.

Red Blood Cells as Therapeutic Target to Treat Sickle Cell Disease

Significance: Sickle cell disease (SCD) is the most common inherited diathesis affecting mostly underserved populations globally. SCD is characterized by chronic pain and fatigue, severe acute painful crises requiring hospitalization and opioids, strokes, multiorgan damage, and a shortened life span. Symptoms may appear shortly after birth, and, in less developed countries, most children with SCD die before attaining age 5. Hematopoietic stem cell transplant and gene therapy offer a curative therapeutic approach, but, due to many challenges, are limited in their availability and effectiveness for a majority of persons with SCD. A critical unmet need is to develop safe and effective novel targeted therapies. A wide array of drugs currently undergoing clinical investigation hold promise for an expanded pharmacological armamentarium against SCD. Recent Advances: Hydroxyurea, the most widely used intervention for SCD management, has improved the survival in the Western world and more recently, voxelotor (R-state-stabilizer), l-glutamine, and crizanlizumab (anti-P-selectin antibody) have been approved by the Food and Drug Administration (FDA) for use in SCD. The recent FDA approval emphasizes the need to revisit the advances in understanding the core pathophysiology of SCD to accelerate novel evidence-based strategies to treat SCD. The biomechanical breakdown of erythrocytesis, the core pathophysiology of SCD, is associated with intrinsic factors, including the composition of hemoglobin, membrane integrity, cellular volume, hydration, andoxidative stress. Critical Issues and Future Directions: In this context, this review focuses on advances in emerging nongenetic interventions directed toward the therapeutic targets intrinsic to sickle red blood cells (RBCs), which can prevent impaired rheology of RBCs to impede disease progression and reduce the sequelae of comorbidities, including pain, vasculopathy, and organ damage. In addition, given the intricate pathophysiology of the disease, it is unlikely that a single pharmacotherapeutic intervention will comprehensively ameliorate the multifaceted complications associated with SCD. However, the availability of multiple drug options affords the opportunity for individualized therapeutic regimens tailored to specific SCD-related complications. Furthermore, it opens avenues for combination drug therapy, capitalizing on distinct mechanisms of action and profiles of adverse effects.

C2H2 Zinc Finger Transcription Factors Associated with Hemoglobinopathies

In humans, specific aberrations in β-globin results in sickle cell disease and β-thalassemia, symptoms of which can be ameliorated by increased expression of fetal globin (HbF). Two recent CRISPR-Cas9 screens, centered on ∼1500 annotated sequence-specific DNA binding proteins and performed in a human erythroid cell line that expresses adult hemoglobin, uncovered four groups of candidate regulators of HbF gene expression. They are (1) members of the nucleosome remodeling and deacetylase (NuRD) complex proteins that are already known for HbF control; (2) seven C2H2 zinc finger (ZF) proteins, including some (ZBTB7A and BCL11A) already known for directly silencing the fetal γ-globin genes in adult human erythroid cells; (3) a few other transcription factors of different structural classes that might indirectly influence HbF gene expression; and (4) DNA methyltransferase 1 (DNMT1) that maintains the DNA methylation marks that attract the MBD2-associated NuRD complex to DNA as well as associated histone H3 lysine 9 methylation. Here we briefly discuss the effects of these regulators, particularly C2H2 ZFs, in inducing HbF expression for treating β-hemoglobin disorders, together with recent advances in developing safe and effective small-molecule therapeutics for the regulation of this well-conserved hemoglobin switch.

EHMT2 Inactivation in Pancreatic Epithelial Cells Shapes the Transcriptional Landscape and Inflammation Response of the Whole Pancreas

The Euchromatic Histone Methyl Transferase Protein 2 (EHMT2), also known as G9a, deposits transcriptionally repressive chromatin marks that play pivotal roles in the maturation and homeostasis of multiple organs. Recently, we have shown that EHMT2 inactivation alters growth and immune gene expression networks, antagonizing KRAS-mediated pancreatic cancer initiation and promotion. Here, we elucidate the essential role of EHMT2 in maintaining a transcriptional landscape that protects organs from inflammation. Comparative RNA-seq studies between normal postnatal and young adult pancreatic tissue from EHMT2 conditional knockout animals ( EHMT2 fl/fl ) targeted to the exocrine pancreatic epithelial cells ( Pdx1-Cre and P48 Cre/+ ), reveal alterations in gene expression networks in the whole organ related to injury-inflammation-repair, suggesting an increased predisposition to damage. Thus, we induced an inflammation repair response in the EHMT2 fl/fl pancreas and used a data science-based approach to integrate RNA-seq-derived pathways and networks, deconvolution digital cytology, and spatial transcriptomics. We also analyzed the tissue response to damage at the morphological, biochemical, and molecular pathology levels. The EHMT2 fl/fl pancreas displays an enhanced injury-inflammation-repair response, offering insights into fundamental molecular and cellular mechanisms involved in this process. More importantly, these data show that conditional EHMT2 inactivation in exocrine cells reprograms the local environment to recruit mesenchymal and immunological cells needed to mount an increased inflammatory response. Mechanistically, this response is an enhanced injury-inflammation-repair reaction with a small contribution of specific EHMT2-regulated transcripts. Thus, this new knowledge extends the mechanisms underlying the role of the EHMT2-mediated pathway in suppressing pancreatic cancer initiation and modulating inflammatory pancreatic diseases.

Discovery of Ligands for TRIM58, a Novel Tissue-Selective E3 Ligase

Redirecting E3 ligases to neo-substrates, leading to their proteasomal disassembly, known as targeted protein degradation (TPD), has emerged as a promising alternative to traditional, occupancy-driven pharmacology. Although the field has expanded tremendously over the past years, the choice of E3 ligases remains limited, with an almost exclusive focus on CRBN and VHL. Here, we report the discovery of novel ligands to the PRY-SPRY domain of TRIM58, a RING ligase that is specifically expressed in erythroid precursor cells. A DSF screen, followed by validation using additional biophysical methods, led to the identification of TRIM58 ligand TRIM-473. A basic SAR around the chemotype was established by utilizing a competitive binding assay employing a short FP peptide probe derived from an endogenous TRIM58 substrate. The X-ray co-crystal structure of TRIM58 in complex with TRIM-473 gave insights into the binding mode and potential exit vectors for bifunctional degrader design.

Epigenetic Regulation of β-Globin Genes and the Potential to Treat Hemoglobinopathies through Epigenome Editing

Beta-like globin gene expression is developmentally regulated during life by transcription factors, chromatin looping and epigenome modifications of the β-globin locus. Epigenome modifications, such as histone methylation/demethylation and acetylation/deacetylation and DNA methylation, are associated with up- or down-regulation of gene expression. The understanding of these mechanisms and their outcome in gene expression has paved the way to the development of new therapeutic strategies for treating various diseases, such as β-hemoglobinopathies. Histone deacetylase and DNA methyl-transferase inhibitors are currently being tested in clinical trials for hemoglobinopathies patients. However, these approaches are often uncertain, non-specific and their global effect poses serious safety concerns. Epigenome editing is a recently developed and promising tool that consists of a DNA recognition domain (zinc finger, transcription activator-like effector or dead clustered regularly interspaced short palindromic repeats Cas9) fused to the catalytic domain of a chromatin-modifying enzyme. It offers a more specific targeting of disease-related genes (e.g., the ability to reactivate the fetal γ-globin genes and improve the hemoglobinopathy phenotype) and it facilitates the development of scarless gene therapy approaches. Here, we summarize the mechanisms of epigenome regulation of the β-globin locus, and we discuss the application of epigenome editing for the treatment of hemoglobinopathies.

