Development and Characterization of a Model for Inducing Fetal Hemoglobin Production in Cynomolgus Macaques (Macaca fasicularis)

Hydroxyurea induces production of fetal hemoglobin (HbF), a tetramer of α and γ globin proteins and corresponding heme molecules, normally found in less than 1% of adult RBC. Increases in circulating HbF are correlated with clinical improvement of patients with hemoglobinopathies, and hydroxyurea, as a daily medication, is the standard treatment for sickle cell anemia. Although olive baboons (Papio anubis) are considered a key model species for HbF induction, cynomolgus macaques (Macaca fasicularis) are another species that conserves the ability to produce HbF into maturity. In this study, moderate anemia was experimentally induced in cynomolgus macaques by phlebotomy, to stimulate accelerated erythropoiesis and HbF production. In contrast to previous studies, vascular access ports were implanted for phlebotomy of conscious monkeys, followed by fluid replacement. As total Hgb levels dropped, reticulocyte counts and the percentage of HbF-expressing cells increased. Once total Hgb levels declined to less than 8 g/dL, 2 courses of oral hydroxyurea (once daily for 5 d) were completed, with a 9-d interval between courses. After hydroxyurea dosing, the percentage of HbF-expressing cells and total HbF were increased significantly. In addition, a significant but transient decrease in reticulocyte count and a transient increase in MCV occurred, replicating the characteristic response of patients receiving hydroxyurea. Daily clinical observations revealed no serious health issues or decreases in food consumption or activity levels. Methods were established for assessing the patency of vascular access ports. This study details a new protocol for the safe and routine induction of moderate anemia in cynomolgus macaques and validates its use in the investigation of novel pharmacologic entities to induce the production of HbF.