Rap-536 (Murine ACE-536/Luspatercept) Inhibits Smad2/3 Signaling and Promotes Erythroid Differentiation By Restoring GATA-1 Function in Murine b-Thalassemia

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 751-751 ◽  
Author(s):  
Pedro A. Martinez ◽  
Rajasekhar NVS Suragani ◽  
Manoj Bhasin ◽  
Robert Li ◽  
Robert Scott Pearsall ◽  
...  
Keyword(s):  
Murine Model ◽  
Target Genes ◽  
Erythroid Differentiation ◽  
Heme Biosynthesis ◽  
Ineffective Erythropoiesis ◽  
Down Regulation ◽  
Employment Equity ◽  
Equity Ownership ◽  
Terminal Erythroid Differentiation ◽  
Tgfβ Superfamily

Abstract We have previously reported that Smad2/3 signaling (of the TGFβ superfamily) is elevated in myelodysplastic syndromes (MDS) and β-thalassemia, diseases that are characterized by ineffective erythropoiesis (Suragani et al. 2014). Smad2/3 pathway inhibition using RAP-536 (murine version of ACE-536/luspatercept), a modified activin receptor type IIB ligand trap, decreased ineffective erythropoiesis (IE) and alleviated disease pathology in a murine model of β-thalassemia. In this study, we investigated the a) potential role of different Smad2/3 ligands that bind to luspatercept in the regulation of erythropoiesis and b) molecular mechanism of RAP-536 therapy in the murine model of β-thalassemia. Wild-type (WT) mice were treated with neutralizing antibodies against activin B, GDF8 or GDF8/11 (10mg/kg, s.c, twice weekly for 2- weeks, N=5/group) either as a single agent or in combination, and compared with RAP-536 (10 mg/kg, s.c) treatment. β-thalassemic mice (Hbbth3/+) were administered a single bolus of vehicle (VEH) or RAP-536 (30 mg/kg, i.p) (N=2/group). At 16 hours following administration the splenic basophilic erythroblasts (CD71+ Ter119+ FSChigh) were sorted by flow cytometry and RNA was isolated and subjected to genome wide transcriptome profiling using RNA sequencing analysis. a) Surface plasmon analysis revealed that ACE-536 binds Smad2/3 signaling ligands GDF11 and GDF8 with high affinity and activin B with lower affinity. There was minimal binding detected with Activin A, TGFβ1 or TGFβ3 ligands. Wt mice treated with RAP-536 increased RBC (+19%, P<0.001) and Hgb (+15.2%, P<0.001) compared to VEH treated mice. Treatment with anti-GDF8 or anti-activin B antibodies marginally affected RBC parameters (~2-4%, N.S) where as anti-GDF8/11 treatment alone increased RBC (+6.1%, P<0.05) and Hgb (6.9%, P<0.05) compared to VEH treatment. A combination treatment of anti-GDF8/11 and activin B antibodies synergistically increased RBC (10.7%, P<0.001) and Hgb (11%, P<0.001) compared to VEH treated mice. These data suggests that in addition to GDF11 and activin B, other TGFβ superfamily ligands are possibly involved in the stimulation of erythropoiesis by luspatercept. b) Transcriptome analysis of β-thalassemic erythroblasts revealed a total of 74 genes that were differentially expressed (absolute fold change >1.5, false discovery rate adjusted P value <0.05) in RAP-536 treated samples compared to VEH treatment. To identify molecular mechanisms, we performed gene set enrichment analysis (GSEA) (Subramanian et al., 2005) on data from RAP-536 and VEH treated samples. The analysis depicted significant upregulation of target genes of multiple transcriptional regulators including GATA-1 (erythroid differentiation), NFE2 and heat shock factor (involved in globin expression and protein quality-control). Previously, multiple studies established GATA-1 as a master transcriptional regulator of terminal erythroid differentiation. The individual gene symbols based comparative analysis revealed up-regulation of 53/478 GATA-1 activators and down regulation of 9/342 GATA-1 repressors. The GATA-1 target genes that were up regulated by RAP-536 treatment are involved in heme biosynthesis (such as Ppox, Fech, Alas2 and Abcb10) and erythroid differentiation (such as Klf1, Nfe2, Gypa, Bcl2l, Bnip3l, Bach1, and Ank1). Further GSEA of GATA-1 activator and repressor signatures against RAP-536 treatment data revealed a significant up-regulation of 158/328 activated genes (Normalized Enrichment Score=2.7, P=0) involved in heme biosynthesis, and cell cycle regulation whereas there was no statistically significant down regulation of GATA-1 repressed genes. Consistent with this data, our preliminary results in differentiating mouse erythroleukemic (MEL) cells showed increased Smad2/3 phosphorylation that is correlated with reduced GATA-1 protein levels suggesting that pSmad2/3 may negatively regulate terminal erythroid differentiation by decreasing GATA-1 availability. These data provide a potential mechanistic role for luspatercept treatment in β-thalassemia, by transcriptionally upregulating genes that promote erythroid differentiation and processing of unpaired α-globins. By inhibiting SMAD2/3 signaling, luspatercept relieves the block of terminal erythroid maturation and decreases ineffective erythropoiesis in diseases such as β-thalassemia and MDS. Disclosures Martinez: Acceleron Pharma: Employment. Suragani:Acceleron Pharma Inc: Employment, Equity Ownership, Patents & Royalties: No royalties. Li:Acceleron Pharma: Employment, Equity Ownership. Pearsall:Acceleron Pharma Inc: Employment, Equity Ownership, Patents & Royalties. Kumar:Acceleron Pharma: Employment, Equity Ownership, Patents & Royalties.

