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

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          Abstract

          New treatments directly targeting polymerization of sickle hemoglobin (HbS), the proximate event in the pathophysiology of sickle cell disease (SCD), are needed to address the severe morbidity and early mortality associated with the disease. Voxelotor (GBT440) is a first-in-class oral therapy specifically developed to treat SCD by modulating the affinity of hemoglobin (Hb) for oxygen, thus inhibiting HbS polymerization and downstream adverse effects of hemolytic anemia and vaso-occlusion. GBT440-001 was a phase 1/2 randomized, double-blind, placebo-controlled, single and multiple ascending dose study of voxelotor in adult healthy volunteers and patients with SCD, followed by a single-arm, open-label extension study. This report describes results of voxelotor (500-1000 mg per day) in patients with sickle cell anemia. The study evaluated the safety, tolerability, pharmacokinetic, and pharmacodynamic properties of voxelotor and established proof of concept by improving clinical measures of anemia, hemolysis, and sickling. Thirty-eight patients with SCD received 28 days of voxelotor 500, 700, or 1000 mg per day or placebo; 16 patients received 90 days of voxelotor 700 or 900 mg per day or placebo. Four patients from the 90-day cohort were subsequently enrolled in an extension study and treated with voxelotor 900 mg per day for 6 months. All patients who received multiple doses of voxelotor for ≥28 days experienced hematologic improvements including increased Hb and reduction in hemolysis and percentage of sickled red cells, supporting the potential of voxelotor to serve as a disease-modifying therapy for SCD. Voxelotor was well tolerated with no treatment-related serious adverse events and no evidence of tissue hypoxia. These trials were registered at www.clinicaltrials.gov as #NCT02285088 and #NCT03041909.

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          Deconstructing sickle cell disease: reappraisal of the role of hemolysis in the development of clinical subphenotypes.

          Hemolysis, long discounted as a critical measure of sickle cell disease severity when compared with sickle vaso-occlusion, may be the proximate cause of some disease complications. New mechanistic information about hemolysis and its effects on nitric oxide (NO) biology and further examination of the subphenotypes of disease requires a reappraisal and deconstruction of the clinical features of sickle cell disease. The biology underlying clinical phenotypes linked to hemolysis may increase our understanding of the pathogenesis of other chronic hemolytic diseases while providing new insights into treating sickle cell disease. The pathophysiological roles of dysregulated NO homeostasis and sickle reticulocyte adherence have linked hemolysis and hemolytic rate to sickle vasculopathy. Nitric oxide binds soluble guanylate cyclase which converts GTP to cGMP, relaxing vascular smooth muscle and causing vasodilatation. When plasma hemoglobin liberated from intravascularly hemolyzed sickle erythrocytes consumes NO, the normal balance of vasoconstriction:vasodilation is skewed toward vasoconstriction. Pulmonary hypertension, priapism, leg ulceration and stroke, all subphenotypes of sickle cell disease, can be linked to the intensity of hemolysis. Hemolysis plays less of a role in the vaso-occlusive-viscosity complications of disease like the acute painful episode, osteonecrosis of bone and the acute chest syndrome. Agents that decrease hemolysis or restore NO bioavailability or responsiveness may have potential to reduce the incidence and severity of the hemolytic subphenotypes of sickle cell disease. Some of these drugs are now being studied in clinical trials.
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            Improvements in haemolysis and indicators of erythrocyte survival do not correlate with acute vaso-occlusive crises in patients with sickle cell disease: a phase III randomized, placebo-controlled, double-blind study of the Gardos channel blocker senicapoc (ICA-17043).

            Red blood cell (RBC) hydration is regulated in part by the Ca(2+) -activated K(+) efflux (Gardos) channel. Senicapoc selectively blocks potassium efflux through the Gardos channel, reducing RBC dehydration and haemolysis, and increasing haemoglobin levels in sickle cell disease (SCD). This randomized, placebo-controlled trial was designed to determine the safety and clinical efficacy of senicapoc in SCD patients. One hundred and forty-five patients were randomized to receive senicapoc and 144 patients to receive placebo for 52 weeks. Consistent with a previous study, patients in the senicapoc group had significantly increased haematocrit, haemoglobin, and decreased numbers of both dense erythrocytes and reticulocytes when compared to the placebo group. The unblinded Data Monitoring Committee terminated this study early due to a lack of efficacy when it determined that, despite improvements in anaemia and haemolysis, no significant improvement in the rate of sickle cell painful crises was observed in patients treated with senicapoc compared to those on placebo (0·38 vs. 0·31, respectively). Comparisons of the times to first, second and third crises between the senicapoc and placebo groups were not statistically significant. Nausea and urinary tract infections occurred more frequently in the senicapoc group than placebo. Serious adverse events were similar in the two groups. © 2011 Blackwell Publishing Ltd.
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              Efficacy and safety of the Gardos channel blocker, senicapoc (ICA-17043), in patients with sickle cell anemia.

              Senicapoc, a novel Gardos channel inhibitor, limits solute and water loss, thereby preserving sickle red blood cell (RBC) hydration. Because hemoglobin S polymerization is profoundly influenced by intracellular hemoglobin concentration, senicapoc could improve sickle RBC survival. In a 12-week, multicenter, phase 2, randomized, double-blind, dose-finding study, we evaluated senicapoc's safety and its effect on hemoglobin level and markers of RBC hemolysis in sickle cell anemia patients. The patients were randomized into 3 treatment arms: placebo; low-dose (6 mg/day) senicapoc; and high-dose (10 mg/day) senicapoc. For the primary efficacy end point (change in hemoglobin level from baseline), the mean response to high-dose senicapoc treatment exceeded placebo (6.8 g/L [0.68 g/dL] vs 0.1 g/L [0.01 g/dL], P < .001). Treatment with high-dose senicapoc also produced significant decreases in such secondary end points as percentage of dense RBCs (-2.41 vs -0.08, P < .001); reticulocytes (-4.12 vs -0.46, P < .001); lactate dehydrogenase (-121 U/L vs -15 U/L, P = .002); and indirect bilirubin (-1.18 mg/dL vs 0.12 mg/dL, P < .001). Finally, senicapoc was safe and well tolerated. The increased hemoglobin concentration and concomitant decrease in the total number of reticulocytes and various markers of RBC destruction following senicapoc administration suggests a possible increase in the survival of sickle RBCs. This study is registered at http://clinicaltrials.gov as NCT00040677.
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                Author and article information

                Journal
                Blood
                American Society of Hematology
                0006-4971
                1528-0020
                April 25 2019
                April 25 2019
                : 133
                : 17
                : 1865-1875
                Affiliations
                [1 ]Guy’s and St. Thomas’ NHS Foundation Trust, London, United Kingdom;
                [2 ]Department of Haematological Medicine, King’s College London, London, United Kingdom;
                [3 ]Queen’s Hospital, Romford, United Kingdom;
                [4 ]Centre for Genomics and Child Health, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom;
                [5 ]Department of Haematology, Hammersmith Hospital Campus, Imperial College London, London, United Kingdom;
                [6 ]Department of Haematology, University College London, London, United Kingdom;
                [7 ]King’s College Hospital NHS Foundation Trust, London, United Kingdom;
                [8 ]IQVIA, Reading, United Kingdom;
                [9 ]Department of Clinical Pharmacology, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom;
                [10 ]Independent Drug Development Consultant, San Francisco, CA; and
                [11 ]Global Blood Therapeutics, Inc, South San Francisco, CA
                Article
                10.1182/blood-2018-08-868893
                6484388
                30655275
                1ddb3c40-a749-4496-9945-ef74eb25199c
                © 2019
                History

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