Voxelotor: alteration of sickle cell disease pathophysiology by a first-in-class polymerization inhibitor

Hydroxyurea in the sickle cell disease modern era

INTRODUCTION

Sickle cell disease is an inherited disorder characterized by hemoglobin S polymerization leading to vaso-occlusion and hemolytic anemia. These result in a variety of pathological events, causing both acute and chronic complications. Millions around the world are affected by sickle cell disease with predominance in sub-Saharan Africa. Hydroxyurea was the first drug approved for use in sickle cell disease to reduce the occurrence of painful crises and blood transfusions in patients with frequent, moderate to severe painful crises.

AREAS COVERED

With the development of new therapeutics, the role of hydroxyurea is evolving. This narrative review aims to provide clinical data, safety information, and supplementary evidence for the role of hydroxyurea in the current era of sickle cell disease. A comprehensive literature search of databases, including PubMed and Cochrane Library, was conducted from 1963 to 2024.

EXPERT OPINION

Even though new medications have been approved for sickle cell disease, hydroxyurea remains the gold standard. Hydroxyurea is not only a disease modifier but it has additional clinical benefits, it is affordable, and its longevity has prompted expanded research in areas such as underutilization and pharmacogenomics. As the treatment landscape evolves, hydroxyurea's long-standing record of efficacy and safety continues to support its role as a key agent in disease management.

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.

Impacts of oxidative stress and anti-oxidants on the development, pathogenesis, and therapy of sickle cell disease: A comprehensive review

Sickle cell disease (SCD) is the most severe monogenic hemoglobinopathy caused by a single genetic mutation that leads to repeated polymerization and depolymerization of hemoglobin resulting in intravascular hemolysis, cell adhesion, vascular occlusion, and ischemia-reperfusion injury. Hemolysis causes oxidative damage indirectly by generating reactive oxygen species through various pathophysiological mechanisms, which include hemoglobin autoxidation, endothelial nitric oxide synthase uncoupling, reduced nitric oxide bioavailability, and elevated levels of asymmetric dimethylarginine. Red blood cells have a built-in anti-oxidant system that includes enzymes like sodium dismutase, catalase, and glutathione peroxidase, along with free radical scavenging molecules, such as vitamin C, vitamin E, and glutathione, which help them to fight oxidative damage. However, these anti-oxidants may not be sufficient to prevent the effects of oxidative stress in SCD patients. Therefore, in line with a recent FDA request that the focus to be placed on the development of innovative therapies for SCD that address the root cause of the disease, there is a need for therapies that target oxidative stress and restore redox balance in SCD patients. This review summarizes the current state of knowledge regarding the role of oxidative stress in SCD and the potential benefits of anti-oxidant therapies. It also discusses the challenges and limitations of these therapies and suggests future directions for research and development.

Child Health and the Pediatric Hematology-Oncology Workforce: 2020-2040

Pediatric hematology-oncology (PHO) is 1 of the oldest recognized pediatric subspecialities. PHO physicians care for infants, children, adolescents, and young adults with all types of cancer and nonmalignant blood conditions, in many cases temporarily assuming the role of a primary care physician because of the complexity and intensity of treatment. However, the number of clinically active PHO subspecialists needed to care for children in the United States remains unknown. Recent papers suggest a potential oversaturation of PHO physicians in some geographic areas. This article is part of a Pediatrics supplement focused on projecting the future supply of the pediatric subspecialty workforce. It draws on information available in the literature, data from the American Board of Pediatrics, and findings from a new microsimulation model estimating the future supply of pediatric subspecialists through 2040. The model predicts a workforce growth in PHO subspecialists of 66% by 2040. Alternative scenarios, including changes in clinical time and fellowship size, resulted in a difference in growth of ±18% from baseline. The model also forecasts significant geographic maldistribution. For example, the current workforce is concentrated in the Northeast Census region and the model predicts the New England Census division will have a 2.9-fold higher clinical workforce equivalent per 100 000 children aged 0 to 18 years than the Mountain Census division by 2040. These findings suggest potential opportunities to improve the PHO subspecialty workforce and the outcomes and experiences of its patient population through educational changes, practice initiatives, policy interventions, and dedicated research.

