Identification of two new synthetic histone deacetylase inhibitors that modulate globin gene expression in erythroid cells from healthy donors and patients with thalassemia

We have identified two new histone deacetylase (HDAC) inhibitors (9 and 24) capable of inducing the expression of γ-globin and/or β-globin promoter-driven reporter genes in a synthetic model of Hb switch. Both compounds also increased, with different mechanisms, the γ/(γ+β) ratio expressed in vitro by normal human erythroblasts. Compound 9 increased the levels of γ-globin mRNA and the γ/(γ+β) ratio (both by 2-fold). Compound 24 increased by 3-fold the level of γ-globin and decreased by 2-fold that of β-globin mRNA, increasing the γ/(γ+β) ratio by 6-fold, and raising (by 50%) the cell HbF content. Both compounds raised the acetylation state of histone H4 in primary cells, an indication that their activity was mediated through HDAC inhibition. Compounds 9 and 24 were also tested as γ/(γ+β) mRNA inducers in erythroblasts obtained from patients with β⁰ thalassemia. Progenitor cells from patients with β⁰ thalassemia generated in vitro morphologically normal proerythroblasts that, unlike normal cells, failed to mature in the presence of EPO and expressed low β-globin levels but 10 times higher-than-normal levels of the α hemoglobin-stabilizing protein (AHSP) mRNA. Both compounds ameliorated the impaired in vitro maturation in β⁰ thalassemic erythroblasts, decreasing AHSP expression to normal levels. In the case of two patients (of five analyzed), the improved erythroblast maturation was associated with detectable increases in the γ/(γ+β) mRNA ratio. The low toxicity exerted by compounds 9 and 24 in all of the assays investigated suggests that these new HDAC inhibitors should be considered for personalized therapy of selected patients with β⁰ thalassemia.