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Fetal hemoglobin (HbF) blocks polymerization of deoxy sickle hemoglobin (HbS), the root cause of sickle cell disease (SCD) pathophysiology, and is the most powerful known disease modifier. (A) Polymerization of deoxy HbS drives all SCD pathophysiology; In contrast to HbF, normal adult hemoglobin (HbA, ẞ-chains) can participate in polymerization. (B) The gene for HbF (HBG) is silenced by DNA methyltransferase 1 (DNMT1). Although DNA-binding factors, e.g., BCL11A, direct this silencing, the biochemical work of epigenetic repression is executed by chromatin-modifying enzymes, amongst which DNMT1 is central. Decitabine depletes DNMT1 and can do so without cytotoxicity because in contrast to other cytidine analogues (e.g., cytarabine) the deoxyribose moiety (green dotted circle) is natural, although higher concentrations do cause anti-metabolite effects and DNA damage, in part by degradation into uridine counterparts that misincorporate into DNA. (C) Several pharmacologic limitations of decitabine hinder safe, effective, practical clinical translation. The limitations have a common cause, the enzyme cytidine deaminase (CDA). Tetrahydrouridine (THU) inhibits CDA. No toxicities have been found for THU in animals or humans.
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Background
Sickle cell disease (SCD), a congenital hemolytic anemia that exacts terrible global morbidity and mortality, is driven by polymerization of mutated sickle hemoglobin (HbS) in red blood cells (RBCs). Fetal hemoglobin (HbF) interferes with this polymerization, but HbF is epigenetically silenced from infancy onward by DNA methyltransferase...
Similar publications
Background
Sickle cell disease (SCD) is caused by an inherited structural abnormality of adult hemoglobin causing polymerization. Fetal hemoglobin interferes with polymerization but is epigenetically silenced by DNA methyltransferase 1 (DNMT1) in adult erythropoiesis. Decitabine depletes DNMT1 and increases fetal and total hemoglobin in SCD patient...
Citations
... This suggests that some of the identified genes may act together in these biological pathways to have a cumulative effect or influence Hydroxyurea treatment response. [55][56][57][58]. The anticipated increase of this trend is poised to align with technological progress facilitating pharmaceutical development. ...
Sickle cell disease (SCD) continues to pose a significant public health challenge, particularly in sub-Saharan Africa. Despite its discovery over a century ago, the progress in developing and accessing effective interventions has been notably restricted. Currently, hydroxyurea stands as the primary drug in widespread use, and has been associated with elevated levels of fetal hemoglobin (HbF) and enhanced clinical outcomes. Notably, a substantial proportion, up to 30%, of patients do not exhibit a positive response to hydroxyurea treatment. There is compelling evidence suggesting that genetic factors play a crucial role in influencing the effectiveness of hydroxyurea. In this study, we present findings on the investigation of genetic variants influencing hydroxyurea response in 13 genetic loci associated with HbF synthesis and hydroxyurea drug metabolism focusing on MYB, HBB, HBG1, HBG2, BCL11A, KLF10, HAO2, NOS1, ARG2, SAR1A, CYP2C9, CYP2E1. We report remarkable genetic associations with CYP2C9, CYP2E1, KLF10, BCL11A, ARG2, HBG1, SAR1A, MYB, and NOS1 loci with hydroxyurea response. We also highlight the associated pathway's enrichment and gene-gene interactions analysis in the context of hydroxyurea treatment response.
... HbF is silenced in infancy by DNA methyltransferase 1 (DNMT1) [28]. Decitabine, in combination with the cytidine deaminase (CDA) inhibitor (tetrahydrouridine (THU)), has been shown to inhibit DNMT1 and induce HbF production [28]. ...
... HbF is silenced in infancy by DNA methyltransferase 1 (DNMT1) [28]. Decitabine, in combination with the cytidine deaminase (CDA) inhibitor (tetrahydrouridine (THU)), has been shown to inhibit DNMT1 and induce HbF production [28]. Two trials are recruiting adult SCD patients to investigate decitabine and THU safety and efficacy (NCT04055818 and NCT05405114). ...
Sickle cell disease (SCD) is the most common genetic blood disorder in the United States, with over 100,000 people suffering from this debilitating disease. SCD is caused by abnormal hemoglobin (Hb) variants that interfere with normal red blood cell (RBC) function. Research on SCD has led to the development and approval of several new SCD therapies in recent years. The recent FDA-approved novel gene therapies are potentially curative, giving patients an additional option besides a hematopoietic bone marrow transplant. Despite the promise of existing therapies, questions remain regarding their long-term pharmacological effects on adults and children. These questions, along with the exorbitant cost of the new gene therapies, justify additional research into more effective therapeutic options. Continual research in this field focuses on not only developing cheaper, more effective cures/treatments but also investigating the physiological effects of the current therapies on SCD patients, particularly on the brain and kidneys. In this article, we undertake a comprehensive review of ongoing clinical trials with completion dates in 2024 or later. Our exploration provides insights into the landscape of current therapeutics and emerging novel therapies designed to combat and potentially eradicate SCD, including the latest FDA-approved gene therapies.
