Safety and efficacy of voxelotor in pediatric patients with sickle cell disease aged 4 to 11 years.

BACKGROUND: Sickle cell disease (SCD) is a devastating, multisystemic disorder that affects millions of people worldwide. The earliest clinical manifestations of SCD can affect infants as young as 6 months of age, and pediatric patients are at risk for acute and life-threatening complications. Early intervention with treatments that target the underlying pathophysiological mechanism of SCD, sickle hemoglobin (HbS) polymerization, are expected to slow disease progression and circumvent disease-associated morbidity and mortality. PROCEDURE: The HOPE-KIDS 1 trial (NCT02850406) is an ongoing four-part, phase 2a, open-label, single- and multiple-dose study to evaluate the pharmacokinetics, efficacy, and safety of voxelotor-a first-in-class HbS polymerization inhibitor-in patients aged 6 months to 17 years with SCD. Initial findings from a cohort of 45 patients aged 4 to 11 years who received voxelotor treatment for up to 48 weeks are reported. RESULTS: Hemoglobin (Hb) response, defined as a >1.0 g/dl increase from baseline, was achieved at week 24 by 47% (n = 16/34) of patients with Hb measurements at baseline and week 24. At week 24, 35% (n = 12/34) and 21% (n = 7/34) of patients had a >1.5 g/dl increase and a >2.0 g/dl increase from baseline in Hb concentration, respectively. Concurrent improvements in hemolytic markers were observed. Voxelotor was well tolerated in this young cohort, with no newly emerging safety signals. CONCLUSIONS: Based on its mechanism as an HbS polymerization inhibitor, voxelotor improves Hb levels and markers of hemolysis and has the potential to mitigate SCD-related complications; these results support its use in patients aged ≥4 years.

Practice patterns of stroke screening and hydroxyurea use in children with sickle cell disease: a survey of health care providers.

Incidence of stroke in sickle cell disease (SCD) has declined with the use of transcranial Doppler ultrasound and chronic transfusion therapy. There is little information regarding their use in genotypes other than HbSS and HbSß. Silent cerebral infarcts (SCIs) have been identified by magnetic resonance imaging (MRI) in SCD patients and it is believed that these may increase the risk of overt stroke. No evidence-based guidelines exist regarding MRI screening for SCIs. Hydroxyurea is a standard therapy in patients with history of acute chest syndrome and severe, recurrent, SCD-associated pain episodes, but has not been established for use with other sickle-associated morbidities. A total of 102 institutions received a survey (with 62 responses) to assess the use of transcranial Doppler ultrasound for stroke screening, use of screening MRI for SCIs, and institutional patterns for prescribing hydroxyurea. Nineteen percent of institutions screen genotypes other than HbSS and HbSß, and 24% use MRI to screen for SCIs. Twenty-six percent of institutions prescribed hydroxyurea in patient found to have SCIs. Results indicate significant variation in stroke screening and hydroxyurea use often correlating with clinic size, number of physician providers, and geographic location. There are currently no evidence-based guidelines to support many of these practices.

Oxidant-mediated modification of the cellular thiols is sufficient for arginase activation in cultured cells.

Increased arginase activity in the vasculature has been implicated in the regulation of nitric oxide (NO) homeostasis, leading to the development of vascular disease and the promotion of tumor cell growth. Recently, we showed that cysteine, in the presence of iron, promotes arginase activity by driving the Fenton reaction. In the present report, we showed that induction of oxidative stress in erythroleukemic cells with the thiol-specific oxidant, diamide, led to an increase in arginase activity by 42% (P = 0.02; vs. control). By using specific antibodies, it was demonstrated that this increase correlated with an increase in arginase-1 levels in the cells and with corresponding decreases in glutathione and protein thiol levels. Treatment of cells with aurothiomalate (ATM), a protein thiol-complexing agent, diminished the activity of arginase and arginase-1 levels by 19.5 and 35.2%, respectively (vs. control) and significantly decreased both glutathione and protein thiol levels, further implicating the thiol redox system in the cellular activation of arginase. Furthermore, diamide significantly altered the kinetics of arginase, resulting in the doubling of its V(max) (vs. control). Our presented data demonstrate, for the first time that the intracellular arginase activation is may be enhanced in part, via a cellular thiol-mediated mechanism.

