A phase 1 dose escalation study of the pyruvate kinase activator mitapivat (AG-348) in sickle cell disease

Multicenter, phase 1 study of etavopivat (FT-4202) treatment for up to 12 weeks in patients with sickle cell disease

ABSTRACT

Etavopivat is an investigational, once daily, oral, selective erythrocyte pyruvate kinase (PKR) activator. A multicenter, randomized, placebo-controlled, double-blind, 3-part, phase 1 study was conducted to characterize the safety and clinical activity of etavopivat. Thirty-six patients with sickle cell disease (SCD) were enrolled into 4 cohorts: 1 single-dose, 2 multiple ascending doses, and 1 open-label (OL). In the OL cohort, 15 patients (median age 33.0 years [range, 17-55]) received 400 mg etavopivat once daily for 12 weeks; 14 patients completed treatment. Consistent with the mechanism of PKR activation, increases in adenosine triphosphate and decreases in 2,3-diphosphoglycerate were observed and sustained over 12 weeks' treatment. This translated clinically to an increase in hemoglobin (Hb; mean maximal increase 1.6 g/dL [range, 0.8-2.8]), with >1 g/dL increase in 11 (73%) patients during treatment. In addition, the oxygen tension at which Hb is 50% saturated was reduced (P = .0007) with a concomitant shift in point of sickling (P = .0034) to lower oxygen tension in oxygen-gradient ektacytometry. Hemolysis markers (absolute reticulocyte count, indirect bilirubin, and lactate dehydrogenase) decreased from baseline, along with matrix metalloproteinase-9 and erythropoietin. In the OL cohort, adverse events (AEs) were mostly grade 1/2, consistent with underlying SCD; 5 patients had serious AEs. Vaso-occlusive pain episode was the most common treatment-emergent AE (n = 7) in the OL cohort. In this, to our knowledge, the first study of etavopivat in SCD, 400 mg once daily for 12 weeks was well tolerated, resulting in rapid and sustained increases in Hb, improved red blood cell physiology, and decreased hemolysis. This trial was registered at www.ClinicalTrials.gov as #NCT03815695.

Novel therapeutic approaches in thalassemias, sickle cell disease, and other red cell disorders

ABSTRACT

In this last decade, a deeper understanding of the pathophysiology of hereditary red cell disorders and the development of novel classes of pharmacologic agents have provided novel therapeutic approaches to thalassemias, sickle cell disease (SCD), and other red cell disorders. Here, we analyze and discuss the novel therapeutic options according to their targets, taking into consideration the complex process of erythroid differentiation, maturation, and survival of erythrocytes in the peripheral circulation. We focus on active clinical exploratory and confirmatory trials on thalassemias, SCD, and other red cell disorders. Beside β-thalassemia and SCD, we found that the development of new therapeutic strategies has allowed for the design of clinic studies for hereditary red cell disorders still lacking valuable therapeutic alternative such as α-thalassemias, congenital dyserythropoietic anemia, or Diamond-Blackfan anemia. In addition, reduction of heme synthesis, which can be achieved by the repurposed antipsychotic drug bitopertin, might affect not only hematological disorders but multiorgan diseases such as erythropoietic protoporphyria. Finally, our review highlights the current state of therapeutic scenarios, in which multiple indications targeting different red cell disorders are being considered for a single agent. This is a welcome change that will hopefully expand therapeutic option for patients affected by thalassemias, SCD, and other red cell disorders.

Functional and multi-omics signatures of mitapivat efficacy upon activation of pyruvate kinase in red blood cells from patients with sickle cell disease

Mitapivat, a pyruvate kinase activator, shows great potential as a sickle cell disease (SCD)-modifying therapy. The safety and efficacy of mitapivat as a long-term maintenance therapy are currently being evaluated in two open-label studies. Here we applied a comprehensive multi-omics approach to investigate the impact of activating pyruvate kinase on red blood cells (RBC) from 15 SCD patients. HbSS patients were enrolled in one of the open-label, extended studies (NCT04610866). Leukodepleted RBC obtained from fresh whole blood at baseline, prior to drug initiation, and at longitudinal timepoints over the course of the study were processed for multi-omics through a stepwise extraction of metabolites, lipids and proteins. Mitapivat therapy had significant effects on the metabolome, lipidome and proteome of SCD RBC. Mitapivat decreased 2,3-diphosphoglycerate levels, increased adenosine triphosphate levels, and improved hematologic and sickling parameters in patients with SCD. Agreement between omics measurements and clinical measurements confirmed the specificity of mitapivat on targeting late glycolysis, with glycolytic metabolites ranking as the top correlates to parameters of hemoglobin S oxygen affinity (p50) and sickling kinetics (t50) during treatment. Mitapivat markedly reduced levels of proteins of mitochondrial origin within 2 weeks of initiation of treatment, with minimal changes in reticulocyte counts. In the first 6 months of treatment there were also transient elevations of lysophosphatidylcholines and oxylipins with depletion of free fatty acids, suggestive of an effect on membrane lipid remodeling. Multi-omics analysis of RBC identified benefits for glycolysis, as well as activation of the Lands cycle.