A specific G9a inhibitor unveils BGLT3 lncRNA as a universal mediator of chemically induced fetal globin gene expression

Sickle cell disease (SCD) is a heritable disorder caused by β-globin gene mutations. Induction of fetal γ-globin is an established therapeutic strategy. Recently, epigenetic modulators, including G9a inhibitors, have been proposed as therapeutic agents. However, the molecular mechanisms whereby these small molecules reactivate γ-globin remain unclear. Here we report the development of a highly selective and non-genotoxic G9a inhibitor, RK-701. RK-701 treatment induces fetal globin expression both in human erythroid cells and in mice. Using RK-701, we find that BGLT3 long non-coding RNA plays an essential role in γ-globin induction. RK-701 selectively upregulates BGLT3 by inhibiting the recruitment of two major γ-globin repressors in complex with G9a onto the BGLT3 gene locus through CHD4, a component of the NuRD complex. Remarkably, BGLT3 is indispensable for γ-globin induction by not only RK-701 but also hydroxyurea and other inducers. The universal role of BGLT3 in γ-globin induction suggests its importance in SCD treatment.

Epigenetic Silencing of CHOP Expression by the Histone Methyltransferase EHMT1 Regulates Apoptosis in Colorectal Cancer Cells

Colorectal cancer (CRC) has a high mortality rate among cancers worldwide. To reduce this mortality rate, chemotherapy (5-fluorouracil, oxaliplatin, and irinotecan) or targeted therapy (bevacizumab, cetuximab, and panitumumab) has been used to treat CRC. However, due to various side effects and poor responses to CRC treatment, novel therapeutic targets for drug development are needed. In this study, we identified the overexpression of EHMT1 in CRC using RNA sequencing (RNA-seq) data derived from TCGA, and we observed that knocking down EHMT1 expression suppressed cell growth by inducing cell apoptosis in CRC cell lines. In Gene Ontology (GO) term analysis using RNA-seq data, apoptosis-related terms were enriched after EHMT1 knockdown. Moreover, we identified the CHOP gene as a direct target of EHMT1 using a ChIP (chromatin immunoprecipitation) assay with an anti-histone 3 lysine 9 dimethylation (H3K9me2) antibody. Finally, after cotransfection with siEHMT1 and siCHOP, we again confirmed that CHOP-mediated cell apoptosis was induced by EHMT1 knockdown. Our findings reveal that EHMT1 plays a key role in regulating CRC cell apoptosis, suggesting that EHMT1 may be a therapeutic target for the development of cancer inhibitors.

Dental stem cell-derived extracellular vesicles transfer miR-330-5p to treat traumatic brain injury by regulating microglia polarization

Traumatic brain injury (TBI) contributes to the key causative elements of neurological deficits. However, no effective therapeutics have been developed yet. In our previous work, extracellular vesicles (EVs) secreted by stem cells from human exfoliated deciduous teeth (SHED) offered new insights as potential strategies for functional recovery of TBI. The current study aims to elucidate the mechanism of action, providing novel therapeutic targets for future clinical interventions. With the miRNA array performed and Real-time PCR validated, we revealed the crucial function of miR-330-5p transferred by SHED-derived EVs (SHED-EVs) in regulating microglia, the critical immune modulator in central nervous system. MiR-330-5p targeted Ehmt2 and mediated the transcription of CXCL14 to promote M2 microglia polarization and inhibit M1 polarization. Identified in our in vivo data, SHED-EVs and their effector miR-330-5p alleviated the secretion of inflammatory cytokines and resumed the motor functional recovery of TBI rats. In summary, by transferring miR-330-5p, SHED-EVs favored anti-inflammatory microglia polarization through Ehmt2 mediated CXCL14 transcription in treating traumatic brain injury.

Pharmacological Induction of Fetal Hemoglobin in β-Thalassemia and Sickle Cell Disease: An Updated Perspective

A significant amount of attention has recently been devoted to the mechanisms involved in hemoglobin (Hb) switching, as it has previously been established that the induction of fetal hemoglobin (HbF) production in significant amounts can reduce the severity of the clinical course in diseases such as β-thalassemia and sickle cell disease (SCD). While the induction of HbF using lentiviral and genome-editing strategies has been made possible, they present limitations. Meanwhile, progress in the use of pharmacologic agents for HbF induction and the identification of novel HbF-inducing strategies has been made possible as a result of a better understanding of γ-globin regulation. In this review, we will provide an update on all current pharmacological inducer agents of HbF in β-thalassemia and SCD in addition to the ongoing research into other novel, and potentially therapeutic, HbF-inducing agents.

Identification of novel γ-globin inducers among all potential erythroid druggable targets

Human γ-globin is predominantly expressed in fetal liver erythroid cells during gestation from 2 nearly identical genes, HBG1 and HBG2, that are both perinatally silenced. Reactivation of these fetal genes in adult red blood cells can ameliorate many symptoms associated with the inherited β-globinopathies, sickle cell disease, and Cooley anemia. Although promising genetic strategies to reactivate the γ-globin genes to treat these diseases have been explored, there are significant barriers to their effective implementation worldwide; alternatively, pharmacological induction of γ-globin synthesis could readily reach the majority of affected individuals. In this study, we generated a CRISPR knockout library that targeted all erythroid genes for which prospective or actual therapeutic compounds already exist. By probing this library for genes that repress fetal hemoglobin (HbF), we identified several novel, potentially druggable, γ-globin repressors, including VHL and PTEN. We demonstrate that deletion of VHL induces HbF through activation of the HIF1α pathway and that deletion of PTEN induces HbF through AKT pathway stimulation. Finally, we show that small-molecule inhibitors of PTEN and EZH induce HbF in both healthy and β-thalassemic human primary erythroid cells.

Dual function NFI factors control fetal hemoglobin silencing in adult erythroid cells

The mechanisms by which the fetal-type β-globin-like genes HBG1 and HBG2 are silenced in adult erythroid precursor cells remain a fundamental question in human biology and have therapeutic relevance to sickle cell disease (SCD) and β-thalassemia. Here, we identify via a CRISPR-Cas9 genetic screen two members of the NFI transcription factor family – NFIA and NFIX – as HBG1/2 repressors. NFIA and NFIX are expressed at elevated levels in adult erythroid cells compared to fetal cells, and function cooperatively to repress HBG1/2 in cultured cells and in human-to-mouse xenotransplants. Genomic profiling, genome editing, and DNA binding assays demonstrate that the potent concerted activity of NFIA and NFIX is explained in part by their ability to stimulate the expression of BCL11A, a known silencer of the HBG1/2 genes, and in part by directly repressing the HBG1/2 genes. Thus, NFI factors emerge as versatile regulators of the fetal-to-adult switch in β-globin production.

Targeting fetal hemoglobin expression to treat β hemoglobinopathies

INTRODUCTION

Sickle cell disease and β thalassemia are the principal β hemoglobinopathies. The complex pathophysiology of sickle cell disease is initiated by sickle hemoglobin polymerization. In β thalassemia, insufficient β-globin synthesis results in excessive free α globin, ineffective erythropoiesis and severe anemia. Fetal hemoglobin (HbF) prevents sickle hemoglobin polymerization; in β thalassemia HbF compensates for the deficit of normal hemoglobin. When HbF constitutes about a third of total cell hemoglobin, the complications of sickle cell disease are nearly totally prevented. Similarly, sufficient HbF in β thalassemia diminishes or prevents ineffective erythropoiesis and hemolysis.

