Mitapivat Improves Transfusion Burden and Reduces Iron Overload in Thalassemic Mice

Mitapivat, an oral activator of pyruvate kinase (PK), was recently shown to improve b-thalassemic anemia with a reduction of ineffective erythropoiesis and an amelioration of b-thalassemic red cell features in a mouse model for b-thalassemia (Hbb ^3th/+ mice).). These changes were also associated with a beneficial effect on iron homeostasis by modulation of duodenal DMT1 expression (Matte A et al JCI 2021). Two clinical studies have shown improvement of anemia and ineffective erythropoiesis with mitapivat treatment in patients with non-transfusion-dependent (NTD) thalassemia (Kuo et al. EHA 2021). Based on these results, Phase 3 studies in both NTD and TD thalassemia are currently on going.

The objective of this preclinical study was to determine if treatment with mitapivat affects the length between transfusion of red blood cells (RBCs) and the liver iron concentration (LIC). Using a previously established murine model of RBCs transfusions (Park Y et al Blood 2020), in Hbb ^3th/+ mice, we used Hb 10.5 g/dL as threshold for RBCs transfusion, with washed RBCs, at 40% Hct (400 uL total volume infused). The animals were divided into two groups: vehicle and mitapivat (50mg/Kg by gavage BID for up to 61 days).The length of the interval between transfusions increased in mitapivat treated compared to vehicle treated animals (transfusion interval: 13.8±1.0 days vs vehicle 10.5±1.0 days respectively n=4 and n=3). In both groups, the transfusion regimen induced a significant reduction in spleen weight/mouse weight ratio and in extramedullary erythropoiesis. We also found a significant reduction in liver iron content (LIC) in mitapivat treated compared to vehicle treated animals. We then evaluated the effects of mitapivat in combination with iron chelation using deferiprone (DFP,1.25 mg/mL, drinking water). Casu et al. have previously shown in the same mouse model for β-thal that DFP did not affect erythropoiesis. In the β-thal mice, we did not find negative effects on hematologic parameters when mitapivat (50 mg/Kg/d by gavage BID) was co-administrated with DFP for 28 days. LIC was reduced in mitapivat treated mice and in mitapivat +DFP treated β-thal mice was further decreased compared to vehicle treated animals. This allowed us to reduce DFP dosage from 1.25 to 0.8 mg/mL in mitapivat treated β-thal mice. These data show that in mouse model of transfused β-thalassemia, mitapivat increases the time interval between transfusions, reduces transfusion burden and allows a reduction of the dosing iron chelation with DFP. Thus, mitapivat might represent an interesting option in transfusion dependent β-thalassemic patients, being transfusion burden still an unmet need in this patient population.