Increased Γ-globin Expression Research Articles

Identifying Novel Regulators of γ-Globin Expression Using a Genome-Scale CRISPR Activation Screen

β-hemoglobinopathies are the most common monogenic disorders worldwide, and are defined based on whether patients have quantitative (β-thalassemia) or qualitative (Sickle Cell Disease (SCD)) defects in β-globin synthesis. Unfortunately, there are limited treatment options for β-hemoglobinopathies, and the majority of patients continue to develop life-threatening complications from their diseases. An alternative β-like subunit, γ-globin, has been shown to inhibit pathogenic hemoglobin polymerization in SCD and to functionally replace β-globin in β-thalassemia. The discovery of novel strategies to upregulate γ-globin expression may lead to effective therapies for β-hemoglobinopathies. To identify novel regulators of γ-globin expression, we performed a genome-wide pooled CRISPR activation (CRISPRa) screen, using the Synergistic Activation Mediator (SAM) system. The screen was performed in the HUDEP-2 cell line, which expresses adult β-globin. We generated a clonal HUDEP-2-MPH cell line, which stably expresses the transcriptional activator complex MPH (MS2-P65-HSF1). This cell line was transduced with a viral library that delivers a VP64 activation domain fused to a catalytically dead Cas9 (dCas9-VP64), a blasticidin resistance cassette, and one of 3 unique sgRNAs targeting virtually every coding gene in the human genome (the library consists of 70,290 sgRNAs). At day 8 of erythroid differentiation, the top and bottom 10% γ-expressing cells were sorted, and integrated sgRNAs were sequenced using NextGen sequencing. As expected, sgRNAs targeting BCL11A and ZBTB7A (known negative regulators of γ-globin) were enriched in the bottom 10% γ-expressing cells, while sgRNAs targeting HIF1A (known positive regulator of γ-globin) were enriched in the top 10% γ-expressing cells. Notably, this screen identified several novel candidate positive regulators of γ-globin expression, including the transcriptional repressor Hypermethylated in Cancer 1 (HIC1). In preliminary validation studies, we used 2 independent sgRNAs to activate HIC1 in HUDEP-2-MPH cells and measured the percentage of γ-globin expressing cells (F-cells) by flow cytometry. Compared to cells transduced with control sgRNAs, increased HIC1 transcription (>200-fold) resulted in a profound increase in the proportion of F-cells, from a baseline of ~6% up to ~76%. Similarly, HIC1 overexpression in HUDEP-2 cells resulted in a ~13-fold increase in γ-globin mRNA levels and reduction in BCL11A mRNA level to ~30% of normal. These results suggest that the increased γ-globin expression resulting from HIC1 overexpression may result, at least in part, from reduced BCL11A levels (which we are currently validating). Recently, increased expression of HIC2, a paralogous protein for HIC1, was reported to result in increased γ-globin expression. To exclude the possibility that HIC1 targeting sgRNAs may also target HIC2, we measured the HIC2 mRNA level in HUDEP-2 cells targeted with sgRNAs aimed at increasing HIC1 expression. HIC2 mRNA was not increased in the latter cells. We next overexpressed HIC1 cDNA in erythroid cells differentiated from primary human CD34+ hematopoietic stem and progenitor cells (HSPCs). In early preliminary results, we found that HIC1 overexpression resulted in increased γ-globin expression, validating the HUDEP-2 data. Additional studies are ongoing to define the role of HIC1 in the regulation of γ-globin expression, and to define the impact of HIC1 overexpression on erythroid differentiation. In summary, our screen uncovered HIC1, and other potential novel regulators of γ-globin expression, which we are currently validating. These findings may result in future therapeutic approaches for β-hemoglobinopathies.

The CDK-Inhibitor p27 Kip1 Regulates Fetal Hemoglobin Expression

γ-globin upregulation has been shown to be beneficial for individuals with Sickle Cell Disease, leading to improvement in morbidity and mortality rates. Intriguingly, small molecules that modulate the cell cycle have been observed to impact γ-globin expression in erythroid cells, though a causal relationship has not been definitively established. Understanding the connection between cell cycle dynamics/regulation and γ-globin production may shed light into a novel molecular mechanism by which γ-globin expression is regulated, with potential therapeutic implications for Sickle Cell Disease. To evaluate if cell cycle speed correlates with γ-globin expression, we labeled HUDEP-2 cells (which express beta-globin) with carboxyfluorescein diacetate succinimidyl ester (CFSE) at different days of differentiation. With each cell division, CFSE dye intensity is expected to be reduced by half; therefore, faster cycling cells retain less CFSE than slower cycling cells. Forty-eight hours post-CFSE labeling, HUDEP-2 cells were analyzed for γ-globin expression by intracellular flow cytometry at days 2, 4, 6, and 8 of differentiation. Starting at Day 6 of differentiation, the slowest cycling (Top 5% CFSE) HUDEP-2 cells exhibited >2-fold increase in γ-globin expressing cells (F-cells) compared to the fastest cycling (bottom 5% CFSE) cells. Notably, these results were confirmed in erythroid cells differentiated from primary human CD34+ hematopoietic stem and progenitor cells (HSPCs), therefore ruling out the possibility that the above findings were an artifact of the immortalized HUDEP-2 cell line. The correlation between slow cell cycling speed and increased γ-globin expression prompted us to genetically perturb the cell cycle machinery and define the impact of these genetic perturbations on γ-globin expression. Using CRISPR activation (CRISPRa), we increased the expression of 8 Cyclin Dependent Kinase Inhibitors (CDKN2A, CDKN2B, CDKN2C, CDKN2D, CDKN1A, CDKN1B, CDKN1C and CDKN3) in HUDEP-2 cells. To do so, we first generated a HUDEP-2-MPH cell line that stably expresses the transcriptional activator complex MPH (MS2-P65-HSF1). We then transduced this cell line with a virus that expresses one of 3 sgRNAs targeting each of the 8 CDKIs, a VP64 activation domain fused to catalytically dead Cas9 (dCas9-VP64), and a blasticidin resistance cassette. We found that activation of CDKN1b (P27 Kip1) in particular, resulted in increased F-cell percentage. Indeed, compared to cells transduced with control sgRNAs, HUDEP-2-MPH cells transduced with a CDKN1B-targeting sgRNA (resulting in a 2-fold higher CDKN1B mRNA level; p= 0.006) exhibited an increased proportion of F-cells, from a baseline of ~6% up to ~20% (p= 0.024). Increased CDKN1B expression resulted in a ~14-fold increase in γ-globin mRNA levels (p= 0.026), associated with a mild reduction in beta-globin mRNA level and a reduction in BCL11A mRNA level to ~65% of normal. These results suggest that the increased γ-globin expression resulting from CDKN1B overexpression may result, at least in part, from reduced BCL11A expression (which we are currently validating). To rule out an off-target effect of the CDKN1B targeting sgRNA, we overexpressed CDKN1B in HUDEP-2 cells, using a cDNA expression construct, and found comparable results as observed with CDKN1B CRISPRa. We next overexpressed CDKN1B cDNA in erythroid cells differentiated from CD34+ HSPCs. In early preliminary results, increased CDKN1B expression in the latter cells resulted in increased γ-globin expression, both at the mRNA and protein level, validating the HUDEP-2 data. Additional studies are ongoing to define the role of CDKN1B in the regulation of γ-globin expression, and to define the impact of CDKN1B overexpression on erythroid differentiation. In summary, our preliminary studies have uncovered a link between cell cycle regulation and γ-globin production. These findings may lay the foundation for the development of new therapeutic strategies for Sickle Cell Disease.