Transfusional iron overload in children with sickle cell anemia on chronic transfusion therapy for secondary stroke prevention.

Chronic transfusion reduces the risk of recurrent stroke in children with sickle cell anemia (SCA) but leads to iron loading. Management of transfusional iron overload in SCA has been reported as suboptimal [1], but studies characterizing monitoring and treatment practices for iron overload in children with SCA, particularly in recent years with the expansion of chelator options, are lacking. We investigated the degree of iron loading and treatment practices of 161 children with SCA receiving transfusions for a history of stroke who participated in the Stroke with Transfusions Changing to Hydroxyurea (SWiTCH) trial. Data obtained during screening, including past and entry liver iron concentration (LIC) measurements, ferritin values, and chelation were analyzed. The mean age at enrollment was 12.9 ± 4 years and the mean duration of transfusion was 7 ± 3.8 years. Baseline LIC (median 12.94 mg/g dw) and serum ferritin (median 3,164 ng/mL) were elevated. Chelation therapy was initiated after a mean of 2.6 years of transfusions. At study entry, 137 were receiving chelation, most of whom (90%) were receiving deferasirox. This study underscores the need for better monitoring of iron burden with timely treatment adjustments in chronically transfused children with SCA.

The impact of parenteral narcotic choice in the development of acute chest syndrome in sickle cell disease.

BACKGROUND: Acute chest syndrome (ACS) represents a serious morbidity and often fatal complication in patients with sickle cell disease. Painful episodes which require hospitalization are most often treated with opioids, which may then influence the development of ACS. Nalbuphine is a parenteral opioid which effectively treats pain and may cause less ACS. PROCEDURE: This retrospective chart review documented 988 admissions for painful episodes at 2 institutions and recorded the incidence of ACS and opioid used. RESULTS: At the Children's Hospital in St Louis, Missouri, the incidence of ACS in patients treated with morphine alone was 10.8% versus at the Children's Mercy Hospital in Kansas City, Missouri, the incidence was 2.1% for patients treated solely with nalbuphine. CONCLUSIONS: When nalbuphine is used alone as the single parenteral opioid agent to treat painful episodes in patients with sickle cell disease, the incidence of ACS is less than when compared with other opioids used to treat pain.

Serum ferritin level changes in children with sickle cell disease on chronic blood transfusion are nonlinear and are associated with iron load and liver injury.

Chronic blood transfusion is increasingly indicated in patients with sickle cell disease. Measuring resulting iron overload remains a challenge. Children without viral hepatitis enrolled in 2 trials for stroke prevention were examined for iron overload (STOP and STOP2; n = 271). Most received desferrioxamine chelation. Serum ferritin (SF) changes appeared nonlinear compared with prechelation estimated transfusion iron load (TIL) or with liver iron concentrations (LICs). Averaged correlation coefficient between SF and TIL (patients/observations, 26 of 164) was r = 0.70; between SF and LIC (patients/observations, 33 of 47) was r = 0.55. In mixed models, SF was associated with LIC (P = .006), alanine transaminase (P = .025), and weight (P = .026). Most patients with SF between 750 and 1500 ng/mL had a TIL between 25 and 100 mg/kg (72.8% +/- 5.9%; patients/observations, 24 of 50) or an LIC between 2.5 and 10 mg/g dry liver weight (75% +/- 0%; patients/observations, 8 of 9). Most patients with SF of 3000 ng/mL or greater had a TIL of 100 mg/kg or greater (95.3% +/- 6.7%; patients/observations, 7 of 16) or an LIC of 10 mg/g dry liver weight or greater (87.7% +/- 4.3%; patients/observations, 11 of 18). Although SF changes are nonlinear, levels less than 1500 ng/mL indicated mostly acceptable iron overload; levels of 3000 ng/mL or greater were specific for significant iron overload and were associated with liver injury. However, to determine accurately iron overload in patients with intermediately elevated SF levels, other methods are required. These trials are registered at www.clinicaltrials.gov as #NCT00000592 and #NCT00006182.

