A phase 1/2 ascending dose study and open-label extension study of voxelotor in patients with sickle cell disease

Concentration of voxelotor in sickle cell disease can be estimated using electrophoresis and high-performance liquid chromatography

OBJECTIVES

Voxelotor can increase hemoglobin levels in patients living with sickle cell disease (SCD). A clinician who is monitoring voxelotor response may want to know whole-blood voxelotor concentration, but this cannot be measured in most clinical settings. However, voxelotor has been demonstrated to cause "peak splitting" in common methods of hemoglobin measurement such as capillary zone electrophoresis (CZE) and high-performance liquid chromatography (HPLC). We hypothesized that we could use the size of the peak split to estimate the whole-blood concentration.

METHODS

Blood from people with SCD was dosed with known concentrations of voxelotor, and multiparameter regression was used to derive the relationship of voxelotor concentration to the degree of peak splitting observed. To validate these equations, 21 patients started on voxelotor at 1500 mg/d had blood samples drawn at days 0, 14, 30, and 60. Samples were sent out for gold standard voxelotor concentration testing. The derived equations were then used to calculate voxelotor concentration.

RESULTS

Calculated concentrations correlated strongly with measured concentrations for both CZE (R2 = 0.83, P < .001) and HPLC (R2 = 0.76, P < .001). Voxelotor concentration also had a significant effect on increases in hemoglobin (R2 = 0.40, P < .001).

CONCLUSIONS

Thus, peak splitting CZE and HPLC can be used to estimate voxelotor concentration.

Advances in pharmacotherapy for sickle cell disease: what is the current state of play?

INTRODUCTION

Despite over 100 years of neglect and insufficient funding, sickle cell disease has risen to the top of the discussions due to the recent approval of two new genetic therapies. Prior to these approvals, there were only four prior approved medications for sickle cell disease in spite of being the most common inherited blood disorder. The advent and expense of these new genetic therapies have finally brought the trials and tribulations associated with SCD including the suffering and early mortality of affected individuals to the much-needed limelight. Presently, questions about how these therapies will be used and what that means for ongoing pharmaceutical development remain.

AREAS COVERED

Here, we wish to highlight the current medications and treatments for SCD using already published literature as well as scrutinize the tedious process of implementation for these newly approved commercial genetic therapies.

EXPERT OPINION

In our expert opinion, despite the progress we have made, significant challenges remain and the most important requirement for any of these treatments is ensuring all affected individuals have access to a sickle cell specialist who can provide comprehensive care.

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.

Evaluation of the effect of voxelotor and darbepoetin alfa on hemoglobin levels in patients with sickle cell disease

BACKGROUND

To date, there is limited evidence on patients utilizing both voxelotor and darbepoetin alfa and its impact on hemoglobin levels. The objective is to evaluate the effect of voxelotor and darbepoetin alfa on hemoglobin levels in patients with SCD.

RESEARCH DESIGN AND METHODS

This was a retrospective chart review study that assessed the primary independent variable as the utilization of either voxelotor alone, darbepoetin alfa alone, or the concurrent administration of voxelotor and darbepoetin alfa. Descriptive statistics were utilized to obtain the mean standard deviation for numerical variables and proportions for categorical variables.

RESULTS

A total of 23 participants were included in this study. When comparing baseline to 2 months and 3 months, participants on voxelotor alone experienced a 3% decrease and a 6.6% increase in hemoglobin, darbepoetin alfa alone group a 4.3% decrease and a 0.6% increase in hemoglobin and voxelotor and darbepoetin group a 4.4% decrease and a 0.5% decrease in hemoglobin levels. Fifty percent of the participants in the voxelotor group and 6 (66.7%) participants in the voxelotor plus darbepoetin alfa group experienced adverse drug events.

CONCLUSIONS

Voxelotor resulted in a clinically significant difference in the percent change of hemoglobin from baseline to 3 months.

The influence of voxelotor on cerebral blood flow and oxygen extraction in pediatric sickle cell disease

ABSTRACT

Voxelotor is an inhibitor of sickle hemoglobin polymerization that is used to treat sickle cell disease. Although voxelotor has been shown to improve anemia, the clinical benefit on the brain remains to be determined. This study quantified the cerebral hemodynamic effects of voxelotor in children with sickle cell anemia (SCA) using noninvasive diffuse optical spectroscopies. Specifically, frequency-domain near-infrared spectroscopy combined with diffuse correlation spectroscopy were used to noninvasively assess regional oxygen extraction fraction (OEF), cerebral blood volume, and an index of cerebral blood flow (CBFi). Estimates of CBFi were first validated against arterial spin-labeled magnetic resonance imaging (ASL-MRI) in 8 children with SCA aged 8 to 18 years. CBFi was significantly positively correlated with ASL-MRI-measured blood flow (R2 = 0.651; P = .015). Next, a single-center, open-label pilot study was completed in 8 children with SCA aged 4 to 17 years on voxelotor, monitored before treatment initiation and at 4, 8, and 12 weeks (NCT05018728). By 4 weeks, both OEF and CBFi significantly decreased, and these decreases persisted to 12 weeks (both P < .05). Decreases in CBFi were significantly correlated with increases in blood hemoglobin (Hb) concentration (P = .025), whereas the correlation between decreases in OEF and increases in Hb trended toward significance (P = .12). Given that previous work has shown that oxygen extraction and blood flow are elevated in pediatric SCA compared with controls, these results suggest that voxelotor may reduce cerebral hemodynamic impairments. This trial was registered at www.ClinicalTrials.gov as #NCT05018728.

Quantitative Model-Based Assessment of Multiple Sickle Cell Disease Therapeutic Approaches Alone and in Combination

Three sickle cell disease (SCD) treatment strategies, stabilizing oxygenated hemoglobin (oxyHb), lowering 2,3-BPG, and inducing fetal hemoglobin (HbF) expression aim to prevent red blood cell (RBC) sickling by reducing tense-state sickle hemoglobin that contributes to polymer formation. Induction of 30% HbF is seen as the gold standard because 30% endogenous expression is associated with a lack of symptoms. However, the level of intervention required to achieve equivalent polymerization protection by the other strategies is uncertain, and there is little understanding of how these approaches could work in combination. We sought to develop an oxygen saturation model that could assess polymerization protection of all three approaches alone or in combination by extending the Monod-Wymann-Changeux model to include additional mechanisms. Applying the model to monotherapies suggests 51% sickle hemoglobin (HbS) occupancy with an oxyHb stabilizer or lowering RBC 2,3 BPG concentrations to 1.8 mM would produce comparable polymerization protection as 30% HbF. The model predictions are consistent with observed clinical response to the oxyHb stabilizer voxelotor and the 2,3-BPG reducer etavopivat. The model also suggests combination therapy will have added benefit in the case of dose limitations, as is the case for voxelotor, which the model predicts could be combined with 20% HbF or 2,3-BPG reduction to 3.75 mM to reach equivalent protection as 30% HbF. The proposed model represents a unified framework that is useful in supporting decisions in preclinical and early clinical development and capable of evolving with clinical experience to gain new and increasingly confident insights into treatment strategies for SCD.