... In the first human clinical trial (NCT01685515) to pharmacologically re-induce HbF by inhibiting DNMT1, two small molecules were combined: decitabine to deplete DNMT1 and tetrahydrouridine (THU) to inhibit cytidine deaminase (CDA), which rapidly inactivates decitabine [36]. This trial aimed to identify minimal effective doses of oral decitabine without cytotoxicity in SCD adults at risk of early death. ...
... This trial aimed to identify minimal effective doses of oral decitabine without cytotoxicity in SCD adults at risk of early death. Patients were randomized to THU-decitabine or placebo in 5 cohorts, treated 2X/week for 8 weeks [36]. The primary endpoint was ≥ grade 3 non-hematologic toxicity, which was not triggered. ...
... Platelets increased, and neutrophils decreased without treatment holds. Limitations of this early phase study include small patient numbers and limited evaluation of clinical benefits [36]. ...
Sickle cell disease encompasses diseases that are pathophysiologically caused by hemoglobin S. The HbS component of total hemoglobin in SCD is normally over 50%. HbS is based on an amino acid substitution at position 6 of the β-globin chain, where glutamic acid is replaced by valine. This substitution replaces a hydrophilic amino acid with a hydrophobic amino acid at an outward-facing position in the h molecule, explaining the reduced water solubility and altered molecular organization of HbS compared to normal hemoglobin. Diseases caused by HbS include homozygous SCD, where both alleles are affected by the sickle cell mutation (SCD-S/S), HbSC disease, where one allele is affected by the sickle cell mutation and the other by the HbC mutation (SCD-S/C), and sickle cell β-thalassemia with mixed heterozygosity for the sickle cell mutation and a β-thalassemia mutation (SCD-S/β-thalassemia). In SCD-S/β-thalassemia, forms are distinguished where the β-thalassemia mutation completely inactivates the affected gene (SCD-S/β0-thalassemia) and forms where the allele with the thalassemia mutation still has residual activity (SCD-S/β+-thalassemia). Rarely, the sickle cell mutation can also be combined with other hemoglobin variants (SCD-S/D, SCD-S/OArab, SCD-S/Lepore). The carrier status for the sickle cell mutation generally has no clinical significance except in extreme situations (e.g., eye trauma or surgeries involving cardiopulmonary bypass). Carriers have a normal life expectancy. However, there are individual reports of complications in heterozygous carriers of the sickle cell mutation under common circumstances such as pregnancy, mountain sports, intense physical activity, or air travel. It is also unclear whether the carrier status is associated with an increased rate of kidney complications. Nevertheless, it is not appropriate to indicate specific medical care needs based on these individual case reports given the frequency of carrier status. However, the familial risk of developing SCD should be considered in adult carriers. This manuscript focus on new targets to treat sickle cell anemia in children.
... This inhibited DNMT1 protein and increased HbF levels and F-cells to 80%. 88,89 A trial was recently conducted in six patients with SCD who were treated with a single formulation in which THU is released first, followed by decitabine (NCT04055818). In 5 of 6 high-risk patients with low HbF levels at baseline and negative prediction markers for response to HU, this formulation, administered only once day/week, produced sustained increases in HbF and F-cell proportions, reduced multiple cellular abnormalities and the frequency of painful events over 12 months of therapy compared to the year prior to the trial, without any dose-limiting toxicities. ...
Beta hemoglobinopathies and thalassemias are caused by diverse molecular mutations of the βA globin chains and modulated by polymorphisms. These are important disorders in medical history, as they became prevalent globally in regions where P. falciparum malaria was endemic. Heterozygous or carrier states conferred a survival advantage; however, doubly heterozygous or homozygous states cause severe hemolytic anemia and multi-organ complications. These disorders are somewhat unique in that all humans have alternate genes for fetal globin chains, which are expressed in fetal life but are silenced on a developmental clock in infancy. An established approach to ameliorating conditions of abnormal adult globin genes is to reactivate, or increase expression, of the endogenous fetal globin genes to replace the missing protein chains in beta thalassemias or inhibit polymerization of hemoglobin S and reduce the red cell abnormalities. This review provides a high-level overview of cell and molecular mechanisms that mediate fetal to adult globin gene switching and pharmacologic therapies that can reactivate fetal globin through different actions. Intermittent or metronomic dosing regimens have overcome challenges of undesirable off-target effects by agents that cause erythroid cell growth arrest. Multiple pharmacologic candidates reactivate or increase the expression of fetal globin protein and proportions of red blood cells containing HbF (F-cells). Hydroxyurea maintains high levels of HbF if begun in infancy, with some decline in mid-childhood. It elicits lower responses in HbF in adult patients, but still has broad clinical benefit in reducing many complications. However, many adult patients do not tolerate optimal hydroxyurea dosing due to cytopenias. Parenterally administered therapies with differing molecular actions, such as demethylating agents and histone deacetylase inhibitors, have shown proof-of-principle in reactivating HbF. Orally bioavailable candidates with complementary molecular mechanisms are in trials. Combining fetal globin-inducing agents with other therapies with complementary mechanisms, such as recombinant erythropoietin that promotes the survival of red blood cells and therapeutics that promote erythroid cell metabolism, should have additive effects. These pharmaceutical candidates offer great clinical potential and global feasibility for ameliorating these serious diseases.
