GBT1118, a voxelotor analog, protects red blood cells from damage during severe hypoxia

A lack of objective metrics in Sickle Cell Disease (SCD) makes it difficult to assess individual patient therapy options or assess the effects of therapy. This is further complicated by mechanisms of action involving multiple interconnected effects, that combine to relieve SCD symptoms. In 2019, based on the increase in hemoglobin concentration observed in the HOPE trial, the Food and Drug Administration approved voxelotor (Oxbryta®, Global Blood Therapeutics) for SCD patients 12 years and older. The main mechanism of action for voxelotor was increased hemoglobin-oxygen affinity, but other mechanisms may apply. In this study, we assessed the effect of GBT1118, an Oxbryta analog, on hypoxia-induced lethal and sub-hemolytic red blood cell (RBC) membrane damage using RBC Mechanical Fragility (MF), a metric of existing membrane damage and prospective hemolysis. RBC MF was measured non-invasively using a proprietary system comprising an electromagnetic bead mill and fiberoptic spectrophotometry detection. Three cycles of severe hypoxia (<5% oxygenated hemoglobin) with follow-up reoxygenation resulted in a significant increase in RBC MF for all SCD (Hb-S >60%) samples. Supplementation with GBT1118 caused no significant changes in pre-hypoxia RBC MF. However, following GBT1118 treatment, cell stability showed significantly less degradation, as evidenced by a significantly smaller RBC MF increase after three cycles of hypoxia-reoxygenation. These findings indicate that GBT1118 prevents hypoxia-induced membrane damage in sickled RBC, in part by alternative mechanisms not associated with induced changes in hemoglobin-oxygen affinity.