Novel Sickle Cell Disease Therapies: Targeting Pathways Downstream of Sickling

A randomized clinical trial of the efficacy and safety of rivipansel for sickle cell vaso-occlusive crisis

The efficacy and safety of rivipansel, a predominantly E-selectin antagonist, were studied in a phase 3, randomized, controlled trial for vaso-occlusive crisis (VOC) requiring hospitalization (RESET). A total of 345 subjects (204 adults and 141 children) were randomized and 320 were treated (162 with rivipansel, 158 with placebo) with an IV loading dose, followed by up to 14 additional 12-hourly maintenance doses of rivipansel or placebo, in addition to standard care. Rivipansel was similarly administered during subsequent VOCs in the Open-label Extension (OLE) study. In the full analysis population, the median time to readiness for discharge (TTRFD), the primary end point, was not different between rivipansel and placebo (-5.7 hours, P = .79; hazard ratio, 0.97), nor were differences seen in secondary end points of time to discharge (TTD), time to discontinuation of IV opioids (TTDIVO), and cumulative IV opioid use. Mean soluble E-selectin decreased 61% from baseline after the loading dose in the rivipansel group, while remaining unchanged in the placebo group. In a post hoc analysis, early rivipansel treatment within 26.4 hours of VOC pain onset (earliest quartile of time from VOC onset to treatment) reduced median TTRFD by 56.3 hours, reduced median TTD by 41.5 hours, and reduced median TTDIVO by 50.5 hours, compared with placebo (all P < .05). A similar subgroup analysis comparing OLE early-treatment with early-treatment RESET placebo showed a reduction in TTD of 23.1 hours (P = .062) and in TTDIVO of 30.1 hours (P = .087). Timing of rivipansel administration after pain onset may be critical to achieving accelerated resolution of acute VOC. Trial Registration: Clinicaltrials.gov, NCT02187003 (RESET), NCT02433158 (OLE).

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.

Demand-only patient-controlled analgesia for treatment of acute vaso-occlusive pain in sickle cell disease

BACKGROUND

Sickle cell disease (SCD) is a chronic illness that is associated with frequent admissions for vaso-occlusive episodes (VOE). Opioids are frequently utilized in pain management, but dosing is often provider dependent. Opioids cause both short-term and long-term side effects, so the minimal effective dose is desired. This study examined demand-only patient-controlled analgesia (PCA) in pediatric patients.

METHODS

A new clinical practice guideline (CPG) for a single institution was implemented, which eliminated basal infusion dosing for PCAs on hospital admission. The primary aim of this retrospective study was to evaluate length of stay (LOS) before and after implementation of a CPG of demand-only PCA and, in a selected subpopulation, addition of short-term methadone. Secondary aims included opioid utilization, acute chest syndrome (ACS), and hypoxia. Inclusion criteria included SCD, ≤21 years of age, uncomplicated VOE admission, and ≥ 3 and ≤ 8 hospital admissions for SCD pain control within one calendar year.

RESULTS

LOS decreased postintervention (7.2 ± 5.1 vs 4.5 ± 3.8 days, P < 0.001). Mean total opioid utilization in morphine equivalents mg/kg markedly decreased between the cohorts (13.3 ± 33.8 vs 3.6 ± 3.0, P < 0.001). ACS (21.9% vs 2.8%, P = 0.004) and hypoxia (28% vs 6.9%, P< 0.001) decreased significantly as well.

CONCLUSION

Bolus PCA dosing of opioids resulted in decreased LOS and reductions in opioid utilization, hypoxia, and ACS.

A systematic review of quality of life in sickle cell disease and thalassemia after stem cell transplant or gene therapy

Patients with sickle cell disease (SCD) and thalassemia experience several complications across their lifespan that lead to impairment in different health-related quality of life (HRQOL) domains. There is increasing interest in curative therapies for patients with SCD and thalassemia, including hematopoietic stem cell transplant (HSCT) and gene therapy; however, the effect of these therapies on various HRQOL domains remains unclear. Our objective was to systematically evaluate the most recent evidence for the effect of HSCT and gene therapy on HRQOL in patients with SCD and thalassemia. A systematic search of medical literature databases was conducted. A total of 16 studies (thalassemia, n = 9; SCD, n = 6; both, n = 1) involving 517 participants met inclusion criteria (thalassemia, n = 416; SCD, n = 101). HSCT was associated with a small to large positive effects in most HRQOL domains (Cohen's d; mean = 0.47; median = 0.37; range, 0.27-2.05). In thalassemia, HSCT was frequently associated with large positive effects in physical and emotional HRQOL domains (median d = 0.79 and d = 0.57, respectively). In SCD, HSCT was associated with large positive effects in all HRQOL domains. Emerging data suggest improvement in HRQOL outcomes across different domains following gene therapy in thalassemia and SCD. The quality of evidence was moderate in 13 studies (81%). HSCT has a positive impact on several HRQOL domains in patients with SCD and thalassemia; however, more longitudinal studies are warranted to assess the sustainability of these effects. Reporting HRQOL outcomes from ongoing gene therapy or gene-editing trials in SCD and thalassemia is key to better understand the benefits of such therapies.

