Targeting sickle cell disease root-cause pathophysiology with small molecules

RNA Editors Sculpt the Transcriptome During Terminal Erythropoiesis

Selective RNA degradation during terminal erythropoiesis results in a globin-rich transcriptome in mature erythrocytes, but the specific RNA decay pathways remain unknown. We found that deficiency of the terminal uridylyl transferase enzyme Zcchc6 and the 3'-5' exoribonuclease Dis3l2 in mouse models led to fetal and perinatal reticulocytosis, an accumulation of RNA-rich precursors of terminal erythroid cells, suggesting their crucial roles in terminal red cell differentiation. Notably, knockout embryos exhibited persistent high-level expression of Hbb-bh1 globin, the ortholog of human fetal γ- globin. Perturbation of the Zcchc6-Dis3l2 pathway in mice engineered to express the human β-globin locus likewise increased γ -globin levels in fetal erythroid cells, suggesting that globin switching entails post-transcriptional mechanisms of mRNA destabilization in addition to transcriptional down-regulation. We cultured human hematopoietic stem and progenitor cells (HSPCs), performed CRISPR/Cas9-mediated knockout of ZCCHC6 and DIS3L2, and observed accumulation of RNA and elevated γ-globin levels in terminal erythroid cells. Our findings reveal a conserved role for the ZCCHC6/DIS3L2 RNA editors in terminal erythropoiesis and demonstrate a post-transcriptional mechanism for γ- globin gene switching, advancing research into in vitro erythrocyte generation and γ- globin stabilization to ameliorate hemoglobinopathies.

Genome editing strategies for targeted correction of β-globin mutation in sickle cell disease: From bench to bedside

Sickle cell disease (SCD) includes a range of genotypes that result in a clinical syndrome, where abnormal red blood cell (RBC) physiology leads to widespread complications affecting nearly every organ system. Treatment strategies for SCD can be broadly categorized into disease-modifying therapies and those aimed toward a cure. Although several disease-modifying drugs have been approved, they do not fully address the complexity and severity of SCD. Recent advances in allogeneic transplantation and autologous gene therapy show promising outcomes in terms of efficacy and safety. While these approaches have improved the lives of many patients, achieving a durable and comprehensive cure for all remains challenging. To address this, gene-editing technologies, including zinc-finger nucleases, TALENs, CRISPR-Cas, base editing, and prime editing, have been explored both ex vivo and in vivo for targeted correction of the β-globin gene (HBB) in SCD. However, direct correction of HBB and its translation from the laboratory to the clinic presents ongoing limitations, with challenges involved in achieving robust mutation-correction efficiency, off-target effects, and high costs of therapies. The optimal strategy for curing SCD remains uncertain, but several promising approaches are emerging. This review touches on past, present, and future developments in HBB correction.

Hemoglobin Variants as Targets for Stabilizing Drugs

Hemoglobin is an oxygen-transport protein in red blood cells that interacts with multiple ligands, e.g., oxygen, carbon dioxide, carbon monoxide, and nitric oxide. Genetic variations in hemoglobin chains, such as those underlying sickle cell disease and thalassemias, present substantial clinical challenges. Here, we review the progress in research, including the use of allosteric modulators, pharmacological chaperones, and antioxidant treatments, which has begun to improve hemoglobin stability and oxygen affinity. According to UniProt (as of 7 August 2024), 819 variants of the α-hemoglobin subunit and 771 variants of the β-hemoglobin subunit have been documented, with over 116 classified as unstable. These data demonstrate the urgent need to develop variant-specific stabilizing options. Beyond small-molecule drugs/binders, novel protein-based strategies-such as engineered hemoglobin-binding proteins (including falcilysin, llama-derived nanobodies, and α-hemoglobin-stabilizing proteins)-offer promising new options. As our understanding of hemoglobin's structural and functional diversity grows, so does the potential for genotype-driven approaches. Continued research into hemoglobin stabilization and ligand-binding modification may yield more precise, effective treatments and pave the way toward effective strategies for hemoglobinopathies.