Transmembrane Protein ANTXR1 Regulates γ-Globin Expression by Targeting the Wnt/β-Catenin Signaling Pathway.

Reactivation of fetal hemoglobin (HbF, α2γ2) alleviates clinical symptoms in patients with β-thalassemia and sickle cell disease, although the regulatory mechanisms of γ-globin expression have not yet been fully elucidated. Recent studies found that interfering with the expression of the membrane protein ANTXR1 gene upregulated γ-globin levels. However, the exact mechanism by which ANTXR1 regulates γ-globin levels remains unclear. Our study showed that overexpression and knockdown of ANTXR1 in K562, cord blood CD34+, and HUDEP-2 cells decreased and increased γ-globin expression, respectively. ANTXR1 regulates the reactivation of fetal hemoglobin (HbF, α2γ2) in K562, cord blood CD34+, and adult peripheral blood CD34+ cells through interaction with LRP6 to promote the nuclear entry of β-catenin and activate the Wnt/β-catenin signaling pathway. The overexpression or knockdown of ANTXR1 on γ-globin and Wnt/β-catenin signaling in K562 cells was reversed by the inhibitor XAV939 and the activator LiCl, respectively, where XAV939 inhibits the transcription of β-catenin in the Wnt pathway, but LiCl inhibits GSK3-β. We also showed that the binding ability of the rank4 site in the transcriptional regulatory region of the SOX6 gene to c-Jun was significantly increased after overexpression of ANTXR1 in K562 cells. SOX6 protein expression was increased significantly after overexpression of the c-Jun gene, indicating that the transcription factor c-Jun initiated the transcription of SOX6, thereby silencing γ-globin. Our findings may provide a new intervention target for the treatment of β-hemoglobinopathies.

Induction of Fetal Hemoglobin by Introducing Natural Hereditary Persistence of Fetal Hemoglobin Mutations in the γ-Globin Gene Promoters for Genome Editing Therapies for β-Thalassemia.

Reactivation of γ-globin expression is a promising therapeutic approach for β-hemoglobinopathies. Here, we propose a novel Cas9/AAV6-mediated genome editing strategy for the treatment of β-thalassemia: Natural HPFH mutations −113A > G, −114C > T, −117G>A, −175T > C, −195C > G, and −198T > C were introduced by homologous recombination following disruption of BCL11A binding sites in HBG1/HBG2 promoters. Precise on-target editing and significantly increased γ-globin expression during erythroid differentiation were observed in both HUDEP-2 cells and primary HSPCs from β-thalassemia major patients. Moreover, edited HSPCs maintained the capacity for long-term hematopoietic reconstitution in B-NDG hTHPO mice. This study provides evidence of the effectiveness of introducing naturally occurring HPFH mutations as a genetic therapy for β-thalassemia.

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. [Display omitted] DisclosuresSaunthararajah: 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.

Oral Administration of the LSD1 Inhibitor OG-S1335 Increases Fetal Hemoglobin in Humanized Transgenic Sickle Cell Disease Mice and in Baboons

Increased levels of fetal hemoglobin (HbF) lessen the severity of symptoms and increase the life span of patients with sickle cell disease (SCD). New and more effective strategies to increase HbF are needed because the current standard of care, hydroxyurea, is not effective in a significant proportion of patients. Although BM transplantation, gene therapy, and gene editing technologies offer the promise of a cure, it is unlikely that these methodologies can be implemented to treat the large numbers of patients projected worldwide, including those in developing nations that could most easily be treated with an effective, orally administered drug therapy that increased HbF. The lysine-specific demethylase 1A (KDM1A, also referred to as LSD1), is a component of co-repressor complexes that repress γ-globin gene expression and a therapeutic target for HbF reactivation (Shi et al, Nat Med 19:291, 2013). Our laboratory has shown that subcutaneous administration of RN-1, a pharmacological inhibitor of LSD1, increased γ-globin expression in SCD transgenic mice (Rivers et al, Exp Hematol 43:546, 2015; Cui et al, Blood 126:386, 2015) and in baboons (Rivers et al, Haematol 101:688, 2016), widely acknowledged as the best animal model to test the activity of HbF-inducing drugs due to conservation of structure and developmental regulation of the β-globin locus among simian primates. The objective of this investigation was to test whether oral administration of a new LSD1 inhibitor, OG-S1335, could increase HbF in SCD transgenic mice and baboons. Oral administration of varying doses (0.25, 0.5, 1.0mg/kg/d; 4d) of OG-S1335 to SCD mice (3 mice per dose) increased γ-globin expression and the percentage of circulating erythrocytes and reticulocytes positive for HbF (F cells and F retics; Table 1). In baboons, dose escalation was initially performed by administering the drug to a single animal in cycles of 3 days, followed by 1-2 weeks of observation to measure effects on blood parameters. Increased levels of F retics were initially observed at a dose of 100μg/kg/d and subsequently 4 additional baboons were treated with OG-S1335 (by oral gavage) at a dose of either 100 or 200μg/kg/d (7 separate experiments in total). The data presented are in the mean+SD format, with “post-dose” indicating the time point when the highest variation from baseline levels was reported. Increased F retics (pre=8.4+8.9%, post=43.0+27.9%; p<0.01), γ-globin chain synthesis (pre=0.05+0.05 γ/γ+β, post=0.28+0.18 γ/γ+β; p<0.01), and γ-globin mRNA (pre=0.02 +0.02 γ/γ+β, post=0.20+0.11 γ/γ+β) were observed with maximal levels achieved 7 days after administration of the first dose (d8). A decrease in the absolute number of reticulocytes (pre=72.8+17.8 X104/μL, post=35.4+17.8 X 104/μL; p<0.05; nadir on d6-8), neutrophils (pre=4634+994/μL, post=2655+1257/μL; p<0.02; nadir on d13-17), and platelets (pre=406+86 X103/μL, post=168+98 X103/μL; p<0.01; nadir on d8) was also reported, together with increased monocytes (pre=200+68/μL, post=541+213/μL; p<0.01; peak on d10-15). A negative correlation between decreased platelet counts and F retics (r= -0.55), γ-globin chain synthesis (r= -0.92), and γ-globin mRNA (r= -0.80) suggests that variability in drug exposure in addition to possible genetic factors regulating γ-globin expression may be responsible for the observed variability between animals. Additional experiments were performed in two phlebotomized anemic baboons to test the effect of the drug in a model with increased relevance to sickle cell disease. OG-S1335 (100μg/kg/d; 3d) induced high levels of F retics (PA8695, pre-dose=24%, post=66.8%; PA8698: pre-dose=13%, post=93.6%), γ-globin chain synthesis (PA8695: pre-dose=0.07 γ/γ+β, post=0.20 γ/γ+β; PA8698: pre-dose=0.02 γ/γ+β, post=0.44 γ/γ+β) and γ-globin mRNA (PA8695: pre-dose=0.06 γ/γ+β, post=0.18 γ/γ+β; PA8698: pre-dose=0.03 γ/γ+β, post=0.33 γ/γ+β) in each animal. We conclude that oral administration of the LSD1 inhibitor OG-S1335 significantly increased F retics, γ-globin chain synthesis, and γ-globin mRNA in SCD mice and in baboons, supporting further efforts toward the development of this drug for SCD therapy. [Display omitted] DisclosuresCiceri:Oryzon Genomics SA: Employment. Cavalcanti:Oryzon Genomics SA: Employment.