AREAS COVERED

This article examines the pathophysiology of β hemoglobinopathies, the physiology of HbF, intracellular distribution and the regulation of HbF expression. Inducing high levels of HbF by targeting its regulatory pathways pharmacologically or with cell-based therapeutics provides major clinical benefit and perhaps a "cure."

EXPERT OPINION

Erythrocytes must contain about 10 pg of HbF to "cure" sickle cell disease. If HbF is the only hemoglobin present, much higher levels are needed to "cure" β thalassemia. These levels of HbF can be obtained by different iterations of gene therapy. Small molecule drugs that can achieve even modest pancellular HbF concentrations are a major unmet need.

CRISPR-Cas9 to induce fetal hemoglobin for the treatment of sickle cell disease

Genome editing is potentially a curative technique available to all individuals with β-hemoglobinopathies, including sickle cell disease (SCD). Fetal hemoglobin (HbF) inhibits sickle hemoglobin (HbS) polymerization, and it is well described that naturally occurring hereditary persistence of HbF (HPFH) alleviates disease symptoms; therefore, reawakening of developmentally silenced HbF in adult red blood cells (RBCs) has long been of interest as a therapeutic strategy. Recent advances in genome editing platforms, particularly with the use of CRISPR-Cas9, have paved the way for efficient HbF induction through the creation of artificial HPFH mutations, editing of transcriptional HbF silencers, and modulating epigenetic intermediates that govern HbF expression. Clinical trials investigating BCL11A enhancer editing in patients with β-hemoglobinopathies have demonstrated promising results, although follow-up is short and the number of patients treated to date is low. While practical, economic, and clinical challenges of genome editing are well recognized by the scientific community, potential solutions to overcome these hurdles are in development. Here, we review the recent progress and obstacles yet to be overcome for the most effective and feasible HbF reactivation practice using CRISPR-Cas9 genome editing as a curative strategy for patients with SCD.

Recent Approaches for Manipulating Globin Gene Expression in Treating Hemoglobinopathies

Tissue oxygenation throughout life depends on the activity of hemoglobin (Hb) one of the hemeproteins that binds oxygen in the lungs and secures its delivery throughout the body. Hb is composed of four monomers encoded by eight different genes the expression of which is tightly regulated during development, resulting in the formation of distinct hemoglobin tetramers in each developmental stage. Mutations that alter hemoglobin structure or its regulated expression result in a large group of diseases typically referred to as hemoglobinopathies that are amongst the most common genetic defects worldwide. Unprecedented efforts in the last decades have partially unraveled the complex mechanisms that control globin gene expression throughout development. In addition, genome wide association studies have revealed protective genetic traits capable of ameliorating the clinical manifestations of severe hemoglobinopathies. This knowledge has fueled the exploration of innovative therapeutic approaches aimed at modifying the genome or the epigenome of the affected cells to either restore hemoglobin function or to mimic the effect of protective traits. Here we describe the key steps that control the switch in gene expression that concerns the different globin genes during development and highlight the latest efforts in altering globin regulation for therapeutic purposes.

Thalassemias: From gene to therapy

Thalassemias (α, β, γ, δ, δβ, and εγδβ) are the most common genetic disorders worldwide and constitute a heterogeneous group of hereditary diseases characterized by the deficient synthesis of one or more hemoglobin (Hb) chain(s). This leads to the accumulation of unstable non-thalassemic Hb chains, which precipitate and cause intramedullary destruction of erythroid precursors and premature lysis of red blood cells (RBC) in the peripheral blood. Non-thalassemic Hbs display high oxygen affinity and no cooperativity. Thalassemias result from many different genetic and molecular defects leading to either severe or clinically silent hematologic phenotypes. Thalassemias α and β are particularly diffused in the regions spanning from the Mediterranean basin through the Middle East, Indian subcontinent, Burma, Southeast Asia, Melanesia, and the Pacific Islands, whereas δβ-thalassemia is prevalent in some Mediterranean regions including Italy, Greece, and Turkey. Although in the world thalassemia and malaria areas overlap apparently, the RBC protection against malaria parasites is openly debated. Here, we provide an overview of the historical, geographic, genetic, structural, and molecular pathophysiological aspects of thalassemias. Moreover, attention has been paid to molecular and epigenetic pathways regulating globin gene expression and globin switching. Challenges of conventional standard treatments, including RBC transfusions and iron chelation therapy, splenectomy and hematopoietic stem cell transplantation from normal donors are reported. Finally, the progress made by rapidly evolving fields of gene therapy and gene editing strategies, already in pre-clinical and clinical evaluation, and future challenges as novel curative treatments for thalassemia are discussed.

Chemogenomics for drug discovery: clinical molecules from open access chemical probes

In recent years chemical probes have proved valuable tools for the validation of disease-modifying targets, facilitating investigation of target function, safety, and translation. Whilst probes and drugs often differ in their properties, there is a belief that chemical probes are useful for translational studies and can accelerate the drug discovery process by providing a starting point for small molecule drugs. This review seeks to describe clinical candidates that have been inspired by, or derived from, chemical probes, and the process behind their development. By focusing primarily on examples of probes developed by the Structural Genomics Consortium, we examine a variety of epigenetic modulators along with other classes of probe.

HRI depletion cooperates with pharmacologic inducers to elevate fetal hemoglobin and reduce sickle cell formation

Increasing fetal hemoglobin (HbF) provides clinical benefit in patients with sickle cell disease (SCD). We recently identified heme-regulated inhibitor (HRI, EIF2AK1), as a novel HbF regulator. Because HRI is an erythroid-specific protein kinase, it presents a potential target for pharmacologic intervention. We found that maximal HbF induction required >80% to 85% HRI depletion. Because it remains unclear whether this degree of HRI inhibition can be achieved pharmacologically, we explored whether HRI knockdown can be combined with pharmacologic HbF inducers to achieve greater HbF production and minimize potential adverse effects associated with treatments. Strongly cooperative HbF induction was observed when HRI depletion was combined with exposure to pomalidomide or the EHMT1/2 inhibitor UNC0638, but not to hydroxyurea. Mechanistically, reduction in the levels of the HbF repressor BCL11A reflected the cooperativity of HRI loss and pomalidomide treatment, whereas UNC0638 did not modulate BCL11A levels. In conjunction with HRI loss, pomalidomide maintained its HbF-inducing activity at 10-fold lower concentrations, in which condition there were minimal observed detrimental effects on erythroid cell maturation and viability, as well as fewer alterations in the erythroid transcriptome. When tested in cells from patients with SCD, combining HRI depletion with pomalidomide or UNC0638 achieved up to 50% to 60% HbF and 45% to 50% HbF, respectively, as measured by high-performance liquid chromatography, and markedly counteracted cell sickling. In summary, this study provides a foundation for the exploration of combining future small-molecule HRI inhibitors with additional pharmacologic HbF inducers to maximize HbF production and preserve erythroid cell functionality for the treatment of SCD and other hemoglobinopathies.

Heterogeneity of fetal hemoglobin production in adult red blood cells

PURPOSE OF REVIEW

Small amounts of fetal hemoglobin can be expressed in a subset of adult red blood cells called F-cells. This review examines the potential mechanisms and clinical implications of the heterogeneity of fetal hemoglobin expression.

