Effect of the NAMPT Activator P7C3-A20 on γ-Globin Expression in Baboon CD34+ Erythroid Cell Cultures

Increased levels of Fetal Hemoglobin (HbF) reduce the symptoms of sickle cell disease (SCD) and lengthen the life span of patients. New, more effective pharmacological agents that can be safely administered long term to increase HbF levels in SCD patients are highly sought. Expression of the γ-globin gene in adult erythroid cells is normally repressed by the recruitment of multi-protein co-repressor complexes to the γ-globin promoter by sequence-specific DNA binding proteins including BCL11A, LRF1 and TR2/TR4. Enzymes contained within these co-repressor complexes, such as DNMT1, LSD1, G9A, and HDACs, modify the chromatin surrounding the γ-globin promoter by catalyzing repressive epigenetic modifications to both histones and DNA. Small molecule pharmacological inhibitors of these enzymes are potent inducers of HbF in various in cell culture and animal models and in SCD patients, but the use of these drugs in patients has been hindered by their dose-dependent effects on hematopoietic differentiation. An alternative strategy to the use of these pharmacological inhibitors to increase HbF would be to employ pharmacological activators that increase the activity of proteins that positively promote γ-globin expression. Previous studies have shown that pharmacological activators of the Sirtuin 1 protein deacetylase increased γ-globin expression in cultured human CD34+ erythroid progenitor cell cultures (Dai et al; Am J Hematol 92:1177-1186, 2017). Because Sirtuin deacetylase activity is dependent upon nicotinamide adenine dinucleotide (NAD) as a co-factor, we tested the hypothesis that increased concentrations of nicotinamide, an NAD precursor, would also increase γ-globin expression. Baboon bone marrow derived CD34+ erythroid progenitor cells from 4 individual baboons were cultured on AFT024 monolayers for 14 days in the presence and absence of varying concentrations of nicotinamide. Globin chain expression was measured in cell lysates by high performance liquid chromatography (HPLC). Nicotinamide (500μM) appeared to increase γ-globin 2 fold (0.015±0.098 γ/γ+β) compared to untreated controls (0.072±0.04 γ/γ+β; n=4; p<0.08). Because the nicotinamide levels used in this experiments are higher than can be easily achieved by dietary supplementation, additional experiments were performed to test the effect of P7C3-A20, an allosteric activator of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD synthesis, on γ-globin expression. Addition of P7C3-A20 (2.5μM) to CD34+ erythroid progenitor cultures on d1, 4, 7, and 10 increased γ-globin 2.7 fold (0.247±0.10 γ/γ+β) compared to vehicle-treated controls (0.090±0.06 γ/γ+β; n=5; p<0.01). P7C3-A20 treatment did not affect cell viability or growth at concentration< 2.5μM and dose-response experiments showed increased γ-globin in cultures treated with submicromolar concentrations of the drug. Addition of P7C3-A20 to cultures on days 1 and 4 resulted in near maximal stimulation of γ-globin expression with lesser effects when the drug was added on later days (d4 and7 or d7 and 10) strongly suggesting that the drug targets cells at an early stage of differentiation. Additional experiments showed that the effect of P7C3-A20 (2.5μM) in combination with either the DNMT1 inhibitor decitabine (DAC) or the LSD1 inhibitor tranylcypromine (TCP) resulted in a greater than additive effects on γ-globin expression in the absence of cytotoxicity (Figure 1). In conclusion, the NAMPT activator P7C3-A20 increased γ-globin expression in baboon CD34+ erythroid progenitor cells with greater than additive effects in combination with DAC or TCP. P7C3-A20 has potent in vivo effects as a neuroprotective drug in mouse models and non-human primates. Therefore, the potential of this drug for in vivo HbF induction warrants further investigation. Figure 1 Figure 1. Disclosures Saunthararajah: EpiDestiny: Consultancy, Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.