Rabbit muscle pyruvate kinase activators: Synthesis, molecular docking and theoretical studies of N-substituted sulfonamide derivatives

Pyruvate kinase (PK) activators have potential therapeutic applications in diseases such as sickle cell anemia. In this study, N-Substituted sulfonamide derivatives of 1,4-dihydropyridines were synthesized and evaluated as PK activators in vitro and using molecular docking studies. The compounds were synthesized by reacting dicarbonyl compounds with ammonium acetate, 5-nitrobenzaldehyde, and alumina sulfuric acid (ASA), followed by reduction and sulfonylation. The structures of the compounds were analyzed using spectroscopic techniques. DFT calculations provided insights into the electronic properties. Molecular docking of the compounds into the active site of PK showed favorable binding interactions. ADME evaluation indicated suitable solubility, BBB permeation, and lack of CYP450 inhibition. Overall, this study demonstrates the potential of new hybrid 1,4-dihydropyridine substituted sulfonamides as PK activators for further development. According to AC50 values, the compound (DTSF7, 0.97μM) is about 100-fold higher affective than the clinically used sulfonamide compound (AC50 = 90μM) for PK.

Endogenous small molecule effectors in GATA transcription factor mechanisms governing biological and pathological processes

Transcriptional mechanisms establish and maintain complex genetic and protein networks to control cell state transitions. The hematopoietic transcription factor GATA1 is a master regulator of erythropoiesis and megakaryopoiesis, and human GATA1 genetic variants cause anemia and megakaryoblastic leukemia. Multiomic analyses revealed that GATA1 controls expression of transporters and metabolic enzymes that dictate intracellular levels of endogenous small molecules, including heme, metal ions, and sphingolipids. Besides its canonical function as a hemoglobin component, heme facilitates or antagonizes GATA1 function to regulate erythropoiesis via mechanisms dependent or independent of the heme-binding transcription factor BTB domain and CNC homology 1 (BACH1). GATA1 regulates the expression of genes encoding heme biosynthetic enzymes and BACH1. GATA1 maintains homeostasis of bioactive ceramides during erythroid differentiation by regulating genes encoding sphingolipid metabolic enzymes. Disrupting ceramide homeostasis impairs critical cytokine signaling and is detrimental to erythroid cells. During erythroid maturation, GATA1 induces a zinc transporter switch that favors export versus import, thus dictating the intracellular zinc level, erythroblast survival, and differentiation. In aggregate, these studies support an emerging paradigm in which GATA factor-dependent transcriptional mechanisms control the intracellular levels of endogenous small molecules and small molecule-dependent feedback loops that serve as vital effectors of transcription factor activity, genome function, and cell state transitions.

Modulation of the allosteric and vasoregulatory arms of erythrocytic oxygen transport

Efficient distribution of oxygen (O2) to the tissues in mammals depends on the evolved ability of red blood cell (RBC) hemoglobin (Hb) to sense not only O2 levels, but metabolic cues such as pH, PCO2, and organic phosphates, and then dispense or take up oxygen accordingly. O2 delivery is the product of not only oxygen release from RBCs, but also blood flow, which itself is also governed by vasoactive molecular mediators exported by RBCs. These vascular signals, including ATP and S-nitrosothiols (SNOs) are produced and exported as a function of the oxygen and metabolic milieu, and then fine-tune peripheral metabolism through context-sensitive vasoregulation. Emerging and repurposed RBC-oriented therapeutics can modulate either or both of these allosteric and vasoregulatory activities, with a single molecule or other intervention influencing both arms of O2 transport in some cases. For example, organic phosphate repletion of stored RBCs boosts the negative allosteric effector 2,3 biphosphoglycerate (BPG) as well as the anti-adhesive molecule ATP. In sickle cell disease, aromatic aldehydes such as voxelotor can disfavor sickling by increasing O2 affinity, and in newer generations, these molecules have been coupled to vasoactive nitric oxide (NO)-releasing adducts. Activation of RBC pyruvate kinase also promotes a left shift in oxygen binding by consuming and lowering BPG, while increasing the ATP available for cell health and export on demand. Further translational and clinical investigation of these novel allosteric and/or vasoregulatory approaches to modulating O2 transport are expected to yield new insights and improve the ability to correct or compensate for anemia and other O2 delivery deficits.