RECENT FINDINGS

Although the heterocellular nature of fetal hemoglobin expression in adult red blood cells has been noted for over 70 years, the molecular basis of this phenomenon has been unclear. Recent discoveries of novel regulators of fetal hemoglobin as well as technological advances have shed new light on these cells.

SUMMARY

Fetal hemoglobin reactivation in adult red blood cells through genetic or pharmacological approaches can involve both increasing the number of F-cells and cellular fetal hemoglobin content. New technologies enable the study and eventually the improvement of these parameters in patients with sickle cell disease and β-thalassemia.

Fetal hemoglobin in sickle cell anemia

Fetal hemoglobin (HbF) can blunt the pathophysiology, temper the clinical course, and offer prospects for curative therapy of sickle cell disease. This review focuses on (1) HbF quantitative trait loci and the geography of β-globin gene haplotypes, especially those found in the Middle East; (2) how HbF might differentially impact the pathophysiology and many subphenotypes of sickle cell disease; (3) clinical implications of person-to-person variation in the distribution of HbF among HbF-containing erythrocytes; and (4) reactivation of HbF gene expression using both pharmacologic and cell-based therapeutic approaches. A confluence of detailed understanding of the molecular basis of HbF gene expression, coupled with the ability to precisely target by genomic editing most areas of the genome, is producing important preliminary therapeutic results that could provide new options for cell-based therapeutics with curative intent.

Epigenetic inactivation of ERF reactivates γ-globin expression in β-thalassemia

The fetal-to-adult hemoglobin switch is regulated in a developmental stage-specific manner and reactivation of fetal hemoglobin (HbF) has therapeutic implications for treatment of β-thalassemia and sickle cell anemia, two major global health problems. Although significant progress has been made in our understanding of the molecular mechanism of the fetal-to-adult hemoglobin switch, the mechanism of epigenetic regulation of HbF silencing remains to be fully defined. Here, we performed whole-genome bisulfite sequencing and RNA sequencing analysis of the bone marrow-derived GYPA⁺ erythroid cells from β-thalassemia-affected individuals with widely varying levels of HbF groups (HbF ≥ 95th percentile or HbF ≤ 5th percentile) to screen epigenetic modulators of HbF and phenotypic diversity of β-thalassemia. We identified an ETS2 repressor factor encoded by ERF, whose promoter hypermethylation and mRNA downregulation are associated with high HbF levels in β-thalassemia. We further observed that hypermethylation of the ERF promoter mediated by enrichment of DNMT3A leads to demethylation of γ-globin genes and attenuation of binding of ERF on the HBG promoter and eventually re-activation of HbF in β-thalassemia. We demonstrated that ERF depletion markedly increased HbF production in human CD34⁺ erythroid progenitor cells, HUDEP-2 cell lines, and transplanted NCG-Kit-V831M mice. ERF represses γ-globin expression by directly binding to two consensus motifs regulating γ-globin gene expression. Importantly, ERF depletion did not affect maturation of erythroid cells. Identification of alterations in DNA methylation of ERF as a modulator of HbF synthesis opens up therapeutic targets for β-hemoglobinopathies.

Identification of Transcriptomic Differences between Lower Extremities Arterial Disease, Abdominal Aortic Aneurysm and Chronic Venous Disease in Peripheral Blood Mononuclear Cells Specimens

Several human tissues are investigated in studies of molecular biomarkers associated with diseases development. Special attention is focused on the blood and its components due to combining abundant information about systemic responses to pathological processes as well as high accessibility. In the current study, transcriptome profiles of peripheral blood mononuclear cells (PBMCs) were used to compare differentially expressed genes between patients with lower extremities arterial disease (LEAD), abdominal aortic aneurysm (AAA) and chronic venous disease (CVD). Gene expression patterns were generated using the Ion S5XL next-generation sequencing platform and were analyzed using DESeq2 and UVE-PLS methods implemented in R programming software. In direct pairwise analysis, 21, 58 and 10 differentially expressed genes were selected from the comparison of LEAD vs. AAA, LEAD vs. CVD and AAA vs. CVD patient groups, respectively. Relationships between expression of dysregulated genes and age, body mass index, creatinine levels, hypertension and medication were identified using Spearman rank correlation test and two-sided Mann-Whitney U test. The functional analysis, performed using DAVID website tool, provides potential implications of selected genes in pathological processes underlying diseases studied. Presented research provides new insight into differences of pathogenesis in LEAD, AAA and CVD, and selected genes could be considered as potential candidates for biomarkers useful in diagnosis and differentiation of studied diseases.

Sickle cell disease: progress towards combination drug therapy

Dr. John Herrick described the first clinical case of sickle cell anaemia (SCA) in the United States in 1910. Subsequently, four decades later, Ingram and colleagues characterized the A to T substitution in DNA producing the GAG to GTG codon and replacement of glutamic acid with valine in the sixth position of the β^S -globin chain. The establishment of Comprehensive Sickle Cell Centers in the United States in the 1970s was an important milestone in the development of treatment strategies and describing the natural history of sickle cell disease (SCD) comprised of genotypes including homozygous haemoglobin SS (HbSS), HbSβ⁰ thalassaemia, HbSC and HbSβ⁺ thalassaemia, among others. Early drug studies demonstrating effective treatments of HbSS and HbSβ⁰ thalassaemia, stimulated clinical trials to develop disease-specific therapies to induce fetal haemoglobin due to its ability to block HbS polymerization. Subsequently, hydroxycarbamide proved efficacious in adults with SCA and was Food and Drug Administration (FDA)-approved in 1998. After two decades of hydroxycarbamide use for SCD, there continues to be limited clinical acceptance of this chemotherapy drug, providing the impetus for investigators and pharmaceutical companies to develop non-chemotherapy agents. Investigative efforts to determine the role of events downstream of deoxy-HbS polymerization, such as endothelial cell activation, cellular adhesion, chronic inflammation, intravascular haemolysis and nitric oxide scavenging, have expanded drug targets which reverse the pathophysiology of SCD. After two decades of slow progress in the field, since 2018 three new drugs were FDA-approved for SCA, but research efforts to develop treatments continue. Currently over 30 treatment intervention trials are in progress to investigate a wide range of agents acting by complementary mechanisms, providing the rationale for ushering in the age of effective and safe combination drug therapy for SCD. Parallel efforts to develop curative therapies using haematopoietic stem cell transplant and gene therapy provide individuals with SCD multiple treatment options. We will discuss progress made towards drug development and potential combination drug therapy for SCD with the standard of care hydroxycarbamide.

Discovery of DS79932728: A Potent, Orally Available G9a/GLP Inhibitor for Treating β-Thalassemia and Sickle Cell Disease

Therapeutic reactivation of the γ-globin genes for fetal hemoglobin (HbF) production is an attractive strategy for treating β-thalassemia and sickle cell disease. It was reported that genetic knockdown of the histone lysine methyltransferase EHMT2/1 (G9a/GLP) is sufficient to induce HbF production. The aim of the present work was to acquire a G9a/GLP inhibitor that induces HbF production sufficiently. It was revealed that tetrahydroazepine has versatility as a side chain in various skeletons. We ultimately obtained a promising aminoindole derivative (DS79932728), a potent and orally bioavailable G9a/GLP inhibitor that was found to induce γ-globin production in a phlebotomized cynomolgus monkey model. This work could facilitate the development of effective new approaches for treating β-thalassemia and sickle cell disease.

