Discovery of Osivelotor (GBT021601): A Potent, Next-Generation Sickle Hemoglobin Polymerization Inhibitor

This report details the discovery path of GBT021601 (osivelotor) ( 16 ), a novel, small molecule, sickle hemoglobin (HbS) polymerization inhibitor. Following a streamlined testing funnel with cassette dosing in rat pharmacokinetic (PK) studies, we identified this next-generation HbS polymerization inhibitor, which had improved PK properties compared with the first-in-class drug, voxelotor ( 1 ). GBT021601 has ∼4.8-fold greater exposure and a ∼3.5-fold longer half-life in rats compared with voxelotor. In a murine model of sickle cell disease (SCD), GBT021601 treatment resulted in an increase in hemoglobin oxygen affinity, a reduction in sickling of red blood cells (RBCs), and an increase in both RBC half-life and hemoglobin levels not seen with voxelotor preclinically. The improved half-life and exposure appear to translate to similar levels of HbS occupancy at lower doses than voxelotor, thus reducing treatment burden. GBT021601 is being investigated in a phase 2/3 clinical trial for the treatment of patients with SCD (NCT05431088).