The Pyruvate Kinase Activator Mitapivat Ameliorates Anemia and Prevents Iron Overload in a Mouse Model of Hereditary Spherocytosis

Hereditary spherocytosis (HS) is the most common cause of inherited red cell membranopathy, due to mutations in genes encoding for membrane or cytoskeletal proteins, including band 3, ankyrin, spectrin, band 4.1 or band 4.2. Membrane instability results in membrane surface area loss and generation of spherocytic red cells with elevated MCHC, decreased cellular deformability and reduced red cell survival, due to splenic sequestration. Clinical management of the hemolytic anemia due to HS depends on the age of the patient and the severity of anemia. Splenectomy is indicated in children with symptomatic anemia. A classic diagnostic test for HS is the incubated osmotic fragility: this test highlights the crucial role that ATP content plays in maintenance of normal RBC function including membrane stability: it is generally believed that the increased fragility of HS is the result of abnormal ATP depletion over the 24hr incubation. We explored the hypothesis that pyruvate kinase activator, mitapivat, by modulating ATP content could have potential beneficial effects for HS RBCs in band 4.2^-/- mice, a well-established model of HS (Peters LL et al JCI 103: 1527, 1999). 4.2^-/- mice exhibit moderate anemia which recapitulates most of the features of typical human HS without showing the profound anemization seen in other mouse models. Oral AG-348 administration to band 4.2^-/- mice at dosages of 200 mg/kg/day over 6 months resulted in (i) improvement of anemia with reduced reticulocyte count (Hb 11.6±0.035 g/dL, n=17 vs 13.104±0.09 g/dL, n=9; P<0.05; retics: 11.4±0.1%, n=16 vs 7.6±0.2%, n=7 % P<0.05) and decrease hemolytic indices (LDH, total bilirubin) with decreased spleen weight/mouse weight ratio (8.41±0.08 vs 6.53±0.06, n=8 P<0.05); (ii) reduced hepatic and splenic iron overload; (iii) reduction in the proportion of phosphatidylserine positive RBCs, measured with Annexin V binding (2.4±0.02 vs 1.5±0.06 % P<0.05); (iv) reduction of naturally occurring antibody (NAb) bound to band 4.2^-/- RBC membrane. The decreased hemolysis was associated with reduction in serum erythropoietin (EPO: 1001.2±41.7 U/L vs 472 ± 12.5 U/L, n=7, P<0.05), supporting the beneficial effect of mitapivat on HS anemia. These data indicate that mitapivat ameliorates anemia of band 4.2^-/- mice, reduces chronic hemolysis and improves band 4.2^-/- mouse RBC features. Thus, mitapivat might represent an interesting therapeutic option for HS patients.