Genetic modifiers of fetal hemoglobin affect the course of sickle cell disease in patients treated with hydroxyurea

The course of sickle cell disease (SCD) is modified by polymorphisms boosting fetal hemoglobin (HbF) synthesis. However, it has remained an open question how these polymorphisms affect patients who are treated with the HbF-inducing drug hydroxyurea/hydroxycarbamide. The German SCD registry offers the opportunity to answer this question, because >90% of patients are treated according to national guidelines recommending the use of hydroxyurea in all patients above 2 years of age. We analyzed the modifying effect of HbF-related genetic polymorphisms in 417 patients with homozygous SCD >2 years who received hydroxyurea. HbF levels were correlated with higher total hemoglobin levels, lower rates of hemolysis, a lower frequency of painful crises and of red blood cell transfusions. The minor alleles of the polymorphisms in the γ-globin promoter (rs7482144), BCL11A (rs1427407) and HMIP (rs66650371) were strongly associated with increased HbF levels. However, these associations did not translate into lower frequencies of vasoocclusive events that did not differ between patients either carrying or not carrying the HMIP and BCL11A polymorphisms. Patients on hydroxyurea carrying the γ- globin promoter polymorphism demonstrated substantially higher hemoglobin levels (p

hGATA1 Under the Control of a μLCR/β-Globin Promoter Rescues the Erythroid but Not the Megakaryocytic Phenotype Induced by the Gata1low Mutation in Mice

The phenotype of mice carrying the Gata1low mutation that decreases expression of Gata1 in erythroid cells and megakaryocytes, includes anemia, thrombocytopenia, hematopoietic failure in bone marrow and development of extramedullary hematopoiesis in spleen. With age, these mice develop myelofibrosis, a disease sustained by alterations in stem/progenitor cells and megakaryocytes. This study analyzed the capacity of hGATA1 driven by a μLCR/β-globin promoter to rescue the phenotype induced by the Gata1low mutation in mice. Double hGATA1/Gata1low/0 mice were viable at birth with hematocrits greater than those of their Gata1low/0 littermates but platelet counts remained lower than normal. hGATA1 mRNA was expressed by progenitor and erythroid cells from double mutant mice but not by megakaryocytes analyzed in parallel. The erythroid cells from hGATA1/Gata1low/0 mice expressed greater levels of GATA1 protein and of α- and β-globin mRNA than cells from Gata1low/0 littermates and a reduced number of them was in apoptosis. By contrast, hGATA1/Gata1low/0 megakaryocytes expressed barely detectable levels of GATA1 and their expression of acetylcholinesterase, Von Willebrand factor and platelet factor 4 as well as their morphology remained altered. In comparison with Gata1+/0 littermates, Gata1low/0 mice contained significantly lower total and progenitor cell numbers in bone marrow while the number of these cells in spleen was greater than normal. The presence of hGATA1 greatly increased the total cell number in the bone marrow of Gata1low/0 mice and, although did not affect the total cell number of the spleen which remained greater than normal, it reduced the frequency of progenitor cells in this organ. The ability of hGATA1 to rescue the hematopoietic functions of the bone marrow of the double mutants was confirmed by the observation that these mice survive well splenectomy and did not develop myelofibrosis with age. These results indicate that hGATA1 under the control of µLCR/β-globin promoter is expressed in adult progenitors and erythroid cells but not in megakaryocytes rescuing the erythroid but not the megakaryocyte defect induced by the Gata1low/0 mutation.

Trienone analogs of curcuminoids induce fetal hemoglobin synthesis via demethylation at Gγ-globin gene promoter

The reactivation of γ-globin chain synthesis to combine with excess free α-globin chains and form fetal hemoglobin (HbF) is an important alternative treatment for β-thalassemia. We had reported HbF induction property of natural curcuminoids, curcumin (Cur), demethoxycurcumin (DMC) and bis-demethoxycurcumin (BDMC), in erythroid progenitors. Herein, the HbF induction property of trienone analogs of the three curcuminoids in erythroleukemic K562 cell lines and primary human erythroid progenitor cells from β-thalassemia/HbE patients was examined. All three trienone analogs could induce HbF synthesis. The most potent HbF inducer in K562 cells was trienone analog of BDMC (T-BDMC) with 2.4 ± 0.2 fold increase. In addition, DNA methylation at CpG − 53, − 50 and + 6 of Gγ-globin gene promoter in K562 cells treated with the compounds including T-BDMC (9.3 ± 1.7%, 7.3 ± 1.7% and 5.3 ± 0.5%, respectively) was significantly lower than those obtained from the control cells (30.7 ± 3.8%, 25.0 ± 2.9% and 7.7 ± 0.9%, respectively P < 0.05). The trienone compounds also significantly induced HbF synthesis in β-thalassemia/HbE erythroid progenitor cells with significantly reduction in DNA methylation at CpG + 6 of Gγ-globin gene promoter. These results suggested that the curcuminoids and their three trienone analogs induced HbF synthesis by decreased DNA methylation at Gγ-globin promoter region, without effect on Aγ-globin promoter region.