Novel Conjugates of Butyrate and δ-Aminolevulinate Increase γ-Globin Gene Expression and Fetal Hemoglobin Synthesis in Erythroid Progenitors

Pharmacologic induction of fetal hemoglobin (HbF) expression reduces the clinical severity of sickle cell disease (SCD) and improves long-term survival. Research efforts to develop effective and safe therapies have focused on a wide variety of agents however, Hydroxyurea is the only FDA-approved drug proven to mediate HbF induction in about 50% of adult SCD patients. Our group previously reported potent HbF-induction by sodium butyrate through p38 MAPK activation and CREB1 binding to the Gγ-globin cyclic AMP response element (Sangerman et al., Blood 2006). However, oral administration of butyrate derivatives to SCD patients was ineffective due to rapid metabolic inactivation by the liver. Therefore to address this critical barrier of limited treatment options for SCD, we investigated the prodrugs 1-(butyryloxy)ethyl 5-amino-4-oxopentanoate (AN233) and 1-(butyryloxy)butyl 5-amino-4-oxopentanoate (AN908), esters of δ-aminolevulinate (ALA) and butyric acid as HbF inducers in erythroid cells. Oral administration of AN233 and AN908 to BALB/c mice increased total hemoglobin levels without causing tissue toxicity (Rephaeli et al., Eur J Pharm Sci 2016).To test the ability of prodrugs to induce HbF, both K562 and KU812 cells and the immortalized human umbilical cord blood-derived erythroid progenitor 1 (HUDEP1) model were used. Treatment of K562 cells with 0.125-0.50 mM concentrations of AN233 produced cell toxicity at the 0.50 mM concentration, however >90% viability was observed by Trypan blue exclusion for 0.25 mM AN233 without evidence of caspace-3 cleavage. Using this concentration of AN233, a 1.5-fold and 6-fold (p<0.05) increase in γ-globin mRNA and HbF levels respectively, were observed supporting robust intracellular activation of AN233. Flow cytometry analysis confirmed a 1.5-fold increase in the percent of HbF positive cells (F-cells). Preliminary studies in HUDEP1 cells showed 0.25 mM AN233 increased γ-globin expression by 1.5 fold and HbF protein synthesis by 2.2 fold. Mechanistically, AN233 mediated a 53% decrease in phosphorylation levels of the kinase, eIF2α (eukaryotic initiation factor 2α) which favors conditions for protein synthesis. As further evidence that both prodrugs induce HbF synthesis in different cell types, KU812 cells expressing the γ-globin and β-globin genes were treated with AN908 (0.125-0.50 mM). In contrast to AN233, cell toxicity was not observed at the 0.50 mM AN908 concentration where 93% cell viability was maintained. Treating KU812 cells with 0.25 mM AN908 for 48 h produced a 1.4-fold increase in γ-globin transcription and HbF synthesis by western blot. In addition, F-cell levels increased from 45% to 70% and HbF levels (by mean fluorescence intensity) 2.2-fold (p<0.05). Interestingly, when 0.25 mM AN908 was combined with hydroxyurea (100 μM) we observed an additive increase in HbF and F-cells levels.Collectively, these findings support the oral active prodrugs AN233 and AN908 as HbF inducers in erythroid cells. Furthermore, the combination of AN908 and hydroxyurea produced an additive effect without increasing cell toxicity. Studies are underway to determine the EC50 of both prodrugs in normal and sickle primary erythroid progenitors and mechanisms of γ-globin regulation through epigenetic modifications. DisclosuresNo relevant conflicts of interest to declare.

Screening Fetal Hemoglobin Inducing Compounds in Human Umbilical Cord Blood-Derived Erythroid Progenitor Cells

Background: Human Umbilical Cord Blood-Derived Erythroid Progenitor Cells-2 (HUDEP-2) cells are an immortalized human CD34+ hematopoietic stem and progenitor cell (HSPC)-derived erythroid precursor cell line that expresses BCL11A and β-globin. HUDEP-1 cells are an immortalized human CD34+ HSPC-derived erythroid precursor cell line that does not express BCL11A, predominantly expresses γ-globin, and exhibits an increase in γ-globin after differentiation. High baseline γ-globin and difficulty in distinguishing between true γ-globin induction and changes in HUDEP-1 differentiation, which increases g-globin, combined with the lack of β-globin expression, make HUDEP-1 cells a suboptimal system in which to study hemoglobin switching. HUDEP-2 cells have been used successfully to demonstrate HbF induction in several gene editing experiments involving deletion of BCL11A enhancer regions and substitution mutations in the γ-globin locus. HUDEP-2 also express very low levels of γ-globin; this has led to the hope that potential HbF inducing compounds can be screened in HUDEP-2 cells, causing them to express significant amounts of γ-globin, and potentially a reduction in β-globin expression, demonstrating hemoglobin switching.Objectives: Determine if HUDEP-2 cell lines are suitable systems in which to examine pharmacologic hemoglobin switching. We will determine if γ-globin induction can be achieved in HUDEP-2 cells from hydroxyurea, metformin, piceatannol, decitabine, or pomalidomide at doses that induce HbF in human HSPCs and raise γ-globin expression in HUDEP-1 cells.Methods: We performed drug treatment on differentiated HUDEP-1 andHUDEP-2 cells as well as hematopoietic stem and progenitor cells (HSPCs) from SCD patients with hydroxyurea, metformin, piceatannol, decitabine and pomalidomide at different doses. The effect of the drugs on HUDEP-1 differentiation was determined by measurement of Band3 by quantitative western blot. After 7 days of drug treatment, HbF was measured by western blot and HPLC in HSPCs, and by RT-qPCR (gamma globin expression) and western blot in HUDEP-1 and HUDEP-2.Results: Hydroxyurea, metformin, piceatannol, decitabine and pomalidomide all significantly increased γ-globin expression in HUDEP-1 cells, and HbF in HSPCs derived from patients with SCD. However, metformin was shown to increase HUDEP-1 differentiation, as measured by a rise in Band 3, which could explain the rise in γ-globin expression. HPLC analysis of the culture of HSPCs derived from patients with SCD showed that drug treatment with 30 µM hydroxyurea, 100 µM Metformin, 25 µM piceatannol or 200 nM decitabine produced a 2.3 fold, 2.1 fold, 3.1 fold, and 2.9 fold increase in HbF respectively. No change was observed in γ-globin expression or HbF in HUDEP-2 cells with any of the 5 drugs tested.Conclusions: γ-globin is not inducible in HUDEP-2 cells using hydroxyurea, metformin, piceatannol, decitabine and pomalidomide, known HbF inducing drugs that are believed to act through different pathways and mechanisms. It is therefore unlikely that HUDEP-2 cells will be effective in screening drug compounds for HbF induction activity. HUDEP-1 cells do show increased γ -globin levels in response to these agents, but care must be taken to show that the rise in γ-globin is not due to further differentiation of HUDEP-1 cells. DisclosuresNo relevant conflicts of interest to declare.

