Safety and efficacy of mitapivat, an oral pyruvate kinase activator, in sickle cell disease: A phase 2, open-label study

Sickle cell disease: combination new therapies vs. CRISPR-Cas9 potential and challenges - review article

In 2022, sickle cell disease (SCD) continues to affect the lives of millions of people, being one of the most frequently inherited blood disorders worldwide. Recently, several new therapies have been FDA approved for the treatment of SCD. The complexity of the pathophysiology of sickling has given opportunity to the evolution of several modalities of therapies. Nonetheless, the potential for complementary targeting of HbS polymerization, vasocclusion, and other inflammatory pathways remains controversial. None of these drugs can be considered a single curative line of treatment. With the advancement of CRISPR/Cas9 technology, autologous transplant of gene-edited hematopoietic stem cells could possibly provide a cure for most patients with SCD. The advantage of this approach over the conventional stem cell transplantation is that it decreases the need for immuno-suppressive drugs and the risk of graft-versus-host disease. In addition, recent technological advances can reduce the off-target effects, but long-term monitoring is needed to ensure the reliability of these methods in the clinical setting. This review explores the efficacy and safety of combination therapies and contrasting this alternative with the challenges that exist with sickle cell gene therapy using CRISPR.

Designing a single-arm phase 2 clinical trial of mitapivat for adult patients with erythrocyte membranopathies (SATISFY): a framework for interventional trials in rare anaemias - pilot study protocol

INTRODUCTION

Membranopathies encompass haemolytic disorders arising from genetic variants in erythrocyte membrane proteins, including hereditary spherocytosis and stomatocytosis. Congenital dyserythropoietic anaemia type II (CDA II) is associated with the SEC23B gene and can exhibit phenotypic similarities to membranopathies. Current treatment options for these conditions, apart from splenectomy, are primarily supportive. Mitapivat, a novel pyruvate kinase (PK) activator, has demonstrated efficacy in increasing haemoglobin levels and reducing haemolysis in patients with PK deficiency, thalassemia, sickle cell disease and a mouse model of hereditary spherocytosis.

METHODS AND ANALYSES

Safety and efficacy of mitapivat sulfate in adult patients with erythrocyte membranopathies (SATISFY) is a prospective, multicentre, single-arm phase two trial involving approximately 25 adult patients (≥18 years) diagnosed with a membranopathy or CDA II. During the 8-week dose escalation period, subjects will receive an initial dose of 50 mg mitapivat two times per day and may increase to 100 mg two times per day at week 4 based on the safety and changes in haemoglobin levels. Patients tolerating mitapivat well may be eligible to continue in two consecutive 24-week fixed dose periods.The primary objective of this study is to evaluate the safety of mitapivat, assessed through the occurrence of treatment-emergent adverse events. Secondary objectives include assessing the effects of mitapivat on haemoglobin levels, haemolysis, erythropoiesis, patient-reported outcome measures and spleen size.SATISFY aims to assess the safety and efficacy of mitapivat in adult patients with red blood cell membranopathies and CDA II, with the aim of establishing proof-of-concept in patients living with these rare conditions.

ETHICS AND DISSEMINATION

NCT05935202/CTIS:2023-503271-24-01. Findings will be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

Clinicaltrials.gov, NCT05935202. CTIS:2023-503271-24-01. Registered 07-July-2023. Protocol number: 2.1. https://clinicaltrials.gov/study/NCT05935202.

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.

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.

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.

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.

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.

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.

The invisible string of coagulation, complement, iron, and inflammation in sickle cell disease

PURPOSE OF REVIEW

This review provides an update on recent advances in mechanistic studies of thromboinflammatory mechanisms that contribute to the disease pathology in sickle cell disease (SCD). There is a focus on novel pathways, clinical relevance, and translational potential of these findings. We hope to encourage more advances in this area to reduce organ damage in young patients prior to gene therapy, and to serve the aging SCD patient population.