Complement in Sickle Cell Disease: Are We Ready for Prime Time?

Sickle cell disease (SCD) is a widely spread inherited hemoglobinopathy that includes a group of congenital hemolytic anemias, all characterized by the predominance of sickle hemoglobin (HbS). Its features are anemia, predisposal to bacterial infections and complications such as vaso-occlusive crisis (VOC) or delayed hemolytic transfusion reaction (DHTR), which lead to increased rate of morbidity and mortality even in the era of hydroxyurea. The interaction between sickle cells, neutrophils, platelets or endothelial cells in small vessels results in hemolysis and has been considered the disease’s main pathophysiological mechanism. Complement activation has been reported in small cohorts of SCD patients, but the governing mechanism has not been fully elucidated. This will be important to predict the patient group that would benefit from complement inhibition. Until now, eculizumab-mediated complement inhibition has shown beneficial effects in DHTR, with limited reports in patients with VOC. In the meantime, several innovative agents are under clinical development Our state-of-the-art review summarizes current data on 1) complement activation in SCD both in steady state and crisis, 2) underlying mechanisms of complement over-activation for the clinician in the context of SCD, 3) actions of hydroxyurea and new therapeutic approaches including indirect involvement in complement activation, and 4) novel paradigms in complement inhibition.

Microvascular thrombosis: experimental and clinical implications

A significant amount of clinical and research interest in thrombosis is focused on large vessels (eg, stroke, myocardial infarction, deep venous thrombosis, etc.); however, thrombosis is often present in the microcirculation in a variety of significant human diseases, such as disseminated intravascular coagulation, thrombotic microangiopathy, sickle cell disease, and others. Further, microvascular thrombosis has recently been demonstrated in patients with COVID-19, and has been proposed to mediate the pathogenesis of organ injury in this disease. In many of these conditions, microvascular thrombosis is accompanied by inflammation, an association referred to as thromboinflammation. In this review, we discuss endogenous regulatory mechanisms that prevent thrombosis in the microcirculation, experimental approaches to induce microvascular thrombi, and clinical conditions associated with microvascular thrombosis. A greater understanding of the links between inflammation and thrombosis in the microcirculation is anticipated to provide optimal therapeutic targets for patients with diseases accompanied by microvascular thrombosis.

Randomized phase 2 trial of Intravenous Gamma Globulin (IVIG) for the treatment of acute vaso-occlusive crisis in patients with sickle cell disease: Lessons learned from the midpoint analysis

Sickle Cell Disease (SCD) is a chronic hemolytic disorder associated with frequent pain episodes, end organ damage and a shortened lifespan. Currently there exist no disease specific targeted therapies for the treatment of acute vaso-occlusive crisis (VOC) and management with analgesics and hydration is purely supportive. Improvement in understanding of disease pathophysiology has resulted in a great interest in disease modifying novel therapies and many are being evaluated in clinical trials. Here we report the results from the pre-specified mid-point analysis of the Phase 2 study of Intravenous Gamma Globulin (IVIG) for the treatment of acute VOC in patients with SCD and lessons learned.