BCL11A Polymorphism in Egyptian Children with β-Thalassemia: Relation to Phenotypic Heterogeneity.

Fetal hemoglobin (HbF) is a potent genetic modifier of β-thalassemia phenotype. B-cell lymphoma 11A ( BCL11A ) gene results in significant silencing of HbF. The aim of this study was to assess the prevalence of different BCL11A genotypes among a cohort of Egyptian children with β-thalassemia and to correlate them to HbF and clinical severity score. Eighty-two children with β-thalassemia (aged 12.95 ± 3.63 years) were recruited from the Pediatric Hematology Clinic, Ain Shams University. They were divided based on the clinical severity of β-thalassemia into three subgroups: 20 mild (24.4%), 24 moderate (29.3%), and 38 severe (46.3%). Age, gender, age of diagnosis, initial HbF level, transfusion history, and history of splenectomy were assessed. Anthropometric measures, signs of anemia and hemosiderosis, and the severity score were determined. Laboratory investigations such as complete blood picture, ferritin, and single gene polymorphism genotyping of the rs11886868 were also performed. Our findings showed that 16 children had CC genotype (19.5%), 38 had TC genotype (46.3%), and 28 had TT genotype (34.1%) of the rs#. β-thalassemia children with TT genotype had significantly higher severity scoring than the other two groups ( p < 0.001). Moreover, mean initial HbF was found to be lower in children with TT genotype followed by TC and CC genotypes ( p < 0.001). Increased γ-globin expression associated with BCL11A gene polymorphism is associated with better clinical severity of β-thalassemia.

Effect of Nicotinamide, 1-Methylnicotinamide, and N’-Methylnicotinamide on Erythroid Colony Formation and γ-Globin Expression in Cultured Baboon CD34+ Cells

Pharmacological treatments designed to increase Fetal Hemoglobin (HbF) levels offer great promise to alleviate the symptoms and improve the lifespan of the vast numbers of patients afflicted with sickle cell disease (SCD) and β-thalassemia. Hydroxyurea can increase HbF, but a large fraction of patients with SCD do not respond to the drug. DNMT1 and LSD1 inhibitors are the most powerful drugs to increase HbF but are limited by side effects that include neutropenia, thrombophilia and/or thrombocytopenia. The development of new, more effective, and safer pharmacological strategies to augment HbF levels in the blood thus continues to be an important goal. Previous studies have shown that γ-globin gene expression is dynamically regulated during erythroid differentiation (Papayannopoulou et al PNAS 74:2923-2927, 1977). The proportion of γ-globin gene expression is higher at earlier stages (BFUe) of erythroid differentiation than at more advanced stages (CFUe). Therefore, we suggest the hypothesis that expansion of primitive, less differentiated progenitors might favor increased γ-globin, particularly when combined other HbF-inducing drugs. To investigate this hypothesis, we have tested whether nicotinamide (NAM), the major NAM metabolite 1-methylnicotinamide (1-mNAM), and N'-methylnicotinamide (N'-mNAM), a chemical derivative of NAM, can foster expansion of erythroid colony-forming cells (BFUe and CFUe) and increase γ-globin expression of cultured baboon CD34+ cells. Previous observations have shown that NAM facilitates in vitro expansion of cord blood CD34+ cells and enhanced long term engraftment in transplanted recipients (Horwitz et al J Clin Invest 124:3121, 2014). Contrasting effects of NAM, 1-mNAM, and N'-mNAM on differentiation and proliferation of the murine erythroleukemia cell line (MEL) have been previously reported (Terada et al PNAS 76:6414, 1979; Kuykendall et al Toxicol In Vitro 21:1656, 2007). While both NAM and N'-mNAM induced MEL cell differentiation, N'-mNAM was far more potent. In contrast, 1-mNAM increased cell proliferation, reduced spontaneous differentiation, and blocked differentiation induced by NAM and N'-mNAM. The effect of all three forms of NAM was examined using bone marrow (BM) CD34+ cells from a pre-clinical non-human primate large animal model. To test the effect of NAM, 1-mNAM, and N'-mNAM on expansion of erythroid colony-forming cells, the agents (5mM) were added to liquid cultures of baboon CD34+ bone marrow cells previously expanded for 5 days in serum-free expansion media (SFEM). Colony assays were performed on d8. In two experiments total erythroid colonies (BFUe and CFUe) were 2 fold higher in cultures treated with 1-mNAM compared to untreated controls (p&amp;lt;0.05) while no effect was observed in cultures treated with NAM. No colonies were observed in cultures treated with N'-mNAM (Figure 1A). Observation of Wright's stained cytospin preparations showed extensive erythroid differentiation on d8 in cells treated with N'-mNAM (Figure 1B). The effect of NAM, 1-mNAM, and N'-NAM on γ-globin expression was tested in baboon CD34+ cells grown in co-culture with the AFT024 cell line. NAM, 1-mNAM, or N'-mNAM (5mM) were added to cultures on d7. Expression of γ- and β-globin mRNA was measured by RT-PCR on d17. Increased γ-globin expression (0.57±0.04 γ/γ+β)) was observed in cells treated with N'-mNAM on d7 compared to untreated controls (0.20±0.09 γ/γ+β; p&amp;lt;0.001). NAM and 1-mNAM had no significant effect on γ-globin gene expression (Figure 1C). These results thus show that while erythroid colonies are increased by 1-mNAM, N'-mNAM is a potent inducer of erythroid differentiation and increases γ-globin expression in primary cultures of baboon CD34+ cells. In conclusion, 1-mNAM and N'-mNAM have contrasting effects on erythroid differentiation in primary baboon CD34+ cell cultures, confirming previous experiments in the MEL cell line. Future experiments are planned to test the effect of these agents on HbF in the baboon. Disclosures Saunthararajah: EpiDestiny: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties.