Metabolic blood profile and response to treatment with the pyruvate kinase activator mitapivat in patients with sickle cell disease

Mitapivat is an investigational, oral, small-molecule allosteric activator of pyruvate kinase (PK). PK is a regulatory glycolytic enzyme that is key in providing the red blood cell (RBC) with sufficient amounts of adenosine triphosphate (ATP). In sickle cell disease (SCD), decreased 2,3-DPG levels increase the oxygen affinity of hemoglobin, thereby preventing deoxygenation and polymerization of sickle hemoglobin. The PK activator mitapivat has been shown to decrease levels of 2,3-DPG and increase levels of ATP in RBCs in patients with SCD. In this phase 2, investigator-initiated, open-label study (https://www.clinicaltrialsregister.eu/ NL8517; EudraCT 2019-003438-18), untargeted metabolomics was used to explore the overall metabolic effects of 8-week treatment with mitapivat in the dose-finding period. In total, 1773 unique metabolites were identified in dried blood spots of whole blood from ten patients with SCD and 42 healthy controls (HCs). The metabolic phenotype of patients with SCD revealed alterations in 139/1773 (7.8%) metabolites at baseline when compared to HCs (false discovery rate-adjusted p < 0.05), including increases of (derivatives of) polyamines, purines, and acyl carnitines. Eight-week treatment with mitapivat in nine patients with SCD altered 85/1773 (4.8%) of the total metabolites and 18/139 (12.9%) of the previously identified altered metabolites in SCD (unadjusted p < 0.05). Effects were observed on a broad spectrum of metabolites and were not limited to glycolytic intermediates. Our results show the relevance of metabolic profiling in SCD, not only to unravel potential pathophysiological pathways and biomarkers in multisystem diseases but also to determine the effect of treatment.

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.

Recent developments in the use of pyruvate kinase activators as a new approach for treating sickle cell disease

ABSTRACT

Pyruvate kinase (PK) is a key enzyme in glycolysis, the sole source of adenosine triphosphate, which is essential for all energy-dependent activities of red blood cells. Activating PK shows great potential for treating a broad range of hemolytic anemias beyond PK deficiency, because they also enhance activity of wild-type PK. Motivated by observations of sickle-cell complications in sickle-trait individuals with concomitant PK deficiency, activating endogenous PK offers a novel and promising approach for treating patients with sickle-cell disease.

Metabolic regulation of erythrocyte development and disorders

The formation of new red blood cells (RBC) (erythropoiesis) has served as a paradigm for understanding cellular differentiation and developmental control of gene expression. The metabolic regulation of this complex, coordinated process remains poorly understood. Each step of erythropoiesis, including lineage specification of hematopoietic stem cells, proliferation, differentiation, and terminal maturation into highly specialized oxygen-carrying cells, has unique metabolic requirements. Developing erythrocytes in mammals are also characterized by unique metabolic events such as loss of mitochondria with switch to glycolysis, ejection of nucleus and organelles, high-level heme and hemoglobin synthesis, and antioxidant requirement to protect hemoglobin molecules. Genetic defects in metabolic enzymes, including pyruvate kinase and glucose-6-phosphate dehydrogenase, cause common erythrocyte disorders, whereas other inherited disorders such as sickle cell disease and β-thalassemia display metabolic abnormalities associated with disease pathophysiology. Here we describe recent discoveries on the metabolic control of RBC formation and function, highlight emerging concepts in understanding the erythroid metabolome, and discuss potential therapeutic benefits of targeting metabolism for RBC disorders.

An update review of new therapies in sickle cell disease: the prospects for drug combinations

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.

Oxygen gradient ektacytometry-derived biomarkers are associated with acute complications in sickle cell disease

ABSTRACT

We investigated the potential of the point of sickling (PoS; the pO2 tension at which red cells start to sickle), determined by oxygen gradient ektacytometry to serve as a biomarker associated with the incidence of acute sickle cell disease-related complications in 177 children and 50 adults. In the pediatric cohort, for every 10 mmHg increase in PoS reflecting a greater likelihood of sickling, the likelihood of an individual experiencing >1 type of acute complication increased; the adjusted odds ratio (aOR) was 1.65. For every 0.1 increase in minimum elongation index (EImin; reflecting improved red blood cell deformability at hypoxia), the aOR was 0.50. In the adult cohort, for every 10 mmHg increase in PoS, we found an aOR of 3.00, although this was not significant after correcting for multiple testing. There was a trend for an association between higher PoS and greater likelihood of vaso-occlusive episodes (VOEs; children aOR, 1.35; adults aOR, 2.22). In children, only EImin was associated with VOEs (aOR, 0.68). When data of both cohorts were pooled, significant associations with PoS and/or EImin were found for all acute complications, independently and when >1 type of acute complication was assessed. These findings indicate that oxygen gradient ektacytometry generates novel biomarkers and provides a rationale for further development of these biomarkers in the assessment of clinical severity, evaluation of novel therapies, and as surrogate clinical trial end points. These biomarkers may be useful in assessing efficacy of novel therapies like pyruvate kinase activators, voxelotor, and L-glutamine.