Growth inhibitory and differentiation effects of chloroquine and its analogue on human leukemic cells potentiate fetal hemoglobin production by targeting the polyamine pathway.

Elevated arginase activity has been implicated in several pathological conditions in sickle cell disease (SCD) and other inflammatory disorders. Recently, we showed that chloroquine (CQ), an anti-malarial and anti-rheumatoid drug, displays a competitive mode of inhibition on sickle erythrocyte arginase. However, the effects of CQ and its analogue, hydroxychloroquine (HCQ) on erythroid differentiation leading to induced fetal hemoglobin (Hb F) production is unknown. In the present study, we obtained evidence of the anti-proliferative and differentiation effects of CQ and HCQ at pharmacologically attainable concentrations. This differentiation effect was linked to a dose-dependent inhibition of arginase activity and induced hemoglobinization, as Hb F synthesis was increased by 3.4- and 3.2-fold for CQ or HCQ, respectively. Treatment of K562 cells with lipopolysaccharide (LPS) or 8-bromo-cAMP (Br-cAMP) failed to reverse the inhibitory effects of CQ or HCQ on arginase activity. Indeed, the combination of Br-cAMP with CQ in LPS-treated cells resulted in a significant enhancement of Hb F and total hemoglobin production. Further, we showed that CQ or HCQ maximally stimulated intracellular cGMP levels by 6.6- and 3.0-fold at 6 and 3h, respectively, as demonstrated by immunosorbent assay. However, co-treatment of K562 cells with CQ or HCQ in the presence of inhibitors of sGC-PKG-pathways reduced Hb F stimulation, suggesting the possible involvement of the sGC-PKG pathway. This is the first evidence demonstrating the capacity of anti-rheumatoid drugs to modulate the arginine-pathway and result in the enhancement of Hb F production, and thus may provide a paradigm for targeted therapy of hemoglobinopathies and other inflammation-related disorders.

Cysteine-iron promotes arginase activity by driving the Fenton reaction.

Impairment of nitric oxide bioavailability secondary to increased arginase activity and overproduction of reactive oxygen species (ROS) is thought to be a major cause of vascular complications in sickle cell disease (SCD). However, the role of ROS in the induction of arginase activity is unknown. This study investigated whether the mechanism of arginase activation involves the ROS produced during oxidative stress. Our study reveals that cysteine-iron dose-dependently stimulated arginase activity with a corresponding increase in (.)OH radical formation. The ()OH radicals produced were significantly inhibited by salicylic acid derivatives and superoxide dismutase. Surprisingly, the inhibition of (.)OH radicals parallels the inhibition of arginase activity, thus suggesting the role of cysteine-iron in the stimulation of arginase via the Fenton reaction. This is the first evidence demonstrating the participation of (.)OH radicals in the stimulation of arginase activity, and thus provides novel avenues for therapeutic modalities in hemoglobinopathies and other inflammation-mediated diseases.

Disseminated nontuberculous mycobacterial infections in sickle cell anemia patients.

Nontuberculous mycobacteria (NTM) are ubiquitous in nature and have been implicated in skin/soft-tissue, pulmonary, middle ear, bone, and surgical/traumatic wound infections. Disseminated disease occurs infrequently and almost exclusively in the immunocompromised. We describe the first 2 reported cases of disseminated Mycobacterium fortuitum infection in teenagers with sickle hemoglobinopathy. Both had central venous catheters (CVCs), frequent admissions for vaso-occlusive painful episode and received hydroxyurea. Diagnosis was confirmed by multiple positive blood cultures and pulmonary dissemination occurred in both. Both had successful treatment after CVC removal and combination drug therapy. Positive cultures persisted in 1 patient due to drug resistance emphasizing the need for accurate susceptibility data. NTM infection should be added to the list of pathogens in sickle cell patients with CVCs and fever. Investigation for disseminated disease should be undertaken based on clinical signs and symptoms. Although some routine blood culture systems can identify NTM, specific mycobacterial blood culture is optimal. Removal of involved CVCs is essential and treatment of NTM must be guided by susceptibilities. As dissemination almost always occurs in those with impaired cellular immunity, human immunodeficiency virus testing should be performed. Hydroxyurea may be a risk factor for dissemination and needs further evaluation.