Combinatorial Administration of Pharmacological Inhibitors Targeting DNMT1 and KDM1A Produces Synergistic and Additive Increases in F Retiulocytes and γ-Globin Expression in Normal Baboons

Sickle cell disease (SCD) is an inherited blood disorder that severely impacts the quality of life and reduces the life expectancy of approximately 100,000 patients in the U.S. and millions worldwide. Elevated levels of Fetal Hemoglobin (HbF; α2γ2) reduce the severity of symptoms and lengthen the life span of patients with sickle cell disease by inhibiting deoxy HbS polymerization. Hydroxyurea (HU), the only FDA-approved drug shown to increase HbF, is not effective in a subset of patientsand importantly, in the refractory individuals the increased HbFis heterogeneously distributed within the erythrocyte population resulting in a large fraction of erythrocytes lacking protective levels. Simian primates such as the baboon are widely acknowledged as the best animal models for testing the ability of new drugs to increase γ-globin expression because results in baboons are predictive of effects in man due to conservation of the structure and developmental stage-specific regulation of the β-like globin genes in simian primates. Our previous studies in baboons have shown that the most powerful drugs for reactivation of HbF are DNMT1 and KDM1A inhibitors targeting enzymes located within the co-repressor complexes that act to establish and maintain repressive epigenetic modifications at the γ-globin promoter to repress γ-globin expression. Treatment of baboons with either decitabine, an inhibitor of DNMT1, or RN-1, an inhibitor of KDM1A, strongly stimulates HbF. Dose-limiting effects of these drugs include neutropenia, thrombocytopenia, and/or thrombophilia. In this investigation we have explored the hypothesis that a treatment regimen comprised of both decitabine and RN-1 could achieve additive or synergistic effects on HbF while minimizing adverse hematological side effects. Three baboons (PA8695, PA8697, PA8698) were treated with two courses of different doses of RN-1 (0.25 and 0.125mg/kg/d) administered subcutaneously for 3 days to select an optimal RN-1 dose for each animal. The response to RN-1 varied between individual animals and was associated with pretreatment levels of γ-globin expression. Higher pretreatment levels of γ-globin expression were observed in PA8697 (0.08 γ/γ+β) compared to PA8695 (0.014+0.005 γ/γ+β) and PA8698 (0.004+0.0007 γ/γ+β) and the effect on γ-globin expression in PA8697 (0.24+0.5 γ/γ+β) at the 0.125mg/kg/d dose was greater than the effect of 0.25 mg/kg/d dose in PA8695 (0.17+0.05 γ/γ+β) and PA8698 (0.121+0.006 γ/γ+β). For combinatorial studies with decitabine, an RN-1 dose of 0.125mg/kg/d was chosen for PA8697 and 0.25mg/kg/d for PA8695 and 8698. Decitabine (0.3mg/kg/d; 2d), administered as a single agent subcutaneously for two days increased F retics nearly 3 fold (23.6+12.5%; p&amp;lt;0.02) compared to pretreatment levels (8.26+9.90%) but changes in γ-globin expression (0.066+0.076 γ/γ+β) compared to the pretreatment levels (0.03+0.042 γ/γ+β) were not significant. For combinatorial experiments, decitabine (0.3mg/kg/d) was administered for 2 days followed by administration of RN-1 (0.25mg/kg/d PA8695 and 8698; 0.125mg/kg/d PA8697) for 3 days. This staggered dose schedule was used to avoid any possible effects of RN-1 on cell cycle kinetics that could potentially reduce incorporation of decitabine during S phase. The decitabine/RN-1 combination produced significantly higher increases in F retics (63.0+23.6%; p&amp;lt;0.002) than either RN-1 (29.9+27.1%) or decitabine (23.6+12.5%) alone. The effect of the decitabine/RN-1 combination on F retics was greater than additive (p&amp;lt;0.01; Figure 1A) in the two low HbF animals, PA8695 and 8698, and additive for the high HbF animal PA8697 (Figure 1B). Although increased levels of γ-globin expression produced by the decitabine/RN-1 combination (0.22+0.08 γ/γ+β) were not significantly different overall from those induced by RN-1 alone (0.178+0.06 γ/γ+β), individual analysis of PA8697 revealed an additive effect (Figure 1C). Plt and ANC remained with the normal range. In conclusion, targeting separate components of the γ-globin co-repressor complex by combinatorial administration of decitabine and RN-1 generated synergistic and additive increases in F retics and γ-globin expression in the absence of hematological toxicity. Future experiments will explore different doses, alternative schedules, and the effect of longer term treatment regimens. Disclosures Saunthararajah: EpiDestiny: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties.

KLF4 Is Needed for Optimal Hydroxyurea Induction of Gamma-Globin in K562 Cells

Background: Hydroxyurea (HU) is highly clinically beneficial in patients with sickle cell disease (SCD). While HU reduces leukocytosis and inflammation, in general, patients with high levels of fetal hemoglobin (HbF) induction experience the greatest clinical benefit from HU. Despite over 25 years of use in patients with SCD, and intense study, the mechanism by which HU induces HbF has not been elucidated, nor the reasons for the considerable inter-individual variability in the amount of HU-mediated HbF induction. Proposed mechanisms of HbF induction by HU include erythropoietic stress response, production of nitric oxide, or reduction of BCL11A, KLF-1, and MYB, negative regulators of HbF. Various signaling pathways have been implicated in HU-mediated HbF induction, such as the activation of the ERK-1/ERK-2 by erythropoietin; Giα/JNK/Jun; p38/MAPK/CREB1; histone deacetylase (HDAC) and DNA methyl-transferase (DNMT) inhibitor-mediated epigenetic modification of γ-globin expression. To identify new genes and pathways involved in HU activity, we studied the in vivo effects of HU on the gene expression profile of paired samples obtained from the reticulocytes of children with SCD before and after HU treatment. Methods : 25 paired RNA samples were collected before HU treatment (pre-HU) and at the stable maximum tolerated dose (MTD) from peripheral blood CD71+ reticulocytes of pediatric patients from Texas Children's Hospital. Subjects were 1.2 to 19.1 years of age at the time of pre-HU sample collection (23 HbSS, 2 HbSβ0) and 48% were female. Hematologic indices were extracted from patient's medical record. RNA sequencing was performed through Illumina platform, paired-end 150 bps, with at least 20 million read in-depth. Quality control of raw sequence data was done with FastQC software. We used Kallisto to determine the compatibility of reads with targets and quantify abundances of transcripts. Then, we used Sleuth to implement statistical algorithms for differential analysis. After validation of results through relative quantity assessment of selected genes by RT-qPCR, the Enrichr web server was used for gene set enrichment (GSE) and pathway analysis. We chose two candidate genes, KLF4 and STAT5A, to analyze functionally based on differential expression, inclusion in enriched pathway analysis, and reported involvement in relevant biological processes, including erythroid maturation or HbF induction. siRNA knockdown of KLF4, and STAT5A in K562 cells was performed by chemical transfection (DharmaFECT) and was verified by RT-qPCR. K562 cells were treated with HU at 50 µM for 24 hours; RNA was extracted and analyzed for γ-globin expression levels by RT-qPCR. Results and conclusions: We compared our pre-HU and at MTD paired samples using a two-fold change expression cut-off and 0.1 FDR multiple comparison correction threshold. Using this threshold, 139 genes had statistically significant differential levels of expression.135 were upregulated and 4 downregulated in response to HU treatment. Pathway analysis primarily grouped the upregulated genes more into the EPO, IL-2, and IL-3 signaling pathways (adjusted p-value&amp;lt;0.05). The functional study using siRNA knockdown experiment revealed that while HU treatment increased γ-globin expression in control cells by 1.7-fold; 70% knockdown of KLF4 resulted in 50% less HU-mediated γ-globin induction compared to control (Figure 1). Scramble (non-targeting) siRNA did not reduce HU induction of γ-globin. Our preliminary results did not show a consistent effect of STAT5A KD on γ-globin induction by HU. We will verify these results in primary erythroid culture, and investigate KLF4 as a potential direct pharmacologic target for HbF induction. Disclosures No relevant conflicts of interest to declare.