Revolutionising healing: Gene Editing's breakthrough against sickle cell disease

Recent advancements in gene editing illuminate new potential therapeutic approaches for Sickle Cell Disease (SCD), a debilitating monogenic disorder caused by a point mutation in the β-globin gene. Despite the availability of several FDA-approved medications for symptomatic relief, allogeneic hematopoietic stem cell transplantation (HSCT) remains the sole curative option, underscoring a persistent need for novel treatments. This review delves into the growing field of gene editing, particularly the extensive research focused on curing haemoglobinopathies like SCD. We examine the use of techniques such as CRISPR-Cas9 and homology-directed repair, base editing, and prime editing to either correct the pathogenic variant into a non-pathogenic or wild-type one or augment fetal haemoglobin (HbF) production. The article elucidates ways to optimize these tools for efficacious gene editing with minimal off-target effects and offers insights into their effective delivery into cells. Furthermore, we explore clinical trials involving alternative SCD treatment strategies, such as LentiGlobin therapy and autologous HSCT, distilling the current findings. This review consolidates vital information for the clinical translation of gene editing for SCD, providing strategic insights for investigators eager to further the development of gene editing for SCD.

Voxelotor improves red blood cell functionality in children with sickle cell anaemia: An ancillary study of the HOPE-KIDS 1 trial

INTRODUCTION

Sickle haemoglobin (HbS) polymerisation perturbs red blood cell (RBC) rheology and drives sickle cell disease (SCD) pathophysiology. Voxelotor is an HbS polymerisation inhibitor that increases haemoglobin (Hb)-oxygen affinity.

METHODS/RESULTS

In this 48-week, prospective, single-centre translational study, 10 children aged 4-11 years with SCD were treated with voxelotor. Improvements in RBC deformability were observed using osmotic/oxygen gradient ektacytometry, with increases in minimal and maximal elongation index and reductions in point of sickling. Increased Hb and reduced markers of haemolysis were also observed.

CONCLUSION

These findings suggest that voxelotor treatment is associated with reduced RBC sickling and haemolysis in children with SCD.

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.

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.

An expert review of voxelotor for the treatment of hemolytic anemia in patients with sickle cell disease: 'bridging the gap between laboratory data and patient related outcomes'

INTRODUCTION

Until recently, the treatment of sickle cell disease (SCD) for a long time has been limited to hydroxycarbamide alone. SCD is characterized by hemoglobin (Hb) polymerization, hemolysis, and ischemia. Voxelotor, a first-in-class Hb modulator that increases Hb-oxygen affinity and reduces RBC polymerization, is approved for the treatment of hemolytic anemia in SCD patients.

AREAS COVERED

This review is to examine the evidence supporting the laboratory and clinical benefits of voxelotor in SCD. The search keywords were as follows: hemolytic anemia, SCD, voxelotor/GBT 440. A total 19 articles were reviewed. Most studies report voxelotor's significant reduction in hemolysis; however, data related to positive effects on clinical outcomes, namely Vaso-occlusive crisis (VOCs), are sparse. We note the ongoing trials that have different endpoints related to the brain, kidney, and skin. Additional information from real-life post-marketing observational studies may shed more light on the benefits of voxelotor in SCD. Further research is required with the view to using related outcomes as end points e.g. VOCs, renal impairment. This is need to be undertaken in sub Saharan Africa, the epicentre of SCD.

EXPERT OPINION

Our recommendation remains to offer and optimize hydroxycarbamide therapy and consider voxelotor in situations with severe anemia and related sequelae affecting the brain or kidney.

The oxygen dissociation curve of blood in COVID-19-An update

An impressive effect of the infection with SARS-Co-19 is the impairment of oxygen uptake due to lung injury. The reduced oxygen diffusion may potentially be counteracted by an increase in oxygen affinity of hemoglobin. However, hypoxia and anemia associated with COVID-19 usually decrease oxygen affinity due to a rise in [2,3-bisphosphoglycerate]. As such, COVID-19 related changes in the oxygen dissociation curve may be critical for oxygen uptake and supply, but are hard to predict. A Pubmed search lists 14 publications on oxygen affinity in COVID-19. While some investigations show no changes, three large studies found an increased affinity that was related to a good prognosis. Exact causes remain unknown. The cause of the associated anemia in COVID-19 is under discussion. Erythrocytes with structural alterations of membrane and cytoskeleton have been observed, and virus binding to Band 3 and also to ACE2 receptors in erythroblasts has been proposed. COVID-19 presentation is moderate in many subjects suffering from sickle cell disease. A possible explanation is that COVID-19 counteracts the unfavorable large right shift of the oxygen dissociation curve in these patients. Under discussion for therapy are mainly affinity-increasing drugs.

Contemporary Management and Prevention of Vaso-Occlusive Crises (VOCs) in Adults With Sickle Cell Disease

Sickle cell disease (SCD) is a hematological disorder that primarily affects individuals of African descent from sub-Saharan Africa and along the mediterranean. The main complications leading to hospitalizations include vaso-occlusive crises (VOCs) and acute chest syndrome (ACS). Therefore, the main objective of this paper was to identify and evaluate evidence-based management and prevention of VOCs in patients with SCD. A literature search of PubMed, Medline Cochrane and Google Scholar database (January 1985 to April 2020) was performed using the following search terms "vaso-occlusive crises", "sickle cell disease", "hydroxyurea", "L-glutamine", "voxelotor", "crizanlizumab", "treatment" and "prevention" as well as a combination of these terms. All English-language interventional studies assessing the efficacy and safety of VOC outcomes were evaluated. Literature was excluded if published in a language other than English or if it was a review article. A total of 69 articles were identified and there were 7 articles that met the search criteria. Majority of the studies focused on mean and median annual rates of VOCs as primary outcomes while median time to first sickle cell crises, median rates of hospitalizations etc were evaluated as secondary outcomes. After reviewing the literature, many patients with VOCs will still benefit from hydroxyurea therapy since long term efficacy data and cost is still a concern for the newer agents including L-glutamine, voxelotor and crizanlizumab. Other factors such as cost or compliance may also be taken into consideration when making recommendations for therapy.