RECENT FINDINGS

Novel insights into the roles of neutrophils, the ADAMTS-13/VWF axis, oxidative stress, and the intrinsic coagulation cascade, as well as relevant clinical trials, are discussed.

SUMMARY

Several studies implicate dysregulation of the ADAMTS-13/VWF axis as playing a major role in vaso-occlusive events (VOE) in SCD. Another highlight is reducing iron overload, which has beneficial effects on erythrocyte and neutrophil function that reduce VOE and inflammation. Multiple studies suggest that targeting HO-1/ROS in erythrocytes, platelets, and endothelium can attenuate disease pathology. New insights into coagulation activation identify intrinsic coagulation factor XII as a central regulator of many thromboinflammatory pathologies in SCD. The complement cascade and modulators of neutrophil function and release of neutrophil extracellular traps are also discussed.

Emerging Therapies and Advances in Sickle Cell Disease with a Focus on Renal Manifestations

The underlying mechanisms of disease in sickle cell disease (SCD) contribute to a multifaceted nephropathy, commonly manifested as albuminuria. In severe SCD genotypes ( e.g. , Hemoglobin SS [HbSS]), albuminuria and CKD are major predictors of mortality in this population. Therefore, the monitoring and management of renal function is an intrinsic part of comprehensive care in SCD. Management of nephropathy in SCD can be accomplished with SCD-directed therapies and/or CKD-directed therapies. In the past 5 years, novel disease-modifying and palliative therapies have been approved in SCD to target aspects of the disease, such as anemia, inflammation, and vasculopathy. Along with conventional hydroxyurea and chronic transfusion, l -glutamine, crizanlizumab, and voxelotor have all been shown to mitigate some adverse effect of SCD, and their effect on nephropathy is being investigated. CKD-directed therapies such as renin-angiotensin-aldosterone system blockers have long been used in SCD nephropathy; however, more complete long-term studies on benefits are needed. Given the effect of renal disease on survival, further assessment of the mechanisms and efficacy of these SCD-directed or CKD-directed therapeutic agents is essential.

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.

Rise of the planet of rare anemias: An update on emerging treatment strategies

Therapeutic options for rare congenital (hemoglobinopathies, membrane and enzyme defects, congenital dyserythropoietic anemia) and acquired anemias [warm autoimmune hemolytic anemia (wAIHA), cold agglutinin disease CAD, paroxysmal nocturnal hemoglobinuria (PNH), and aplastic anemia (AA)] are rapidly expanding. The use of luspatercept, mitapivat and etavopivat in beta-thalassemia and pyruvate kinase deficiency (PKD) improves transfusion dependence, alleviating iron overload and long-term complications. Voxelotor, mitapivat, and etavopivat reduce vaso-occlusive crises in sickle cell disease (SCD). Gene therapy represents a fascinating approach, although patient selection, the toxicity of the conditioning regimens, and the possible long-term safety are still open issues. For acquired forms, wAIHA and CAD will soon benefit from targeted therapies beyond rituximab, including B-cell/plasma cell targeting agents (parsaclisib, rilzabrutinib, and isatuximab for wAIHA), complement inhibitors (pegcetacoplan and sutimlimab for CAD, ANX005 for wAIHA with complement activation), and inhibitors of extravascular hemolysis in the reticuloendothelial system (fostamatinib and FcRn inhibitors in wAIHA). PNH treatment is moving from the intravenous anti-C5 eculizumab to its long-term analog ravulizumab, and to subcutaneous and oral proximal inhibitors (anti-C3 pegcetacoplan, factor D and factor B inhibitors danicopan and iptacopan). These drugs have the potential to improve patient convenience and ameliorate residual anemia, although patient compliance becomes pivotal, and long-term safety requires further investigation. Finally, the addition of eltrombopag significantly ameliorated AA outcomes, and data regarding the alternative agent romiplostim are emerging. The accelerated evolution of treatment strategies will need further effort to identify the best candidate for each treatment in the precision medicine era.

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.