Manipulation of Developmental Gamma-Globin Gene Expression: an Approach for Healing Hemoglobinopathies

β-Hemoglobinopathies are the most common monogenic disorders, and a century of research has provided us with a better understanding of the attributes of these diseases. Allogenic stem cell transplantation was the only potentially curative option available for these diseases until the discovery of gene therapy. The findings on the protective nature of fetal hemoglobin in sickle cell disease (SCD) and thalassemia patients carrying hereditary persistence of fetal hemoglobin (HPFH) mutations has given us the best evidence that the cure for β-hemoglobinopathies remains hidden in the hemoglobin locus. The detailed understanding of the developmental gene regulation of gamma-globin (γ-globin) and the emergence of gene manipulation strategies offer us the opportunity for developing a γ-globin gene-modified autologous stem cell transplantation therapy. In this review, we summarize different therapeutic strategies that reactivate fetal hemoglobin for the gene therapy of β-hemoglobinopathies.

Targeted Protein Degradation as a Promising Tool for Epigenetic Upregulation of Fetal Hemoglobin

The level of fetal hemoglobin (HbF) is an important disease modifier for β-thalassemia and sickle cell disease patients. Indeed, genetic tinkering with the HbF repression machinery has demonstrated great potential for disease mitigation. Such genetic treatments are costly and the high incidence of β-hemoglobinopathies in low-income countries, therefore, calls for the development of affordable, off-the-shelf, oral treatments. The use of PROTAC (PRoteolysis TArgeting Chimeras) technology to influence the epigenetic mechanisms involved in HbF suppression may provide a solution. In this minireview, we briefly explain the HbF repression network highlighting the epigenetic factors that could be targeted for degradation by PROTACs. We hope that this review will inspire clinicians, molecular and chemical biologists to collaborate and contribute to this fascinating field, which should ultimately deliver drugs that reactivate HbF expression with high specificity and low toxicity.

Epigenetic activities in erythroid cell gene regulation

Interest in the role of epigenetic mechanisms in human biology has exponentially increased over the past several decades. The multitude of opposing and context-dependent chromatin-modifying enzymes/coregulator complexes is just beginning to be understood at a molecular level. This science has benefitted tremendously from studies of erythropoiesis, in which a series of β-globin genes are in sequence turned "on" and "off," serving as a fascinating model of coordinated gene expression. We, therefore, describe here epigenetic complexes about which we know most, using erythropoiesis as the context. The biochemical insights lay the foundation for proposing and developing novel treatments for diseases of red cells and of erythropoiesis, identifying for example epigenetic enzymes that can be drugged to manipulate β-globin locus regulation, to favor activation of unmutated fetal hemoglobin over mutated adult β-globin genes to treat sickle cell disease and β-thalassemias. Other potential translational applications are in redirecting hematopoietic commitment decisions, as treatment for bone marrow failure syndromes.

Deciphering the Key Pharmacological Pathways and Targets of Yisui Qinghuang Powder That Acts on Myelodysplastic Syndromes Using a Network Pharmacology-Based Strategy

Background

Yisui Qinghuang powder (YSQHP) is an effective traditional Chinese medicinal formulation used for the treatment of myelodysplastic syndromes (MDS). However, its pharmacological mechanism of action is unclear.

Materials and Methods

In this study, the active compounds of YSQHP were screened using the traditional Chinese medicine systems pharmacology (TCMSP) and HerDing databases, and the putative target genes of YSQHP were predicted using the STITCH and DrugBank databases. Then, we further screened the correlative biotargets of YSQHP and MDS. Finally, the compound-target-disease (C-T-D) network was conducted using Cytoscape, while GO and KEGG analyses were conducted using R software. Furthermore, DDI-CPI, a web molecular docking analysis tool, was used to verify potential targets and pathways. Finally, binding site analysis was performed to identify core targets using MOE software.

Results

Our results identified 19 active compounds and 273 putative target genes of YSQHP. The findings of the C-T-D network revealed that Rb1, CASP3, BCL2, and MAPK3 showed the most number of interactions, whereas indirubin, tryptanthrin, G-Rg1, G-Rb1, and G-Rh2 showed the most number of potential targets. The GO analysis showed that 17 proteins were related with STPK activity, PUP ligase binding, and kinase regulator activity. The KEGG analysis showed that PI3K/AKT, apoptosis, and the p53 pathways were the main pathways involved. DDI-CPI identified the top 25 proteins related with PI3K/AKT, apoptosis, and the p53 pathways. CASP8, GSK3B, PRKCA, and VEGFR2 were identified as the correlative biotargets of DDI-CPI and PPI, and their binding sites were found to be indirubin, G-Rh2, and G-Rf.

Conclusion

Taken together, our results revealed that YSQHP likely exerts its antitumor effects by binding to CASP8, GSK3B, PRKCA, and VEGFR2 and by regulating the apoptosis, p53, and PI3K/AKT pathways.

Fetal Hemoglobin in Sickle Hemoglobinopathies: High HbF Genotypes and Phenotypes

Fetal hemoglobin (HbF) usually consists of 4 to 10% of total hemoglobin in adults of African descent with sickle cell anemia. Rarely, their HbF levels reach more than 30%. High HbF levels are sometimes a result of β-globin gene deletions or point mutations in the promoters of the HbF genes. Collectively, the phenotype caused by these mutations is called hereditary persistence of fetal hemoglobin, or HPFH. The pancellularity of HbF associated with these mutations inhibits sickle hemoglobin polymerization in most sickle erythrocytes so that these patients usually have inconsequential hemolysis and few, if any, vasoocclusive complications. Unusually high HbF can also be associated with variants of the major repressors of the HbF genes, BCL11A and MYB. Perhaps most often, we lack an explanation for very high HbF levels in sickle cell anemia.

Discovery of novel histone lysine methyltransferase G9a/GLP (EHMT2/1) inhibitors: Design, synthesis, and structure-activity relationships of 2,4-diamino-6-methylpyrimidines

The discovery and optimization of a novel series of G9a/GLP (EHMT2/1) inhibitors are described. Starting from known G9a/GLP inhibitor 5, efforts to explore the structure-activity relationship and optimize drug properties led to a novel compound 13, the side chain of which was converted to tetrahydroazepine. Compound 13 showed increased G9a/GLP inhibitory activity compared with compound 5. In addition, compound 13 exhibited improved human ether-a-go-go related gene (hERG) inhibitory activity over compound 5 and also improved pharmacokinetic profile in mice (oral bioavailability: 17 to 40%). Finally, the co-crystal structure of G9a in complex with compound 13 provides the basis for the further development of tetrahydroazepine-based G9a/GLP inhibitors.

UNC0638 induces high levels of fetal hemoglobin expression in β-thalassemia/HbE erythroid progenitor cells

Increased expression of fetal hemoglobin (HbF) improves the clinical severity of β-thalassemia patients. EHMT1/2 histone methyltransferases are epigenetic modifying enzymes that are responsible for catalyzing addition of the repressive histone mark H3K9me2 at silenced genes, including the γ-globin genes. UNC0638, a chemical inhibitor of EHMT1/2, has been shown to induce HbF expression in human erythroid progenitor cell cultures. Here, we report the HbF-inducing activity of UNC0638 in erythroid progenitor cells from β-thalassemia/HbE patients. UNC0638 treatment led to significant increases in γ-globin mRNA, HbF expression, and HbF-containing cells in the absence of significant cytotoxicity. Moreover, UNC0638 showed additive effects on HbF induction in combination with the immunomodulatory drug pomalidomide and the DNMT1 inhibitor decitabine. These studies provide a scientific proof of concept that a small molecule targeting EHMT1/2 epigenetic enzymes, used alone or in combination with pomalidomide or decitabine, is a potential therapeutic approach for HbF induction. Further development of structural analogs of UNC0638 with similar biological effects but improved pharmacokinetic properties may lead to promising therapies and possible clinical application for the treatment of β-thalassemia.