A critical review of therapeutic interventions in sickle cell disease: Progress and challenges

Sickle cell disease (SCD) is an autosomal recessive genetic disorder that occurs due to the point mutation in the β-globin gene, which results in the formation of sickle hemoglobin (HbS) in the red blood cells (RBCs). When HbS is exposed to an oxygen-depleted environment, it polymerizes, resulting in hemolysis, vaso-occlusion pain, and impaired blood flow. Still, there is no affordable cure for this inherited disease. Approved medications held promise but were met with challenges due to limited patient tolerance and undesired side effects, thereby inhibiting their ability to enhance the quality of life across various individuals with SCD. Progress has been made in understanding the pathophysiology of SCD during the past few decades, leading to the discovery of novel targets and therapies. However, there is a compelling need for research to discover medications with improved efficacy and reduced side effects. Also, more clinical investigations on various drug combinations with different mechanisms of action are needed. This review comprehensively presents therapeutic approaches for SCD, including those currently available or under investigation. It covers fundamental aspects of the disease, such as epidemiology and pathophysiology, and provides detailed discussions on various disease-modifying agents. Additionally, expert insights are offered on the future development of pharmacotherapy for SCD.

A pharmacodynamic assay to monitor treatment with the hypomethylating cytosine analogs, decitabine and azacitidine

Hypomethylating therapies using decitabine or azacitidine are actively investigated to treat acute myeloid leukemia, myelodysplastic syndromes, as maintenance therapy after allogenic stem cell transplant and hemoglobinopathies. The therapeutic mechanism is to de-repress genes that have been turned off through oncogenesis or development via methylation. The therapy can be non-cytotoxic at low dosage, sparing healthy stem cells and operating on committed precursors. Because the methods of determining maximum tolerated dose are not well suited to this paradigm, and because the mechanism of action, which is depletion of DNA methylase 1 (DNMT1), is complex and dependent on passing through a cell cycle, a pharmacodynamic assay that measures DNMT1 can inform clinical trials aimed at establishing and improving therapy. Herein, we provide an assay that measures DNMT1 relative levels in circulating T cells of peripheral blood.

In Vitro Interaction of Tetrahydrouridine with Key Human Nucleoside Transporters

NDec is a novel combination of oral decitabine and tetrahydrouridine that is currently under clinical development for the treatment of sickle cell disease (SCD). Here, we investigate the potential for the tetrahydrouridine component of NDec to act as an inhibitor or substrate of key concentrative nucleoside transporters (CNT1-3) and equilibrative nucleoside transporters (ENT1-2). Nucleoside transporter inhibition and tetrahydrouridine accumulation assays were performed using Madin-Darby canine kidney strain II (MDCKII) cells overexpressing human CNT1, CNT2, CNT3, ENT1, and ENT2 transporters. Results showed that tetrahydrouridine did not influence CNT- or ENT-mediated uridine/adenosine accumulation in MDCKII cells at the concentrations tested (25 and 250 µM). Accumulation of tetrahydrouridine in MDCKII cells was initially shown to be mediated by CNT3 and ENT2. However, while time- and concentration-dependence experiments showed active accumulation of tetrahydrouridine in CNT3-expressing cells, allowing for estimation of Km (3,140 µM) and Vmax (1,600 pmol/mg protein/min), accumulation of tetrahydrouridine was not observed in ENT2-expressing cells. Potent CNT3 inhibitors are a class of drugs not generally prescribed to patients with SCD, except in certain specific circumstances. These data suggest that NDec can be administered safely with drugs that act as substrates and inhibitors of the nucleoside transporters included in this study.

Knowledge and perception related to sickle cell disease among tribal community, India: A mixed-method study

BACKGROUND

Sickle cell disease (SCD) is a public health problem. In absence of a pan-country intervention program in India, SCD prevalence is ascending without control. Since knowledge and perception of a community is a prerequisite for developing an intervention strategy, the current study was designed to assess it in a high SCD burden tribal-dominated district of Odisha.

