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

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 >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 >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 >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.

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