Iron Restricted Erythropoiesis Under Hepcidin Mimetic Treatment (PN23114) Improved Disease Parameters in a Mouse Model for Sickle Cell Disease

Abstract

Sickle Cell Disease (SCD) is an inherited hemolytic disorder that results from a single point mutation in the hemoglobin-beta (HBB) gene that encodes for the beta-globin subunit of hemoglobin, causing the production of abnormal hemoglobin S (HbS). HbS polymerizes under low oxygen conditions, causing sickling effects on red blood cells (RBCs). Sickling of RBCs initiates vaso-occlusion, downstream inflammatory responses, and hemolysis (Zhang D, et al., Blood. 2016;127:801-9). Previous studies have shown that polymerization under low oxygen conditions is extremely sensitive to HbS concentrations within the RBCs (Hofrichter J, et al, Proc Natl Acad Sci USA. 1974;71:4864-8; Sunshine HR, et al. Nature. 1978;275:238-40). Controlling iron delivery for erythropoiesis provides a mechanism to potentially down-modulate the HbS concentration, thereby reducing the potential for HbS polymerization and sickling of RBCs (Parrow NL, et al., Blood. 2021;137:1553-5). The potent hepcidin mimetic peptide PN23114 targets the iron exporter membrane protein ferroportin to trigger its degradation, thus preventing iron export from cells. We hypothesize that the resulting pharmacodynamic effect of limiting iron availability for erythropoiesis should reduce HbS concentrations within the RBCs that may prevent sickling and hemolysis. Townes mice (genetically altered to contain the human SCD HbSS homozygous mutation) are a well-established experimental model for human SCD (Li-Chen W, et al., Blood. 2006;108:1183-8). They exhibit severe hemolysis as indicated by elevated bilirubin and lactate dehydrogenase (LDH) levels, and a shortened RBC half-life compared to wild type (WT) mice. These mice also develop vaso-occlusive events and elevated inflammatory responses (for example, increases in peripheral blood white blood cell [WBC] and neutrophil counts). To test whether iron restriction mediated by a hepcidin mimetic may alter outcomes in this model, PN23114 was administered subcutaneously to Townes HbSS mice. Mice were treated over 4-weeks (3 times weekly) with vehicle or PN23114 at 1 or 2.5 mg/kg (vehicle treated WT mice served as controls). At the end of 4 weeks, total bilirubin was elevated in the HbSS-vehicle group compared to WT-vehicle (Figure 1A). Total bilirubin was dose-dependently reduced by PN23114 treatment compared to the HbSS-vehicle group (Figure 1A). LDH was also elevated in the HbSS-vehicle group and was dose-dependently reduced with PN23114 treatment (557±105 units/L in WT-vehicle, 809±145 units/L in HbSS-vehicle, 611±341 units/L in HbSS-PN23114-1mg/kg and 372±71 units/L in HbSS-PN23114-2.5mg/kg groups). Peripheral blood WBC counts were dose-dependently reduced by PN23114 treatment compared to HbSS-vehicle (Figure 1B), with concomitant decreases in peripheral blood neutrophil counts. Reduction in hemoglobin values was observed with PN23114 treatment in HbSS (5.9±0.9 g/dL in HbSS-1mg/kg group and 4.4±0.4 g/dL in HbSS-2.5 mg/kg group) compared to the HbSS-vehicle group (7.1±0.3 g/dL). These results suggest that pharmacologic iron restriction with PN23114, a hepcidin mimetic peptide, led to a reduction in hemolysis and inflammatory markers in a SCD model. Therefore, a hepcidin mimetic therapeutic could potentially be a novel approach to prevent hemolysis, inflammation and downstream clinical complications associated with human SCD.