Doping control approach: Identification of equine in vitro metabolites of voxelotor (GBT440), a hemoglobin S polymerization inhibitor

RATIONALE

Sickle cell disease, a debilitating genetic disorder affecting numerous newborns globally, has historically received limited attention in pharmaceutical research. However, recent years have witnessed a notable shift, with the Food and Drug Administration approving three innovative disease-modifying medications. Voxelotor, also known as GBT440, is a promising compound that effectively prevents sickling, providing a safe approach to alleviate chronic hemolytic anemia in sickle cell disease. It is a novel, orally bioavailable small molecule that inhibits hemoglobin S polymerization by enhancing oxygen affinity to hemoglobin. The investigation demonstrated that voxelotor led to an unintended elevation of hemoglobin levels in healthy individuals by increasing serum erythropoietin levels.

METHODS

Voxelotor and its metabolites in an in vitro setting utilizing equine liver microsomes were discussed. Plausible structures of the identified metabolites were inferred through the application of liquid chromatography in conjunction with high-resolution mass spectrometry.

RESULTS

Under the experimental conditions, a total of 31 metabolites were detected, including 16 phase I metabolites, two phase II metabolites, and 13 conjugates of phase I metabolites. The principal phase I metabolites were generated through processes such as hydroxylation, reduction, and dissociation. The presence of glucuronide and sulfate conjugates of the parent drug were also observed, along with hydroxylated, reduced, and dissociated analogs.

CONCLUSIONS

The data acquired will accelerate the identification of voxelotor and related compounds, aiding in the detection of their illicit use in competitive sports. It is crucial to emphasize that the metabolites detailed in this manuscript were identified through in vitro experiments and their detection in an in vivo study may not be guaranteed.

Practical Guidance for the Use of Voxelotor in the Management of Sickle Cell Disease

Sickle cell disease (SCD) is one of the most common inherited blood disorders. Deoxygenated hemoglobin S (HbS) polymerizes and causes anemia and various end organ effects. Voxelotor acts by increasing HbS oxygen affinity, decreasing anemia and hemolysis. Voxelotor is approved for use in individuals with SCD age 4 years and older. Phase 3 trials demonstrated an increase in hemoglobin levels and a decrease in markers of hemolysis; however, data or benefits related to clinical and quality of life outcomes are relatively limited and varied across different studies. This review summarizes the published clinical trials and research studies focused on the use of voxelotor in SCD to provide an evidence-based practical guide for hematology providers on its utilization in clinical settings, including physicians and independent licensed practitioners.

OcclusionChip: A functional microcapillary occlusion assay complementary to ektacytometry for detection of small-fraction red blood cells with abnormal deformability

Red blood cell (RBC) deformability is a valuable hemorheological biomarker that can be used to assess the clinical status and response to therapy of individuals with sickle cell disease (SCD). RBC deformability has been measured by ektacytometry for decades, which uses shear or osmolar stress. However, ektacytometry is a population based measurement that does not detect small-fractions of abnormal RBCs. A single cell-based, functional RBC deformability assay would complement ektacytometry and provide additional information. Here, we tested the relative merits of the OcclusionChip, which measures RBC deformability by microcapillary occlusion, and ektacytometry. We tested samples containing glutaraldehyde-stiffened RBCs for up to 1% volume fraction; ektacytometry detected no significant change in Elongation Index (EI), while the OcclusionChip showed significant differences in Occlusion Index (OI). OcclusionChip detected a significant increase in OI in RBCs from an individual with sickle cell trait (SCT) and from a subject with SCD who received allogeneic hematopoietic stem cell transplant (HSCT), as the sample was taken from normoxic (pO2:159 mmHg) to physiologic hypoxic (pO2:45 mmHg) conditions. Oxygen gradient ektacytometry detected no difference in EI for SCT or HSCT. These results suggest that the single cell-based OcclusionChip enables detection of sickle hemoglobin (HbS)-related RBC abnormalities in SCT and SCD, particularly when the HbS level is low. We conclude that the OcclusionChip is complementary to the population based ektacytometry assays, and providing additional sensitivity and capacity to detect modest abnormalities in red cell function or small populations of abnormal red cells.

Emerging drugs for the treatment of sickle cell disease: a review of phase II/III trials

INTRODUCTION

The substitution of glutamic acid by valine on the ß-globin gene produces the hemoglobin S variant responsible for sickle cell disease (SCD), a disorder that affects millions of people worldwide and leads to acute and cumulative organ damage. Even though life expectancy has significantly improved where the best medical care is available, there are still few therapeutic options for SCD and those are limited by their availability, cost, and individual toxicities.

AREAS COVERED

This review summarizes the clinical data on current treatments for SCD and emerging therapies studied in the acute setting as well as potential disease-modifying agents, with an emphasis on the FDA-approved agents.