Rational Targeting of a NuRD Sub-Complex for Fetal Hemoglobin Induction Following Comprehensive in Situ Mutagenesis

Sickle cell disease and β-thalassemia are major hemoglobin disorders for which induction of fetal hemoglobin (HbF) can mitigate disease severity. However, the molecular mechanisms underlying the developmental repression of HbF remain incompletely understood. The nucleosome remodeling and deacetylase (NuRD) complex is a major negative regulator of HbF level. In this study, we sought to identify possible rational therapeutic strategies targeting critical NuRD determinants.We employed comprehensive dense mutagenesis using pooled CRISPR screening in HUDEP-2 human erythroid precursors to disrupt protein coding sequences of all 13 genes of the NuRD complex, including CHD, MTA, GATAD2, HDAC, MBD, and RBBP family members. The custom sgRNA library included 5,038 sgRNAs. We found that only 5 genes, CHD4, MTA2, GATAD2A, HDAC2, and MBD2, were required for HbF repression, suggesting that a non-redundant NuRD sub-complex contributes to HbF silencing. We validated the existence of this NuRD sub-complex by mass spectrometry analysis after immunoprecipitation of CHD4 and MTA2 as well as MTA2-BioID2 mediated proximity labeling. Remarkably, 5 of the 6 NuRD subunit proteins commonly detected by these three methods were identified as functional by CRISPR screening (MTA2, RBBP4, CHD4, GATAD2A, HDAC2).Disruption of CHD4 resulted in the highest HbF induction of any of the NuRD subunits. However, unlike the other NuRD genes, CHD4 disruption also led to cellular toxicity. We observed a small group of sgRNAs within the CHDCT2 domain of CHD4 associated with high HbF induction yet relatively modest negative fitness. We validated by electroporation of Cas9:sgRNA to CD34+ HSPC primary erythroid precursors that in-frame mutations of CHD4 CHDCT2 escape cellular toxicity while inducing HbF. Similarly, we targeted homologous amino acid residues within mouse Chd4 CHDCT2 domain by Cas9 mutagenesis in mouse oocytes. While loss of Chd4 is lethal at the blastocyst stage, homozygous in-frame deletions within the Chd4 CHDCT2 domain are tolerated in mouse embryos and result in increased γ-globin expression in mid-gestation embryos bearing transgenic human β-globin gene clusters.To investigate the mechanism whereby in-frame deletions at CHD4 CHDCT2 impact NuRD, we performed glycerol gradient density sedimentation, which revealed that these in-frame mutations impair the recruitment of CHD4 to the NuRD complex. A recent study demonstrated that the previously poorly characterized CHD4 CHDCT2 domain directly binds to GATAD2 factors (Torrado et al, FEBS J, 2017). We observed a cluster of sgRNAs associated with heightened HbF enrichment scores at the C-terminal region of GATAD2A encompassing a C2C2-type GATA zinc finger. We hypothesized that ectopic expression of this GATAD2A zinc finger might competitively bind to CHD4 and displace CHD4 from NuRD. Overexpression of the GATAD2A zinc finger in both HUDEP-2 and CD34+ HSPC derived primary erythroid precursors led to robust induction of HbF without negatively impacting cellular fitness. Immunoprecipitation of the GATAD2A zinc finger enriched CHD4 but not other endogenous NuRD components, such as GATAD2A or MBD2. Moreover, glycerol gradient density sedimentation showed that the GATAD2A zinc finger co-sedimented with sub-NuRD fractions of CHD4. Together these data suggest that expression of the GATAD2A zinc finger sequesters CHD4 from NuRD, yet spares cytotoxicity.In summary, we show that biochemical disruption of the CHD4-GATAD2A interaction could serve as a rational therapeutic strategy to potently induce HbF for the β-hemoglobin disorders while preventing cellular toxicity associated with complete CHD4 inhibition. DisclosuresNo relevant conflicts of interest to declare.

The LSD1 Inhibitor RN-1 Increases γ-Globin Expression in Baboons By Targeting an Early Event Responsible for γ-Globin Repression

The HbF to HbA developmental globin switch is recapitulated during adult erythroid differentiation and involves the acquisition of repressive epigenetic marks at the γ-globin promoter catalyzed by “druggable” enzymes such as histone deacetylases (HDACs), DNA methyltransferase (DNMT1), LSD1 (KDM1A), and G9A (EHMT2) that are functional components of multiprotein co-repressors recruited to the γ-globin gene promoter by the trans-acting repressors TR2/TR4, BCL11A, and ZBTB7A. A logical approach to increase HbF that has been successfully pursued by our laboratory is to intervene with the epigenetic repression mechanism that executes the switch from HbF to HbA using pharmacological inhibitors of these enzymes. Simian primates such as the baboon are widely acknowledged as the best animal models for testing the ability of new drugs to increase γ-globin expression because results in baboons are predictive of effects in man due to conservation of the structure and developmental stage-specific regulation of the β-like globin genes in simian primates.Our laboratory has developed and utilized an in vivo baboon model for over thirty years to investigate globin gene regulation and the ability of pharmacological inhibitors of enzymes that catalyze repressive epigenetic modifications to increase HbF, generating results with DNMT inhibitors that were extended and confirmed in a number of clinical studies in patients with SCD and β-thalassemia. Following studies that identified LSD1 as an additional therapeutic target (Shi et al, Nat Med 19:291, 2013), we showed that the LSD1 inhibitor RN-1 dramatically increased HbF, F cells and F retics in baboons (Rivers et al, Haematol 101:698, 2015) and that these effects were sustained upon long-term treatment (>265d; Ibanez et al, Blood 129:260, 2017). ChIP analysis showed increased levels of Histone H3 di and tri-methyl K4 at the γ-globin gene, consistent with LSD1 inhibition. This current investigation seeks to identify the stage in the erythroid differentiation pathway targeted by LSD1 inhibitors to increase HbF and also to characterize additional effects of these drugs on erythroid differentiation that potentially impact mechanism of action. Subpopulations of bone marrow (BM) cells highly enriched in BFUe (CD105+CD34+CD117+bRBC-), CFUe (CD105+CD34+CD117+bRBC+), proerythroblasts (CD105+CD34-CD117+bRBC+) were purified from RN-1 treated (0.25mg/kg/d; 3d) and untreated baboons by immunomagnetic column separation combined with FACS. RT-PCR analysis of γ-globin expression within purified BM erythroid subpopulations showed that relative levels of γ-globin mRNA (γ/γ+β) in untreated baboons were 4 fold higher in BFUe than in CFUe and 11 fold higher in BFUe than in proerythroblasts consistent with repression of the γ-globin gene during the BFUe to CFUe transition. RN-1 treatment increased relative γ-globin expression (γ/γ+β) 4 fold in BFUe, 25 fold in CFUe, and >100 fold in proerythroblasts compared to untreated controls and thus partially prevented repression of the γ-globin expression at early stages of differentiation. Additional effects of the LSD1 inhibitor RN-1 on erythroid differentiation were measured by flow cytometry in baboon BM aspirates following RN-1 administration. RN-1 treatment (0.25mg/kg/d; 3d) increased the proportion of CD105+CD117+bRBC+BM cells (proerythroblasts) (24.2% pre-treatment; 48.4% post-treatment; p<0.02) and decreased the proportion of CD105+CD117-bRBC+ terminal erythroid BM cells (51.1% pre-treatment; 29.1% post-treatment; p<0.02). RNAseq analysis of CD105+CD34-CD117+bRBC+ FACS-purified BM cells (proerythroblasts) of untreated control (n=2) and RN-1 treated baboons (0.25mg/kg/d; 3d; n=4; 2 treated for 3d; 2 treated >265d) identified a common set of 41 genes whose expression was increased while the expression of 6 genes was decreased. RT-PCR assays confirmed increased expression of γ-globin, GATA-2, GFi-1B, DAP, IFI6, and Lyn in proerythroblasts of RN-1-treated baboons. We conclude that the LSD1 inhibitor RN-1 administered to baboons 1) restrains erythroid differentiation by modulating the expression of genes such as GATA-1 and GFi-1B that regulate erythroid differentiation, and 2) targets an early event responsible for γ-globin repression to increase γ-globin expression. DisclosuresSaunthararajah:Novo Nordisk, A/S: Patents & Royalties; EpiDestiny, LLC: Patents & Royalties. Lavelle:Global Blood therapeutics: Research Funding.

