Eltrombopag for Moderate Aplastic Anemia

Moderate aplastic anemia (MAA) is a blood disease which can be effectively treated with immunosuppressive drug regimens. However, a significant number of patients have persistent cytopenias. Currently, the treatment of these patients is regular transfusion, which are expensive, inconvenient, and associated with serious side effects related to iron overload, or cytokines such as erythropoietin or G-CSF, which are expensive, and not effective in many patients.

Thrombopoietin (TPO) is a protein made by the body that is important for normal production of platelets by the bone marrow. TPO may also be able to stimulate bone marrow stem cells to produce red cells and white cells. TPO cannot be given by mouth, and as an alternative, a drug, eltrombopag, has been designed that acts in the same way as TPO but is stable and active when given by mouth. Eltrombopag has been shown to safely increase platelet numbers in healthy volunteers and in patients with chronic immune thrombocytopenic purpura (ITP). It has been recently granted accelerated approval by FDA on November 20, 2008 for the treatment of patients with chronic immune thrombocytopenic purpura (ITP) who have had an insufficient response to standard therapies.

We have previously shown encouraging results when eltrombopag is used to treat patients with severe aplastic anemia, with some patients responding with increases in platelets, red cells and white cells. Given these encouraging early preliminary results in our clinical trial using eltrombopag in Severe Aplastic Anemia (SAA), and low toxicity and ease of administration of this drug, we now propose a non-randomized pilot phase II study of eltrombopag in moderate aplastic anemia patients with clinically significant thrombocytopenia or anemia. Patients with MAA may not reach criteria for SAA, but none the less may be transfusion-dependent or have significant symptoms from cytopenias. We hypothesize that patients with MAA as compared to SAA may have a better chance of response, due to better residual marrow function in MAA patients compared to SAA.

Eligible patients can have treated or untreated MAA, as well as counts meeting criteria for MAA following a partial response to treatment with immunosuppression for SAA. We will also include patients with bone marrow failure and unilineage cytopenia. Treatment response for the platelet lineage is defined as platelet count increases to 20,000/microL above baseline at 16 to 20 weeks, or freedom from platelet transfusions for greater than or equal to 8 weeks in transfusion-dependent patients. For patients with anemia (untransfused hemoglobin less than or equal to 8.5 g/dL), a treatment response will be an increase in Hb by greater than or equal to 1.5g/dl at four months, measured on at least 2 serial measurements and sustained for 1 month or more without transfusion support OR for transfusion dependent patients, reduction of units of RCC transfused by 50 percent/8 weeks compared with the pretreatment transfusion number in the previous 8 weeks or transfusion independence (no transfusions for greater than or equal to 8 weeks). Subjects with evidence for a clinical response in any lineage at 16 weeks but not yet meeting full primary endpoint response criteria, and who are tolerating investigational treatment, may receive an additional 4 weeks of eltrombopag and be reassessed after 20 weeks. At that time, if they meet primary endpoint response criteria, they will be eligible to enter the extended access part of the study. If they do not meet primary endpoint response criteria, eltrombopag will be discontinued.

The primary objective is to assess the safety and efficacy of the oral thrombopoietin receptor agonist (TPO-R agonist) eltrombopag in moderate aplastic anemia patients or patients with bone marrow failure and unilineage cytopenia. Secondary objectives include the analysis of the incidence and severity of bleeding, clonal evolution to PNH, clonal chromosomal population in bone marrow, myelodysplasia by morphology, or acute leukemia and the impact on quality of life.