RAP-536 Promotes Terminal Erythroid Differentiation and Reduces Anemia in a Murine Model of Myelodysplastic Syndromes

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3796-3796 ◽  
Author(s):  
Rajasekhar NVS Suragani ◽  
Robert Li ◽  
Dianne Sako ◽  
Asya Grinberg ◽  
R. Scott Pearsall ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Bone Marrow ◽  
Erythroid Differentiation ◽  
Severe Anemia ◽  
Ineffective Erythropoiesis ◽  
Employment Equity ◽  
Erythroid Hyperplasia ◽  
Erythroid Precursors ◽  
Equity Ownership ◽  
Terminal Erythroid Differentiation

Abstract Abstract 3796 Myelodysplastic syndromes (MDS) are a group of hematopoietic stem cell disorders characterized by peripheral blood cytopenias such as anemia, neutropenia or thrombocytopenia. Ineffective erythropoiesis due to increased proliferation and abortive maturation of precursors leads to severe anemia, the most common cytopenia observed in MDS syndromes. Despite elevated erythropoietin (EPO) and erythroid hyperplasia, MDS patients are often given recombinant EPO therapy to stimulate erythropoiesis. However, only a small proportion of patients respond to EPO therapy. Frequent blood transfusions as supportive care result in iron overloading and recently iron overloading is also linked to enhanced progression to AML. Therefore, alternative therapies are necessary to treat anemia in MDS patients. Signaling by members of the TGFβ superfamily are known regulators of erythropoiesis. We developed ACE-536, a ligand trap consisting of a modified activin receptor Type IIB extracellular domain linked to a human Fc domain. In vitro assays revealed that ACE-536 inhibits smad 2/3 ligands of the signaling pathway but not smad 1/5/8 ligands. Dose dependent studies using ACE-536 in mice, rats and monkeys revealed that ACE-536 treatment resulted in increased red blood parameters but did not affect other cell types. These data suggests that ACE-536 inhibits smad 2/3 phosphorylation modulating the expression of downstream genes involved in erythroid development pathway. BFU-E and CFU-E colony formation assays from bone marrow and spleen in mice following ACE-536 treatment revealed that ACE-536 did not affect the proliferation stages of erythropoiesis. In mice, terminal erythroid differentiation analysis by flow cytometry at 72hrs following RAP-536 (10mg/kg) treatment demonstrated decreased basophilic and increased ortho- and poly-chromatophilic erythroblasts and reticulocytes compared to VEH treatment. Cell cycle analysis of bone marrow and splenic erythroblasts counterstained with BrdU and 7-AAD after RAP-536 (10mg/kg, for 24 hours) or VEH treatment to EPO pre-treated (1500 units/kg, for 40 hours) mice (N=5/group) revealed that EPO+RAP-536 treatment resulted in significant decrease in S-phase and increase in G1/G2-phases of cell cycle compared to EPO+VEH treatment. In addition, EPO+RAP-536 treatment resulted in a greater increase in RBC parameters than either of the treatments alone. Together, these results demonstrate that ACE-536 increases red blood cell formation by promoting maturation of late stage erythroblasts. We then investigated the effect of ACE-536 on anemia in NUP98-HOXD13 (NHD13) transgenic murine model of MDS. NHD13 mice develop anemia, neutropenia and lymphopenia, with normal or hyper cellular bone marrow. A Majority of the mice die by 14 months due to severe pancytopenia or progression to acute myeloid leukemia. In this study, mice were divided into three groups based on age. Early (∼4 months old), mid (∼8 months old) and late stage (∼10 months) groups were randomized and dosed with either RAP-536 at 10 mg/kg or VEH twice per week for 6–8 weeks. NHD13 mice in each group had severe anemia characterized by reduced RBC, Hemoglobin and HCT and compared to wild-type littermates prior to treatment. Treatment of RAP-536 for 6–8 weeks significantly increased RBC parameters and reversed anemia at all stages. Peripheral blood smear analysis revealed no indication of increased leukemic progression due to RAP-536 treatment. Cell differential and flow cytometric evaluation of erythroid precursors from bone marrow demonstrated decreased erythroid precursors and hyperplasia after RAP-536 treatment compared to vehicle treated control. Our data demonstrate that RAP-536 can increase hematology parameters by enhancing maturation of terminally differentiated red blood cells. We have shown RAP-536 corrects ineffective erythropoiesis, decreases erythroid hyperplasia and normalizes myeloid: erythroid ratios without enhanced progression to AML in a murine MDS model. Therefore ACE-536 may represent a novel treatment for anemia associated with MDS, particularly in patients that are refractory to EPO therapy. ACE-536 has completed Phase I clinical trials in healthy human volunteers and Phase II study in MDS patients is planned. Disclosures: Suragani: Acceleron Pharma Inc: Employment, Equity Ownership. Li:Acceleron Pharma Inc: Employment, Equity Ownership. Sako:Acceleron Pharma Inc: Employment, Equity Ownership. Grinberg:Acceleron Pharma Inc: Employment, Equity Ownership. Pearsall:Acceleron Pharma Inc: Employment, Equity Ownership. Kumar:Acceleron Pharma Inc: Employment, Equity Ownership.

