Induction of Human γ Globin Gene Expression by Histone Deacetylase Inhibitors.

In previous studies we have showed that HDAC inhibitors including hydroxamic acid derivatives of short chain fatty acids butyryl hydroxamate, propionyl hydroxamate, subericbis hydroxamic acid (SBHA), and suberoylanilide hydroxamic acid (SAHA), are potent inducers of γ globin gene expression in in vitro luciferase assays and in cultures of human adult erythroid progenitor cells. In this present study, we used μLCR ^Aγ transgenic mice to test whether these compounds can also induce γ gene expression in vivo. We found that in addition to γ gene induction these compounds have considerable erythropoiesis activity. Thus, Propionyl and butyryl hydroxamate increased reticulocytes of mice by 71% and 139%, the in vivo BFUe counts by 75% and 51% and the in vivo γ gene expression by 33.9% and 71% respectively. SBHA and SAHA had no erythropoietic activity in vivo. We conclude that Hydroxamic acid derivatives can stimulate both the in vivo erythropoiesis and fetal globin production in a thalassemic murine model.

Cyclic depsipeptide FK228 is a highly potent histone deacetylase inhibitor, currently in clinical trials in cancer patients. We investigated whether FK228 also functions as inducer of human γ globin gene expression and compared Hb F induction by FK228 to that of four other HDAC inhibitors, including hydroxamic acids (TSA), synthetic benzamides (MS-275), and two cyclic tetrapeptides, Apicidin and HC-Toxin. Our results showed that FK228 is the most potent fetal hemoglobin inducer among all the HDAC inhibitors tested in our laboratory. In a concentration of 0.84 nanomolar, FK228 induces γ gene promoter activity in the dual luciferase assay by 7.81 fold. In the human erythroid progenitor cell cultures it increases the levels of γ mRNA by 8.48 fold in a concentration of 0.143 nM. In contrast, fetal hemoglobin induction by other HDAC inhibitors is achieved in concentrations that are 100 to 1000 fold higher. We conclude that FK228 is a promising compound for induction of Hb F in patients with sickle cell disease and thalassemia.