Novel therapeutic candidates, identified by molecular modeling, induce γ-globin gene expression in vivo

HDAC-an important target for improving tumor radiotherapy resistance

Radiotherapy is an important means of tumor treatment, but radiotherapy resistance has been a difficult problem in the comprehensive treatment of clinical tumors. The mechanisms of radiotherapy resistance include the repair of sublethal damage and potentially lethal damage of tumor cells, cell repopulation, cell cycle redistribution, and reoxygenation. These processes are closely related to the regulation of epigenetic modifications. Histone deacetylases (HDACs), as important regulators of the epigenetic structure of cancer, are widely involved in the formation of tumor radiotherapy resistance by participating in DNA damage repair, cell cycle regulation, cell apoptosis, and other mechanisms. Although the important role of HDACs and their related inhibitors in tumor therapy has been reviewed, the relationship between HDACs and radiotherapy has not been systematically studied. This article systematically expounds for the first time the specific mechanism by which HDACs promote tumor radiotherapy resistance in vivo and in vitro and the clinical application prospects of HDAC inhibitors, aiming to provide a reference for HDAC-related drug development and guide the future research direction of HDAC inhibitors that improve tumor radiotherapy resistance.

The state of the art of fetal hemoglobin-inducing agents

INTRODUCTION

Sickle cell anemia (SCA) is a hematological genetic disorder caused by a mutation in the gene of the β-globin. Pharmacological treatments will continue to be an important approach, including the strategy to induce fetal hemoglobin (HbF).

AREAS COVERED

Here, we analyzed the articles described in the literature regarding the drug discovery of HbF inducers. The main approaches for such strategy will be discussed, highlighting those most promising.

EXPERT OPINION

The comprehension of the mechanisms involved in the β-globin regulation is the main key to design new drugs to induce HbF. Among the strategies, gamma-globin regulation by epigenetic enzymes seems to be a promising approach to be pursued, although the comprehension of the selectivity role for those new drugs is crucial to reduce adverse effects. The low druggability of transcription factors and their vital role in embryonic human development are critical points that should be taken in account for drug design. The guanylate cyclase and the NO/cGMP signaling pathway seem to be promising not only for HbF induction, but also for the protective effects in the cardiovascular system. The association of drugs acting through different mechanisms to induce HbF seems to be promising for the discovery of new drugs.

Animal models of β-hemoglobinopathies: utility and limitations

The structural and functional conservation of hemoglobin throughout mammals has made the laboratory mouse an exceptionally useful organism in which to study both the protein and the individual globin genes. Early researchers looked to the globin genes as an excellent model in which to examine gene regulation – bountifully expressed and displaying a remarkably consistent pattern of developmental activation and silencing. In parallel with the growth of research into expression of the globin genes, mutations within the β-globin gene were identified as the cause of the β-hemoglobinopathies such as sickle cell disease and β-thalassemia. These lines of enquiry stimulated the development of transgenic mouse models, first carrying individual human globin genes and then substantial human genomic fragments incorporating the multigenic human β-globin locus and regulatory elements. Finally, mice were devised carrying mutant human β-globin loci on genetic backgrounds deficient in the native mouse globins, resulting in phenotypes of sickle cell disease or β-thalassemia. These years of work have generated a group of model animals that display many features of the β-hemoglobinopathies and provided enormous insight into the mechanisms of gene regulation. Substantive differences in the expression of human and mouse globins during development have also come to light, revealing the limitations of the mouse model, but also providing opportunities to further explore the mechanisms of globin gene regulation. In addition, animal models of β-hemoglobinopathies have demonstrated the feasibility of gene therapy for these conditions, now showing success in human clinical trials. Such models remain in use to dissect the molecular events of globin gene regulation and to identify novel treatments based upon the reactivation of developmentally silenced γ-globin. Here, we describe the development of animal models to investigate globin switching and the β-hemoglobinopathies, a field that has paralleled the emergence of modern molecular biology and clinical genetics.

Current and future alternative therapies for beta-thalassemia major

Beta-thalassemia is a group of frequent genetic disorders resulting in the synthesis of little or no β-globin chains. Novel approaches are being developed to correct the resulting α/β-globin chain imbalance, in an effort to move beyond the palliative management of this disease and the complications of its treatment (e.g. life-long red blood cell transfusion, iron chelation, splenectomy), which impose high costs on healthcare systems. Three approaches are envisaged: fetal globin gene reactivation by pharmacological compounds injected into patients throughout their lives, allogeneic hematopoietic stem cell transplantation (HSCT), and gene therapy. HSCT is currently the only treatment shown to provide an effective, definitive cure for β-thalassemia. However, this procedure remains risky and histocompatible donors are identified for only a small fraction of patients. New pharmacological compounds are being tested, but none has yet made it into common clinical practice for the treatment of beta-thalassemia major. Gene therapy is in the experimental phase. It is emerging as a powerful approach without the immunological complications of HSCT, but with other possible drawbacks. Rapid progress is being made in this field, and long-term efficacy and safety studies are underway.

