Expression of γ-globin genes in β-thalassemia patients treated with sirolimus: results from a pilot clinical trial (Sirthalaclin)

Introduction: beta-thalassemia is caused by autosomal mutations in the beta-globin gene, which induce the absence or low-level synthesis of beta-globin in erythroid cells. It is widely accepted that a high production of fetal hemoglobin (HbF) is beneficial for patients with pthalassemia. Sirolimus, also known as rapamycin, is a lipophilic macrolide isolated from a strain of Streptomyces hygroscopicus that serves as a strong HbF inducer in vitro and in vivo. In this study, we report biochemical, molecular, and clinical results of a sirolimus-based NCT03877809 clinical trial (a personalized medicine approach for beta-thalassemia transfusiondependent patients: testing sirolimus in a first pilot clinical trial, Sirthalaclin). Methods: Accumulation of gamma-globin mRNA was analyzed using reverse-transcription quantitative polymerase chain reaction (PCR), while the hemoglobin pattern was analyzed using high-performance liquid chromatography (HPLC). The immunophenotype was analyzed using a fluorescence-activated cell sorter (FACS), with antibodies against CD3, CD4, CD8, CD14, CD19, CD25 (for analysis of peripheral blood mononuclear cells), or CD71 and CD235a (for analysis of in vitro cultured erythroid precursors). Results: The results were obtained in eight patients with the beta(+)/beta(+) and beta(+)/beta(0) genotypes, who were treated with a starting dosage of 1 mg/day sirolimus for 24-48 weeks. The first finding of this study was that the expression of gamma-globin mRNA increased in the blood and erythroid precursor cells isolated from beta-thalassemia patients treated with low-dose sirolimus. This trial also led to the important finding that sirolimus influences erythropoiesis and reduces biochemical markers associated with ineffective erythropoiesis (excess free alpha-globin chains, bilirubin, soluble transferrin receptor, and ferritin). A decrease in the transfusion demand index was observed in most (7/8) of the patients. The drug was well tolerated, with minor effects on the immunophenotype, and an only side effect of frequently occurring stomatitis. Conclusion: The data obtained indicate that low doses of sirolimus modify hematopoiesis and induce increased expression of gamma-globin genes in a subset of patients with beta-thalassemia. Further clinical trials are warranted, possibly including testing of the drug in patients with less severe forms of the disease and exploring combination therapies.

Automated summary

The study demonstrates that low-dose sirolimus treatment in patients with beta-thalassemia can increase the expression of gamma-globin genes and reduce biochemical markers associated with ineffective erythropoiesis. This finding provides important insights for the development of new therapeutic approaches.