Study on Hydroxyurea Response in Hemoglobinopathies Patients Using Genetic Markers and Liquid Erythroid Cultures.

Increased expression of fetal hemoglobin (HbF) may ameliorate the clinical course of hemoglobinopathies. Hydroxyurea (HU) is the only inducer approved for the treatment of these diseases able to stimulate HbF production but patients' response is highly variable indicating the utility of the identification of pharmacogenomic biomarkers in order to predict pharmacological treatment efficacy. To date few studies to evaluate the role of genetic determinants in HU response have been conducted showing contradictory results. In this study we analyzed BCL11A, GATA-1, KLF-1 genes and γ-globin promoter in 60 alleles from 30 hemoglobinopathies patients under HU treatment to assess the role of these markers in HU response. We did not find any association between these genetic determinants and HU response. Before treatment started, the same patients were analyzed in vitro using liquid erythroid cultures in a test able to predict their response to HU. The results of our analysis confirm the absence of pharmacogenomic biomarker associated to HU response indicating that, the quantification of γ-globin mRNA fold increase remains the only method able to predict in vivo patients response to the drug.

Efficacy of Rapamycin as Inducer of Hb F in Primary Erythroid Cultures from Sickle Cell Disease and ß-Thalassemia Patients.

Phenotypic improvement of hemoglobinopathies such as sickle cell disease and ß-thalassemia (ß-thal) has been shown in patients with high levels of Hb F. Among the drugs proposed to increase Hb F production, hydroxyurea (HU) is currently the only one proven to improve the clinical course of these diseases. However, Hb F increase and patient's response are highly variable, indicating that new pharmacological agents could be useful for patients not responding to HU or showing a reduction of response during long-term therapy. In this study we evaluated the efficacy of rapamycin, a lypophilic macrolide used for the prevention of acute rejection in renal transplant recipients, as an inducer of Hb F production. The analyses were performed in cultured erythroid progenitors from 25 sickle cell disease and 25 ß-thal intermedia (ß-TI) patients. The use of a quantitative Real-Time-polymerase chain reaction ReTi-PCR technique and high performance liquid chromatography (HPLC) allowed us to determine the increase in γ-globin mRNA expression and Hb F production in human erythroid cells treated with rapamycin. The results of our study demonstrated an increase in vitro of γ-globin mRNA expression in 15 sickle cell disease and 14 ß-TI patients and a corresponding Hb F increase. The induction by rapamycin, even if lower or similar in most of samples analyzed, in some cases was higher than HU. These data suggest that rapamycin could be a good candidate to be used in vivo for the treatment of hemoglobinopathies.

Quantification of HBG mRNA in primary erythroid cultures: prediction of the response to hydroxyurea in sickle cell and beta-thalassemia.

BACKGROUND AND OBJECTIVE: Increased expression of fetal hemoglobin (HbF) may ameliorate the clinical course of hemoglobinopathies like sickle cell disease (SCD) and ß-thalassemia. Hydroxyurea (HU) can stimulate HbF production in these diseases but the response is highly variable indicating the utility of developing an in vitro test to predict the patient's response to HU. We assessed whether the HbF response of patients with SCD and thalassemia intermedia (TI) to HU correlates with HBG (both γ-globin genes) expression in their cultured erythroid progenitors following exposure to HU. PATIENTS AND METHODS: We exposed primary erythroid cultures from peripheral blood mononuclear cells from 30 patients with SCD and 15 with TI to HU and measured HBG mRNA by real-time quantitative PCR. The same patients were then treated with HU and their HbF response after treatment with a stable dose of HU was compared with the mRNA results in cultured cells. RESULTS AND CONCLUSION: The fold increase in HBG mRNA in erythroid progenitors was similar to the fold increase in HbF in vivo. Quantification of HBG mRNA in erythroid progenitor cell cultures from patients with SCD and TI is predictive of their clinical response to HU.