Mouse models of sickle cell disease: Imperfect and yet very informative

The root cause of sickle cell disease (SCD) has been known for nearly a century, however, few therapies to treat the disease are available. Over several decades of work, with advances in gene editing technology and after several iterations of mice with differing genotype/phenotype relationships, researchers have developed humanized SCD mouse models. However, while a large body of preclinical studies has led to huge gains in basic science knowledge about SCD in mice, this knowledge has not led to the development of effective therapies to treat SCD-related complications in humans, thus leading to frustration with the paucity of translational progress in the SCD field. The use of mouse models to study human diseases is based on the genetic and phenotypic similarities between mouse and humans (face validity). The Berkeley and Townes SCD mice express only human globin chains and no mouse hemoglobin. With this genetic composition, these models present many phenotypic similarities, but also significant discrepancies that should be considered when interpreting preclinical studies results. Reviewing genetic and phenotypic similarities and discrepancies and examining studies that have translated to humans and those that have not, offer a better perspective of construct, face, and predictive validities of humanized SCD mouse models.

One-year safety and efficacy of mitapivat in sickle cell disease: follow-up results of a phase 2, open-label study

Targeting the primary pathogenic event of sickle cell disease (SCD), the polymerization of sickle hemoglobin (HbS), may prevent downstream clinical events. Mitapivat, an oral pyruvate kinase (PK) activator, has therapeutic potential by increasing adenosine triphosphate (ATP) and decreasing 2,3-diphosphoglycerate (2,3-DPG), a glycolytic red blood cell (RBC) intermediate. In the previously reported 8-week dose-finding period of this phase 2, investigator-initiated, open-label study, mitapivat was well tolerated and showed efficacy in SCD. Here, the 1-year fixed-dose extension period is reported in which 9 of 10 included patients (90%) aged ≥16 years with SCD (HbSS, HbS/β0, or HbS/β+) continued with mitapivat. Mostly mild treatment-emergent adverse events (AEs) (most commonly, transaminase increase and headache) were still reported. Apart from the reported nontreatment-related serious AE (SAE) of a urinary tract infection in the dose-finding period, 1 nontreatment-related SAE occurred in the fixed-dose extension period in a patient who died of massive pulmonary embolism due to COVID-19. Importantly, sustained improvement in Hb level (mean increase, 1.1 ± 0.7 g/dL; P = .0014) was seen, which was accompanied by decreases in markers of hemolysis. In addition, the annualized rate of vaso-occlusive events reduced significantly from a historic baseline of 1.33 ± 1.32 to 0.64 ± 0.87 (P = .0489) when combining the dose-finding period and fixed-dose extension period. Cellularly, the ATP:2,3-DPG ratio and Hb-oxygen affinity significantly increased and RBC sickling (point of sickling) nonsignificantly reduced. Overall, this study demonstrated 1-year safety and efficacy of treatment with mitapivat in SCD, supporting further evaluation in ongoing phase 2/3 study (RISE UP, NCT05031780). This trial was registered at https://www.clinicaltrialsregister.eu/ as NL8517 and EudraCT 2019-003438-18.

Pyruvate kinase activators: targeting red cell metabolism in sickle cell disease

Hemoglobin S (HbS) polymerization, red blood cell (RBC) sickling, chronic anemia, and vaso-occlusion are core to sickle cell disease (SCD) pathophysiology. Pyruvate kinase (PK) activators are a novel class of drugs that target RBC metabolism by reducing the buildup of the glycolytic intermediate 2,3-diphosphoglycerate (2,3-DPG) and increasing production of adenosine triphosphate (ATP). Lower 2,3-DPG level is associated with an increase in oxygen affinity and reduction in HbS polymerization, while increased RBC ATP may improve RBC membrane integrity and survival. There are currently 3 PK activators in clinical development for SCD: mitapivat (AG-348), etavopivat (FT-4202), and the second-generation molecule AG-946. Preclinical and clinical data from these 3 molecules demonstrate the ability of PK activators to lower 2,3-DPG levels and increase ATP levels in animal models and patients with SCD, as well as influence a number of potential pathways in SCD, including hemoglobin oxygen affinity, RBC sickling, RBC deformability, RBC hydration, inflammation, oxidative stress, hypercoagulability, and adhesion. Furthermore, early-phase clinical trials of mitapivat and etavopivat have demonstrated the safety and tolerability of PK activators in patients with SCD, and phase 2/3 trials for both drugs are ongoing. Additional considerations for this novel therapeutic approach include the balance between increasing hemoglobin oxygen affinity and tissue oxygen delivery, the cost and accessibility of these drugs, and the potential of multimodal therapy with existing and novel therapies targeting different disease mechanisms in SCD.