Therapeutic fetal-globin inducers reduce transcriptional repression in hemoglobinopathy erythroid progenitors through distinct mechanisms

Pharmacologic augmentation of γ-globin expression sufficient to reduce anemia and clinical severity in patients with diverse hemoglobinopathies has been challenging. In studies here, representative molecules from four chemical classes, representing several distinct primary mechanisms of action, were investigated for effects on γ-globin transcriptional repressors, including components of the NuRD complex (LSD1 and HDACs 2-3), and the downstream repressor BCL11A, in erythroid progenitors from hemoglobinopathy patients. Two HDAC inhibitors (MS-275 and SB939), a short-chain fatty acid derivative (sodium dimethylbutyrate [SDMB]), and an agent identified in high-throughput screening, Benserazide, were studied. These therapeutics induced γ-globin mRNA in progenitors above same subject controls up to 20-fold, and increased F-reticulocytes up to 20%. Cellular protein levels of BCL11A, LSD-1, and KLF1 were suppressed by the compounds. Chromatin immunoprecipitation assays demonstrated a 3.6-fold reduction in LSD1 and HDAC3 occupancy in the γ-globin gene promoter with Benserazide exposure, 3-fold reduction in LSD-1 and HDAC2 occupancy in the γ-globin gene promoter with SDMB exposure, while markers of gene activation (histone H3K9 acetylation and H3K4 demethylation), were enriched 5.7-fold. These findings identify clinical-stage oral therapeutics which inhibit or displace major co-repressors of γ-globin gene transcription and may suggest a rationale for combination therapy to produce enhanced efficacy.

A cell-based high-throughput screen for novel chemical inducers of fetal hemoglobin for treatment of hemoglobinopathies

Decades of research have established that the most effective treatment for sickle cell disease (SCD) is increased fetal hemoglobin (HbF). Identification of a drug specific for inducing γ-globin expression in pediatric and adult patients, with minimal off-target effects, continues to be an elusive goal. One hurdle has been an assay amenable to a high-throughput screen (HTS) of chemicals that displays a robust γ-globin off-on switch to identify potential lead compounds. Assay systems developed in our labs to understand the mechanisms underlying the γ- to β-globin gene expression switch during development has allowed us to generate a cell-based assay that was adapted for a HTS of 121,035 compounds. Using chemical inducer of dimerization (CID)-dependent bone marrow cells (BMCs) derived from human γ-globin promoter-firefly luciferase β-globin promoter-Renilla luciferase β-globin yeast artificial chromosome (γ-luc β-luc β-YAC) transgenic mice, we were able to identify 232 lead chemical compounds that induced γ-globin 2-fold or higher, with minimal or no β-globin induction, minimal cytotoxicity and that did not directly influence the luciferase enzyme. Secondary assays in CID-dependent wild-type β-YAC BMCs and human primary erythroid progenitor cells confirmed the induction profiles of seven of the 232 hits that were cherry-picked for further analysis.

α:Non-α and Gγ:Aγ globin chain ratios in thalassemia intermedia patients treated with hydroxyurea

OBJECTIVES

To elucidate the possible ways by which hydroxyurea molecules affect globin chain (α or β-like) synthesis.

METHODS

A total of 23 thalassemia intermedia patients (13 male and 10 female) aged between 5 and 26 years were treated for five months with 15 mg/(kg·day) of hydroxyurea. Hemoglobins electrophoresis and globin chain electrophoresis was performed on each sample at different time points before and during the treatment.

RESULTS

Fetal hemoglobin increased significantly in most patients and average episodes of transfusion decreased. Both Gγ and Aγ-globin chains increased significantly and α-globin:Nonα-globin chain as well as Gγ-globin:Aγ globin chains ratios decreased.

CONCLUSIONS

Improvement in α:non-α ratio and consequent decrease of free α-globin chain might be the cause of beneficial effects of hydroxyurea therapy. Two patients who felt better didn't show significant increase in their fetal hemoglobin level, and this is in contradiction with the hypothesis claiming that the HbF level increase is the cause of such therapeutic effect. In spite of the unclear mechanism of action of this drug, hydroxyurea therapy had noticeable impacts on thalassemia intermedia and also sickle cell disease and even patients suffering from thalassemia major.

