TREATMENT OF BETA-THALASSEMIA PATIENTS WITH RAPAMYCIN (SIROLIMUS): FROM PRE-CLINICAL RESERCH TO A CLINICAL TRIAL

Beta-thalassemias are hereditary blood disorders caused by reduced or absent synthesis of hemoglobin beta chains, resulting in severe anemia. Treatment of beta-thalassemia is based on regular blood transfusion and iron chelation therapy. Survival is increased in most countries, but the quality of life is still poor for most patients and complication(s) of frequent transfusions is/are a major problem. In some beta-thalassemia patients, an anomalous expression of gamma-globin genes has been observed, with a consequent rise in HbF (Fetal Hemoglobin) levels. The cases with very high HbF levels display a clinical phenotype known as “Hereditary Persistence of Fetal Hemoglobin” and exhibit a positive clinical status, since the activation of gamma-globin genes is associated with HbF increase, and this partly overcomes the problems caused by the lack of adult hemoglobin. Objectives. The overall aim of the project is a reduction of transfusions in beta-thalassemia patients, through a pharmacologically mediated increased levels of HbF. There is strong evidence that Sirolimus is able to induce HbF production in vitro in erythroid precursor cells (ErPCs) from beta-thalassemia and sickle-cell patients and in vivo in transgenic mice. Therefore, the THALA-RAP objective is to verify whether HbF increases occur in beta-thalassemia patients treated with Sirolimus in peripheral blood and isolated ErPCs. A second list of parameters is the lifespan and the oxidative stress status of the beta-thalassemia red blood cells. Both outcomes support the possible clinical relevance of in vivo effects of Sirolimus. Furthermore, a cost-effectiveness analysis of the patients’treatment toward the conventional one is conducted. Methods. (a) Short-term treatment. We plan to apply for the first trial an initial dose of 1 mg/day. Sirolimus whole blood concentrations will be measured in about 10 days, with dosage adjustment to maintain at maximum concentrations between 2.5-5 ng/mL. Response to Sirolimus in terms of HbF will be measured in two ways: analysis of (a) HbF level in peripheral blood and (b) gamma globin RNA and HbF production by isolated ErPCs. These analyses will be performed after 20/30, 40/60 and 60/90 days of administration. OMICS (transcriptomic, proteomic) analyses will be useful to determine the effects of the overall gene expression, including assessment of potentials risks. (b) Long term treatment. After a first period of treatment, if HbF is increased by Sirolimus in a limited number of patients, we will continue treatment in the responding patients in order to reach a duration of 12 months. We will also add more patients, to test more than one dose, defining the other ones on the basis of the ongoing observations. An observation period of 12 months is necessary to verify if in some patients, initially responding, sirolimus loses efficacy rapidly. (c) Non responders. All the beta-thalassemia patients who did not respond to the first Sirolimus treatment will be treated with increasing Sirolimus dosages (up to a maximum dose of 2 mg/day). (d) The THALA-RAP large clinical trial. In the case of response demonstrating a Sirolimus in vivo “activity” or “efficacy” (focused also on identification and validation of optimal doses of Sirolimus) a large trial will be proposed in the future with the EMA protocol assistance. With regard to a most important end point, on the basis of the available clinical data on HU and experimental data on Sirolimus, we estimate that a significant decrease in transfusion need can be measured analyzing about 40-60 patients treated with Sirolimus for a period of one year. Expected results. The outcomes of the trial will be assessed in terms of “activity” of Sirolimus treatment (i.e. the demonstration that Sirolimus induces significant changes on specific parameters) as well as “efficacy” of the treatment (i.e. the achievement of clear-cut clinically relevant outcomes) and cost-effectiveness.