Effects of 2,3-DPG knockout on SCD phenotype in Townes SCD model mice

Sickle cell disease (SCD) is a severe, multisystemic hematological disorder that impacts nearly every major organ in adults. The current approved treatments for SCD directly target mutant hemoglobin or address downstream disease pathology. Several compounds targeting reduction of 2,3-DPG by activation of Pyruvate Kinase-R are currently being evaluated in SCD patients. In this study, we genetically engineered a mouse lacking 2,3-DPG on the Townes SCD mouse model background and evaluated the effects of 2,3-DPG loss on disease pathology. Animals lacking 2,3-DPG showed improvements in hematological markers and reductions in RBC sickling relative to native Townes mice, however, minimal difference in organ damage was observed in 2,3-DPG deficient mice compared to native Townes animals. When animals lacking 2,3-DPG were dosed with a compound designed to increase hemoglobin oxygen affinity, oxygen delivery related toxicity was observed.

The evolving treatment landscape for children with sickle cell disease

Sickle cell disease is the most common inherited pathological haemoglobinopathy. Over the past 30 years, disease-related morbidity and mortality have improved in high-income countries due to advances in preventive care and treatments. Established disease-modifying therapies, such as hydroxyurea (hydrocarbamide), are continuing to have an important role in the treatment of sickle cell disease, and newer agents also show promise. In the past 5 years, the US Food and Drug Administration approved three additional sickle cell disease-modifying medications, and new gene therapies have been developed as an alternative curative treatment to haematopoietic stem-cell transplantation. In this Review, we discuss the current treatment landscape for paediatric sickle cell disease and emerging innovations in care. We also review the need for close, long-term management for children receiving newer therapies and the importance of ongoing investment in people with sickle cell disease in low-income and middle-income countries.

Le globule rouge drépanocytaire : données fonctionnelles

Sickle cell anemia is a genetic disorder that affects hemoglobin leading to the production of an abnormal hemoglobin, called HbS. HbS has the property to polymerize under deoxygenated conditions, causing a mechanical distortion of red blood cells; a phenomenon called sickling. These sickle red blood cells are more fragile and rigid, leading to chronic hemolytic anemia and painful vaso-occlusive crises, as well as chronic vascular complications that can affect many organs. The abnormal functional properties of these sickle red blood cells are responsible for a wide range of clinical expression of the disease. HbS polymerization can be influenced by many factors, such as the hydration state of the red blood cells or the affinity of hemoglobin for oxygen. Moreover, the rheological characteristics of red blood cells, including their deformability and aggregation properties, are associated with specific clinical phenotypes. The pro-inflammatory and pro-oxidant state, as well as the repeated polymerization of HbS, accelerate the senescence of sickle red blood cells, promoting the release of microparticles and contributing to vascular dysfunction. Patients' red blood cells also have molecular characteristics that promote their adhesion to the endothelium and other circulating cells, contributing to the onset of vascular complications. Massive intravascular hemolysis, due to increased erythrocyte fragility, is also responsible for chronic vascular complications. These different alterations are privileged therapeutic targets, leading to the emergence of new specific treatments. © 2023 Société nationale française de médecine interne (SNFMI). Published by Elsevier Masson SAS. All rights reserved.

Mitapivat reprograms the RBC metabolome and improves anemia in a mouse model of hereditary spherocytosis

Hereditary spherocytosis (HS) is the most common, nonimmune, hereditary, chronic hemolytic anemia after hemoglobinopathies. The genetic defects in membrane function causing HS lead to perturbation of the RBC metabolome, with altered glycolysis. In mice genetically lacking protein 4.2 (4.2-/-; Epb42), a murine model of HS, we showed increased expression of pyruvate kinase (PK) isoforms in whole and fractioned RBCs in conjunction with abnormalities in the glycolytic pathway and in the glutathione (GSH) system. Mitapivat, a PK activator, metabolically reprogrammed 4.2-/- mouse RBCs with amelioration of glycolysis and the GSH cycle. This resulted in improved osmotic fragility, reduced phosphatidylserine positivity, amelioration of RBC cation content, reduction of Na/K/Cl cotransport and Na/H-exchange overactivation, and decrease in erythroid vesicles release in vitro. Mitapivat treatment significantly decreased erythrophagocytosis and beneficially affected iron homeostasis. In mild-to-moderate HS, the beneficial effect of splenectomy is still controversial. Here, we showed that splenectomy improves anemia in 4.2-/- mice and that mitapivat is noninferior to splenectomy. An additional benefit of mitapivat treatment was lower expression of markers of inflammatory vasculopathy in 4.2-/- mice with or without splenectomy, indicating a multisystemic action of mitapivat. These findings support the notion that mitapivat treatment should be considered for symptomatic HS.

Activation of pyruvate kinase as therapeutic option for rare hemolytic anemias: Shedding new light on an old enzyme

Novel developments in therapies for various hereditary hemolytic anemias reflect the pivotal role of pyruvate kinase (PK), a key enzyme of glycolysis, in red blood cell (RBC) health. Without PK catalyzing one of the final steps of the Embden-Meyerhof pathway, there is no net yield of adenosine triphosphate (ATP) during glycolysis, the sole source of energy production required for proper RBC function and survival. In hereditary hemolytic anemias, RBC health is compromised and therefore lifespan is shortened. Although our knowledge on glycolysis in general and PK function in particular is solid, recent advances in genetic, molecular, biochemical, and metabolic aspects of hereditary anemias have improved our understanding of these diseases. These advances provide a rationale for targeting PK as therapeutic option in hereditary hemolytic anemias other than PK deficiency. This review summarizes the knowledge, rationale, (pre)clinical trials, and future advances of PK activators for this important group of rare diseases.