Quality of life among children with sickle cell disease receiving chronic transfusion therapy.

Sickle cell disease (SCD) is a genetic disorder that is most prevalent among those of African American and Mediterranean descent. Hemoglobin SS is the most severe form of SCD and carries an increased risk for stroke. Although the initial treatment for stroke is an exchange transfusion, the use of routine, chronic transfusion therapy (CTT) has been shown to help prevent this neurological injury. The treatment plan is rigorous and time consuming, both of which impact one's quality of life (QoL). The purpose of this study was to explore QoL, from the child's perspective, as it is affected by CTT Semistructured interviews were performed on 10 children undergoing CIT: Five themes emerged from the data: (a) pain, (b) school issues, (c) disease knowledge, (d) transfusion therapy, and (e) having a stroke. Data from this study reveal that CTT does have an impact on QoL. This information is important to share with those making CTT treatment decisions.

Stroke and conversion to high risk in children screened with transcranial Doppler ultrasound during the STOP study.

The Stroke Prevention Trial in Sickle Cell Anemia (STOP) was a randomized multicenter controlled trial comparing prophylactic blood transfusion with standard care in sickle cell anemia (SCA) children aged 2 to 16 years selected for high stroke risk by transcranial Doppler (TCD). More than 2000 children were screened with TCD to identify the 130 high-risk children who entered the randomized trial. A total of 5613 TCD studies from 2324 children were evaluated. We also collected information on stroke. We describe the changes in TCD with repeated testing and report the outcome without transfusion in the STOP screened cohort. Risk of stroke was higher with abnormal TCD than with normal or conditional TCD (P <.001) or inadequate TCD (P =.002), and risk with conditional TCD was higher than with normal TCD (P <.001). Repeated TCD in 1215 children showed that the condition of 9.4% of children became abnormal during observation. Younger patients and those with higher initial flow velocities were most likely to convert to abnormal TCDs. Screening in STOP confirmed the predictive value of TCD for stroke. Substantial differences in the probability of conversion to abnormal TCD were observed, with younger children and those with higher velocity more likely to have an abnormal TCD with rescreening.

Alpha Thalassemia is associated with decreased risk of abnormal transcranial Doppler ultrasonography in children with sickle cell anemia.

PURPOSE: Cerebrovascular complications of sickle cell disease (SCD) are common, but the risk factors remain unclear. The multicenter Stroke Prevention Trial in Sickle Cell Anemia (STOP) provided an opportunity to examine alpha thalassemia-2 as a modifying risk factor, using abnormal transcranial Doppler ultrasonography (TCD) as a surrogate marker for cerebrovascular disease. The authors hypothesized that children with abnormal TCD are less likely to have alpha thalassemia-2, and an increased hemoglobin level accounts for this protective effect. METHODS: A retrospective study was conducted of children with SCD who had both alpha gene and TCD data from STOP: 128 with TCD of at least 200 cm/s (abnormal TCD) and 172 with TCD less than 170 cm/s (normal TCD). RESULTS: Alpha thalassemia-2 was more frequent in the normal TCD group compared with the abnormal TCD group. The odds ratio for normal TCD and alpha thalassemia-2 was 4.1. Adjusting for either hemoglobin level or red cell size (mean corpuscular volume) reduced the odds ratio only slightly. Age, normal TCD, and alpha thalassemia-2 had significant statistical interaction, so that alpha thalassemia-2 was not related to TCD for age 10 years or older. CONCLUSIONS: The frequency of alpha thalassemia-2 was significantly higher in children with normal TCD. Speculation on mechanisms of effect includes improved erythrocyte deformability, reduced red cell adhesion, and reduced nitric oxide scavenging in alpha thalassemia-2. The association of alpha thalassemia-2 and normal TCD adds to the evidence on the protective effects of alpha thalassemia-2 in SCD and highlights the contribution of epistatic factors.