Transcriptional regulators Myb and BCL11A interplay with DNA methyltransferase 1 in developmental silencing of embryonic and fetal β-like globin genes

The clinical symptoms of hemoglobin disorders such as β-thalassemia and sickle cell anemia are significantly ameliorated by the persistent expression of γ-globin after birth. This knowledge has driven the discovery of important regulators that silence γ-globin postnatally. Improved understanding of the γ- to β-globin switching mechanism holds the key to devising targeted therapies for β-hemoglobinopathies. To further investigate this mechanism, we used the murine erythroleukemic (MEL) cell line containing an intact 183-kb human β-globin locus, in which the (G)γ- and β-globin genes are replaced by DsRed and eGFP fluorescent reporters, respectively. Following RNA interference (RNAi)-mediated knockdown of two key transcriptional regulators, Myb and BCL11A, we observed a derepression of γ-globin, measured by DsRed fluorescence and qRT-PCR (P<0.001). Interestingly, double knockdown of Myb and DNA methyltransferase 1 (DNMT1) resulted in a robust induction of ε-globin, (up to 20% of total β-like globin species) compared to single knockdowns (P<0.001). Conversely, double knockdowns of BCL11A and DNMT1 enhanced γ-globin expression (up to 90% of total β-like globin species) compared to single knockdowns (P<0.001). Moreover, following RNAi treatment, expression of human β-like globin genes mirrored the expression levels of their endogenous murine counterparts. These results demonstrate that Myb and BCL11A cooperate with DNMT1 to achieve developmental repression of embryonic and fetal β-like globin genes in the adult erythroid environment.

Combining gene therapy and fetal hemoglobin induction for treatment of β-thalassemia

β-thalassemias are caused by nearly 300 mutations of the β-globin gene, leading to a low or absent production of adult hemoglobin (HbA). Two major therapeutic approaches have recently been proposed: gene therapy and induction of fetal hemoglobin (HbF) with the objective of achieving clinically relevant levels of Hbs. The objective of this article is to describe the development of therapeutic strategies based on a combination of gene therapy and induction of HbFs. An increase of β-globin gene expression in β-thalassemia cells can be achieved by gene therapy, although de novo production of clinically relevant levels of adult Hb may be difficult to obtain. On the other hand, an increased production of HbF is beneficial in β-thalassemia. The combination of gene therapy and HbF induction appears to be a pertinent strategy to achieve clinically relevant results.

A randomized phase I/II trial of HQK-1001, an oral fetal globin gene inducer, in β-thalassaemia intermedia and HbE/β-thalassaemia

β-thalassaemia intermedia (BTI) syndromes cause haemolytic anaemia, ineffective erythropoiesis, and widespread complications. Higher fetal globin expression within genotypes reduces globin imbalance and ameliorates anaemia. Sodium 2,2 dimethylbutyrate (HQK-1001), an orally bioavailable short-chain fatty acid derivative, induces γ-globin expression experimentally and is well-tolerated in normal subjects. Accordingly, a randomized, blinded, placebo-controlled, Phase I/II trial was performed in 21 adult BTI patients (14 with HbE/β(0) thalassaemia and seven with β(+)/β(0) thalassaemia intermedia, to determine effective doses for fetal globin induction, safety, and tolerability. HQK-1001 or placebo were administered once daily for 8 weeks at four dose levels (10, 20, 30, or 40 mg/kg per day), and subjects were monitored for laboratory and clinical events. Pharmacokinetic profiles demonstrated a t(1/2) of 10-12 h. Adverse events with HQK-1001 treatment were not significantly different from placebo treatment. The 20 mg/kg treatment doses increased median HbF above baseline levels by 6·6% and 4·4 g/l (P < 0·01) in 8/9 subjects; total haemoglobin (Hb) increased by a mean of 11 g/l in 4/9 subjects. These findings identified a safe oral therapeutic which induces fetal globin in BTI. Further investigation of HQK-1001 with longer dosing to definitively evaluate its haematological potential appears warranted.