Hope on the Horizon: New and Future Therapies for Sickle Cell Disease

This article provides an overview of conventional, new, and future treatment options for sickle cell disease (SCD), a genetic disorder affecting the production of hemoglobin. Current treatments include hydroxyurea, a conventional SCD treatment that increases the levels of fetal hemoglobin, and new treatments such as voxelotor, a recently approved SCD treatment that selectively binds hemoglobin, preventing formation of sickled red blood cells. In addition to discussing the mechanisms of action of current SCD treatments, potential side effects are also discussed, highlighting the need for new treatments that can address the limitations of current treatments and improve the quality of life for people with SCD. Future treatments, such as gene therapy, are also explored as promising treatment options for SCD patients.

In vivo evaluation of the effect of sickle cell hemoglobin S, C and therapeutic transfusion on erythrocyte metabolism and cardiorenal dysfunction

Despite a wealth of exploratory plasma metabolomics studies in sickle cell disease (SCD), no study to date has evaluate a large and well phenotyped cohort to compare the primary erythrocyte metabolome of hemoglobin SS, SC and transfused AA red blood cells (RBCs) in vivo. The current study evaluates the RBC metabolome of 587 subjects with sickle cell sickle cell disease (SCD) from the WALK-PHaSST clinical cohort. The set includes hemoglobin SS, hemoglobin SC SCD patients, with variable levels of HbA related to RBC transfusion events. Here we explore the modulating effects of genotype, age, sex, severity of hemolysis, and transfusion therapy on sickle RBC metabolism. Results show that RBCs from patients with Hb SS genotypes-compared to AA RBCs from recent transfusion events or SC RBCs-are characterized by significant alterations of RBC acylcarnitines, pyruvate, sphingosine 1-phosphate, creatinine, kynurenine and urate metabolism. Surprisingly, the RBC metabolism of SC RBCs is dramatically different from SS, with all glycolytic intermediates significantly elevated in SS RBCs, with the exception of pyruvate. This result suggests a metabolic blockade at the ATP-generating phosphoenolpyruvate to pyruvate step of glycolysis, which is catalyzed by redox-sensitive pyruvate kinase. Metabolomics, clinical and hematological data were collated in a novel online portal. In conclusion, we identified metabolic signatures of HbS RBCs that correlate with the degree of steady state hemolytic anemia, cardiovascular and renal dysfunction and mortality.

CRISPR/Cas9-based gene-editing technology for sickle cell disease

Sickle cell disease (SCD) is the most common monogenic hematologic disorder and is essentially congenital hemolytic anemia caused by an inherited point mutation in the β-globin on chromosome 11. Although the genetic basis of SCD was revealed as early as 1957, treatment options for SCD have been very limited to date. Hematopoietic stem cell transplantation (HSCT) was thought to hold promise as a cure for SCD, but the available donors were still only 15% useful. Gene therapy has advanced rapidly into the 21st century with the promise of a cure for SCD, and gene editing strategies based on the cluster-based regularly interspaced short palindromic repeat sequence (CRISPR)/Cas9 system have revolutionized the field of gene therapy by precisely targeting genes. In this paper, we review the pathogenesis and therapeutic approaches of SCD, briefly summarize the delivery strategies of CRISPR/Cas9, and finally discuss in depth the current status, application barriers, and solution directions of CRISPR/Cas9 in SCD. Through the review in this paper, we hope to provide some references for gene therapy in SCD.

Erythrocyte pyruvate kinase activation in red cell disorders

PURPOSE OF REVIEW

In red cells, pyruvate kinase is a key enzyme in the final step of glycolytic degradative process, which generates a constant energy supply via ATP production. This commentary discusses recent findings on pyruvate kinase activators as new therapeutic option in hereditary red cell disorders such as thalassemic syndromes or sickle cell disease (SCD).

RECENT FINDINGS

Mitapivat and etavopivat are two oral pyruvate kinase activators. Studies in a mouse model for β thalassemia have shown beneficial effects of mitapivat on both red cell survival and ineffective erythropoiesis, with an amelioration of iron homeostasis. This was confirmed in a proof-of-concept study in patients with nontransfusion-dependent thalassemias. Both mitapivat and etavopivat have been evaluated in mouse models for SCD, showing an increased 2-3DPG/ATP ratio and a reduction in haemolysis as well as in sickling. These data were confirmed in proof-of-concept clinical studies with both molecules carried in patients with SCD.

