Introduction
Sickle cell disease is a severe hereditary disorder affecting newborns worldwide and has historically received limited attention in drug development. Recent progress in pharmacotherapy has led to the approval of novel disease-modifying agents, including voxelotor (GBT440), an orally bioavailable compound that prevents hemoglobin polymerization by increasing oxygen affinity. While effective in reducing sickling and alleviating anemia, voxelotor has also been shown to elevate hemoglobin levels in healthy individuals through increased serum erythropoietin, raising concerns about its misuse in competitive sports. Consequently, the World Anti-Doping Agency (WADA) has classified voxelotor under category M1 of the 2023 Prohibited List. Despite its clinical significance, limited information exists on the drug’s metabolism in humans and animals.
Methods
The present study explored the metabolic profile of voxelotor using both in vitro equine liver microsome incubations and in vivo oral administration in Thoroughbred horses. Metabolite identification was carried out using liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS). Structural elucidation of metabolites was performed through interpretation of fragmentation patterns.
Results
In vitro experiments identified 31 metabolites, comprising 16 phase I metabolites (hydroxylation, reduction, dissociation), and 15 phase II metabolites including glucuronides and sulfates. In vivo analysis in horses revealed 35 metabolites, with 14 phase I metabolites, 15 glucuronide conjugates, and 6 sulfonic acid conjugates derived from both parent and modified forms. Hematological evaluation indicated changes in red blood cell count, hemoglobin concentration, packed cell volume, and platelet count, suggesting physiological effects linked to voxelotor administration.
Conclusion
This study provides the first detailed characterization of voxelotor metabolism in horses, demonstrating the formation of diverse phase I and phase II metabolites. The findings highlight voxelotor’s potential to alter hematological parameters and reinforce its inclusion in anti-doping monitoring programs.
Keywords
Voxelotor, Sickle cell disease therapeutics, Anti-doping detection, Equine metabolism, LC-HRMS, Drug metabolites