Oxbryta prevents red blood cell sickling in SCD children: Study

Medication may aid oxygen delivery, per report from Phase 2a trial

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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An illustration shows a close-up view of red blood cells.

Oxbryta (voxelotor), an oral medication approved to treat sickle cell disease (SCD), prevented children’s red blood cells from stiffening into a characteristic sickle-like shape and breaking down, possibly helping more oxygen to get into tissues in the body.

That’s according to a study reporting data on 10 children taking part in HOPE-KIDS 1 (NCT02850406), an ongoing Phase 2a clinical trial testing the safety of Oxbryta and how well it works when given once daily at a weight-based dose.

The study, “Voxelotor improves red blood cell functionality in children with sickle cell anaemia: An ancillary study of the HOPE-KIDS 1 trial,” was published as a short report in the eJHaem journal.

SCD occurs when a faulty version of hemoglobin, the protein that carries oxygen to tissues in the body, clumps together to form rigid chains that cause red blood cells to take on the sickle-like shape characteristic of the disease.

Sickle-shaped red blood cells become stiff and sticky and are more likely to break down quickly in a process called hemolysis, leaving fewer red blood cells and less working hemoglobin available to deliver a continuous stream of oxygen to tissues.

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Chatting with mothers of children with sickle cell disease

Getting more oxygen to tissues

Developed by Global Blood Therapeutics, now part of Pfizer, Oxbryta is approved in the U.S. to treat SCD in adults and children as young as 4. It’s approved for patients 12 and older in the European Union, the U.K., and some countries in the Middle East.

Oxbryta works by helping hemoglobin hold on to oxygen, preventing it from forming rigid chains inside red blood cells. This in turn helps red blood cells maintain their normal shape, leading to a rapid and sustained increase in hemoglobin levels and reducing hemolysis.

Researchers from Emory Children’s Center in Atlanta and Pfizer set out to understand how Oxbryta improves the way red blood cells work. They focused on evaluating deformability, a feature that allows red blood cells to change shape and travel through even the smallest blood vessels.

The study tracked 10 children with SCD, ages 4 to 11, who received treatment with Oxbryta for 48 weeks as part of the HOPE-KIDS 1 clinical trial. Before treatment, their mean hemoglobin levels were lower than normal, ranging from 76 to 100 grams per liter (g/L).

After 24 weeks (about six months) of treatment, seven (70%) of the children had an increase in hemoglobin levels of at least 10 g/L, with six (60%) reaching levels greater than 100 g/L. Markers of hemolysis decreased from 12 weeks onward.

To check the effect of Oxbryta on red blood cell deformability, researchers used ektacytometry, a gold-standard technique that allows them to measure the degree to which red blood cells change shape when subject to shear stress. Shear stress is a type of stress that tends to cause deformation in a material or cell.

Up to 48 weeks of treatment with Oxbryta led to improvements in red blood cell deformability across an osmotic gradient, that is, increasing differences in concentration between two solutions. Improvements in deformability were also observed in the presence of low oxygen levels, likely because Oxbryta increased the binding of oxygen to hemoglobin.

These “improvements may lead to prolonged sickle [red blood cell] survival and oxygen delivery to tissues,” the researchers wrote. However, as deformability “is highest in the early years of life, these findings may not be generalizable to adults with SCD,” they wrote.