METHODS

A mixed-method study combining qualitative and quantitative methods was conducted in the Kandhamal district, Odisha, India. A cross-sectional survey was conducted among randomly selected 1600 individuals, using a pre-tested questionnaire and 26 in-depth interviews were conducted with key informants.

RESULTS

Although 74.2% of the participants in the studied area had heard about the disease, only 13.6% know the cause of the disease. 69% had the knowledge to opt for modern medication. However, treatment compliance was poor, patients resort to using medications only during the crisis stage. Individuals who had knowledge about disease aetiology got to know about SCD from lived experiences of themselves, close relatives, or villagers and rarely from health workers. The community members had no clarity regarding which health centre to be approached for routine medication and management of SCD crisis.

CONCLUSION

The area is endemic for SCD, yet, the community lacks knowledge about the cause and treatment modality of the disease. In addition, currently there is no government-run intervention programme for screening and management of SCD related morbidity. Hence, a community based intervention strategy needs to be implemented urgently for enhancing the knowledge, perception, and aptitude related to SCD.

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.

Reduction in seroprevalence of viral transfusion-transmitted infections in southwest Nigeria in children with sickle cell disease using an enhanced screening strategy

Blood transfusion is an integral component in the management of children and adults with sickle cell disease (SCD). Concerns about blood safety due to the high risk of bloodborne infections in sub-Saharan Africa limits the application of this cost-effective strategy in the management of individuals with SCD. In a single-centre, retrospective, longitudinal study in southwest Nigeria, we hypothesised that the use of stringent blood donor selection, along with very sensitive enzyme-linked immunosorbent assay (ELISA) screening methods would reduce transfusion-transmitted infections (TTIs). Among 45 002 eligible blood donors at the Lagos University Teaching Hospital in Nigeria, over a 5-year review period (2015-2019), the seroprevalence rate of viral TTIs was 9.83%. The seroprevalence rates for human immunodeficiency, hepatitis B, and hepatitis C viruses were 1.37%, 6.2%, and 2.25% respectively. Among 172 children with SCD, 71% (122/172) on regular blood transfusion and 29% (50/172) who had never been transfused or had less than two transfusions per lifetime, none acquired any TTIs using our enhanced screening approach during the study period. Thus, safe blood transfusion practices can be provided for children with SCD in sub-Saharan Africa with the use of stringent donor selection protocols and fourth-generation ELISA kits for TTI screening.

Functional foods: promising therapeutics for Nigerian Children with sickle cell diseases

Sickle cell disease (SCD), also known as sickle cell anemia (SCA) is one of the structural hemoglobinopathies that occurs due to a single nucleotide mutation from GAG to GTG, which changes the amino acid of a β-globin chain of hemoglobin (Hb) from glutamate to valine. This singular mutation results to disorderliness in red blood cells (RBCs) with advent of changes in RBC morphology and other pathological conditions. In the 1980s, intermittent red blood cell transfusions, opioids, and penicillin prophylaxis were the only available therapy for SCA and were commonly reserved for acute, life threatening complications. So far, the US Food and Drug Administration (FDA) has granted a total of four drugs approval for the prophylaxis and treatment of the clinical complications of SCD. Due to limitations (adherence, safety, adverse effects) of existing therapies in the prophylaxis and treatment of SCD complications in Nigerian children and their inaccessibility to approved drugs, the present study discusses the therapeutic effects of readily available functional food as one of the therapies or an adjunct therapy to tackle the sickle cell crisis in Nigerian Children.