... Clinically significant increases in HbF were achieved with the highest dose administered (0.16 mg/kg). Laboratory biomarkers of hemolysis, coagulation, and inflammation also improved [22]. Another clinical trial with THU-decitabine, ASCENT1, is still in progress. ...
Introduction:
Sickle cell disease (SCD) is an inherited disorder characterised by polymerisation of deoxygenated haemoglobin S and microvascular obstruction. The cardinal feature is generalised pain referred to as vaso-occlusive crises (VOC), multi-organ damage and premature death. SCD is the most prevalent inherited life-threatening disorders in the world and over 85% of world's 400,000 annual births occur low-and-middle-income countries. Hydroxyurea remained the only approved disease modifying therapy (1998) until the FDA approved L-glutamine (2017), Crizanlizumab and Voxelotor (2019) and gene therapies (Exa-cel and Lovo-cel, 2023).
Areas covered:
Clinical trials performed in the last 10 years (November 2013 - November 2023) were selected for the review. They were divided according to the mechanisms of drug action. The following pubmed central search terms [sickle cell disease] or [sickle cell anaemia] Hydroxycarbamide/ Hydroxyurea, L-Glutamine, Voxelotor, Crizanlizumab, Mitapivat, Etavopivat, gene therapy, haematopoietic stem cell transplantation, and combination therapy.
Expert opinion:
We recommend future trials of combination therapies for specific complications such as VOCs, chronic pain and renal impairment as well as personalised medicine approach based on phenotype and patient characteristics. Following recent approval of gene therapy for SCD, the challenge is addressing the role of shared decision-making with families, global access and affordability.
... An increased expression of Hb F has been demonstrated to be associated with an abnormal DNA hypomethylation pattern in the g-globin promoters (Goren et al., 2006). Accordingly, DNA methyltransferase (DNMT) inhibitors, such as decitabine, and new compounds, such as GSK3482364 have been used to treat patients with SCD to increase Hb F levels (Molokie et al., 2017;Gilmartin et al., 2021). ...
... Therefore, simian primates, including the baboon, are considered excellent animal models for testing new pharmacol1ogical agents to stimulate in vivo HbF production during adult-stage erythropoiesis to develop new therapies for sickle cell disease [27][28][29]. Experimental findings of HbF-inducing drugs in baboons [30,31] are predictive of responses in man and have allowed direct translation of experimental baboon studies to clinical trials in patients with sickle cell disease [32][33][34][35][36][37]. The goal of this study was to investigate the in vivo mechanism of action of RN-1 in baboons by determining the effect of RN-1 administration in vivo on γ-globin expression during erythroid differentiation in highly purified subpopulations of bone marrow erythroid cells isolated directly from baboons treated with RN-1 and also its effect on the global transcriptome. ...
Elevated levels of Fetal Hemoglobin interfere with polymerization of sickle hemoglobin thereby reducing anemia, lessening the severity of symptoms, and increasing life span of patients with sickle cell disease. An affordable, small molecule drug that stimulates HbF expression in vivo would be ideally suited to treat the large numbers of SCD patients that exist worldwide. Our previous work showed that administration of the LSD1 (KDM1A) inhibitor RN-1 to normal baboons increased Fetal Hemoglobin (HbF) and was tolerated over a prolonged treatment period. HbF elevations were associated with changes in epigenetic modifications that included increased levels of H3K4 di-and tri-methyl lysine at the γ-globin promoter. While dramatic effects of the loss of LSD1 on hematopoietic differentiation have been observed in murine LSD1 gene deletion and silencing models, the effect of pharmacological inhibition of LSD1 in vivo on hematopoietic differentiation is unknown. The goal of these experiments was to investigate the in vivo mechanism of action of the LSD1 inhibitor RN-1 by determining its effect on γ-globin expression in highly purified subpopulations of bone marrow erythroid cells enriched for varying stages of erythroid differentiation isolated directly from baboons treated with RN-1 and also by investigating the effect of RN1 on the global transcriptome in a highly purified population of proerythroblasts. Our results show that RN-1 administered to baboons targets an early event during erythroid differentiation responsible for γ-globin repression and increases the expression of a limited number of genes including genes involved in erythroid differentiation such as GATA2, GFi-1B, and LYN.