Increased expression of EHMT2 associated with H3K9me2 level contributes to the poor prognosis of gastric cancer

Di-methylated lysine 9 of histone H3 (H3K9me2), regulated by histone methyltransferases, is involved in the epigenetic regulation of tumor-associated genes. The present study aimed to evaluate whether the H3K9me2 methylation level is associated with the expression level of euchromatic histone lysine methyltransferase 2 (EHMT2) in the prognosis of gastric cancer (GC). H3K9me2 methylation level and EHMT2 expression level were detected by immunohistochemistry in 118 GC samples. The clinicopathological significance of H3K9me2 and EHMT2 in patients with GC was assessed using a paired Student's t-test, χ² test, Kaplan-Meier analysis with a log-rank test and Cox's proportional hazard analysis. Strong positive immunostaining of H3K9me2 and EHMT2 was observed in cancerous tissues compared with adjacent non-cancerous tissues. Positive immunostaining of EHMT2 and H3K9me2 was associated with lymph node metastasis, pathological grade and tumor-node-metastasis stage. H3K9me2 expression level was increased in tumor tissue and associated with worse specific-disease and disease-free survival time. In addition, EHMT2 protein expression levels were associated with the expression levels of H3K9me2. Low expression levels of H3K9me2 and EHMT2 predicted a better prognosis of patients with GC. The survival time of patients with a high expression of H3K9me2 and/or EHMT2 was significantly shorter compared with that of the patients with a low expression of H3K9me2 and/or EHMT2. In conclusion, an overexpression pattern of H3K9me2 and/or EHMT2 may be associated with clinicopathological features of GC and may be predictor markers of progression and prognosis in patients with GC, in addition to putative therapeutic targets.

Bioinformatics enrichment analysis of genes and pathways related to maternal type 1 diabetes associated with adverse fetal outcomes

Maternal type 1 diabetes mellitus (T1DM) may affect fetal development by altering the gene expression profile of the umbilical cord. The present study aimed to explore the T1DM-induced gene expression changes in the fetal umbilical cord. The raw gene expression profiles (ID: GSE51546) of umbilical cord tissue obtained from six normal mothers (non-diabetic) and six type 1 diabetic mothers were used to identify the differentially expressed genes. Genes that correspond to official gene symbols were selected for protein-protein interaction (PPI) and sub-network construction (combined score > 0.4). Functional annotation for Gene Ontology (GO) and pathway enrichment analysis were performed for genes involved in networking. A total of 110 differentially expressed genes were identified of which 38 were up-regulated while 72 were down-regulated. Only 37 genes were identified to significantly interact with each other. Hub genes including HSPA4, KCTD6, UBE2G1, FBXL19, and EHMT1 were up-regulated while KBTBD7, TRIM32, and NUP were down-regulated. T1DM had a major effect on the expression of genes involved in cellular death and differentiation, cell signaling and communication, protein modification and regulation of GTPase activity. Total 27 pathways were enriched and genes related to Wnt signaling, VEGF signaling, inflammation mediated by chemokine and cytokine signaling pathways, FGF signaling pathways and GnRH receptor pathways were found significantly affected by T1DM. Our results suggest that the T1DM environment seems to alter umbilical cord gene expression involved in the regulation of pathophysiology of the diabetic mother which in turn may lead to long-term consequences in various tissues in infants. This study provides insight into the molecular mechanism underlying the adverse pregnancy outcomes of maternal T1DM.

Small molecule therapeutics to treat the β-globinopathies

PURPOSE OF REVIEW

The current review focuses on recent insights into the development of small molecule therapeutics to treat the β-globinopathies.

RECENT FINDINGS

Recent studies of fetal γ-globin gene regulation reveal multiple insights into how γ-globin gene reactivation may lead to novel treatment for β-globinopathies.

SUMMARY

We summarize current information regarding the binding of transcription factors that appear to be impeded or augmented by different hereditary persistence of fetal hemoglobin (HPFH) mutations. As transcription factors have historically proven to be difficult to target for therapeutic purposes, we next address the contributions of protein complexes associated with these HPFH mutation-affected transcription factors with the aim of defining proteins that might provide additional targets for chemical molecules to inactivate the corepressors. Among the enzymes associated with the transcription factor complexes, a group of corepressors with currently available inhibitors were initially thought to be good candidates for potential therapeutic purposes. We discuss possibilities for pharmacological inhibition of these corepressor enzymes that might significantly reactivate fetal γ-globin gene expression. Finally, we summarize the current clinical trial data regarding the inhibition of select corepressor proteins for the treatment of sickle cell disease and β-thalassemia.

Small Molecules Targeting H3K9 Methylation Prevent Silencing of Reactivated FMR1 Alleles in Fragile X Syndrome Patient Derived Cells

In fragile X syndrome (FXS), expansion of a CGG repeat tract in the 5′-untranslated region of the FMR1 gene to >200 repeats causes transcriptional silencing by inducing heterochromatin formation. Understanding the mechanism of FMR1 silencing is important as gene reactivation is a potential treatment approach for FXS. To date, only the DNA demethylating drug 5-azadeoxycytidine (AZA) has proved effective at gene reactivation; however, this drug is toxic. The repressive H3K9 methylation mark is enriched on the FMR1 gene in FXS patient cells and is thus a potential druggable target. However, its contribution to the silencing process is unclear. Here, we studied the effect of small molecule inhibitors of H3K9 methylation on FMR1 expression in FXS patient cells. Chaetocin showed a small effect on FMR1 gene reactivation and a synergistic effect on FMR1 mRNA levels when used in combination with AZA. Additionally, chaetocin, BIX01294 and 3-Deazaneplanocin A (DZNep) were able to significantly delay the re-silencing of AZA-reactivated FMR1 alleles. These data are consistent with the idea that H3K9 methylation precedes DNA methylation and that removal of DNA methylation is necessary to see the optimal effect of histone methyl-transferase (HMT) inhibitors on FMR1 gene expression. Nonetheless, our data also show that drugs targeting repressive H3K9 methylation marks are able to produce sustained reactivation of the FMR1 gene after a single dose of AZA.

Omics Studies in Hemoglobinopathies

Hemoglobinopathies include all genetic diseases of hemoglobin and are grouped into thalassemia syndromes and structural hemoglobin variants. The β-thalassemias constitute a group of severe anemias with monogenic inheritance, caused by β-globin gene mutations. This review is focused on omics studies in hemoglobinopathies and mainly β-thalassemia, and discusses genomic, epigenomic, transcriptomic, proteomic and metabolomic findings. Omics analyses have identified various disease modifiers with an impact on disease severity and efficacy of treatments. These modifiers have contributed to the understanding of globin genes regulation/hemoglobin switching and the development of novel therapies. How omics data and their integration can contribute to efficient patient stratification, therapeutic management, improvements in existing treatments and application of novel personalized therapies is discussed.