Desensitization to hydroxycarbamide following long-term treatment of thalassaemia intermedia as observed in vivo and in primary erythroid cultures from treated patients.

Hydroxycarbamide (HC) is a pharmacological agent capable of stimulating fetal haemoglobin (HbF) production during adult life. High levels of HbF may ameliorate the clinical course of ß-thalassaemia and sickle cell disease. The efficacy of HC for the treatment of thalassaemia major and thalassaemia intermedia is variable. Although an increase of HbF has been observed in most patients, only some patients experience significant improvement in total haemoglobin levels. This study aimed to determine the effectiveness and safety of short- (1 year) and long-term (mean follow-up 68 months) HC treatment in 24 thalassaemia intermedia patients. Additionally, we evaluated if primary erythroid progenitor cells cultured from treated patients responded to HC treatment in a manner similar to that observed in vivo. Our results confirm a good response to HC after a short-term follow-up in 70% of thalassaemia intermedia patients and a reduction of clinical response in patients with a long follow-up. Erythroid cultures obtained from patients during treatment reproduced the observed in vivo response. Interestingly, haematopoietic stem cells from long-term treated patients showed reduced ability to develop into primary erythroid cultures some months before the reduction of the 'in vivo' response. The mechanism of this loss of response to HC remains to be determined.

The sea urchin sns5 insulator protects retroviral vectors from chromosomal position effects by maintaining active chromatin structure.

Silencing and position-effect (PE) variegation (PEV), which is due to integration of viral vectors in heterochromatin regions, are considered significant obstacles to obtaining a consistent level of transgene expression in gene therapy. The inclusion of chromatin insulators into vectors has been proposed to counteract this position-dependent variegation of transgene expression. Here, we show that the sea urchin chromatin insulator, sns5, protects a recombinant gamma-retroviral vector from the negative influence of chromatin in erythroid milieu. This element increases the probability of vector expression at different chromosomal integration sites, which reduces both silencing and PEV. By chromatin immunoprecipitation (ChIP) analysis, we demonstrated the specific binding of GATA1 and OCT1 transcription factors and the enrichment of hyperacetylated nucleosomes to sns5 sequences. The results suggest that this new insulator is able to maintain a euchromatin state inside the provirus locus with mechanisms that are common to other characterized insulators. On the basis of its ability to function as barrier element in erythroid milieu and to bind the erythroid specific factor GATA1, the inclusion of sns5 insulator in viral vectors may be of practical benefit in gene transfer applications and, in particular, for gene therapy of erythroid disorders.

Induction of gamma-globin gene transcription by hydroxycarbamide in primary erythroid cell cultures from Lepore patients.

Increased expression of fetal haemoglobin (HbF) may ameliorate the clinical course of beta-thalassemia and sickle cell disease. Some pharmacological agents, such as hydroxycarbamide (HC), can increase fetal haemoglobin synthesis during adult life. Cellular selection and/or molecular mechanisms have been proposed to account for this increase. To explore the mechanism of action of HC we focused on homozygous Hb-Lepore patients that presented with high fetal haemoglobin levels and were good responders to HC treatment "in vivo". We performed primary erythroid cultures from peripheral blood of four homozygous Lepore patients. The increase in HBG (gamma-globin) transcription levels and HbF content in these cultures, after HC treatment, were detected by quantitative real time polymerase chain reaction analysis and flow cytometric analysis. Primary transcript "in-situ" hybridization analysis showed a 2-fold increase in the number of cells expressing both HBG alleles in HC-treated erythroid cultures. These studies, demonstrating the larger number of biallelic HBG expressing cells, suggest that HC is able to stimulate the activation of HBG transcription. These observations provide evidences that the molecular mechanism of action is involved in the increase of fetal haemoglobin production by HC.

A genetic strategy to treat sickle cell anemia by coregulating globin transgene expression and RNA interference.