Pyrazole-containing pharmaceuticals: target, pharmacological activity, and their SAR studies

Pyrazole is a five-membered heterocycle bearing two adjacent nitrogen atoms. Both pharmaceutical agents and natural products with pyrazole as a nucleus have exhibited a broad spectrum of biological activities. In the last few decades, more than 40 pyrazole-containing drugs have been approved by the FDA for the treatment of a broad range of clinical conditions including celecoxib (anti-inflammatory), CDPPB (antipsychotic), difenamizole (analgesic), etc. Owing to the unique physicochemical properties of the pyrazole core, pyrazole-containing drugs may exert better pharmacokinetics and pharmacological effects compared with drugs containing similar heterocyclic rings. The purpose of this paper is to provide an overview of all the existing drugs bearing a pyrazole nucleus that have been approved or in clinical trials, involving their pharmacological activities and SAR studies.

A decade of approved first-in-class small molecule orphan drugs: Achievements, challenges and perspectives

In the past decade (2011-2020), there was a growing interest in the discovery and development of orphan drugs for the treatment of rare diseases. However, rare diseases only account for a population of 0.65‰-1‰ which usually occur with previously unknown biological mechanisms and lack of specific therapeutics, thus to increase the demands for the first-in-class (FIC) drugs with new biological targets or mechanisms. Considering the achievements in the past 10 years, a total of 410 drugs were approved by U.S. Food and Drug Administration (FDA), which contained 151 FIC drugs and 184 orphan drugs, contributing to make up significant numbers of the approvals. Notably, more than 50% of FIC drugs are developed as orphan drugs and some of them have already been milestones in drug development. In this review, we aim to discuss the FIC small molecules for the development of orphan drugs case by case and highlight the R&D strategy with novel targets and scientific breakthroughs.

Barriers to hydroxyurea use from the perspectives of providers, individuals with sickle cell disease, and families: Report from a U.S. regional collaborative

Sickle cell disease (SCD) is an inherited blood disorder that affects about 100,000 people in the U.S., primarily Blacks/African-Americans. A multitude of complications negatively impacts quality of life. Hydroxyurea has been FDA approved since 1998 as a disease-modifying therapy for SCD, but is underutilized. Negative and uninformed perceptions of hydroxyurea and barriers to its use hinder adherence and promotion of the medication. As the largest real-world study to date that assessed hydroxyurea use for children and adults with SCD, we gathered and analyzed perspectives of providers, individuals with SCD, and families. Participants provided information about socio-demographics, hospital and emergency admissions for pain, number of severe pain episodes interfering with daily activities, medication adherence, and barriers to hydroxyurea. Providers reported on indications for hydroxyurea, reasons not prescribed, and current laboratory values. We found that hydroxyurea use was reported in over half of eligible patients from this large geographic region in the U.S., representing a range of sickle cell specialty clinical settings and practices. Provider and patient/caregiver reports about hydroxyurea use were consistent with one another; adults 26 years and older were least likely to be on hydroxyurea; and the likelihood of being on hydroxyurea decreased with one or more barriers. Using the intentional and unintentional medication nonadherence framework, we found that, even for patients on hydroxyurea, challenges to taking the medicine at the right time and forgetting were crucial unintentional barriers to adherence. Intentional barriers such as worry about side effects and “tried and it did not work” were important barriers for young adults and adults. For providers, diagnoses other than HgbSS or HgbS-β0 thalassemia were associated with lower odds of prescribing, consistent with evidence-based guidelines. Our results support strengthening provider understanding and confidence in implementing existing SCD guidelines, and the importance of shared decision making. Our findings can assist providers in understanding choices and decisions of families; guide individualized clinical discussions regarding hydroxyurea therapy; and help with developing tailored interventions to address barriers. Addressing barriers to hydroxyurea use can inform strategies to minimize similar barriers in the use of emerging and combination therapies for SCD.

Molecular Mechanisms of Hepatic Dysfunction in Sickle Cell Disease: Lessons From The Townes Mouse Model

Sickle cell disease (SCD) is an autosomal-recessive-genetic disorder that affects ~100,000 Americans and millions of people worldwide. Erythrocyte sickling, vaso-occlusion, sterile inflammation and hemolysis are the major pathophysiological pathways leading to liver injury in SCD. Although hepatic dysfunction affects up to 10-40% of SCD patients, therapeutic approaches to prevent liver injury in SCD are not known, and the molecular mechanisms promoting progressive liver injury in SCD remain poorly understood. Animal models have been beneficial in bridging the gap between preclinical and translational research in SCD. Recent advances in methodology have allowed the development of several humanized mouse models to address various aspects of SCD related liver diseases. This review provides an overview of current knowledge of the molecular mechanisms and potential therapeutic options of SCD associated liver dysfunction using the Townes mouse model.

Patient perception of voxelotor treatment benefit in sickle cell disease

Patients with sickle cell disease (SCD) experience a range of clinical symptoms, including acute and chronic pain, fatigue, and respiratory problems, as well as chronic organ complications that can lead to disability and accelerated mortality. Voxelotor is a first-in-class therapy that targets sickle hemoglobin polymerization, the root cause of SCD. It is approved by the US Food and Drug Administration for treatment of SCD in patients aged 4 years and older and in the European Union and United Arab Emirates for the treatment of SCD in patients aged 12 years and older. Here, we report the single-center experience of both clinician-determined and patient-reported benefits of voxelotor in 27 consecutive patients treated for at least 8 weeks. Clinical Global Impression of Change and Patient Global Impression of Change rating scales were used to capture clinicians’ and patients’ perceptions of change in overall patient health-related quality-of-life with voxelotor treatment. Laboratory data were also collected to assess clinical response to treatment. As observed in previous clinical studies, hemoglobin concentrations and markers of hemolysis were improved in patients treated with voxelotor. Most patients reported marked improvement in disease symptoms, which correlated well with the clinicians’ assessments. Although limited by the retrospective open-label study design, these findings suggest that voxelotor use has a positive impact on outcomes in patients with SCD.

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

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

Model‐informed drug development of voxelotor in sickle cell disease: Exposure‐response analysis to support dosing and confirm mechanism of action

Sickle cell disease (SCD) is characterized by the production of sickle hemoglobin (HbS), which when deoxygenated, polymerizes leading to red blood cell damage and hemolytic anemia, a defining feature of SCD. Voxelotor (Oxbryta) is a small molecule inhibitor of HbS polymerization that disrupts the polymerization mechanism by binding HbS to increase HbS oxygen affinity. Voxelotor is approved in the United States for the treatment of SCD in patients greater than or equal to 12 years of age at a 1500 mg once‐daily (q.d.) dose. These exposure‐response analyses aimed to evaluate the relationships between voxelotor whole blood concentration and change from baseline (CFB) in clinical measures of anemia and hemolysis and between voxelotor whole blood and plasma concentrations and the incidence of selected safety end points to confirm the voxelotor mechanism of action and to support the clinical dose recommendation. In patients treated with voxelotor up to 72 weeks, CFB hemoglobin (Hb) increased linearly (p < 0.001) with increasing voxelotor concentration and percent Hb occupancy and increases in CFB Hb corresponded to improvements in measures of hemolysis. The target 1 g/dl increase in CFB Hb was achieved with 1500 mg voxelotor q.d. Significant relationships were observed between voxelotor exposures and grade greater than or equal to 1 increased alanine aminotransferase and decreased white blood cell count; however, most events were grade 1. No clinically important covariate effects on voxelotor efficacy or safety were observed. Overall, these analyses support 1500 mg q.d. as the therapeutic dose for voxelotor in adults and adolescents.

