Cooperative Regulation of the Activity of Factor Xa within Prothrombinase by Discrete Amino Acid Regions from Factor Va Heavy Chain†

ABSTRACT: The prothrombinase complex catalyzes the activation of prothrombin to R-thrombin. We have repetitively shown that amino acid region 695DYDY698 from the COOH terminus of the heavy chain of factor Va regulates the rate of cleavage of prothrombin at Arg271 by prothrombinase. We have also recently demonstrated that amino acid region 334DY335 is required for the optimal activity of prothrombinase. To assess the effect of these six amino acid residues on cofactor activity, we created recombinant factor Va molecules combining mutations at amino acid regions 334–335 an

Results from Part A of the Hemoglobin Oxygen Affinity Modulation to Inhibit HbS Polymerization (HOPE) Trial (GBT440-031), a Placebo-Controlled Randomized Study Evaluating Voxelotor (GBT440) in Adults and Adolescents with Sickle Cell Disease

Abstract Background: Sickle cell disease (SCD) is a genetic disorder in which deoxygenation results in polymerization of mutated hemoglobin S (HbS) and triggers the downstream effects of red blood cell (RBC) deformation (sickling), hemolytic anemia, vaso-occlusion, inflammation, predisposition to infection, and chronic organ damage. Two distinct pathophysiologic mechanisms of SCD-severe anemia and vasculopathy-overlap to cause severe morbidity. Chronic anemia and recurrent cycles of ischemia-reperfusion injury, often manifesting as fatigue and/or pain (vaso-occlusive crisis [VOC]), accumulate over the lifespan, resulting in end-organ parenchymal damage. The severity of steady-state anemia predicts CNS injury (including stroke and neurocognitive impairment), renal disease, and cardiopulmonary dysfunction (pulmonary hypertension). Long-term complications contribute to decreased quality of life and are associated with early death. Voxelotor (GBT440) is an oral once-daily therapy that modulates Hb affinity for oxygen, thereby inhibiting HbS polymerization and the resultant sickling of RBCs, potentially interrupting the molecular pathogenesis of the disease. The Hemoglobin Oxygen Affinity Modulation to Inhibit HbS PolymErization (HOPE) study (NCT03036813) is an ongoing, phase 3, randomized, double-blind, placebo-controlled, multicenter study to evaluate the efficacy and safety of voxelotor in patients with SCD aged 12 to 65 years. Methods: Part A of the HOPE study encompasses the first approximately 150 randomized patients, a group pre-specified in the protocol for analysis. Part A is a comparison of 2 doses of voxelotor (900 and 1500 mg/day) with placebo in patients treated for at least 12 weeks. The primary endpoint is an increase in Hb &gt;1 g/dL from baseline (Hb responder). Secondary endpoints include SCD symptom assessment using a novel patient-reported outcome (PRO) measure, VOC during the treatment period, and change from baseline in measures of hemolysis (including % reticulocytes and unconjugated bilirubin). Eligible patients must have SCD (HbSS, HbSC, HbSβ0 thalassemia, or other variants), Hb ≥5.5 and ≤10.5 g/dL, and at least 1 VOC in the 12 months prior to study entry. Hydroxyurea is allowed if the dose has been stable for at least 90 days prior to study entry. Results: 154 patients with a median age of 28 years (range, 12-59), 42% male, have received treatment for a median of 21.9 weeks (voxelotor overall, range 1.7- 65.1) and 22.4 weeks (placebo, range 1.7-44.7). The majority have HbSS/HbSB0 genotype: 94% (900 mg), 92% (1500 mg), and 90% (placebo). Hydroxyurea use at study entry was 67% (900 mg), 62% (1500 mg), and 64% (placebo). Median Hb at study entry was 8.3 g/dL (900 mg; range, 6.3-10.8), 8.6 g/dL (1500 mg; range, 5.9-10.8), and 8.5 g/dL (placebo; range, 6.1-10.4). Data for Hb and measures of hemolysis at week 12 are available for 40 patients in the 900 and 1500 mg arms and 44 patients in the placebo arm. At week 12, the proportion of patients with a &gt;1-g/dL increase in Hb from baseline was significantly larger for both voxelotor 900 mg and 1500 mg arms, compared with placebo (Table 1). Consistent with the improvements in Hb, treatment with voxelotor resulted in concordant and statistically significant improvement in measures of hemolysis (reticulocytes and indirect bilirubin) from baseline. Change from baseline in Hb at week 12 is shown in Table 2 and Figure 1. Treatment-related adverse events reported in 3 or more patients in any of the treatment arms were diarrhea (3 at 900 mg, 3 at 1500 mg, 1 on placebo), nausea (3 at 900 mg, 2 at 1500 mg, 3 on placebo), and vomiting (2 at 900 mg, 0 at 1500 mg, 3 on placebo). Data on additional endpoints will be provided at the time of the presentation. Conclusions: Data from Part A of the HOPE study demonstrate that treatment with voxelotor resulted in a dose-dependent increase in Hb with a large proportion of patients achieving Hb &gt;1 g/dL improvement from baseline compared with placebo at 12 weeks. In addition, there was a dose-dependent decrease in hemolysis markers. Voxelotor was generally well tolerated at both doses. Hemolytic anemia of SCD has severe and life-threatening consequences and presents an unmet medical need. Voxelotor has potential to ameliorate complications of anemia associated with SCD. Disclosures Vichinsky: bluebird bio: Membership on an entity's Board of Directors or advisory committees; Protagonist: Research Funding; Global Blood Therapeutics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Howard:Novartis: Speakers Bureau; Terumo: Speakers Bureau; Addmedica: Speakers Bureau; Global Blood Therapeutics: Consultancy. Ataga:Modus Therapeutics: Honoraria; Pfizer: Research Funding; Bioverativ: Honoraria, Membership on an entity's Board of Directors or advisory committees; Global Blood Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals: Honoraria. Brown:Global Blood Therapeutics: Consultancy, Research Funding. Hassab:Global Blood Therapeutics: Research Funding. Telfer:Pfizer: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Honoraria, Research Funding; Global Blood Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Terumo: Honoraria; ApoPharma Inc.: Membership on an entity's Board of Directors or advisory committees. Kanter:Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; bluebird bio: Membership on an entity's Board of Directors or advisory committees, Research Funding; ASH: Membership on an entity's Board of Directors or advisory committees; Sancilio: Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Apopharma: Research Funding; Global Blood Therapeutics: Research Funding; NHLBI: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding. Lehrer-Graiwer:Global Blood Therapeutics: Employment. Sherman:Global Blood Therapeutics: Employment. Tonda:Global Blood Therapeutics: Employment. Intondi:Global Blood Therapeutics: Employment. Yaron:Global Blood Therapeutics: Employment. Ware:Bristol Myers Squibb: Research Funding; Addmedica: Research Funding; Nova Laboratories: Consultancy; Biomedomics: Research Funding; Global Blood Therapeutics: Other: advisory board; Agios: Other: advisory board; Novartis: Membership on an entity's Board of Directors or advisory committees. </jats:sec

