Orally bioactive compounds that induce γ globin gene expression at tolerable doses are needed for optimal treatment of the β-hemoglobinopathies. Short-chain fatty acids (SCFAs) of 2 to 6 carbons in length induce γ globin expression in animal models, and butyrate, phenylbutyrate, and valproate induce γ globin in human patients. The usefulness of these compounds, however, is limited by requirements for large doses because of their rapid metabolism and their tendency to inhibit cell proliferation, which limits the pool of erythroid progenitors in which γ globin can be induced. Selected short-chain fatty acid derivatives (SCFADs) were recently found to induce γ globin and to stimulate the proliferation of hematopoietic cells in vitro. These SCFADs are now evaluated in vivo in nonanemic transgenic mice containing the human β globin gene locus and in anemic phlebotomized baboons. In mice treated with a SCFAD once daily for 5 days, γ globin mRNA increased 2-fold, reticulocytes increased 3- to 7-fold, and hematocrit levels increased by 27%. Administration of 3 SCFADs in anemic baboons increased F-reticulocytes 2- to 15-fold over baseline and increased total hemoglobin levels by 1 to 2 g/dL per week despite ongoing significant daily phlebotomy. Pharmacokinetic studies demonstrated 90% oral bioavailability of 2 SCFADs, and targeted plasma levels were maintained for several hours after single oral doses equivalent to 10% to 20% of doses required for butyrate. These findings identify SCFADs that stimulate γ globin gene expression and erythropoiesis in vivo, activities that are synergistically beneficial for treatment of the β hemoglobinopathies and useful for the oral treatment of other anemias.

Summary: Sickle cell leg ulcers are often debilitating, refractory to healing, and prone to recurrence. Healing of leg ulcers was incidentally observed during dose‐ranging trials of Arginine Butyrate in beta haemoglobinopathies. Here, a controlled Phase II trial was performed in sickle cell patients who had lower extremity ulcers refractory to standard care for at least 6 months. Patients were randomized to receive standard local care alone (Control Arm) or standard care with Arginine Butyrate administered 5 d/week (Treatment Arm), for 12 weeks. Ulcers were photographed weekly, traced, and ulcer areas were calculated by computerized planimetry and compared between the two study arms. Twenty‐seven study courses were evaluated. Control Arm subjects had 25 ulcers with a mean area of 25·7 cm² initially and 23·2 cm² after 12 weeks; 2/25 (8%) healed completely. Treatment Arm subjects had 37 ulcers with a mean area of 50·6 cm² initially and 28·3 cm² at 12 weeks; 11/37 of these (30%) healed completely. After 3 months, proportions of ulcers which healed were 6/25 (24%) and 29/37 (78%), in the Control and Treatment Arms respectively (P < 0·001). These findings strongly suggest that Arginine Butyrate merits further evaluation for the treatment of refractory sickle cell leg ulcers in larger trials.

The β thalassemias are one of a few medical conditions in which reactivation of a gene product that is expressed during fetal life can functionally replace a deficiency of essential proteins expressed at a later developmental stage. The fetal globin genes are present and normally integrated in hematopoietic stem cells, and at least one fetal gene appears accessible for reactivation, particularly in β° thalassemia. However, rapid cellular apoptosis from α globin chain precipitation, and relatively low levels of endogenous erythropoietin (EPO) in some β⁺ thalassemia patients contribute to the anemia in β thalassemia syndromes.

High-level induction of fetal (γ) globin gene expression for therapy of β-hemoglobinopathies likely requires local chromatin modification and dissociation of repressor complexes for γ-globin promoter activation. A novel γ-globin–inducing short-chain fatty acid derivative (SCFAD), RB7, which was identified through computational modeling, produced a 6-fold induction in a reporter assay that detects only strong inducers of the γ-globin gene promoter and in cultured human erythroid progenitors. To elucidate the molecular mechanisms used by high-potency SCFADs, chromatin immunoprecipitation (ChIP) assays performed at the human γ- and β-globin gene promoters in GM979 cells and in erythroid progenitors demonstrate that RB7 and butyrate induce dissociation of HDAC3 (but not HDAC1 or HDAC2) and its adaptor protein NCoR, specifically from the γ-globin gene promoter. A coincident and proportional recruitment of RNA polymerase II to the γ-globin gene promoter was observed with exposure to these γ-globin inducers. Knockdown of HDAC3 by siRNA induced transcription of the γ-globin gene promoter, demonstrating that displacement of HDAC3 from the γ-globin gene promoter by the SCFAD is sufficient to induce γ-globin gene expression. These studies demonstrate new dynamic alterations in transcriptional regulatory complexes associated with SCFAD-induced activation of the γ-globin gene and provide a specific molecular target for potential therapeutic intervention.