DNA methylation patterns of β-globin cluster in β-thalassemia patients

Background Reactivation of fetal hemoglobin (HbF, α2γ2) holds a therapeutic target for β-thalassemia and sickle cell disease. Although many HbF regulators have been identified, the methylation patterns in β-globin cluster driving the fetal-to-adult hemoglobin switch remains to be determined. Results Here, we evaluated DNA methylation patterns of the β-globin cluster from peripheral bloods of 105 β0/β0 thalassemia patients and 44 normal controls. We also recruited 15 bone marrows and 4 cord blood samples for further evaluation. We identified that the CpG sites in the locus control region (LCR) DNase I hypersensitive site 4 and 3 (HS4-3) regions, and γ- and β-globin promoters displayed hypomethylation in β0/β0-thalassemia patients, especially for the patients with high HbF level, as compared with normal controls. Furthermore, hypomethylations in most of CpG sites of the HS4-3 core regions were also observed in bone marrows (BM) of β0/β0-patients compared with normal controls; and methylation level of γ-globin promoter -50 and + 17 CpG sites showed lower methylation level in patients with high HbF level compared with those with low HbF level and a negative correlation with HbF level among β0-thalassemia patients. Finally, γ-globin promoter + 17 and + 50 CpG sites also displayed significant hypomethylation in cord blood (CB) tissues compared with BM tissues from normal controls. Conclusions Our findings revealed methylation patterns in β-globin cluster associated with β0 thalassemia disease and γ-globin expression, contributed to understand the epigenetic modification in β0 thalassemia patients and provided candidate targets for the therapies of β-hemoglobinopathies.

RNA LEVER Mediates Long-Range Regulation of ε-globin by Keeping PRC2 in Check

SummaryPolycomb Repressive Complex 2 (PRC2) is an epigenetic regulator required for gene silencing during embryonic development. Previous studies have reported that PRC2 interacts with RNA in a promiscuous manner, but the biological functions of such interaction are unknown. Here we present a seesaw mechanism for the regulation of ε-globin through inactivating EZH2 by an upstream non-coding RNA (LEVER). We show that LEVER, a non-coding RNA identified by RNA immunoprecipitation sequencing (RIP-seq) of the PRC2 core subunit EZH2 and Nanopore sequencing, binds PRC2 and thereby prevents the accumulation of H3K27 methylation along the genomic region where LEVER RNA is transcribed. The open chromatin within the LEVER locus in turn competes for the chromatin interaction between the ε-globin promoter and the Locus Control Region (LCR), working as a negative regulatory element of ε-globin expression. Hence, LEVER RNA negatively regulates ε-globin by sequestering PRC2 from repressing the LEVER locus, which is a competitor of the ε-globin-LCR interaction.

Combining HPFH Mutations in Human Adult HSCs to Enhance Reactivation of Fetal Hemoglobin

Despite the significant advances in developing novel therapies for hemoglobinopathies, developing a universal and robust therapeutic approach, able to achieve an event-free result in all β0/β0 thalassemic and sickle cell patients is a work in progress. It is known that increase of Fetal hemoglobin (HbF) can lead to an ameliorated clinical picture up to transfusion independency. Inactivation via genome editing of γ-globin suppressors or introduction of Hereditary Persistence of Fetal Hemoglobin (HPFH) mutations in the promoter of hemoglobin gamma (HBG) have been shown to significantly increase the endogenous HbF expression. Here we studied the effect in HbF reactivation by targeting the binding site of the two main HbF silencers, BCL11a and LRF and how it compares to the well-established editing of the BCL11a erythroid enhancer. Furthermore, in order to achieve higher levels of fetal hemoglobin, we assayed the effect of all combinations of these cis and trans acting mutations. We first observed that all single knock outs had similar effects in HbF reactivation. Interestingly, by targeting both sites in the gamma globin promoter we observed a decrease in HbF induction compared to each single edit, suggesting a possible binding of a gamma globin activator in the in-between region. However, editing of the BCL11a erythroid enhancer and either of the two silencer binding sites yielded maximum levels of fetal hemoglobin, with pancellular HbF expression, both in vitro and in vivo following xeno-transplantation in NSGW mice. Collectively, our data suggest that the combination of two fetal globin reactivation mutations, one cis and one trans, have the potential to significantly increase HbF both totally and on per cell basis. This strategy has the potential to induce higher levels of HbF reactivation with a clinical benefit in patients with beta globin disorders. Disclosures No relevant conflicts of interest to declare.