In Vitro and In Vivo Studies for the Investigation of γ-Globin Gene Induction by Adhatoda vasica: A Pre-Clinical Study of HbF Inducers for β-Thalassemia

Fetal hemoglobin (HbF) is a potent genetic modifier, and the γ-globin gene induction has proven to be a sustainable therapeutic approach for the management of β-thalassemia. In this study, we have evaluated the HbF induction ability of A. vasica in vitro and in vivo, and the identification of potential therapeutic compounds through a bioassay-guided approach. In vitro benzidine-Hb assay demonstrated strong erythroid differentiation of K562 cells by A. vasica extracts. Subsequently, an in vivo study with an aqueous extract of A. vasica (100 mg/kg) showed significant induction of the γ-globin gene and HbF production. While in the acute study, the hematological and biochemical indices were found to be unaltered at the lower dose of A. vasica. Following the bioassay-guided approach, two isolated compounds, vasicinol (1) and vasicine (2) strongly enhanced HbF levels and showed prominent cellular growth kinetics with ample accumulation of total hemoglobin in K562 cultures. High HbF levels were examined by immunofluorescence and flow cytometry analysis, concomitant with the overexpression in the γ-globin gene level. Compound 1 (0.1 µM) and compound 2 (1 µM) resulted in a greater increase in F-cells (90 and 83%) with marked up (8-fold and 5.1-fold) expression of the γ-globin gene, respectively. Molecular docking studies indicated strong binding affinities of (1) and (2) with HDAC2 and KDM1 protein that predict the possible mechanism of compounds in inhibition of these epigenetic regulators in the γ-globin gene reactivation. Altogether, these observations demonstrated the therapeutic usefulness of A. vasica for fostering HbF production in clinical implications for blood disorders.

In vitro drug-drug interactions of decitabine and tetrahydrouridine involving drug transporters and drug metabolising enzymes

1. NDec is a novel, oral, fixed-dose formulation of decitabine and tetrahydrouridine that is currently being developed for the treatment of patients with sickle cell disease. Here, we examine the potential for both components of NDec to interact with key drug metabolising enzymes (tetrahydrouridine only) and drug transporters (decitabine and tetrahydrouridine).2. This study assessed the inhibition and induction of cytochrome P450 (CYP) enzymes by tetrahydrouridine, as well as the involvement of specific drug metabolising enzymes in tetrahydrouridine metabolism. Inhibition of efflux and uptake transporters by both decitabine and tetrahydrouridine was also studied.3. Tetrahydrouridine did not inhibit or induce relevant CYP enzymes at concentrations ranging from 0.1 to 100 μM. Metabolism of tetrahydrouridine did not occur in the presence of the human drug metabolising enzymes tested. Tetrahydrouridine showed weak inhibition towards the MATE2-K transporter (∼30% inhibition at 5 and 50 μM), which was not deemed clinically relevant. Tetrahydrouridine did not inhibit any of the remaining uptake or efflux transporters. Decitabine (0.5 and 5 μM) did not inhibit any of the evaluated uptake or efflux drug transporters.4. Data presented confirm that tetrahydrouridine and decitabine are unlikely to be involved in metabolism- or transporter-based drug-drug interactions.

5-Aza-4'-thio-2'-deoxycytidine, a New Orally Bioavailable Nontoxic "Best-in-Class": DNA Methyltransferase 1-Depleting Agent in Clinical Development