Emerging disease-modifying therapies for sickle cell disease

Sickle cell disease afflicts millions of people worldwide and approximately 100,000 Americans. Complications are myriad and arise as a result of complex pathological pathways ‘downstream’ to a point mutation in DNA, and include red blood cell membrane damage, inflammation, chronic hemolytic anemia with episodic vaso-occlusion, ischemia and pain, and ultimately risk of cumulative organ damage with reduced lifespan of affected individuals. The National Heart, Lung, and Blood Institute’s 2014 evidence-based guideline for sickle cell disease management states that additional research is needed before investigational curative therapies will be widely available to most patients with sickle cell disease. To date, sickle cell disease has been cured by hematopoietic stem cell transplantation in approximately 1,000 people, most of whom were children, and significantly ameliorated by gene therapy in a handful of subjects who have only limited follow-up thus far. During a timespan in which over 20 agents were approved for the treatment of cystic fibrosis by the Food and Drug Administration, similar approval was granted for only two drugs for sickle cell disease (hydroxyurea and L-glutamine) despite the higher prevalence of sickle cell disease. This trajectory appears to be changing, as the lack of multimodal agent therapy in sickle cell disease has spurred engagement among many in academia and industry who, in the last decade, have developed new drugs poised to prevent complications and alleviate suffering. Identified therapeutic strategies include fetal hemoglobin induction, inhibition of intracellular HbS polymerization, inhibition of oxidant stress and inflammation, and perturbation of the activation of the endothelium and other blood components (e.g. platelets, white blood cells, coagulation proteins) involved in the pathophysiology of sickle cell disease. In this article, we present a crash-course review of disease-modifying approaches (minus hematopoietic stem cell transplant and gene therapy) for patients with sickle cell disease currently, or recently, tested in clinical trials in the era following approval of hydroxyurea.

New and emerging treatments for vaso-occlusive pain in sickle cell disease

Introduction: Acute pain from episodic vaso-occlusion (VOC) spans the lifespan of almost everyone with sickle cell disease (SCD), while additional chronic pain develops in susceptible individuals in early adolescences. Frequent acute pain with chronic pain causes significant physical and psychological morbidity, and frequent health-care utilization. Available pharmacologic therapies reduce acute pain frequency but few evidence-based therapies are available for chronic pain. Areas covered: An extensive PubMed literature search was performed with appropriate search criteria. The pathophysiology of acute pain from VOC in SCD is very complex with many events subsequent to sickle polymer formation. Sensitization of pain pathways and alterations of brain networks contributes to the experience of chronic pain. Numerous therapies targeting putative VOC mechanisms are in clinical trials, and show considerable promise. Alternative analgesic treatments for acute and chronic pain have been examined in small patient cohorts, but formal clinical trials are lacking. Expert opinion: Childhood is likely a critical window for prevention of acute and later chronic pain. New multimodal analgesic therapies are needed, particularly for chronic pain, and should be examined in clinical trials. Given the multifactorial nature of both pain and VOC, simultaneously targeting multiple mechanisms may be the optimal approach for effective preventive therapies.

Pharmacokinetics and pharmacodynamics of voxelotor (GBT440) in healthy adults and patients with sickle cell disease

Aims

Voxelotor (previously GBT440) is a haemoglobin (Hb) modulator that increases Hb‐oxygen affinity, thereby reducing Hb polymerization and sickling of red blood cells (RBCs), being developed as a once‐daily oral drug to treat sickle cell disease (SCD). This first‐in‐human study evaluated the safety, tolerability, pharmacokinetics and pharmacodynamics of voxelotor in healthy volunteers and SCD patients.

Methods

A total of 40 healthy volunteers (100, 400, 1000, 2000 or 2800 mg) and 8 SCD patients (1000 mg) were randomly assigned to a single dose of voxelotor once daily (n = 6 per group) or placebo (n = 2 per group). Twenty‐four healthy volunteers received multiple doses of voxelotor once daily for 15 days (300, 600 or 900 mg, n = 6 per group) or placebo (n = 2 per group).

Results

Voxelotor was well tolerated and exhibited a linear pharmacokinetic profile and a half‐life ranging from 61 ± 7 h to 85 ± 7 h. High partitioning into the RBC compartment provides evidence of highly specific binding to Hb. Voxelotor exhibited a concentration‐dependent left‐shift of oxygen equilibrium curves. Percent Hb modification following 900 mg voxelotor for 15 days was 38 ± 9%. Terminal half‐life of voxelotor in SCD patients (50 ± 3 h) was shorter than in healthy volunteers. Evaluation of erythropoietin, exercise testing, and haematologic parameters were consistent with normal oxygen delivery during both rest and exercise.

Conclusion

This first‐in‐human study demonstrates voxelotor was well tolerated in SCD patients and healthy volunteers and established proof of mechanism on increasing Hb‐oxygen affinity.

New insights into the pathophysiology and development of novel therapies for sickle cell disease

Although the seminal event in sickle cell disease is the polymerization of abnormal hemoglobin, the downstream pathophysiology of vasoocclusion results from heterotypic interactions between the altered, adhesive sickle cell red blood cells, neutrophils, endothelium, and platelets. Ischemia reperfusion injury, hemolysis, and oxidant damage all contribute to heightened inflammation and activation of the hemostatic system. These various pathways are the focus of emerging treatments with potential to ameliorate disease manifestations. This review summarizes the considerable progress in development of these agents despite challenges in selection of study end points and complex pathophysiology.