The application of RNA interference (RNAi) to stem cell-based therapies will require highly specific and lineage-restricted gene silencing. Here we show the feasibility and therapeutic potential of coregulating transgene expression and RNAi in hematopoietic stem cells. We encoded promoterless small-hairpin RNA (shRNA) within the intron of a recombinant gamma-globin gene. Expression of both gamma-globin and the lariat-embedded small interfering RNA (siRNA) was induced upon erythroid differentiation, specifically downregulating the targeted gene in tissue- and differentiation stage-specific fashion. The position of the shRNA within the intron was critical to concurrently achieve high-level transgene expression, effective siRNA generation and minimal interferon induction. Lentiviral transduction of CD34(+) cells from patients with sickle cell anemia led to erythroid-specific expression of the gamma-globin transgene and concomitant reduction of endogenous beta(S) transcripts, thus providing proof of principle for therapeutic strategies that require synergistic gene addition and gene silencing in stem cell progeny.

Allele-specific transcription of fetal genes in primary erythroid cell cultures from Lepore and deltabeta degrees thalassemia patients.

OBJECTIVE: Autonomous gene silencing and gene competition by globin promoters for locus control region (LCR) function have been proposed as mechanisms in developmental regulation of beta-like genes. deltabeta degrees thalassemias are syndromes presenting an increased production of fetal hemoglobin in adult life; the majority of them are due to various deletions in beta-globin gene cluster. We studied samples from double heterozygotes for beta-thalassemia and for Lepore or Sicilian deltabeta degrees deletions, both lacking beta-promoter sequence. Our goal was to address the question of whether the allele carrying the deltabeta degrees deletion is responsible for high level of fetal hemoglobin (HbF) production. PATIENTS AND METHODS: We analyzed the globin gene transcription in human erythroid cell cultures from peripheral blood stem cells, using primary transcript in situ hybridization. We performed primary erythroid cultures from patients with the following genotypes: Lepore/beta degrees 39, Sicilian deltabeta degrees /beta degrees 39, and, as controls, two thalassemia patients with nondeletional mutations (IVS1,6/IVS1,6; IVS1,6/beta degrees 39), and one normal individual. RESULTS: The cells where it is possible to unambiguously assign gamma genes transcription in cis with the deletion (gamma:beta) are strongly represented with respect to the nine other combinations of gamma and beta hybridization signals. These cells are at least nine times more represented than those expressing the gamma allele in trans to the deletion. CONCLUSION: The allele-specific transcription of fetal genes in cis with the deletion is favored in both deletional genotypes. The absence of the adult promoter may influence LCR recruitment by fetal promoter, supporting the hypothesis that competition mechanism and gene silencing can coexist in regulating human globin gene transcription.

Functional characterization of the sea urchin sns chromatin insulator in erythroid cells.

Chromatin insulators are regulatory elements that determine domains of genetic functions. We have previously described the characterization of a 265 bp insulator element, termed sns, localized at the 3' end of the early histone H2A gene of the sea urchin Paracentrotus lividus. This sequence contains three cis-acting elements (Box A, Box B, and Box C + T) all needed for the enhancer-blocking activity in both sea urchin and human cells. The goal of this study was to further characterize the sea urchin sns insulator in the erythroid environment. We employed colony assays in human (K562) and mouse (MEL) erythroid cell lines. We tested the capability of sns to interfere with the communication between the 5'HS2 enhancer of the human beta-globin LCR and the gamma-globin promoter. We found that the sns sequence displays directional enhancer-blocking activity. By the use of antibodies against known DNA binding proteins, in electrophoretic mobility shift assays, we demonstrated the binding of the erythroid-specific GATA-1 and the ubiquitous Oct-1 and Sp1 transcription factors. These factors bind to Box A, Box B, and Box C + T, respectively, in both K562 and MEL nuclear extracts. These results may have significant implications for the conservation of insulator function in evolutionary distant organisms and may prove to be of practical benefit in gene transfer applications for erythroid disorders such as hemoglobinopathies and thalassemias.