Oral administration of the LSD1 inhibitor ORY-3001 increases fetal hemoglobin in sickle cell mice and baboons

Increased levels of fetal hemoglobin (HbF) lessen the severity of symptoms and increase the life span of patients with sickle cell disease (SCD). More effective strategies to increase HbF are needed because the current standard of care, hydroxyurea, is not effective in a significant proportion of patients. Treatment of the millions of patients projected worldwide would best be accomplished with an orally administered drug therapy that increased HbF. LSD1 is a component of corepressor complexes that repress γ-globin gene expression and are a therapeutic target for HbF reactivation. We have shown that subcutaneous administration of RN-1, a pharmacological LSD1 inhibitor, increased γ-globin expression in SCD mice and baboons, which are widely acknowledged as the best animal model in which to test the activity of HbF-inducing drugs. The objective of this investigation was to test the effect of oral administration of a new LSD1 inhibitor, ORY-3001. Oral administration of ORY-3001 to SCD mice (n = 3 groups) increased γ-globin expression, Fetal Hemoglobin (HbF)-containing (F) cells, and F reticulocytes (retics). In normal baboons (n = 7 experiments) treated with ORY-3001, increased F retics, γ-globin chain synthesis, and γ-globin mRNA were observed. Experiments in anemic baboons (n = 2) showed that ORY-3001 increased F retics (PA8695, predose = 24%, postdose = 66.8%; PA8698: predose = 13%, postdose = 93.6%), γ-globin chain synthesis (PA8695: predose = 0.07 γ/γ+β, postdose = 0.20 γ/γ+β; PA8698: predose = 0.02 γ/γ+β, postdose = 0.44 γ/γ+β), and γ-globin mRNA (PA8695: predose = 0.06 γ/γ+β, postdose = 0.18 γ/γ+β; PA8698: predose = 0.03 γ/γ+β, postdose = 0.33 γ/γ+β). We conclude that oral administration of ORY-3001 increases F retics, γ-globin chain synthesis, and γ-globin mRNA in baboons and SCD mice, supporting further efforts toward the development of this drug for SCD therapy.

HDAd5/35++ Adenovirus Vector Expressing Anti-CRISPR Peptides Decreases CRISPR/Cas9 Toxicity in Human Hematopoietic Stem Cells

We generated helper-dependent HDAd5/35++ adenovirus vectors expressing CRISPR/Cas9 for potential hematopoietic stem cells (HSCs) gene therapy of β-thalassemia and sickle cell disease through re-activation of fetal γ-globin expression (HDAd-globin-CRISPR). The process of CRISPR/Cas9 gene transfer using these vectors was not associated with death of human CD34+ cells and did not affect their in vitro expansion and erythroid differentiation. However, functional assays for primitive HSCs, e.g., multi-lineage progenitor colony formation and engraftment in irradiated NOD/Shi-scid/interleukin-2 receptor γ (IL-2Rγ) null (NSG) mice, revealed toxicity of HDAd-globin-CRISPR vectors related to the prolonged expression and activity of CRISPR/Cas9. To control the duration of CRISPR/Cas9 activity, we generated an HDAd5/35++ vector that expressed two anti-CRISPR (Acr) peptides (AcrII4 and AcrII2) capable of binding to the CRISPR/Cas9 complex (HDAd-Acr). CD34+ cells that were sequentially infected with HDAd-CRISPR and HDAd-Acr engrafted at a significantly higher rate. Target site disruption frequencies in engrafted human cells were similar to those in pre-transplantation CD34+ cells, indicating that genome-edited primitive HSCs survived. In vitro differentiated HSCs isolated from transplanted mice demonstrated increased γ-globin expression as a result of genome editing. Our data indicate that the HDAd-Acr vector can be used as a tool to reduce HSC cytotoxicity of the CRISPR/Cas9 complex.

Efficacy and Safety of Long-Term Treatment with the LSD1 Inhibitor RN-1 to Increase HbF in Normal, Non-Anemic Baboons

