A Selective ORAL GLYT1 Inhibitor, Improves Anemia and RED CELL Survival in a MOUSE MODEL of Beta-Thalassemia

The unbalanced hemoglobin chain synthesis in beta-thalassemias leads to hemichrome-induced damage that contributes to ineffective erythropoiesis, hemolysis and reduced red cell survival. Iron overload related to ineffective erythropoiesis and abnormally low Hepcidin (Hamp), combined with the cytotoxic effects of free heme with free-alpha-chains play a key role in the increased generation of reactive oxygen species (ROS) in beta thalassemias.[2][HA{3] Here we used a specific and selective inhibitor of the plasma membrane expressed glycine transporter GlyT1 (Ro4917838). Use of Ro4917838 has been associated with a dose-dependent decrease in MCH, Hb, soluble transferrin receptor, and increase in absolute reticulocytes and RBC counts in several animal species, attributed to reduce glycine bioavailability in erythroblasts and decreased heme synthesis. In rats, Ro4917838 reduces heme synthesis, and down-regulates erythroid transferrin receptor, but does not interfere with hepcidin regulation and systemic iron homeostasis (Winter et al. Exp Hematol, DOI: 10.1016/j.exphem.2016.07.003). We aimed to determine if reduced cellular availability of glycine in erythroblasts may reduce heme synthesis, and impact pathologic erythropoiesis in a mouse model for b-thalassemia. Wild-type control (WT) C57B6/2J, and beta-thalassemia Hbbth3/+ mice were treated with either vehicle or Ro4917838 at dosages of 3, 10, 30 mg/kg/d administered over 4 weeks once daily by gavage. [6]RO4917838 administration was associated with significant improvements of central hallmarks of the b-thalassemia pathology. Reduced erythrocyte destruction was seen bydemonstrated by [8][WM{9]as significant improvements in erythrocyte morphology and amelioration of hemoglobin reduction in reticulocytes. We also observed an impressively quick reduction of the circulating erythroblast count within 1 week of initiating treatment. This was also associated with decreased hemolysis biomarkers. Ro4917838 induced a significant reduction in extramedullary erythropoiesis and reduction in orthochromatic erythroblasts as well as insoluble alpha chain aggregates in circulating red cells. Red cell survival of b-thal mice treated with 30 mg/kg/day Ro4917838 significantly increased by more than 50%. CD71+ erythroid precursors significantly decreased in WT mice treated with Ro4917838 at 30 mg/kg and in b-thal mice at the dosage of 30 mg/kg/ d. [10]These data suggest that Ro4917838 ameliorates anemia in a b-thalassemia mouse model and positively affects ineffective erythropoiesis and red cell survival in peripheral circulation. Ro4917838 may represent a novel therapeutic approach for the treatment of anemia in b-thalassemia patients. [1] I do see the point for beta-thalassemia, but this does not apply for all thalassemias, I mean the free alpha chains. The ROS yes, they have in common. In this sentence it seems to be that the alpha chains are culprit for ROS in all thalassemias. [HA{3]I do see the point for beta-thalassemia, but this does not apply for all thalassemias, I mean the free alpha chains. The ROS yes, they have in common. In this sentence it seems to be that the alpha chains are culprit for ROS in all thalassemias. ROS was not measured, therefore I would refrain mentioning it. No data is shown. [HA{5]ROS was not measured, therefore I would refrain mentioning it. No data is shown. I propose deletion of the PK info. Although the information is correct I don't think this is the level of detail needed for the abstract. It may even be confusing as it is not the focus of the abstract to do a cross species comparison. [AK7]I propose deletion of the PK info. Although the information is correct I don't think this is the level of detail needed for the abstract. It may even be confusing as it is not the focus of the abstract to do a cross species comparison. Dosing and dosing frequency is already described above, we do not need to repeat this here. [WM{9]Dosing and dosing frequency is already described above, we do not need to repeat this here. Was the liver expression determined or the serum Hepcidin levels measured? I would rephrase it if latter is the case. [HA{11]Was the liver expression determined or the serum Hepcidin levels measured? I would rephrase it if latter is the case.