A Phase 3 Randomized Trial of Voxelotor in Sickle Cell Disease

In a trial evaluating two daily-dose levels of voxelotor, which binds to sickle hemoglobin and prevents polymerization under hypoxic conditions, hemoglobin levels increased by more than 1 g per deciliter in approximately half the patients who received the drug, and markers of hemolysis decreased. Toxic effects were mainly low grade and not different from those with placebo.Background Deoxygenated sickle hemoglobin (HbS) polymerization drives the pathophysiology of sickle cell disease. Therefore, direct inhibition of HbS polymerization has potential to favorably modify disease outcomes. Voxelotor is an HbS polymerization inhibitor. Methods In a multicenter, phase 3, double-blind, randomized, placebo-controlled trial, we compared the efficacy and safety of two dose levels of voxelotor (1500 mg and 900 mg, administered orally once daily) with placebo in persons with sickle cell disease. The primary end point was the percentage of participants who had a hemoglobin response, which was defined as an increase of more than 1.0 g per deciliter from baseline at week 24 in the intention-to-treat analysis. Results A total of 274 participants were randomly assigned in a 1:1:1 ratio to receive a once-daily oral dose of 1500 mg of voxelotor, 900 mg of voxelotor, or placebo. Most participants had sickle cell anemia (homozygous hemoglobin S or hemoglobin S beta(0)-thalassemia), and approximately two thirds were receiving hydroxyurea at baseline. In the intention-to-treat analysis, a significantly higher percentage of participants had a hemoglobin response in the 1500-mg voxelotor group (51%; 95% confidence interval [CI], 41 to 61) than in the placebo group (7%; 95% CI, 1 to 12). Anemia worsened between baseline and week 24 in fewer participants in each voxelotor dose group than in those receiving placebo. At week 24, the 1500-mg voxelotor group had significantly greater reductions from baseline in the indirect bilirubin level and percentage of reticulocytes than the placebo group. The percentage of participants with an adverse event that occurred or worsened during the treatment period was similar across the trial groups. Adverse events of at least grade 3 occurred in 26% of the participants in the 1500-mg voxelotor group, 23% in the 900-mg voxelotor group, and 26% in the placebo group. Most adverse events were not related to the trial drug or placebo, as determined by the investigators. Conclusions In this phase 3 randomized, placebo-controlled trial involving participants with sickle cell disease, voxelotor significantly increased hemoglobin levels and reduced markers of hemolysis. These findings are consistent with inhibition of HbS polymerization and indicate a disease-modifying potential. (Funded by Global Blood Therapeutics; HOPE ClinicalTrials.gov number, .