SUMMARY

Preclinical and clinical evidence indicate that pyruvate kinase activators represent new therapeutic option in hemoglobinopathies or SCD. Other red cell disorders such as hereditary spherocytosis or hereditary anaemias characterized by defective erythropoiesis might represent additional areas to investigate the therapeutic impact of pyruvate kinase activators.

Updates and advances in pyruvate kinase deficiency

Mutations in the PKLR gene lead to pyruvate kinase (PK) deficiency, causing chronic hemolytic anemia secondary to reduced red cell energy, which is crucial for maintenance of the red cell membrane and function. Heterogeneous clinical manifestations can result in significant morbidity and reduced health-related quality of life. Treatment options have historically been limited to supportive care, including red cell transfusions and splenectomy. Current disease-modifying treatment considerations include an oral allosteric PK activator, mitapivat, which was recently approved for adults with PK deficiency, and gene therapy, which is currently undergoing clinical trials. Studies evaluating the role of PK activators in other congenital hemolytic anemias are ongoing. The long-term effect of treatment with disease-modifying therapy in PK deficiency will require continued evaluation.

Management of Older Adults with Sickle Cell Disease: Considerations for Current and Emerging Therapies

People with sickle cell disease (SCD) are living longer than ever before, with the median survival increasing from age 14 years in 1973, beyond age 40 years in the 1990s, and as high as 61 years in recent cohorts from academic centers. Improvements in survival have been attributed to initiatives, such as newborn screening, penicillin prophylaxis, vaccination against encapsulated organisms, better detection and treatment of splenic sequestration, and improved transfusion support. There are an estimated 100,000 people living with SCD in the United States and millions of people with SCD globally. Given that the number of older adults with SCD will likely continue to increase as survival improves, better evidence on how to manage this population is needed. When managing older adults with SCD (defined herein as age ≥ 40 years), healthcare providers should consider the potential pitfalls of extrapolating evidence from existing studies on current and emerging therapies that have typically been conducted with participants at mean ages far below 40 years. Older adults with SCD have historically had little to no representation in clinical trials; therefore, more guidance is needed on how to use current and emerging therapies in this population. This article summarizes the available evidence for managing older adults with SCD and discusses potential challenges to using approved and emerging drugs in this population.

In vivo evaluation of the effect of sickle cell hemoglobin S, C and therapeutic transfusion on erythrocyte metabolism and cardiorenal dysfunction

Despite a wealth of exploratory plasma metabolomics studies in sickle cell disease (SCD), no study to date has evaluate a large and well phenotyped cohort to compare the primary erythrocyte metabolome of hemoglobin SS, SC and transfused AA red blood cells (RBCs) in vivo . The current study evaluates the RBC metabolome of 587 subjects with sickle cell sickle cell disease (SCD) from the WALK-PHaSST clinical cohort. The set includes hemoglobin SS, hemoglobin SC SCD patients, with variable levels of HbA related to RBC transfusion events, and HbF related to hydroxyurea therapy. Here we explore the modulating effects of genotype, age, sex, severity of hemolysis, and hydroxyurea and transfusion therapy on sickle RBC metabolism. Data - collated in an online portal - show that the Hb SS genotype is associated with significant alterations of RBC acylcarnitines, pyruvate, sphingosine 1-phosphate, creatinine, kynurenine and urate metabolism. Surprisingly, the RBC metabolism of SC RBCs is dramatically different from SS, with all glycolytic intermediates significantly elevated in SS RBCs, with the exception of pyruvate. This result suggests a metabolic blockade at the ATP-generating phosphoenolpyruvate to pyruvate step of glycolysis, which is catalyzed by redox-sensitive pyruvate kinase. Increasing in vivo concentrations of HbA improved glycolytic flux and normalized the HbS erythrocyte metabolome. An unexpectedly limited metabolic effect of hydroxyurea and HbF was observed, possibly related to the modest induction of HbF in this cohort. The metabolic signature of HbS RBCs correlated with the degree of steady state hemolytic anemia, cardiovascular and renal dysfunction and mortality.

Key points

In vivo dysregulation of RBC metabolism by HbS is evaluated by metabolic profiling of 587 patients with variable HbA, HbC and HbF levels;RBC acyl-carnitines, urate, pyruvate metabolism, S1P, kynurenine relate to hemolysis and cardiorenal dysfunction, respond to transfusion.

Risk of vaso-occlusive episodes in patients with sickle cell disease exposed to systemic corticosteroids: a comprehensive review

INTRODUCTION

Sickle cell disease (SCD) is the most frequent inherited disorder in the world. It is caused by a single amino acid mutation on the beta-globin chain, which lead to red blood cell deformation, haemolysis, and chronic inflammation. Clinical consequences are vaso-occlusives crisis, acute chest syndrome, thrombosis, infection, and chronic endothelial injury.