The potential role of cell penetrating peptides in the intracellular delivery of proteins for therapy of erythroid related disorders

The erythroid related disorders (ERDs) represent a large group of hematological diseases, which in most cases are attributed either to the deficiency or malfunction of biosynthetic enzymes or oxygen transport proteins. Current treatments for these disorders include histo-compatible erythrocyte transfusions or allogeneic hematopoietic stem cell (HSC) transplantation. Gene therapy delivered via suitable viral vectors or genetically modified HSCs have been under way. Protein Transduction Domain (PTD) technology has allowed the production and intracellular delivery of recombinant therapeutic proteins, bearing Cell Penetrating Peptides (CPPs), into a variety of mammalian cells. Remarkable progress in the field of protein transduction leads to the development of novel protein therapeutics (CPP-mediated PTs) for the treatment of monogenetic and/or metabolic disorders. The “concept” developed in this paper is the intracellular protein delivery made possible via the PTD technology as a novel therapeutic intervention for treatment of ERDs. This can be achieved via four stages including: (i) the production of genetically engineered human CPP-mediated PT of interest, since the corresponding native protein either is missing or is mutated in the erythroid progenitor cell (ErPCs) or mature erythrocytes of patients; (ii) isolation of target cells from the peripheral blood of the selected patients; (iii) ex vivo transduction of cells with the CPP-mediated PT of interest; and (iv) re-administration of the successfully transduced cells back into the same patients.

Alternative options for DNA-based experimental therapy of β-thalassemia

INTRODUCTION

Beta-thalassemias are caused by more than 200 mutations of the β-globin gene, leading to low or absent production of adult hemoglobin. Achievements have been made with innovative therapeutic strategies for β-thalassemias, based on research conducted at the levels of gene structure, transcription, mRNA processing and protein synthesis.

AREAS COVERED

The objective of this review is to describe the development of therapeutic strategies employing viral and non-viral DNA-based approaches for treatment of β-thalassemia.

EXPERT OPINION

Modification of β-globin gene expression in β-thalassemia cells has been achieved by gene therapy, correction of the mutated β-globin gene and RNA repair. In addition, cellular therapy has been proposed for β-thalassemia, including reprogramming of somatic cells to generate induced pluripotent stem cells to be genetically corrected. Based on the concept that increased production of fetal hemoglobin (HbF) is beneficial in β-thalassemia, DNA-based approaches to increase HbF production have been optimized, including treatment of target cells with lentiviral vectors carrying γ-globin genes. Finally, DNA-based targeting of α-globin gene expression has been applied to reduce the excess of α-globin production by β-thalassemia cells, one of the major causes of the clinical phenotype.

Generation of a genomic reporter assay system for analysis of γ- and β-globin gene regulation

A greater understanding of the regulatory mechanisms that govern γ-globin expression in humans, especially the switching from γ- to β-globin, which occurs after birth, would help to identify new therapeutic targets for patients with β-hemoglobinopathy. To further elucidate the mechanisms involved in γ-globin expression, a novel fluorescent-based cellular reporter assay system was developed. Using homologous recombination, two reporter genes, DsRed and EGFP, were inserted into a 183-kb intact human β-globin locus under the control of (G)γ- or (A)γ-globin promoter and β-globin promoter, respectively. The modified constructs were stably transfected into adult murine erythroleukaemic (MEL) cells and human embryonic or fetal erythroleukemic (K562) cells, allowing for rapid and simultaneous analysis of fetal and adult globin gene expression according to their developmental stage-specific expression. To demonstrate the utility of this system, we performed RNA interference (RNAi)-mediated knockdown of BCL11A in the presence or absence of known fetal hemoglobin inducers and demonstrated functional derepression of a γ-globin-linked reporter in an adult erythroid environment. Our results demonstrate that the cellular assay system represents a promising approach to perform genetic and functional genomic studies to identify and evaluate key factors associated with γ-globin gene suppression.

Expression of fetal hemoglobin in adult humans exposed to high altitude hypoxia

In humans, acute erythroid expansion can lead to maturation of red blood cell (RBC) precursors containing fetal hemoglobin (F red cells). This can occur in patients after recovery from bone marrow transplantation, or in individuals affected by sickle cell or thalassemic syndromes. An accelerated erythroid lineage expansion is also a hallmark of the adaptive response to high altitude hypoxia. To explore the possible effect of this environment on F red cell production, we analyzed RBCs from five subjects during and after 17 days spent at high altitude and investigated the expression of fetal hemoglobin by different methodological approaches. By flow cytometry, we found a moderate increase of circulating F red cells during and after the hypoxia exposure, with respect to control cells analyzed before a stay at high altitude. The increased expression of γ-globin (as the specific subunit contained in F hemoglobin together with α-globin) was further confirmed by immunoblotting of young RBC hemolysates and quantitative RT-PCR of transcripts purified from a reticulocyte-enriched RBC fraction. Thus, in healthy adults the exposure to high altitude hypoxia induces maturation of F red cells at a level higher than under normal condition. The effect appears reduced after return to normoxia.