DNA methyltransferase (DNMT) 1 is an enzyme that functions as a maintenance methyltransferase during DNA replication, and depletion of this enzyme from cells is considered to be a rational goal in DNA methylation-dependent disorders. Two DNMT1-depleting agents 5-aza-2'-deoxycytidine (aza-dCyd, decitabine) and 5-aza-cytidine (aza-Cyd, azacitidine) are currently used for the treatment of myelodysplastic syndromes and acute myeloid leukemia and have also been investigated for nononcology indications, such as sickle cell disease. However, these agents have several off-target activities leading to significant toxicities that limit dosing and duration of treatment. Development of more selective inhibitors of DNMT1 could therefore afford treatment of long durations at effective doses. We have discovered that 5-aza-4'-thio-2'-deoxycytidine (aza-T-dCyd) is as effective as aza-dCyd in depleting DNMT1 in mouse tumor models but with markedly low toxicity. In this review we describe the preclinical studies that led to the development of aza-T-dCyd as a superior DNMT1-depleting agent with respect to aza-dCyd and will describe its pharmacology, metabolism, and mechanism of action. In an effort to understand why aza-T-dCyd is a more selective DNMT1 depleting agent than aza-dCyd, we will also compare and contrast the activities of these two agents. SIGNIFICANCE STATEMENT: Aza-T-dCyd is a potent DNMT1-depleting agent. Although similar in structure to decitabine (aza-dCyd), its metabolism and mechanism of action is different than that of aza-dCyd, resulting in less off-target activity and less toxicity. The larger therapeutic index of aza-T-dCyd (DNMT1 depletion vs. toxicity) in mice suggests that it would be a better clinical candidate to selectively deplete DNMT1 from target cells and determine whether or not depletion of DNMT1 is an effective target for various diseases.

Exploring epigenetic and microRNA approaches for γ-globin gene regulation

Therapeutic interventions aimed at inducing fetal hemoglobin and reducing the concentration of sickle hemoglobin is an effective approach to ameliorating acute and chronic complications of sickle cell disease, exemplified by the long-term use of hydroxyurea. However, there remains an unmet need for the development of additional safe and effective drugs for single agent or combination therapy for individuals with β-hemoglobinopathies. Regulation of the γ-globin to β-globin switch is achieved by chromatin remodeling at the HBB locus on chromosome 11 and interactions of major DNA binding proteins, such as KLF1 and BCL11A in the proximal promoters of the globin genes. Experimental evidence also supports a role of epigenetic modifications including DNA methylation, histone acetylation/methylation, and microRNA expression in γ-globin gene silencing during development. In this review, we will critically evaluate the role of epigenetic mechanisms in γ-globin gene regulation and discuss data generated in tissue culture, pre-clinical animal models, and clinical trials to support drug development to date. The question remains whether modulation of epigenetic pathways will produce sufficient efficacy and specificity for fetal hemoglobin induction and to what extent targeting these pathways form the basis of prospects for clinical therapy.

Early initiation of hydroxyurea (hydroxycarbamide) using individualised, pharmacokinetics-guided dosing can produce sustained and nearly pancellular expression of fetal haemoglobin in children with sickle cell anaemia

Hydroxyurea (hydroxycarbamide) is an effective treatment for sickle cell anaemia (SCA), but clinical responses depend primarily upon the degree of fetal haemoglobin (HbF) induction and the heterogeneity of HbF expression across erythrocytes. The number and characteristics of HbF-containing cells (F-cells) are not assessed by traditional HbF measurements. Conventional hydroxyurea dosing (e.g. fixed doses or low starting doses with stepwise escalation) produces a moderate heterocellular HbF induction, but haemolysis and clinical complications continue. Robust, pancellular HbF induction is needed to minimise or fully inhibit polymerisation of sickle haemoglobin. We treated children with hydroxyurea using an individualised, pharmacokinetics-guided regimen starting at predicted maximum tolerated dose (MTD). We observed sustained HbF induction (mean >30%) for up to 6 years, which was not dependent on genetic determinants of HbF expression. Nearly 70% of patients had ≥80% F-cells (near-pancellular), and almost half had ≥90% F-cells (pancellular). The mean HbF/F-cell content was ~12 pg. Earlier age of initiation and better medication adherence were associated with high F-cell responses. In summary, early initiation of hydroxyurea using pharmacokinetics-guided starting doses at predicted MTD can achieve sustained near-pancellular or pancellular HbF expression and should be considered an achievable goal for children with SCA treated with hydroxyurea at optimal doses. Clinical trial registration number: NCT02286154 (clinicaltrials.gov).