Comparing the Safety and Efficacy of L-Glutamine, Voxelotor, and Crizanlizumab for Reducing the Frequency of Vaso-Occlusive Crisis in Sickle Cell Disease: A Systematic Review

Sickle cell disease (SCD) is a group of inherited red blood cell disorders affecting millions worldwide. The median life expectancy of someone with SCD remains significantly low despite improvements in standards of care and the implementation of hydroxyurea therapy. Notably, a 20-year interval existed (after the implementation of hydroxyurea therapy) prior to the approval of other sickle cell medications, namely, l-glutamine, voxelotor, and crizanlizumab. In this systematic review, these new medications' impact on the occurrences of vaso-occlusive crisis (VOC) events were analyzed and the adverse events of each were noted. Further, a secondary analysis was conducted to determine the effect of combination therapies, whether synergistic, antagonistic, or additive. The systematic review was conducted following the PRISMA 2020 guidelines. The effect-based and dose-effect-based approaches were utilized to determine the combined drugs combination index based on the recommended dosage to achieve an efficacy of 50%. L-glutamine and crizanlizumab were effective in reducing the frequency of VOC (p= 0.0216 and p = 0.02). Voxelotor effect on the reduction of VOC occurrences was not significant, however, its effect on increasing hemoglobin levels was significant (p= <0.001). In all three therapies, pain was the most common adverse event reported by participants. The analysis of combination therapies revealed that voxelotor plus l-glutamine was synergistic, voxelotor plus crizanlizumab was antagonistic, and l-glutamine plus crizanlizumab was additive. Thus, voxelotor plus l-glutamine combination therapy may be more beneficial to sickle cell disease patients. As such, robust combination drug studies for approved therapies used in SCD should be initiated with a specific focus on voxelotor plus l-glutamine. Additionally, the development of medications that lessen the pain burden in sickle cell disease patients should also be prioritized.

High-Throughput Assay to Screen Small Molecules for Their Ability to Prevent Sickling of Red Blood Cells

Sickle cell disease (SCD) is an inherited disorder of hemoglobin (Hb); approximately 300,000 babies are born worldwide with SCD each year. In SCD, fibers of polymerized sickle Hb (HbS) form in red blood cells (RBCs), which cause RBCs to develop their characteristic "sickled" shape, resulting in hemolytic anemia and numerous vascular complications including vaso-occlusive crises. The development of novel antisickling compounds will provide new therapeutic options for patients with SCD. We developed a high-throughput "sickling assay" that is based on an automated high-content imaging system to quantify the effects of hypoxia on the shape and size of RBCs from HbSS SCD patients (SS RBCs). We used this assay to screen thousands of compounds for their ability to inhibit sickling. In the assay, voxelotor (an FDA-approved medication used to treat SCD) prevented sickling with a z'-factor > 0.4, suggesting that the assay is capable of identifying compounds that inhibit sickling. We screened the Broad Repurposing Library of 5393 compounds for their ability to prevent sickling in 4% oxygen/96% nitrogen. We identified two compounds, SNS-314 mesylate and voxelotor itself, that successfully prevented sickling. SNS-314 mesylate prevented sickling in the absence of oxygen, while voxelotor did not, suggesting that SNS-314 mesylate acts by a mechanism that is different from that of voxelotor. The sickling assay described in this study will permit the identification of additional, novel antisickling compounds, which will potentially expand the therapeutic options for SCD.

Modulating hemoglobin allostery for treatment of sickle cell disease: current progress and intellectual property

INTRODUCTION

Sickle cell disease (SCD) is a debilitating inherited disorder that affects millions worldwide. Four novel SCD therapeutics have been approved, including the hemoglobin (Hb) modulator Voxelotor.

AREAS COVERED

This review provides an overview of discovery efforts toward modulating Hb allosteric behavior as a treatment for SCD, with a focus on aromatic aldehydes that increase Hb oxygen affinity to prevent the primary pathophysiology of hypoxia-induce erythrocyte sickling.

EXPERT OPINION

The quest to develop small molecules, especially aromatic aldehydes, to modulate Hb allosteric properties for SCD began in the 1970s; however, early promise was dogged by concerns that stalled support for research efforts. Persistent efforts eventually culminated in the discovery of the anti-sickling agent 5-HMF in the 2000s, and reinvigorated interest that led to the discovery of vanillin analogs, including Voxelotor, the first FDA approved Hb modulator for the treatment of SCD. With burgeoning interest in the field of Hb modulation, there is a growing landscape of intellectual property, including drug candidates at various stages of preclinical and clinical investigations. Hb modulators could provide not only the best chance for a highly effective oral therapy for SCD, especially in the under-developed world, but also a way to treat a variety of other human conditions.

Influence of Haptoglobin Polymorphism on Stroke in Sickle Cell Disease Patients

This review outlines the current clinical research investigating how the haptoglobin (Hp) genetic polymorphism and stroke occurrence are implicated in sickle cell disease (SCD) pathophysiology. Hp is a blood serum glycoprotein responsible for binding and removing toxic free hemoglobin from the vasculature. The role of Hp in patients with SCD is critical in combating blood toxicity, inflammation, oxidative stress, and even stroke. Ischemic stroke occurs when a blocked vessel decreases oxygen delivery in the blood to cerebral tissue and is commonly associated with SCD. Due to the malformed red blood cells of sickle hemoglobin S, blockage of blood flow is much more prevalent in patients with SCD. This review is the first to evaluate the role of the Hp polymorphism in the incidence of stroke in patients with SCD. Overall, the data compiled in this review suggest that further studies should be conducted to reveal and evaluate potential clinical advancements for gene therapy and Hp infusions.

[A new approach to combat the sepsis including COVID-19 by accelerating detoxification of hemolysis-related DAMPs]

Sepsis is one of the leading cause of death worldwide. Recently, several studies suggested that free-hemoglobin and heme derived from hemolysis are important factors which may be associated with severity of septic patients including COVID-19. In other words, hemolysis-derived products enhance the inflammatory responses as damage-associated molecular patterns (DAMPs) in both intravascular and extravascular space. In addition, hemoglobin has vasoconstrictive activity by depleting nitric oxide, whereas heme or Fe²⁺ produce reactive oxygen species (ROS) through Fenton reaction leading to tissue injury. At present, we have no therapeutic options against sepsis-related hemolysis in clinical settings, however, there might be two therapeutic strategies in this regard. One is supplemental therapy of depleted scavenging proteins such as haptoglobin and hemopexin, the other is activation of the internal scavenging system including macrophage-CD163 pathway. These novel targets against sepsis are also critical for the next pandemic. In this review, we summarize the current issues regarding sepsis-related hemolysis including COVID-19, as well as for future perspectives.

l-glutamine, crizanlizumab, voxelotor, and cell-based therapy for adult sickle cell disease: Hype or hope?