Targeting sickle cell disease root-cause pathophysiology with small molecules

The complex, frequently devastating, multi-organ pathophysiology of sickle cell disease has a single root cause: polymerization of deoxygenated sickle hemoglobin. A logical approach to disease modification is, therefore, to interdict this root cause. Ideally, such interdiction would utilize small molecules that are practical and accessible for worldwide application. Two types of such small molecule strategies are actively being evaluated in the clinic. The first strategy intends to shift red blood cell precursor hemoglobin manufacturing away from sickle hemoglobin and towards fetal hemoglobin, which inhibits sickle hemoglobin polymerization by a number of mechanisms. The second strategy intends to chemically modify sickle hemoglobin directly in order to inhibit its polymerization. Important lessons have been learnt from the pre-clinical and clinical evaluations to date. Open questions remain, but this review summarizes the valuable experience and knowledge already gained, which can guide ongoing and future efforts for molecular mechanism-based, practical and accessible disease modification of sickle cell disease.

MS-275 Chemical Analogues Promote Hemoglobin Production and Erythroid Differentiation of K562 Cells

β-Thalassemia (β-thal) is a hemoglobinopathy characterized by reduced or absent β-globin production. Pharmacological reactivation of the γ-globin gene for the production of fetal hemoglobin (Hb F) presents an attractive treatment strategy. In an effort to identify promising therapeutic agents, we evaluated 80 analogues of the histone deacetylase inhibitor MS-275, a known Hb F inducer. The chemical analogues were identified via molecular modeling and targeted chemical modifications. Nine novel agents exhibited significant hemoglobin (Hb)-inducing and erythroid differentiation activities in the human K562 erythroleukemia cell line. Five of them appeared to be stronger inducers than the lead compound, MS-275, demonstrating the effectiveness of our method.

Fetal hemoglobin and F-cell variance in mobilized CD34+ cell-transplanted rhesus monkeys

Elevated fetal hemoglobin (HbF) is associated with reduced severity of sickle cell disease. Therefore, γ-globin protein levels and F-cell (HbF-positive red blood cell) percentages are used for estimation of clinical benefit. Here, we monitored transplantation-related changes in HbF and F-cell percentages for rhesus macaques (Macaca mulatta) following total body irradiation or busulfan conditioning prior to CD34⁺ cell transplantation. HbF protein expression peaked in the first 4-9 weeks posttransplant (0.99%-2.53%), and F-cells increased in the first 6-17 weeks posttransplant (8.7%-45.3%). HbF and F-cell ratios gradually decreased and stabilized to levels similar to those of control animals (1.96 ± 1.97% for F cells and 0.49 ± 0.19% γ-globin expression) 4-7 months post-transplant. These findings confirm and expand on previous reports of transient induction in HbF and F-cell percentages in rhesus macaques following CD34⁺ cell transplantation, an observation that must be taken into consideration when evaluating therapeutic strategies that aim to specifically elevate HbF expression, which are currently in clinical development.

Target Identification Using Chemical Probes

Chemical probes are small molecules with potency and selectivity for a single or small number of protein targets. A good chemical probe engages its target intracellularly and is accompanied by a chemically similar, but inactive molecule to be used as a negative control in cellular phenotypic screening. The utility of these chemical probes is ultimately governed by how well they are developed and characterized. Chemical probes either as single entities, or in chemical probes sets are being increasingly used to interrogate the biological relevance of a target in a disease model. This chapter lays out the core properties of chemical probes, summarizes the seminal and emerging techniques used to demonstrate robust intracellular target engagement. Translation of target engagement assays to disease-relevant phenotypic assays using primary patient-derived cells and tissues is also reviewed. Two examples of epigenetic chemical probe discovery and utility are presented whereby target engagement pointed to novel disease associations elucidated from poorly understood protein targets. Finally, a number of examples are discussed whereby chemical probe sets, or "chemogenomic libraries" are used to illuminate new target-disease links which may represent future directions for chemical probe utility.

CARM1-mediated methylation of protein arginine methyltransferase 5 represses human γ-globin gene expression in erythroleukemia cells

Protein arginine methyltransferase 5 (PRMT5) is a member of the arginine methyltransferase protein family that critically mediates the symmetric dimethylation of Arg-3 at histone H4 (H4R3me2s) and is involved in many key cellular processes, including hematopoiesis. However, the post-translational modifications (PTMs) of PRMT5 that may affect its biological functions remain less well-understood. In this study, using MS analyses, we found that PRMT5 itself is methylated in human erythroleukemia Lys-562 cells. Biochemical assays revealed that coactivator-associated arginine methyltransferase 1 (CARM1) interacts directly with and methylates PRMT5 at Arg-505 both in vivo and in vitro. Substitutions at Arg-505 significantly reduced PRMT5's methyltransferase activity, decreased H4R3me2s enrichment at the γ-globin gene promoter, and increased the expression of the γ-globin gene in Lys-562 cells. Moreover, CARM1 knockdown consistently reduced PRMT5 activity and activated γ-globin gene expression. Importantly, we show that CARM1-mediated methylation of PRMT5 is essential for the intracellular homodimerization of PRMT5 to its active form. These results thus reveal a critical PTM of PRMT5 that represses human γ-globin gene expression. We conclude that CARM1-mediated asymmetric methylation of PRMT5 is critical for its dimerization and methyltransferase activity leading to the repression of γ-globin expression. Given PRMT5's crucial role in diverse cellular processes, these findings may inform strategies for manipulating its methyltransferase activity for managing hemoglobinopathy or cancer.

Dual Inhibition of DNA and Histone Methyltransferases Increases Viral Mimicry in Ovarian Cancer Cells

Ovarian cancer ranks as the most deadly gynecologic cancer, and there is an urgent need to develop more effective therapies. Previous studies have shown that G9A, a histone methyltransferase that catalyzes mono- and dimethylation of histone H3 lysine9, is highly expressed in ovarian cancer tumors, and its overexpression is associated with poor prognosis. Here we report that pharmacologic inhibition of G9A in ovarian cancer cell lines with high levels of G9A expression induces synergistic antitumor effects when combined with the DNA methylation inhibitor (DNMTi) 5-aza-2'-deoxycytidine (5-aza-CdR). These antitumor effects included upregulation of endogenous retroviruses (ERV), activation of the viral defense response, and induction of cell death, which have been termed "viral mimicry" effects induced by DNMTi. G9Ai treatment further reduced H3K9me2 levels within the long terminal repeat regions of ERV, resulting in further increases of ERV expression and enhancing "viral mimicry" effects. In contrast, G9Ai and 5-aza-CdR were not synergistic in cell lines with low basal G9A levels. Taken together, our results suggest that the synergistic effects of combination treatment with DNMTi and G9Ai may serve as a novel therapeutic strategy for patients with ovarian cancer with high levels of G9A expression.Significance: Dual inhibition of DNA methylation and histone H3 lysine 9 dimethylation by 5-aza-CdR and G9Ai results in synergistic upregulation of ERV and induces an antiviral response, serving as a basis for exploring this novel combination treatment in patients with ovarian cancer. Cancer Res; 78(20); 5754-66. ©2018 AACR.

