Pharmacological Inhibition of TMPRSS6 Decreases Hemoglobin Concentration and Red Blood Cell (RBC) Hemolysis in a Mouse Model of Sickle Cell Disease

Sickle cell disease (SCD) is an inherited hemolytic anemia due to a single point mutation in the gene encoding for the beta-globin subunit of hemoglobin (Hgb) and resulting in the production of hemoglobin S (HbS). The clinical manifestations of SCD are due to HbS polymerization under low oxygen conditions, which causes RBC sickling and intravascular hemolysis, leading to anemia, expansion of erythropoiesis, inflammation, vaso-occlusion, and eventually, organ failure. Polymerization of HbS is highly dependent on HbS concentration within the RBC. Case reports and observational studies showed that iron deficiency in patients with SCD is associated with a reduction of HbS concentration, intravascular hemolysis, and vaso-occlusive crises (Haddy, 1982; Lionnet, 2012; Padaro, 2019). Iron restriction causing a reduction of HbS concentration in RBCs may therefore be a viable therapeutic strategy for patients with SCD. Hepcidin is a master regulator of iron homeostasis. The expression of hepcidin is downregulated by the transmembrane serine protease 6 (TMPRSS6) through the HJV/BMP/SMAD signaling pathway. DISC-3405 is a humanized monoclonal antibody blocking the biological action of TMPRSS6 with subsequent upregulation of hepcidin, leading to decreased iron absorption by enterocytes and decreased iron release from stores. In preclinical studies, the murine analog of DISC-3405, r4K12B, significantly increased hepcidin production, suppressed serum iron levels, and demonstrated efficacy in mouse models of beta-thalassemia and polycythemia vera (Chen, 2023; Chen, 2021). DISC-3405 is currently being evaluated in a Phase 1 study of healthy volunteers (NCT06050915). In this study, we tested the efficacy of r4K12B in the Townes mouse model of SCD. r4K12B was intraperitoneally administered to homozygous SS mice at 2 dose levels (3 and 10 mg/kg) weekly for 8 weeks. A vehicle treatment group was included as a control. At the end of the study, complete blood count, bilirubin, lactate dehydrogenase (LDH), and spleen index were measured. While the dose of 3 mg/kg of r4K12B did not have a significant effect in the Townes mice, the 10 mg/kg dose showed greater evidence of iron restriction and decreased hemolysis. Treatment with 10 mg/kg of r4K12B showed a significant reduction in the cellular hemoglobin concentration mean (CHCM) from 25.1±0.7 g/dL in vehicle-treated mice to 24.2±0.9 g/dL (p=0.029) in 10 mg/kg rK12B-treated mice. r4K12B treatment at 10 mg/kg resulted in a significant decrease in hemolysis markers. LDH levels decreased from 2054±525 U/L in vehicle-treated mice to 1076±910 U/L in 10 mg/kg r4K12B-treated mice, and total bilirubin decreased from 2.6 ± 0.2 mg/dL in vehicle-treated mice to 1.9±0.3 mg/dL in 10 mg/kg r4K12B-treated mice. A significant decrease was also observed for Hgb (6.8±1.3 g/dL vs 5.4±0.8 g/dL), hematocrit (HCT) (32.4±5.7% vs 26.8±3.6%), mean corpuscular volume (MCV) (47.0±3.9 fL vs 39.6±5.9 fL), and mean corpuscular hemoglobin (MCH) (10.1±0.5 pg vs 8.0±1.0 pg) in vehicle-treated mice compared to r4K12B-treated mice, respectively. Importantly, no changes in RBC numbers were observed in mice treated with vehicle compared to the r4K12B-treated group, suggesting that the observed iron-restricted erythropoiesis was balanced by decreased RBC hemolysis. Importantly, r4K12B treatment at 10 mg/kg significantly decreased leukocytosis, with white blood cell numbers decreasing from 20.8±7.8 x 109/L in the vehicle group to 10.7±6.8 x 109/L in the treatment group, suggesting decreased inflammation following treatment. r4K12B treatment at 10 mg/kg significantly reduced the spleen index compared to the vehicle group, indicating decreased extramedullary erythropoiesis. Taken together, these results suggest that iron restriction, through inhibition of TMPRSS6, may provide therapeutic benefits to SCD patients by reducing HbS concentration within the RBCs. References: Chen B, Wang J, Zheng B, et al. Blood. 2021;138(Suppl 1):941. Chen B, Wang J, Huang L, et al. Blood. 2023;142(Suppl 1):3837. Haddy TB, Castro O. Arch Intern Med. 1982;142(9):1621-1624. Lionnet F, Hammoudi N, Stojanovic KS, et al. Haematologica. 2012;97(8):1136-1141. Padaro E, Kueviakoe IMD, Agbétiafa K, et al. Med Sante Trop. 2019;29(1):106-107.