For more than two decades, hydroxyurea was the only therapeutic agent approved by the Food and Drug Administration (FDA) for sickle cell disease (SCD). Although curative allogeneic hematopoietic stem cell transplants (allo-HSCT) were also available, only very few patients underwent the procedure due to lack of matched-related donors. However, therapeutic options for SCD patients increased dramatically in the last few years. Three new agents, l-glutamine, crizanlizumab, and voxelotor, were approved by the FDA for use in SCD patients. The number of SCD patients who underwent allo-HSCT also increased as a result of advances in the prevention of graft failure and graft-versus-host disease from using mismatched donor HSC. More recently gene therapy was made available on clinical trials. The increased treatment options for SCD have led to a sense of optimism and excitement among many physicians that these new approaches would alter the clinical course and disease burden. Although these newer agents do provide hope to SCD patients, the hyped-up responses need to be evaluated in the context of reality. In this review, we will discuss and compare these new agents and cell-based therapy, evaluate their clinical and economic impacts, and examine their roles in reducing the disease burden.

Ineffective erythropoiesis in sickle cell disease: new insights and future implications

PURPOSE OF REVIEW

Sickle cell disease (SCD) is a hemolytic anemia caused by a point mutation in the β globin gene leading to the expression of an abnormal hemoglobin (HbS) that polymerizes under hypoxic conditions driving red cell sickling. Circulating red cells have been extensively characterized in SCD, as their destruction and removal from peripheral blood are the major contributors to anemia. However, few reports showed cellular abnormalities during erythropoiesis in SCD, suggesting that anemia could also be influenced by defects of central origin.

RECENT FINDINGS

El Hoss et al. demonstrated ineffective erythropoiesis (IE) in SCD and deciphered the molecular mechanism underlying cell death during the hemoglobin synthesis phase of terminal differentiation. They showed that HbS polymerization induces apoptosis of differentiating erythroblasts and that fetal hemoglobin rescues these cells through its antipolymerization function.

SUMMARY

IE is the major cause of anemia in β-thalassemia patients, and it is generally surmised that it contributes little to anemia of SCD. Recent reports demonstrate the occurrence of IE in SCD patients and show important alterations in the hematopoietic and erythroid niches, both in SCD patients and in the humanized Townes SCD mouse model. This implies that therapeutic strategies initially designed to improve red cell survival in the circulation of SCD patients would also positively impact erythropoiesis and bone marrow cellularity.

Mitochondrial reactive oxygen species scavenging attenuates thrombus formation in a murine model of sickle cell disease

BACKGROUND

Sickle cell disease (SCD) is characterized by hemolysis-associated platelet dysfunction that leads to increased risk of thrombosis and plays a role in the high morbidity and mortality of the disease. The mechanisms by which hemolysis induces platelet activation remain unclear. We recently demonstrated that patients with SCD showed increased platelet mitochondrial reactive oxygen species (mtROS) production that correlates with markers of hemolysis and platelet activation. Experiments in isolated platelets demonstrated that mtROS stimulated platelet activation. However, the role of hemolysis-induced mtROS in thrombus formation in vivo remains unclear.

OBJECTIVES

Here, we hypothesize that scavenging of mtROS attenuates the propensity for thrombosis in mouse models of hemolysis.

METHODS

We used models of hemolysate infusion into wildtype mice as well as the Berkley transgenic mouse model of SCD, a chronic mode of hemolysis, to test the effect of hemolysis on platelet mtROS production and thrombosis.

RESULTS

We show that infusion of hemolysate in wildtype mice induces platelet mtROS production and decreases time to vessel occlusion in a model of ferric chloride-induced carotid artery thrombosis. Increased mtROS and propensity for thrombosis was also observed in the Berkley transgenic mouse model of SCD. Notably, treatment with mtROS scavengers decreased platelet mtROS levels and attenuated the propensity for thrombus formation in both models.

CONCLUSIONS

These data demonstrate that mtROS significantly contribute to the mechanism of hemolysis-induced thrombosis in vivo and suggest a potential role for mitochondrially targeted antioxidant therapy in hemolysis and SCD-related thrombosis.

Increased hemoglobin affinity for oxygen with GBT1118 improves hypoxia tolerance in sickle cell mice

Therapeutic agents that increase the Hb affinity for oxygen (O₂) could, in theory, lead to decreased O₂ release from Hb and impose a hypoxic risk to tissues. In this study, GBT1118, an allosteric modifier of Hb affinity for O₂, was used to assess the impact of increasing Hb affinity for O₂ on brain tissue oxygenation, blood pressure, heart rate, O₂ delivery, and tolerance to hypoxia in Townes transgenic sickle cell disease (SCD) mice. Brain oxygenation and O₂ delivery were studied during normoxia and severe hypoxic challenges. Chronic treatment with GBT1118 increased Hb affinity for O₂, reducing the Po₂ for 50% HbO₂ saturation (P50) in SCD mice from 31 mmHg to 18 mmHg. This treatment significantly reduced anemia, increasing hematocrit by 33%, improved cardiac output (CO), and O₂ delivery and extraction. Chronically increasing Hb affinity for O₂ with GBT1118 preserved cortical O₂ tension during normoxia, improved cortical O₂ tension during hypoxia, and increased tolerance to severe hypoxia in SCD mice. Independent of hematological changes induced by chronic treatment, a single dose of GBT1118 significantly improved tolerance to hypoxia, highlighting the benefits of increasing Hb affinity for O₂ and consequently reducing sickling of RBCs in blood during hypoxia in SCD.NEW & NOTEWORTHY Chronic pharmacologically increased hemoglobin affinity for oxygen in sickle cell disease mice alleviated hematological consequences of sickle cell disease, increasing RBC half-life, hematocrit, and hemoglobin concentration, while also decreasing reticulocyte count. Additionally, chronically increased hemoglobin affinity for oxygen significantly improved survival as well as cortical tissue oxygenation in sickle cell disease mice during hypoxia, suggesting that oxygen delivery and utilization is improved by increased hemoglobin affinity for oxygen.

