Contributions
Abstract: S843
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 11:45 - 12:00
Location: Room K2
Background
Hepcidin is a 25–amino acid peptide synthesized by hepatocytes and is involved in iron homeostasis. The known molecular-target of hepcidin is the ferroportin receptor, which functions as the major trans-membrane channel for the export of cellular iron. Hepcidin induces endocytosis and proteolysis of ferroportin and thereby decreases the export of iron to plasma. Hepcidin is prone to aggregation and is difficult to synthesize, characteristics that hinder its future development. The hormone is a complex 4-disulfide bonded beta-hairpin structure that is highly conserved. Protagonist used a proprietary ‘scaffold hopping’ approach (VectrixTM) to identify a novel peptidic scaffold that matches key pharmacophores of hepcidin. After further optimization PTG-300 was selected as a clinical development candidate, based on its simpler structure and drug-like characteristics, such as human plasma stability t1/2>24h and aqueous solubility >100 mg/mL. It reduces cell surface expression of human ferroportin with an EC50 of 5 nM and in healthy cynomolgus monkeys causes >80% sustained reduction of serum iron over 48 hr after a single subcutaneous dose of 1 mg/kg.
Aims
To evaluate the impact of the hepcidin mimetic PTG-300 on anemia in a mouse model of β-thalassemia
Methods
Wild-type control (WT) C57B6 and b-thalassemia intermedia (Hbbth3/+) mice aged between 4 to 6 weeks were treated with PTG-300 by sc injection at various frequencies and doses. Hematological and iron parameters were examined, including analysis of erythropoiesis, molecular studies of sorted erythroid precursors, indices of hemolysis, various biomarkers (including EPO and liver expression) were carried out.
Results
PTG-300 was injected subcutaneously at several dosing frequencies (Q2D to Q5D) for 4 weeks in six week old Hbbth3+ mice. This resulted in significant erythropoiesis as evidenced by a hemoglobin increase > 1.5 g/d, after Q5D dosing, reticulocyte count and spleen size reductions, and an increase in peripheral red cell number. The minimum effective dose (MED) was determined by comparing various doses levels between the acute mouse model (pharmacodynamic reduction in serum iron) and the Hbbth3+ mouse chronic model (erythropoietic increase in hemoglobin, peripheral red cell number and the decrease in reticulocytes). Using conditions of optimal dosing frequency and MED in Hbbth3/+ mice, flow cytometry studies of bone marrow and spleen erythroid populations from PTG-300 treated animals demonstrated an increase in the relative proportion of mature erythroid cells. Accumulation of tissue iron was also significantly reduced in the liver and spleen but not in the heart and duodenum. RBC survival increased in Hbbth3/+ mice to similar levels as in WT mice while EPO expression was decreased.
Conclusion
Our data suggest that PTG-300 ameliorates ineffective erythropoiesis as a treatment for chronic anemia in a mouse model of β-thalassemia. In conditions characterized by low endogenous hepcidin levels and high serum iron levels, such as β-thalassemia and myelodysplastic syndrome (MDS) patients, we believe that PTG-300 has the potential to treat the dysregulation of iron metabolism thereby reducing iron toxicity in the erythropoietic cascade and the chronic anemia. Ultimately PTG-300 has the potential to treat secondary iron overload by reducing the need for transfusions and by decreasing excessive dietary iron absorption.
Funding: A portion of this work was supported by the NIH SBIR grant National Heart, Lung, And Blood Institute of the National Institutes of Health; Award Number R43HL132702.
Session topic: 28. Thalassemias
Keyword(s): hepcidin, Iron Metabolism, iron overload, Thalassemia
Abstract: S843
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 11:45 - 12:00
Location: Room K2
Background
Hepcidin is a 25–amino acid peptide synthesized by hepatocytes and is involved in iron homeostasis. The known molecular-target of hepcidin is the ferroportin receptor, which functions as the major trans-membrane channel for the export of cellular iron. Hepcidin induces endocytosis and proteolysis of ferroportin and thereby decreases the export of iron to plasma. Hepcidin is prone to aggregation and is difficult to synthesize, characteristics that hinder its future development. The hormone is a complex 4-disulfide bonded beta-hairpin structure that is highly conserved. Protagonist used a proprietary ‘scaffold hopping’ approach (VectrixTM) to identify a novel peptidic scaffold that matches key pharmacophores of hepcidin. After further optimization PTG-300 was selected as a clinical development candidate, based on its simpler structure and drug-like characteristics, such as human plasma stability t1/2>24h and aqueous solubility >100 mg/mL. It reduces cell surface expression of human ferroportin with an EC50 of 5 nM and in healthy cynomolgus monkeys causes >80% sustained reduction of serum iron over 48 hr after a single subcutaneous dose of 1 mg/kg.
Aims
To evaluate the impact of the hepcidin mimetic PTG-300 on anemia in a mouse model of β-thalassemia
Methods
Wild-type control (WT) C57B6 and b-thalassemia intermedia (Hbbth3/+) mice aged between 4 to 6 weeks were treated with PTG-300 by sc injection at various frequencies and doses. Hematological and iron parameters were examined, including analysis of erythropoiesis, molecular studies of sorted erythroid precursors, indices of hemolysis, various biomarkers (including EPO and liver expression) were carried out.
Results
PTG-300 was injected subcutaneously at several dosing frequencies (Q2D to Q5D) for 4 weeks in six week old Hbbth3+ mice. This resulted in significant erythropoiesis as evidenced by a hemoglobin increase > 1.5 g/d, after Q5D dosing, reticulocyte count and spleen size reductions, and an increase in peripheral red cell number. The minimum effective dose (MED) was determined by comparing various doses levels between the acute mouse model (pharmacodynamic reduction in serum iron) and the Hbbth3+ mouse chronic model (erythropoietic increase in hemoglobin, peripheral red cell number and the decrease in reticulocytes). Using conditions of optimal dosing frequency and MED in Hbbth3/+ mice, flow cytometry studies of bone marrow and spleen erythroid populations from PTG-300 treated animals demonstrated an increase in the relative proportion of mature erythroid cells. Accumulation of tissue iron was also significantly reduced in the liver and spleen but not in the heart and duodenum. RBC survival increased in Hbbth3/+ mice to similar levels as in WT mice while EPO expression was decreased.
Conclusion
Our data suggest that PTG-300 ameliorates ineffective erythropoiesis as a treatment for chronic anemia in a mouse model of β-thalassemia. In conditions characterized by low endogenous hepcidin levels and high serum iron levels, such as β-thalassemia and myelodysplastic syndrome (MDS) patients, we believe that PTG-300 has the potential to treat the dysregulation of iron metabolism thereby reducing iron toxicity in the erythropoietic cascade and the chronic anemia. Ultimately PTG-300 has the potential to treat secondary iron overload by reducing the need for transfusions and by decreasing excessive dietary iron absorption.
Funding: A portion of this work was supported by the NIH SBIR grant National Heart, Lung, And Blood Institute of the National Institutes of Health; Award Number R43HL132702.
Session topic: 28. Thalassemias
Keyword(s): hepcidin, Iron Metabolism, iron overload, Thalassemia