Voxelotor Treatment Interferes With Quantitative and Qualitative Hemoglobin Variant Analysis in Multiple Sickle Cell Disease Genotypes

Abstract

Objectives Voxelotor was recently approved for use in the United States as a treatment for sickle cell disease (SCD) and has been shown to interfere with the quantitation of hemoglobin (Hb) S percentage. This study aimed to determine the effect of voxelotor on the quantitation of hemoglobin variant levels in patients with multiple SCD genotypes. Methods In vitro experiments were performed to assess the impact of voxelotor treatment on hemoglobin variant testing. Whole blood samples were incubated with voxelotor and then analyzed by routinely used quantitative and qualitative clinical laboratory methods (high-performance liquid chromatography [HPLC], capillary zone electrophoresis [CZE], and acid and alkaline electrophoresis). Results Voxelotor modified the α-globin chain of multiple hemoglobins, including HbA, HbS, HbC, HbD-Punjab, HbE, HbA2, and HbF. These voxelotor-hemoglobin complexes prevented accurate quantitation of multiple hemoglobin species, including HbS, by HPLC and CZE. Conclusions Technical limitations in quantifying HbS percentage may preclude the use of HPLC or CZE for monitoring patients treated with voxelotor. Furthermore, it is unclear whether HbS-voxelotor complexes are clinically equivalent to HbS. Consensus guidelines for reporting hemoglobin variant percentages for patients taking voxelotor are needed, as these values are necessary for determining the number of RBC units to exchange in acute situations.

How do we monitor hemoglobin S in patients who undergo red blood cell exchange and take voxelotor?

“…The majority of adult hemoglobin is composed of hemoglobin A (HbA), which is a tetramer composed of two alpha and two beta globin chains. Hemoglobin S (HbS) is the result of an autosomal recessive point mutation leading to the substitution of glutamic acid with valine on the beta chain of hemoglobin 1,5 . SCD occurs in individuals who are homozygous for HbS (HbSS) or who inherit HbS with an additional hemoglobinopathy (for example, hemoglobin C or beta thalassemia) 1 .…”

“…Hemoglobin S (HbS) is the result of an autosomal recessive point mutation leading to the substitution of glutamic acid with valine on the beta chain of hemoglobin 1,5 . SCD occurs in individuals who are homozygous for HbS (HbSS) or who inherit HbS with an additional hemoglobinopathy (for example, hemoglobin C or beta thalassemia) 1 . HbS deoxygenation leads to polymerization of HbS, deformation of red blood cells (RBCs), occlusion of microvasculature, and decreased RBC lifespan.…”

“…Voxelotor is a small molecule which acts by reversibly binding to an alpha chain of hemoglobin. This stabilizes oxygenated hemoglobin and prevents hemoglobin polymerization 1,5 . In theory, by decreasing the sickling of RBCs, the overall lifespan of RBCs should be increased and a decrease in adverse events due to sickled cells should be seen 1,5 .…”

“…This stabilizes oxygenated hemoglobin and prevents hemoglobin polymerization 1,5 . In theory, by decreasing the sickling of RBCs, the overall lifespan of RBCs should be increased and a decrease in adverse events due to sickled cells should be seen 1,5 . A phase 3 randomized controlled trial reported that, at 24 weeks, patients who received 1500 mg voxelotor daily (orally) showed greater reductions in indirect bilirubin ( p < .001) and reticulocyte percent ( p < .001) as compared to placebo.…”

“…Voxelotor has recently been approved by the U.S. Food and Drug Administration (FDA) for the treatment of sickle cell disease (SCD). Voxelotor has been reported to interfere with hemoglobin quantification methodologies that are in common use 1‐3 for evaluating patients with hemoglobinopathies. There is still a general lack of awareness of potential voxelotor interference in assays for quantitative analysis of hemoglobin variants.…”