The efficacy of voxelotor, 900 mg in patients with sickle cell anaemia: A meta-analysis of the randomised controlled trials

OBJECTIVE

Sickle cell anaemia (SCA), an inherited chronic hematological disease affecting hundreds of thousand people worldwide, causes significant morbidity and reduced life expectancy about two or three decades. This study aimed to conduct a meta-analysis of the efficacy of voxelotor, 900 mg in patients with SCA.

METHODS

The research protocol was registered at the International Register of Prospective Systematic Reviews (PROSPERO), under the registration number: CRD42020147796. ClinicalTrials.gov, Cochrane Central Register of Controlled Trials, Conference Abstracts, Google Scholar, Ovid Medline, Scopus, Web of Science, and Wiley Online Library from 2015 through July 25, 2019, and bibliographies of review articles and eligible studies. Eleven eligible studies that evaluated the effectiveness of voxelotor, 900 mg in SCA. Based on pre-specified inclusion and exclusion criteria, 2 randomized, placebo-controlled studies were included in the meta-analysis.

RESULTS

The primary outcome measured was hemoglobin elevation, assessed in a highly similar fashion in both trials. There was a significant difference between voxelotor and placebo in haemoglobin change from baseline (mean difference [MD]: 0.87, 95% confidence interval [CI]: 0.67-1.06). Voxelotor also reduced markers of haemolysis, MD: -36.79, 95% CI: (-75.05) to 1.48 for unconjugated bilirubin that changes from baseline; MD: -19.09, 95% CI: (-44.06) to 5.88 for the percentage of reticulocytes that change from baseline and MD: -23.29, 95% CI: (-65.14) to 18.55 for LDH that change from baseline) but the difference was not statistically significant.

CONCLUSIONS

As a conclusion, voxelotor, 900 mg use significantly increased hemoglobin levels which of 1 g/dL elevation predicts a reduced risk of stroke (41%), albuminuria (53%), pulmonary arterial hypertension (57%), and mortality (64%) in recent studies. Voxelotor also reduced markers of hemolysis but failed to reach statistically significance in current evidence. Multicenter, randomized, placebo-controlled studies are on the way and will provide more evidence to see the potential of disease-modifying effects of voxelotor.

Advances in Sickle Cell Disease Treatments

Sickle Cell Disease (SCD) is an inherited disorder of red blood cells that is caused by a single mutation in the β -globin gene. The disease, which afflicts millions of patients worldwide mainly in low income countries, is characterized by high morbidity, mortality and low life expectancy. The new pharmacological and non-pharmacological strategies for SCD is urgent in order to promote treatments able to reduce patient's suffering and improve their quality of life. Since the FDA approval of HU in 1998, there have been few advances in discovering new drugs; however, in the last three years voxelotor, crizanlizumab, and glutamine have been approved as new therapeutic alternatives. In addition, new promising compounds have been described to treat the main SCD symptoms. Herein, focusing on drug discovery, we discuss new strategies to treat SCD that have been carried out in the last ten years to discover new, safe, and effective treatments. Moreover, non-pharmacological approaches, including red blood cell exchange, gene therapy and hematopoietic stem cell transplantation will be presented.

Voxelotor in adolescents and adults with sickle cell disease (HOPE): long-term follow-up results of an international, randomised, double-blind, placebo-controlled, phase 3 trial

BACKGROUND

For decades, patients with sickle cell disease have had only a limited number of therapies available. In 2019, voxelotor (1500 mg), an oral once-daily sickle haemoglobin polymerisation inhibitor, was approved in the USA for the treatment of sickle cell disease in patients aged 12 years and older on the basis of HOPE trial data. To further describe the applicability of voxelotor as a treatment for this chronic illness, we report the long-term efficacy and safety of this drug at 72 weeks of treatment; the conclusion of the placebo-controlled HOPE trial.

METHODS

HOPE is an international, randomised, double-blind, placebo-controlled, phase 3 trial done at 60 clinical sites in Canada, Egypt, France, Italy, Jamaica, Kenya, Lebanon, Netherlands, Oman, Turkey, the USA, and the UK. Patients (aged 12-65 years) with confirmed sickle cell disease, a haemoglobin concentration of 5·5-10·5 g/dL at enrolment, and who had between one and ten vaso-occlusive crisis events in the previous 12 months were enrolled. Patients receiving regularly scheduled transfusion therapy, who had received a transfusion in the previous 60 days, or who had been admitted to hospital for a vaso-occlusive crisis in the previous 14 days were excluded. Patients were randomly assigned (1:1:1) to receive either once-daily oral voxelotor 1500 mg, voxelotor 900 mg, or placebo for 72 weeks. Randomisation was done centrally by use of an interactive web response system, stratified by baseline hydroxyurea use (yes vs no), age group (adolescents [12 to <18 years] vs adults [18 to 65 years]), and geographic region (North America vs Europe vs other). The primary endpoint (already reported) was the proportion of patients who achieved a haemoglobin response at week 24. In this final analysis, we report prespecified long-term efficacy assessments by intention to treat, including changes in haemoglobin concentrations from baseline to week 72, changes in the concentration of haemolysis markers (absolute and percentage reticulocytes, indirect bilirubin concentrations, and lactate dehydrogenase concentrations) from baseline to week 72, the annualised incidence of vaso-occlusive crises, and patient functioning, as assessed with the Clinical Global Impression of Change (CGI-C) scale. Safety was assessed in patients who received at least one dose of treatment (modified intention-to-treat population). This trial is registered with ClinicalTrials.gov, NCT03036813.

FINDINGS

Between Dec 5, 2016, and May 3, 2018, 449 patients were screened, of whom 274 were randomly assigned to the voxelotor 1500 mg group (n=90), the voxelotor 900 mg group (n=92), or the placebo group (n=92). At week 72, the adjusted mean change in haemoglobin concentration from baseline was 1·0 g/dL (95% CI 0·7 to -1·3) in the voxelotor 1500 mg group, 0·5 g/dL (0·3 to -0·8) in the voxelotor 900 mg group, and 0·0 g/dL (-0·3 to 0·3) in the placebo group, with a significant difference observed between the voxelotor 1500 mg group and the placebo group (p<0·0001), and between the voxelotor 900 mg group and the placebo group (p=0·014). Significant improvements in markers of haemolysis, as assessed by the difference in adjusted mean percentage change from baseline at week 72 versus placebo, were observed in the voxelotor 1500 mg group in indirect bilirubin concentrations (-26·6% [95% CI -40·2 to -12·9]) and percentage of reticulocytes (-18·6% [-33·9 to -3·3]). The proportion of patients in the voxelotor 1500 mg group who were rated as "moderately improved" or "very much improved" at week 72 with the CGI-C was significantly greater than in the placebo group (39 [74%] of 53 vs 24 [47%] of 51; p=0·0057). Serious adverse events unrelated to sickle cell disease were reported in 25 (28%) of 88 patients in the voxelotor 1500 mg group, 20 (22%) of 92 patients in the voxelotor 900 mg group, and 23 (25%) of 91 patients in the placebo group. Grade 3 or 4 adverse events were infrequent (ie, occurred in <10% of patients); anaemia occurred in five or more patients (two [2%] patients in the voxelotor 1500 mg group, seven [8%] patients in the voxelotor 900 mg group, and three [3%] patients in the placebo group). Of all 274 patients, six (2%) deaths occurred during the study (two deaths in each treatment group), all of which were judged as unrelated to treatment.