Gene therapy as the new frontier for Sickle Cell Disease

Sickle Cell Disease (SCD) is one of the most common monogenic disorders caused by a point mutation in the β-globin gene. This mutation results in polymerization of hemoglobin (Hb) under reduced oxygenation conditions, causing rigid sickle-shaped RBCs and hemolytic anemia. This clearly defined fundamental molecular mechanism makes SCD a prototypical target for precision therapy. Both the mutant β-globin protein and its downstream pathophysiology are pharmacological targets of intensive research. SCD also is a disease well-suited for biological interventions like gene therapy. Recent advances in hematopoietic stem cell (HSC) transplantation and gene therapy platforms, like Lentiviral vectors and gene editing strategies, expand the potentially curative options for patients with SCD. This review discusses the recent advances in precision therapy for SCD and the preclinical and clinical advances in autologous HSC gene therapy for SCD.

Epigenetic modifier directed therapeutics to unleash healthy genes in unhealthy cells

A common thread through malignant and nonmalignant diseases alerts us to a therapeutic opportunity to seize: disease may originate from genetic mutations, but resulting maladaptive/unhealthy cell fates and functions are mediated by epigenetic enzymes, that are druggable. Epigenetic enzymes modify DNA, and/or the histones around which DNA is organized, to regulate access to genes by the basal transcription factor machinery that transcribes genes. Epigenetic enzymes can be divided usefully into those that facilitate gene transcription ("on" enzymes or coactivators) and those that favor gene repression ("off" enzymes or corepressors). DNA-binding master transcription factors cooperate to recruit coactivators, and repulse corepressors, from thousands of genes, to thereby activate the gene expression programs that define cell fates and functions. In malignancy, this usual exchange of corepressors for coactivators fails, because of mutations to master transcription factors or the coactivators they recruit. Inhibiting corepressor enzymes using small molecules uses pharmacology to redress this coactivator/corepressor imbalance that originates from genetics, to in this way release cancer cells to the terminal lineage-fates intended by their master transcription factor content. Similarly, in nonmalignant β-hemoglobinopathies, inhibiting corepressors exploits transcription factor and lineage-context to activate unmutated fetal over mutated adult globin genes, to thereby treat these nonmalignant genetic diseases. Master transcription factors then are the "natural forces" in the Hippocratic dictum "Natural forces within us are the true healers of disease," and drugging epigenetic enzymes (corepressors) a way to harness these forces to heal.

Systematic Review of Voxelotor: A First-in-Class Sickle Hemoglobin Polymerization Inhibitor for Management of Sickle Cell Disease

Voxelotor, a sickle hemoglobin polymerization inhibitor, was approved by the U.S. Food and Drug Administration to treat sickle cell disease (SCD) in November 2019. This article reviews published data about voxelotor treatment of SCD based on a search of MEDLINE, Embase, and International Pharmaceutical Abstracts. In a phase I/II trial, voxelotor demonstrated a dose-dependent pharmacokinetic and pharmacodynamic response and was well tolerated in healthy volunteers and patients with SCD. In a multi-center, randomized, double-blind, phase III trial (HOPE trial), a significantly higher percentage of patients randomized to voxelotor had increased hemoglobin (> 1 g/dl from baseline) compared to placebo. A greater reduction of hemolytic markers was also observed in the voxelotor-treated group, whereas the incidence of adverse effects was comparable. Three case series or reports also demonstrated the efficacy and safety of voxelotor use in a limited number of SCD patients in the real-world situation, although one patient with SCD, severe anemia, and a history of autoantibody-mediated hemolysis failed to respond to voxelotor. An ongoing trial (HOPE-KIDS) is designed to establish the use of voxelotor in younger pediatric patients with SCD. There is a theoretical concern that voxelotor may impair oxygen delivery, due to modification of the oxygen affinity of hemoglobin, which needs to be further evaluated. As a first-in-class hemoglobin modulator, voxelotor offers a new treatment option targeting the root cause of SCD.

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.