Transfusion independence in Diamond-Blackfan anemia after deferasirox therapy

Eltrombopag Improves Erythroid Differentiation in a Human Induced Pluripotent Stem Cell Model of Diamond Blackfan Anemia

Diamond Blackfan Anemia (DBA) is a congenital macrocytic anemia associated with ribosomal protein haploinsufficiency. Ribosomal dysfunction delays globin synthesis, resulting in excess toxic free heme in erythroid progenitors, early differentiation arrest, and pure red cell aplasia. In this study, DBA induced pluripotent stem cell (iPSC) lines were generated from blood mononuclear cells of DBA patients with inactivating mutations in RPS19 and subjected to hematopoietic differentiation to model disease phenotypes. In vitro differentiated hematopoietic cells were used to investigate whether eltrombopag, an FDA-approved mimetic of thrombopoietin with robust intracellular iron chelating properties, could rescue erythropoiesis in DBA by restricting the labile iron pool (LIP) derived from excessive free heme. DBA iPSCs exhibited RPS19 haploinsufficiency, reduction in the 40S/60S ribosomal subunit ratio and early erythroid differentiation arrest in the absence of eltrombopag, compared to control isogenic iPSCs established by CRISPR/Cas9-mediated correction of the RPS19 point mutation. Notably, differentiation of DBA iPSCs in the presence of eltrombopag markedly improved erythroid maturation. Consistent with a molecular mechanism based on intracellular iron chelation, we observed that deferasirox, a clinically licensed iron chelator able to permeate into cells, also enhanced erythropoiesis in our DBA iPSC model. In contrast, erythroid maturation did not improve substantially in DBA iPSC differentiation cultures supplemented with deferoxamine, a clinically available iron chelator that poorly accesses LIP within cellular compartments. These findings identify eltrombopag as a promising new therapeutic to improve anemia in DBA.

Differential effects of the type of iron chelator on the absolute number of hematopoietic peripheral progenitors in patients with β-thalassemia major

Several studies have established an association between iron chelation therapy with deferasirox and hematopoietic improvement in patients with myelodysplastic syndromes. There are no data from patients with β-thalassemia major. In a cross-sectional study, we evaluated the absolute number of several hematopoietic peripheral progenitors (colony-forming unit-granulocyte/macrophage, erythroid burst-forming units, colony-forming unit-granulocyte/erythrocyte/macrophage/megakaryocyte, and long-term culture-initiating cells) in 30 patients with β-thalassemia major (median age 29.5 years, 40% males) and 12 age-matched controls. For the β-thalassemia major patients, data on splenectomy status, the type of iron chelator used, and serum ferritin levels reflecting changes in iron status on the chelator were also retrieved. All patients had to be using the same iron chelator for at least 6 months with >80% compliance. The absolute number of all hematopoietic peripheral progenitors was higher in β-thalassemia major patients than in controls, and varied between splenectomized and non-splenectomized patients (lower number of erythroid burst-forming units and higher numbers of colony-forming unit-granulocyte/macrophage, colony-forming unit-granulocyte/erythrocyte/macrophage/megakaryocyte, and long-term culture-initiating cells). The number of erythroid burst-forming units was significantly higher in patients taking deferasirox (n=10) than in those taking either deferoxamine (n=10) or deferiprone (n=10) (P<0.05). After adjusting for age, sex, splenectomy status, and serum ferritin changes, the association between a higher absolute number of erythroid burst-forming units in deferasirox-treated patients than in patients taking deferoxamine or deferiprone remained statistically significant (P=0.011). In conclusion, in β-thalassemia major patients, compared with other iron chelators, deferasirox therapy is associated with higher levels of circulating erythroid burst-forming units. This variation is independent of iron status changes and is more likely to be due to the type of chelator.

Progress towards mechanism-based treatment for Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital erythroid hypoplastic anemia, characterized by macrocytic anemia, reticulocytopenia, and severely reduced numbers of erythroid precursors in the bone marrow. For more than fifty years, glucocorticoids have remained the main option for pharmacological treatment of DBA. While continuous glucocorticoid administration increases hemoglobin levels in a majority of DBA patients, it also causes severe side effects. There is therefore a great need for more specific and effective treatments to boost or replace the use of glucocorticoids. Over the years, many alternative therapies have been tried out, but most of them have shown to be ineffective. Here we review previous and current attempts to develop such alternative therapies for DBA. We further discuss how emerging knowledge regarding the pathological mechanism in DBA and the therapeutic mechanism of glucocorticoids treatment may reveal novel drug targets for DBA treatment.

Restoration of hematopoiesis after iron chelation therapy with deferasirox in 2 children with severe aplastic anemia

Iron overload is a significant clinical problem in patients with severe aplastic anemia or other transfusion-dependent bone marrow failure diseases. Iron chelation therapy is more readily available owing to the recent introduction of oral iron chelators. We describe 2 cases of children with severe aplastic anemia and related transfusional iron overload who received iron chelation therapy with oral deferasirox. Our patients experienced restoration of trilineage hematopoiesis after the administration of deferasirox along with the reduction in ferritin levels, and subsequently became transfusion-free. Our report raises the possibility of potential benefit on hematopoiesis from iron chelation therapy and warrants furthermore investigations.