INTERPRETATION

Voxelotor 1500 mg resulted in rapid and durable improvements in haemoglobin concentrations maintained over 72 weeks and has potential to address the substantial morbidity associated with haemolytic anaemia in sickle cell disease.

FUNDING

Global Blood Therapeutics.

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

Sickle cell disease, despite its recognition as a severely debilitating genetic condition affecting hundreds of thousands of neonates throughout the world each year, was not a target of pharmaceutical research focus for most of its 100-year existence in the medical consciousness. This has changed in recent years as many novel therapeutics are currently under investigation, with three new disease-modifying drugs achieving FDA approval in the last 4 years. One of these drugs, voxelotor, is especially encouraging as an inhibitor of sickling for its ability to safely improve the chronic hemolytic anemia of sickle cell disease. This was demonstrated during all clinical phases of investigation by an average improvement in hemoglobin of greater than 1 g/dL, as well as statistically significant improvements in established markers of hemolysis. While anemia itself represents a potential cause of morbidity, it is more importantly a marker of the hemolysis known to cause the long-term vascular and organ damage that makes sickle cell disease so debilitating and frequently fatal early in life. Given the recency of the approval, there has not been sufficient long-term follow-up to demonstrate improvement in the chronic sequelae of sickle cell disease as a result of voxelotor-induced improvements in hemolytic anemia. There is hope, however, based on the experience with hydroxyurea improving morbidity and mortality via reductions in sickling and improved rheology, that voxelotor may have similar long-term benefits by positively manipulating the kinetics of hemoglobin polymerization. This review aims to summarize the targeted pathobiology of sickle cell disease, the mechanism of action of voxelotor, and the safety and efficacy data from preclinical to late clinical stage investigations of this long-awaited medication, in the hopes of better informing the decision-making process behind prescribing or not prescribing it for patients in need of intervention.

Voxelotor for the treatment of sickle cell disease

Introduction: The clinical manifestations of sickle cell disease (SCD) result from an inherited mutation in the beta-globin chain of hemoglobin (Hb) that causes Hb tetramers to polymerize when deoxygenated. The resulting erythrocyte deformation causes mechanical obstruction of blood flow by sickled cells, hemolysis, anemia and end-organ injury. While pain is the hallmark symptom of SCD, chronic organ injury as a result of anemia, inflammation and progressive vasculopathy play a major role in morbidity and mortality. Due to the complex pathophysiology of SCD, the need for an individualized, multi-modal pharmacologic approach is apparent. Until 2018, hydroxyurea was the only disease-modifying pharmacologic therapy approved for use in SCD. Since then, three new agents have been approved including voxelotor, the subject of this review.Areas covered: Published pre-clinical and clinical data are reviewed. Voxelotor is a first-in-class small-molecule agent that binds to Hb and increases oxygen affinity, preventing polymerization. Recent clinical trials have shown that it increases Hb concentration and reduces hemolysis in patients with SCD. This increase in Hb concentration may significantly impact morbidity and mortality from chronic organ injury.Expert opinion: The mechanism of action, published studies and current opinions on the clinical use of voxelotor in SCD are presented.

Xanthine Oxidase Drives Hemolysis and Vascular Malfunction in Sickle Cell Disease

OBJECTIVE

Chronic hemolysis is a hallmark of sickle cell disease (SCD) and a driver of vasculopathy; however, the mechanisms contributing to hemolysis remain incompletely understood. Although XO (xanthine oxidase) activity has been shown to be elevated in SCD, its role remains unknown. XO binds endothelium and generates oxidants as a byproduct of hypoxanthine and xanthine catabolism. We hypothesized that XO inhibition decreases oxidant production leading to less hemolysis. Approach and Results: Wild-type mice were bone marrow transplanted with control (AA) or sickle (SS) Townes bone marrow. After 12 weeks, mice were treated with 10 mg/kg per day of febuxostat (Uloric), Food and Drug Administration-approved XO inhibitor, for 10 weeks. Hematologic analysis demonstrated increased hematocrit, cellular hemoglobin, and red blood cells, with no change in reticulocyte percentage. Significant decreases in cell-free hemoglobin and increases in haptoglobin suggest XO inhibition decreased hemolysis. Myographic studies demonstrated improved pulmonary vascular dilation and blunted constriction, indicating improved pulmonary vasoreactivity, whereas pulmonary pressure and cardiac function were unaffected. The role of hepatic XO in SCD was evaluated by bone marrow transplanting hepatocyte-specific XO knockout mice with SS Townes bone marrow. However, hepatocyte-specific XO knockout, which results in >50% diminution in circulating XO, did not affect hemolysis levels or vascular function, suggesting hepatocyte-derived elevation of circulating XO is not the driver of hemolysis in SCD.

CONCLUSIONS

Ten weeks of febuxostat treatment significantly decreased hemolysis and improved pulmonary vasoreactivity in a mouse model of SCD. Although hepatic XO accounts for >50% of circulating XO, it is not the source of XO driving hemolysis in SCD.

The role of haematopoietic stem cell transplantation for sickle cell disease in the era of targeted disease-modifying therapies and gene editing

Sickle cell disease is one of the most common, life-threatening, non-communicable diseases in the world and a major public health problem. Following the implementation of simple preventive and therapeutic modalities, infant mortality has almost been abolished in high-income countries, but only a small amount of progress has been made in improving survival in adulthood. Progressive end-organ damage, partly related to a systemic vasculopathy, is increasingly recognised. With the availability of a variety of novel disease-modifying drugs, gene addition and gene editing strategies, matched sibling donor haematopoietic stem cell transplantation (HSCT) in children (offering an overall survival rate of 95% and an event-free survival rate of 92%), and encouraging outcomes after alternative donor HSCT, the new challenge is to risk stratify patients, revise transplantation indications, and define the best therapeutic approach for each patient. The ultimate challenge will be to enable these advances in low-income and middle-income countries, where disease prevalence is highest and where innovative strategies are most needed.

