Effect of voxelotor on cardiopulmonary testing in youths with sickle cell anemia in a pilot study

Individuals with sickle cell anemia (SCA) exhibit decreased exercise capacity. Anemia limits oxygen-carrying capacity and affects cardiopulmonary fitness. The drug voxelotor raises hemoglobin in SCA. We hypothesized that voxelotor improves exercise capacity in youths with SCA.

In a single-center, open-label, single-arm, longitudinal interventional pilot study (NCT04581356), SCA patients aged 12 and older, stably maintained on hydroxyurea, were treated with 1500 mg voxelotor daily, and performed cardiopulmonary exercise testing before (CPET#1) and after voxelotor (CPET#2). A modified Bruce Protocol was performed on a motorized treadmill, and breath-by-breath gas exchange data were collected. Peak oxygen consumption (peak VO₂ ), anaerobic threshold, O₂ pulse, VE/VCO₂ slope, and time exercised were compared for each participant. The primary endpoint was change in peak VO₂ . Hematologic parameters were measured before each CPET. Patient Global Impression of Change (PGIC) and Clinician Global Impression of Change (CGIC) surveys were collected.

Ten hemoglobin SS patients aged 12-24 completed the study. All demonstrated expected hemoglobin rise, with average +1.6 g/dL (p = .003) and P₅₀ left shift of average -11 mmHg (p < .0001) with decreased oxygen off-loading at low pO₂ . The change in % predicted peak VO₂ from CPET#1 to CPET#2 ranged from -12.8% to +11.3%, with significant improvement of more than 5% in one subject, more than 5% decrease in five subjects, and insignificant change of less than 5% in four subjects. All 10 CGIC and seven of 10 PGIC responses were positive.

In a plot study of 10 youths with SCA, voxelotor treatment did not improve peak VO₂ in 9 out of 10 patients.