AREAS COVERED

Corticosteroids are an old therapeutic class, that are inexpensive and widely available, which can be administered in different forms. Their adverse effects are numerous and well-known. This class could appear to be useful in SCD treatment due to its anti-inflammatory effect. Moreover, corticosteroids remain an essential therapeutic class for many indications, besides SCD. Although specific adverse effects of corticosteroids have been suspected in SCD patients for decades, recent papers has reported strong evidence of specific and severe adverse effects in this population. Based on a literature review, we will discuss pathophysiological considerations, consequences, and practical use of corticosteroids in SCD.

EXPERT OPINION

High corticosteroid doses, for any indication , induce vaso-occlusive crises, acute chest syndrome, and re-hospitalization in patients with SCD. There is no evidence of any benefits of corticosteroid use in the SCD acute events. Prevention by hydroxyurea and/or red blood cell transfusion or exchange should be discussed when corticosteroid use is indispensable.

Phenotypic screening of the ReFRAME drug repurposing library to discover new drugs for treating sickle cell disease

Stem cell transplantation and genetic therapies offer potential cures for patients with sickle cell disease (SCD), but these options require advanced medical facilities and are expensive. Consequently, these treatments will not be available for many years to the majority of patients suffering from this disease. What is urgently needed now is an inexpensive oral drug in addition to hydroxyurea, the only drug approved by the FDA that inhibits sickle-hemoglobin polymerization. Here, we report the results of the first phase of our phenotypic screen of the 12,657 compounds of the Scripps ReFRAME drug repurposing library using a recently developed high-throughput assay to measure sickling times following deoxygenation to 0% oxygen of red cells from sickle trait individuals. The ReFRAME library is a very important collection because the compounds are either FDA-approved drugs or have been tested in clinical trials. From dose-response measurements, 106 of the 12,657 compounds exhibit statistically significant antisickling at concentrations ranging from 31 nM to 10 μM. Compounds that inhibit sickling of trait cells are also effective with SCD cells. As many as 21 of the 106 antisickling compounds emerge as potential drugs. This estimate is based on a comparison of inhibitory concentrations with free concentrations of oral drugs in human serum. Moreover, the expected therapeutic potential for each level of inhibition can be predicted from measurements of sickling times for cells from individuals with sickle syndromes of varying severity. Our results should motivate others to develop one or more of these 106 compounds into drugs for treating SCD.

An evaluation of mitapivat for the treatment of hemolytic anemia in adults with pyruvate kinase deficiency

INTRODUCTION

Pyruvate kinase deficiency (PKD) is the most common cause of congenital nonspherocytic hemolytic anemia. Until recently, treatment had been limited to supportive management including red blood cell transfusions, splenectomy, and management of chronic disease complications such as iron overload and decreased bone mineral density.

AREAS COVERED

We discuss preclinical data and phase 1, 2, and 3 clinical studies evaluating mitapivat for adult patients with hemolytic anemia secondary to PKD. Mitapivat has been shown to offer early and durable improvement in hemoglobin with reduction in transfusion burden, and preliminary data suggest it can induce a negative iron balance in many patients without the use of dedicated iron chelators.

EXPERT OPINION

Mitapivat is a first-in-class allosteric activator of pyruvate kinase and the first FDA-approved disease directed therapy for PKD. It has a favorable safety profile and clear clinical efficacy. Given the considerable genetic heterogeneity of PKD and the rapid effect on improving hemoglobin and reducing hemolysis, a therapeutic trial of mitapivat should be considered in all patients with PKD who are not homozygous for the PKLR R479H mutation. Further investigations are needed regarding long-term safety and efficacy profiles and whether long-term PKD-associated complications can be reduced or even reversed.

Precision Medicine and Sickle Cell Disease

Sickle cell disease (SCD) is characterized by variable clinical outcomes, with some patients suffering life-threatening complications during childhood, and others living relatively symptom-free into old age. Because of this variability, there is an important potential role for precision medicine, in which particular different treatments are selected for different groups of patients. However, the application of precision medicine in SCD is limited by difficulties in identifying different prognostic groups and the small number of available treatments. The main genetic determinant of outcomes in SCD is the underlying β-globin genotype, with sickle cell anemia (HbSS) and hemoglobin SC disease (HbSC) forming the 2 major forms of the disease in most populations of African origin. Although there are clear differences in clinical outcomes between these conditions, treatments approaches are very similar, with little evidence on how to treat HbSC in particular. Other genomic information, such as the co-inheritance of α-thalassemia, or high fetal hemoglobin (HbF) levels, is of some prognostic value but insufficient to determine treatments. Precision medicine is further limited by the fact that the 2 main drugs used in SCD, penicillin and hydroxyurea, are currently recommended for all patients. Newer treatments, such as crizanlizumab and voxelotor, raise the possibility that groups will emerge who respond best to particular drugs or combinations. Perhaps the best current example of precision medicine in SCD is the selective use of blood transfusions as primary stroke prevention in children with evidence of cerebral vasculopathy. More precise treatments may emerge as we understand more about the pathology of SCD, including problems with erythropoiesis.