Efficacy and safety of recently approved drugs for sickle cell disease: a review of clinical trials

Sickle cell disease is prevalent in several parts of the world. Most hospitalizations of these patients are related to pain crisis episodes. Moreover, levels of hemoglobin are lower in sickle cell disease patients as compared with the general population. Complications related to sickle cell disease are managed with blood transfusions, hydroxyurea, and opioids. Despite these therapies, patients with sickle cell disease experience multiple pain crisis episodes leading to hospitalizations and end-organ damage. The US Food and Drug Administration has approved three new drugs-L-glutamine, voxelotor, and crizanlizumab-for the prophylaxis and treatment of complications related to sickle cell disease. This review was aimed at assessing the efficacy and safety of recently approved drugs for the treatment of sickle cell disease. A comprehensive search was made on PubMed and clinicaltrials.gov to look for clinical trials reporting the efficacy and safety of recently approved drugs for sickle cell disease. Based on the results of clinical trials, L-glutamine, voxelotor, and crizanlizumab were well tolerated by sickle cell disease patients. L-Glutamine and crizanlizumab reduced the number of sickle cell crisis episodes, while voxelotor improved the level of hemoglobin in sickle cell disease patients. These drugs were effective alone and in combination with hydroxyurea.

Voxelotor: A Hemoglobin S Polymerization Inhibitor for the Treatment of Sickle Cell Disease

Sickle cell disease (SCD) affects millions of people throughout the world. Hemoglobin S (HbS) polymerization is the fundamental cause of SCD pathophysiology, which leads to hemolysis, increased viscosity, and acute vaso-occlusive episodes. Novel agents have been developed to target the pathophysiology of SCD and decrease the frequency of SCD complications. Voxelotor (Oxbryta) is an HbS polymerization inhibitor that is approved by the U.S. Food & Drug Administration for the treatment of SCD in adults and pediatric patients 12 years and older.

Pharmacokinetics of Voxelotor in Patients With Renal and Hepatic Impairment

Two open‐label studies assessed the safety, tolerability, and pharmacokinetics of Oxbryta (voxelotor) in subjects with hepatic or renal impairment. Eight subjects with severe renal impairment (estimated glomerular filtration rate <30 mL/min/1.73 m²) and 8 healthy age‐, sex‐, and body mass index–matched controls were administered a single oral dose of voxelotor 900 mg. Seven patients with mild (Child‐Pugh A), moderate (Child‐Pugh B), and severe (Child‐Pugh C) hepatic impairment and healthy age‐, sex‐, and body mass index–matched controls (7:7:7:7) were administered a single oral dose of voxelotor 1500 mg, except those with severe hepatic impairment (600 mg). There was no apparent effect of renal function on the excretion of voxelotor based on comparable half‐life values between subjects with severe renal impairment and healthy matched controls. Mean area under the concentration‐time curve from time 0 to infinity (AUC_0‐inf) values were lower by approximately 50% (plasma) and 25% (whole blood) in subjects with severe renal impairment compared with controls. Accordingly, dose adjustment is not required in patients with severe renal impairment. Voxelotor plasma and whole‐blood exposures were slightly increased in subjects with mild and moderate hepatic impairment. Mean AUC_0‐inf values were approximately 9% to 18% higher compared with those of healthy matched controls. Dose adjustment is therefore not required in patients with mild or moderate hepatic impairment. Voxelotor mean AUC_0‐inf values were approximately 90% higher in subjects with severe hepatic impairment. A lower voxelotor dose (1000 mg) is recommended for patients with severe hepatic impairment. Voxelotor was well tolerated in all treatment groups.

Voxelotor Treatment Interferes With Quantitative and Qualitative Hemoglobin Variant Analysis in Multiple Sickle Cell Disease Genotypes

OBJECTIVES

Voxelotor was recently approved for use in the United States as a treatment for sickle cell disease (SCD) and has been shown to interfere with the quantitation of hemoglobin (Hb) S percentage. This study aimed to determine the effect of voxelotor on the quantitation of hemoglobin variant levels in patients with multiple SCD genotypes.

METHODS

In vitro experiments were performed to assess the impact of voxelotor treatment on hemoglobin variant testing. Whole blood samples were incubated with voxelotor and then analyzed by routinely used quantitative and qualitative clinical laboratory methods (high-performance liquid chromatography [HPLC], capillary zone electrophoresis [CZE], and acid and alkaline electrophoresis).

RESULTS

Voxelotor modified the α-globin chain of multiple hemoglobins, including HbA, HbS, HbC, HbD-Punjab, HbE, HbA2, and HbF. These voxelotor-hemoglobin complexes prevented accurate quantitation of multiple hemoglobin species, including HbS, by HPLC and CZE.

CONCLUSIONS

Technical limitations in quantifying HbS percentage may preclude the use of HPLC or CZE for monitoring patients treated with voxelotor. Furthermore, it is unclear whether HbS-voxelotor complexes are clinically equivalent to HbS. Consensus guidelines for reporting hemoglobin variant percentages for patients taking voxelotor are needed, as these values are necessary for determining the number of RBC units to exchange in acute situations.

Accelerated approval of Oxbryta® (voxelotor): A case study on novel endpoint selection in sickle cell disease

Sickle cell disease (SCD) is an inherited disease characterized by hemolysis, anemia, and vaso-occlusion leading to substantial morbidity and mortality. Development of prior pharmacologic therapies exclusively utilized vaso-occlusive crisis (VOC) as a clinical efficacy endpoint; however, this focus on VOC did not capture the full extent of disease symptomatology and complications and slowed the development of new therapies. Voxelotor, a hemoglobin S polymerization inhibitor, was recently approved in the United States for the treatment of SCD in adults and adolescents 12 years of age and older through an accelerated approval pathway. The rapid approval and availability of voxelotor was facilitated in a collaborative effort with the US Food and Drug Administration (FDA), using hemoglobin, a biologic surrogate endpoint, as reasonably likely to predict clinical benefit. Use of this new endpoint was supported by FDA-led multistakeholder discussions with physician and patient communities to identify unmet needs and potential clinical trial endpoints, as well as by a company-sponsored analysis of external patient-level data to demonstrate a correlation between hemoglobin change and stroke risk. A two-part phase 3 study was used to allow for rank ordering of key secondary endpoints based on a planned interim analysis. Continued open communication with the FDA was essential to gain agreement on hemoglobin as a novel endpoint and to address the unmet and urgent need of new therapies for SCD.

Voxelotor: First Approval

Voxelotor (Oxbryta™) is a haemoglobin S polymerization inhibitor that has been developed for the treatment of sickle cell disease. In November 2019, voxelotor received its first global approval in the USA for the treatment of sickle cell disease in adults and paediatric patients aged ≥ 12 years. The drug was granted accelerated approval based on the results of the phase III HOPE trial. Phase III clinical development of voxelotor for sickle cell disease is ongoing worldwide. Voxelotor also has Orphan Drug designation and Priority Medicine status in Europe for the treatment of sickle cell disease. This article summarizes the milestones in the development of voxelotor leading to this first approval as a disease-modifying agent for sickle cell disease.