Fetal hemoglobin induction during decitabine treatment of elderly patients with high-risk myelodysplastic syndrome or acute myeloid leukemia: a potential dynamic biomarker of outcome

Hematologic responses to hypomethylating agents are often delayed in patients with myelodysplastic syndrome or acute myeloid leukemia. Fetal hemoglobin is a potential novel bio-marker of response: recently, we demonstrated that a high fetal hemoglobin level prior to decitabine treatment was associated with superior outcome. Here we investigated whether early fetal hemoglobin induction during decitabine treatment also had prognostic value, and studied the potential of decitabine to induce erythroid differentiation and fetal hemoglobin expression in vitro Fetal hemoglobin levels were measured by high-performance liquid chromatography in patients with higher-risk myelodysplastic syndrome (n=16) and acute myeloid leukemia (n=37) before treatment and after each course of decitabine. Levels above 1.0% were considered induced. Patients achieving complete or partial remission as best response had attained a median fetal hemoglobin of 1.9% after two courses of treatment, whereas the median value in patients who did not reach complete or partial remission was 0.8% (P=0.015). Fetal hemoglobin induction after two courses of decitabine treatment was associated with early platelet doubling (P=0.006), and its subsequent decrease with hematologic relapse. In patients with myelodysplastic syndrome, induction of fetal hemoglobin after course 2 of treatment was associated with longer overall survival: median of 22.9 versus 7.3 months in patients with or without induction of fetal hemoglobin, respectively [hazard ratio=0.2 (95% confidence interval: 0.1-0.9); P=0.03]. In vitro decitabine treatment of two bi-potential myeloid leukemia cell lines (K562 and HEL) resulted in induction of an erythroid (not megakaryocytic) differentiation program, and of fetal hemoglobin mRNA and protein, associated with GATA1 gene demethylation and upregulation. In conclusion, fetal hemoglobin may provide a useful dynamic biomarker during hypomethylating agent therapy in patients with myelodysplastic syndrome or acute myeloid leukemia.

Potential role of LSD1 inhibitors in the treatment of sickle cell disease: a review of preclinical animal model data

Sickle cell disease (SCD) is caused by a mutation of the β-globin gene (Ingram VM. Nature 180: 326-328, 1957), which triggers the polymerization of deoxygenated sickle hemoglobin (HbS). Approximately 100,000 SCD patients in the United States and millions worldwide (Piel FB, et al. PLoS Med 10: e1001484, 2013) suffer from chronic hemolytic anemia, painful crises, multisystem organ damage, and reduced life expectancy (Rees DC, et al. Lancet 376: 2018-2031, 2010; Serjeant GR. Cold Spring Harb Perspect Med 3: a011783, 2013). Hematopoietic stem cell transplantation can be curative, but the majority of patients do not have a suitable donor (Talano JA, Cairo MS. Eur J Haematol 94: 391-399, 2015). Advanced gene-editing technologies also offer the possibility of a cure (Goodman MA, Malik P. Ther Adv Hematol 7: 302-315, 2016; Lettre G, Bauer DE. Lancet 387: 2554-2564, 2016), but the likelihood that these strategies can be mobilized to treat the large numbers of patients residing in developing countries is remote. A pharmacological treatment to increase fetal hemoglobin (HbF) as a therapy for SCD has been a long-sought goal, because increased levels of HbF (α₂γ₂) inhibit the polymerization of HbS (Poillin WN, et al. Proc Natl Acad Sci USA 90: 5039-5043, 1993; Sunshine HR, et al. J Mol Biol 133: 435-467, 1979) and are associated with reduced symptoms and increased lifespan of SCD patients (Platt OS, et al. N Engl J Med 330: 1639-1644, 1994; Platt OS, et al. N Engl J Med 325: 11-16, 1991). Only two drugs, hydroxyurea and l-glutamine, are approved by the US Food and Drug Administration for treatment of SCD. Hydroxyurea is ineffective at HbF induction in ~50% of patients (Charache S, et al. N Engl J Med 332: 1317-1322, 1995). While polymerization of HbS has been traditionally considered the driving force in the hemolysis of SCD, the excessive reactive oxygen species generated from red blood cells, with further amplification by intravascular hemolysis, also are a major contributor to SCD pathology. This review highlights a new class of drugs, lysine-specific demethylase (LSD1) inhibitors, that induce HbF and reduce reactive oxygen species.

Modelling human haemoglobin switching

Genetic lesions of the β-globin gene result in haemoglobinopathies such as β-thalassemia and sickle cell disease. To discover and test new molecular medicines for β-haemoglobinopathies, cell-based and animal models are now being widely utilised. However, multiple in vitro and in vivo models are required due to the complex structure and regulatory mechanisms of the human globin gene locus, subtle species-specific differences in blood cell development, and the influence of epigenetic factors. Advances in genome sequencing, gene editing, and precision medicine have enabled the first generation of molecular therapies aimed at reactivating, repairing, or replacing silenced or damaged globin genes. Here we compare and contrast current animal and cell-based models, highlighting their complementary strengths, reflecting on how they have informed the scope and direction of the field, and describing some of the novel molecular and precision medicines currently under development or in clinical trial.

Genetic and Epigenetic Mechanisms of β-Globin Gene Switching

Vertebrates have multiple forms of hemoglobin that differ in the composition of their polypeptide chains. During ontogenesis, the composition of these subunits changes. Genes encoding different α- and β-polypeptide chains are located in two multigene clusters on different chromosomes. Each cluster contains several genes that are expressed at different stages of ontogenesis. The phenomenon of stage-specific transcription of globin genes is referred to as globin gene switching. Mechanisms of expression switching, stage-specific activation, and repression of transcription of α- and β-globin genes are of interest from both theoretical and practical points of view. Alteration of balanced expression of globin genes, which usually occurs due to damage to adult β-globin genes, leads to development of severe diseases - hemoglobinopathies. In most cases, reactivation of the fetal hemoglobin gene in patients with β-thalassemia and sickle cell disease can reduce negative consequences of irreversible alterations of expression of the β-globin genes. This review focuses on the current state of research on genetic and epigenetic mechanisms underlying stage-specific switching of β-globin genes.

Fetal Hemoglobin Induction by Epigenetic Drugs

Fetal hemoglobin (HbF) inhibits the root cause of sickle pathophysiology, sickle hemoglobin polymerization. Individuals who naturally express high levels of HbF beyond infancy thus receive some protection from sickle complications. To mimic this natural genetic experiment using drugs, one guiding observation was that HbF is increased during recovery of bone marrow from extreme stress. This led to evaluation and approval of the cytotoxic (cell killing) drug hydroxyurea to treat sickle cell disease. Cytotoxic approaches are limited in potency and sustainability, however, since they require hematopoietic reserves sufficient to repeatedly mount recoveries from stress that destroys their counterparts, and such reserves are finite. HbF induction even by stress ultimately involves chromatin remodeling of the gene for HbF (HBG), therefore, a logical alternative approach is to directly inhibit epigenetic enzymes that repress HBG-implicated enzymes include DNA methyltransferase 1, histone deacetylases, lysine demethylase 1, protein arginine methyltransferase 5, euchromatic histone lysine methyltransferase 2 and chromodomain helicase DNA-binding protein 4. Clinical proof-of-principle that this alternative, noncytotoxic approach can generate substantial HbF and total hemoglobin increases has already been generated. Thus, with continued careful attention to fundamental biological and pharmacologic considerations (reviewed herein), there is potential that rational, molecular-targeted, safe and highly potent disease-modifying therapy can be realized for patients with sickle cell disease, with the accessibility and cost-effective properties needed for world-wide effect.