EXPERT OPINION

Hydroxyurea has been a gold standard for two decades, showing benefits in acute complications and overall survival in sickle cell anemia, although data is lacking for certain genotypes such as hemoglobin SC. As progress is made in our understanding of the pathophysiological networks characterizing SCD, numerous pathways appear to be targetable, with L-glutamine, Crizanlizumab and Voxelotor now approved by the FDA. Pursuing a multi-agent approach could alter the disease course in a more effective fashion and provide an alternative option to curative therapies, but longer clinical studies are needed.

Neurocognitive risk in sickle cell disease: Utilizing neuropsychology services to manage cognitive symptoms and functional limitations

Sickle cell disease (SCD) is an inherited blood disorder that is associated with developmental delays and neurocognitive deficits. This review details key findings related to neurocognitive outcomes for children and adults with emphasis on the impact of neurological correlates and disease severity. Associations between neurocognition, demographic factors and social determinants of health are also reviewed. Emerging literature has reported on the neurocognitive impact of SCD in children and adolescents in Africa and Europe, including children from immigrant communities. Neurocognitive deficits are linked to poor functional outcomes, including transition from paediatric to adult care, medication adherence and unemployment. Integrating neuropsychology into multidisciplinary care for individuals with SCD can assist with identification and management of neurocognitive concerns, intervention development, individualized care plan development and continued multidisciplinary research.

Quercetin Completely Ameliorates Hypoxia-Reoxygenation-Induced Pathophysiology Severity in NY1DD Transgenic Sickle Mice: Intrinsic Mild Steady State Pathophysiology of the Disease in NY1DD Is Also Reversed

The vaso-occlusive crisis (VOC) is a major complication of sickle cell disease (SCD); thus, strategies to ameliorate vaso-occlusive episodes are greatly needed. We evaluated the therapeutic benefits of quercetin in a SCD transgenic sickle mouse model. This disease model exhibited very mild disease pathophysiology in the steady state. The severity of the disease in the NY1DD mouse was amplified by subjecting mice to 18 h of hypoxia followed by 3 h of reoxygenation. Quercetin (200 mg/kg body weight) administered to hypoxia challenged NY1DD mice in a single intraperitoneal (i.p.) dose at the onset of reoxygenation completely ameliorated all hypoxia reoxygenation (H/R)-induced pathophysiology. Additionally, it ameliorated the mild intrinsic steady state pathophysiology. These results are comparable with those seen with semisynthetic supra plasma expanders. In control mice, C57BL/6J, hypoxia reoxygenation-induced vaso-occlusion was at significantly lower levels than in NY1DD mice, reflecting the role of sickle hemoglobin (HbS) in inducing vaso-occlusion; however, the therapeutic benefits from quercetin were significantly muted. We suggest that these findings represent a unique genotype of the NY1DD mice, i.e., the presence of high oxygen affinity red blood cells (RBCs) with chimeric HbS, composed of mouse α-chain and human β^S-chain, as well as human α-chain and mouse β-chain (besides HbS). The anti-anemia therapeutic benefits from high oxygen affinity RBCs in these mice exert disease severity modifications that synergize with the therapeutic benefits of quercetin. Combining the therapeutic benefits of high oxygen affinity RBCs generated in situ by chemical or genetic manipulation with the therapeutic benefits of antiadhesive therapies is a novel approach to treat sickle cell patients with severe pathophysiology.

Genome-based therapeutic interventions for β-type hemoglobinopathies

For decades, various strategies have been proposed to solve the enigma of hemoglobinopathies, especially severe cases. However, most of them seem to be lagging in terms of effectiveness and safety. So far, the most prevalent and promising treatment options for patients with β-types hemoglobinopathies, among others, predominantly include drug treatment and gene therapy. Despite the significant improvements of such interventions to the patient's quality of life, a variable response has been demonstrated among different groups of patients and populations. This is essentially due to the complexity of the disease and other genetic factors. In recent years, a more in-depth understanding of the molecular basis of the β-type hemoglobinopathies has led to significant upgrades to the current technologies, as well as the addition of new ones attempting to elucidate these barriers. Therefore, the purpose of this article is to shed light on pharmacogenomics, gene addition, and genome editing technologies, and consequently, their potential use as direct and indirect genome-based interventions, in different strategies, referring to drug and gene therapy. Furthermore, all the latest progress, updates, and scientific achievements for patients with β-type hemoglobinopathies will be described in detail.