Increased levels of fetal hemoglobin (HbF) lessen the severity of symptoms and increase the life span of patients with sickle cell disease. New and more effective strategies to increase HbF are needed because current therapies are ineffective in a significant proportion of patients. The lysine-specific demethylase, LSD1, an enzyme that demethylates Histone H3 mono- and dimethyl- K4 and K9 residues, is a component of the DRED co-repressor complex that represses the γ-globin gene (Cui et al, Mol Cell Biol 31:3298, 2011). Our laboratory has recently shown that RN-1, a pharmacological inhibitor of LSD1, increases γ-globin expression in sickle cell disease (SCD) transgenic mice (Rivers et al, Exp Hematol 43:546, 2015; Cui et al, Blood 126:386, 2015) and in baboons (Rivers et al, Haematol 101:688, 2016), widely acknowledge as the best animal model to test the activity of HbF-inducing drugs. To evaluate the safety and efficacy of RN-1, two normal, non-anemic baboons were treated for an extended period with RN-1 (PA8695, 264d; PA8698, 278d; 0.25mg/kg/d; 5d/wk, sc) and the effect on HbF, F cells, and hematological parameters evaluated weekly. Both animals exhibited weight gain (PA8695: 14.4%; PA8698: 20%) during the course of the study. F retics were increased 8-10 fold by the second week (d9) and were maintained at high levels throughout the course of the study (PA8695: 55.7±17.7% (mean±SD), median (M)=59.0%; PA8698: 56.4±14.5%, M=56.9%). F cell levels increased until d169 and were maintained thereafter at levels 18-25 times greater than pre-treatment (PA8695: 54.5±3.3%, M=54.2%; PA8698: 51.7±3.2%, M=51.4%). HbF levels also increased until d169 and were also maintained thereafter at levels 10-12 times greater than pre-treatment (PA8695: 12.8±1.7%, M=12.1%; PA8698: 11.4±1.4%, M=11.5%). Elevated levels of γ-globin chain synthesis were observed in the peripheral blood on multiple days (d162, d190, d267) of treatment (PA8695, 0.28±0.08 γ/γ+β;PA8698, 0.26±0.08 γ/γ+β). RT-PCR analysis showed that γ-globin mRNA levels were increased 9-22 fold (p<0.01) in FACS-purified CD105+ CD117+/- glyA+ BM erythroid precursor subpopulations of RN-1 treated baboons compared to normal baboons. Absolute neutrophil counts showed no overall decline compared to pre-treatment (PA8695: pre-treatment=2110/μL, post-treatment=3118±1452/μL, M=2765/μL; PA8698: pre-treatment=2690/μL, post-treatment=2936±696/μL, M=2460/μL) although variations were observed. In PA8695 the ANC declined below 1500/μL twice (1490, 1160) and five times (1250, 1410, 1420, 1330, 1000) in PA8595. Monocytes increased 2-3 fold in each animal (PA8695: pre-treatment=100/μL, post-treatment=252±97/μL, M=246/μL; PA8698: pre-treatment=161/μL, post-treatment=425±319/μL, M=347/μL). Hemoglobin (Hb), RBC, and hematocrit (HCT) levels exhibited small overall decreases during the course of treatment but remained within the normal range. Decreases in RBC, Hb, and HCT were associated with blood loss during menstruation (PA8695) and following an accidental laceration of the perineal swelling (PA8698). Rapid recovery was observed in both animals. Significant changes in MCV, MCH, and MCHC during treatment were not observed. Platelet levels decreased approximately 40% in each animal but nevertheless were maintained within the normal range (PA8695: pre-treatment=351 X 103/μL, post-treatment=236±64 X 103/μL, M=219 X 103/μL; PA8698: pre-treatment=224 X 103/μL, post-treatment=143±78 X 103/μL, M=119 X 103/μL). No significant differences in either PT or aPTT assays were observed compared to normal baboons. In vitro platelet activation assays performed to investigate effects on platelet function showed that the fraction of platelets expressing P-selectin (CD62P) on the surface following addition of thrombin was reduced 14% (p<0.02) and the level of CD62P expression reduced 46% (p<0.0001) in RN-1 treated baboons compared to controls. Normal platelet function was restored 10d post-drug. Elevated platelet activation is associated with the pathogenesis of sickle cell disease and inhibitors of platelet activation are currently in clinical trials. We conclude that long-term treatment with RN-1 increases and maintains elevated levels of HbF and F cells in normal baboons and is well-tolerated. Pharmacological inhibitors of LSD1 are therefore likely to be beneficial in patients with SCD. DisclosuresRivers:Acetylon: Research Funding. DeSimone:EpiDestiny: Consultancy, Other: patents around decitabine and tetrahydrouridine. Lavelle:Acetylon: Research Funding.

Gamma reactivation using the spongy effect of KLF1-binding site sequence: an approach in gene therapy for beta-thalassemia.

β-thalassemia is one of the most common genetic disorders in the world. As one of the promising treatment strategies, fetal hemoglobin (Hb F) can be induced. The present study was an attempt to reactivate the γ-globin gene by introducing a gene construct containing KLF1 binding sites to the K562 cell line. A plasmid containing a 192 bp sequence with two repeats of KLF1 binding sites on β-globin and BCL11A promoters was constructed and used to transfect the K562 cell line. Positive selection was performed under treatment with 150 μg/ml hygromycin B. The remaining cells were expanded and harvested on day 28, and genomic DNA was extracted. The PCR was carried out to verify insertion of DNA fragment to the genome of K562 cells. The cells were differentiated with 15 μg/ml cisplatin. Flowcytometry was performed to identify erythroid differentiation by detection of CD235a+ cells. Real-time RT-PCR was performed to evaluate γ-globin expression in the transfected cells. A 1700 bp fragment was observed on agarose gel as expected and insertion of DNA fragment to the genome of K562 cells was verified. Totally, 84% of cells were differentiated. The transfected cells significantly increased γ-globin expression after differentiation compared to untransfected ones. The findings demonstrate that the spongy effect of KLF1-binding site on BCL11A and β-globin promoters can induce γ-globin expression in K562 cells. This novel strategy can be promising for the treatment of β-thalassemia and sickle cell disease.

Sustained enhancement of OCTN1 transporter expression in association with hydroxyurea induced γ-globin expression in erythroid progenitors.

The clinical benefits of hydroxyurea (HU) treatment in patients with sickle cell disease (SCD) are due largely to increased γ-globinexpression. However, mechanisms that control γ-globin expression by HU in erythroid progenitors are incompletely understood. Here, we investigated the role of two HU transporters, urea transporter B (UTB) and organic cation/carnitine transporter 1 (OCTN1), in this process. Endogenous expression of both transporters peaked toward the end of erythroid differentiation. However, unlike UTB, HU-induced OCTN1 expression correlated positively with γ-globin level and was sustained throughout the period of induction. These results highlight a potential major role for OCTN1 in promoting the efficacy of HU.

Cis-vaccenic acid induces differentiation and up-regulates gamma globin synthesis in K562, JK1 and transgenic mice erythroid progenitor stem cells

Gamma globin induction remains a promising pharmacological therapeutic treatment mode for sickle cell anemia and beta thalassemia, however Hydroxyurea remains the only FDA approved drug which works via this mechanism. In this regard, we assayed the γ-globin inducing capacity of Cis-vaccenic acid (CVA). CVA induced differentiation of K562, JK1 and transgenic mice primary bone marrow hematopoietic progenitor stem cells. CVA also significantly up-regulated γ-globin gene expression in JK-1 and transgenic mice bone marrow erythroid progenitor stem cells (TMbmEPSCs) but not K562 cells without altering cell viability. Increased γ-globin expression was accompanied by KLF1 suppression in CVA induced JK-1 cells. Erythropoietin induced differentiation of JK-1 cells 24h before CVA induction did not significantly alter CVA induced differentiation and γ-globin expression in JK-1 cells. Inhibition of JK-1 and Transgenic mice bone marrow erythroid progenitor stem cells Fatty acid elongase 5 (Elovl5) and Δ(9) desaturase suppressed the γ-globin inductive effects of CVA. CVA treatment failed to rescue γ-globin expression in Elovl5 and Δ(9)-desaturase inhibited cells 48 h post inhibition in JK-1 cells. The data suggests that CVA directly modulates differentiation of JK-1 and TMbmEPSCs, and indirectly modulates γ-globin gene expression in these cells. Our findings provide important clues for further evaluations of CVA as a potential fetal hemoglobin therapeutic inducer.