... Other drugs, such as decitabine, a deoxycytidine analogue that depletes DNMT1, showed effective increases in fetal haemoglobin production in combination with tetrahydrouridine, without substantial adverse events, but data are from small studies. 89 Although repurposing existing therapeutic drugs for individuals with sickle cell disease is appealing for the potential effect on fetal haemoglobin induction, there are several questions regarding downstream effects of epigenetic targets. Furthermore, people living with sickle cell disease are often concerned about the use of cancer therapies for their non-malignant disease. ...
... Epidemiological, clinical, and experimental evidence has demonstrated that people with SCD who have higher levels of HbF, conferred by genetic polymorphisms, have a better quality and quantity of life. [3][4][5][6][7][8] Research into the pharmacological reactivation of HbF led to the evaluation and approval of oral hydroxyurea (HU) to modify the clinical course of SCD. 9 Although HU is widely used to treat SCD, its efficacy reduces over time and exhibits side effects possibly related to a cytotoxic mechanism of action. 7,10-12 Potentially curative interventions for SCD, such as allogeneic stem cell transplant or transplant with ex vivo genetically engineered hematopoietic stem cells, are not feasible or are inaccessible to most SCD patients. ...
... 7 DNMT1-target engagement by decitabine was confirmed by DNA hypomethylation in blood cells, and the resulting elevated HbF levels corresponded to less hemolysis and higher total hemoglobin. 7 Preclinical in vitro studies indicated a low risk of either THU or decitabine inhibiting other drugmetabolizing enzymes. 19,20 Other than weak inhibition of MATE2-K by THU, neither THU nor decitabine inhibited the tested common drug-metabolizing enzymes or transporters, 19 indicating a low risk of drug-drug interactions on concomitant use of THU and decitabine with other medications to manage SCD. ...
... Protection of decitabine by co-administration of a CDA inhibitor has also been applied to the treatment of myeloid malignancies. 16,21 To build on studies that examined oral administration of THU and decitabine separated by 1 h, 7 ...
Background
Sickle cell disease (SCD) is caused by an inherited structural abnormality of adult hemoglobin causing polymerization. Fetal hemoglobin interferes with polymerization but is epigenetically silenced by DNA methyltransferase 1 (DNMT1) in adult erythropoiesis. Decitabine depletes DNMT1 and increases fetal and total hemoglobin in SCD patients, but is rapidly catabolized by cytidine deaminase (CDA) in vivo. Tetrahydrouridine (THU) inhibits CDA, safeguarding decitabine.
Methods
The pharmacokinetics and pharmacodynamics of three oral combination formulations of THU and decitabine, with different coatings producing different delays in decitabine release, were investigated in healthy participants.
Results
Tetrahydrouridine and decitabine were rapidly absorbed into the systemic circulation after a single combination oral dose, with relative bioavailability of decitabine ≥74% in fasted males compared with separate oral administration of THU followed by decitabine 1 h later. THU and decitabine Cmax and area under the plasma concentration versus time curve were higher in females versus males, and fasted versus fed states. Despite sex and food effect on pharmacokinetics, the pharmacodynamic effect of DNMT1 downregulation was comparable in males and females and fasted and fed states. Treatments were well tolerated.
Conclusion
Combination oral formulations of THU with decitabine produced pharmacokinetics and pharmacodynamics suitable for oral DNMT1‐targeted therapy.
... Oral decitabine, an inhibitor of DNA-methyltransferase 1, is being evaluated in combination with tetrahydrouridine (THU), which prevents the degradation of decitabine in the liver, versus nicotinamide (NCT04055818). A phase 1 clinical trial combining oral decitabine and THU showed promising results associated with increased HbF and total hemoglobin levels in persons with SCD [69]. ...
The polymerization of hemoglobin under deoxygenation is the main pathophysiological event in sickle cell diseases, described more than 70 years ago. The last two decades have seen a major increase in knowledge about the cascade of events that follow the polymerization of hemoglobin and the ensuing sickling of red blood cells. Several distinctive therapeutic targets have been discovered as a result, and a few drugs with innovative mechanisms of action are already on the market, while several others are the focus of ongoing trials. The aim of this narrative review is to describe some of the more recent data in the SCD literature regarding pathophysiology and novel treatments.
