Diamond-Blackfan anemia (DBA) is a heritable bone marrow failure (BMF) syndrome characterized by selective erythroid defects typically presenting within the first year of life as a normochromic, macrocytic anemia with reticulocytopenia. More than half of all DBA cases are associated with either inherited or spontaneous mutations in ribosomal proteins, making DBA a prototypic ribosomopathy . Furthermore, although the primary presentation is isolated anemia, as life expectancy has improved, progressive defects in other lineages have now been identified, consistent with a long-term stem cell defect. Current standard of care for DBA is the use of systemic corticosteroids, the mechanism of which is unclear, although only half show an initial response. Even when a response to steroids is observed, long-term steroid therapy carries significant morbidity, especially in children or in combination with transfusion-associated iron overload, and thus most cannot tolerate high-dose steroids long-term. Responses are rare with second-line immunomodulatory agents. Yet other than allogeneic hematopoietic stem cell transplantation in those patients with healthy matched donors, there are no alternative therapies.

In one model for DBA pathogenesis, the defects lead to an overabundance of the iron-carrying moiety heme in primitive erythroid cells, unbound by protein. Free heme is toxic to cells, likely exacerbated over time by iron overload due to transfusions. Ongoing work with eltrombopag (EPAG) has shown that it is capable of acting as a potent iron chelator, including intracellular iron, with evidence that this effect of EPAG can reverse the impact of excess heme and elevated reactive oxygen species. Furthermore, in a recent trial of EPAG for moderate aplastic anemia or hypoproliferative unilineage cytopenias, we identified a robust response to EPAG in the one DBA patient enrolled in this clinical trial. This response has been durable over more than three years since study entry but requires continuous EPAG to maintain transfusion independence. From these data, we hypothesize that EPAG may be able to improve production of red blood cells in DBA patients via chelation of iron and subsequent reduction in heme synthesis, resulting in decreased toxicity to bone marrow stem cells and developing erythroid cells.

We will conduct a single-arm, pilot trial in patients with steroid-refractory or steroid-intolerant DBA, treating with a fixed dose of EPAG for 6 months to assess safety and efficacy at improving hematological manifestations of DBA. Responders at 6 months will be able to continue EPAG on the extension part of this protocol for an additional 3 years. We will examine the hematologic, molecular, cytogenetic and clonal responses to EPAG in responders and non-responders alike. Translational studies will examine the mechanism of activity of EPAG in DBA through its effects on iron metabolism, erythroid differentiation, apoptosis, global transcriptome and TPO signaling pathways in patient s hematopoietic stem and progenitor cells (HSPCs).