ACE-536 Improves Ineffective Erythropoiesis, Anemia and Co-Morbidities in β-Thalassemia

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 248-248 ◽  
Author(s):  
Rajasekhar NVS Suragani ◽  
Robert Li ◽  
Sharon Cawley ◽  
Stefano Rivella ◽  
R. Scott Pearsall ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Treatment Group ◽  
Research Funding ◽  
Erythroid Differentiation ◽  
Blue Staining ◽  
Wild Type ◽  
Ineffective Erythropoiesis ◽  
Employment Equity ◽  
Equity Ownership ◽  
Terminal Erythroid Differentiation

Abstract Abstract 248 β-thalassemia, the most common congenital anemia, is caused by mutations in β-globin gene resulting in partial or complete absence of β-globin protein chains. In the absence of properly paired α- and β-globin chains, the α-globin protein accumulates causing proteotoxicity and apoptosis of erythroid cells. Hemolysis and ineffective erythropoiesis together cause severe anemia in thalassemia syndromes. Increased proliferation with arrest of terminal erythroid differentiation and accelerated apoptosis is the hallmark of ineffective erythropoiesis in β-thalassemia. In chronic patients, blood transfusions are required for survival, but result in severe iron overloading. Non-transfusion dependent thalassemia (NTDT) patients however, are also affected by ineffective erythropoiesis, anemia and iron overload. Recombinant EPO therapy is ineffective and rarely used for β-thalassemia patients, as it does not affect the later stages of erythroid differentiation. Therefore, a pharmacological approach is necessary that can increase hemoglobin levels, prevent splenomegaly, bone abnormalities and iron overloading in β-thalassemia patients. Several members of the TGFβ-superfamily are involved in erythropoiesis. ACE-536 is a modified activin type IIb (ActRIIb) receptor fusion protein that acts as a ligand trap. Unlike wild type ActRIIb, ACE-536 does not inhibit activin A induced signaling but inhibits signaling induced by other members of the TGF-β superfamily such as GDF11. While EPO increases proliferation of erythroid progenitors, ACE-536 promotes maturation of terminally differentiating erythroblasts. We hypothesized that ACE-536 treatment will promote terminal erythroid differentiation, as well as reduce anemia, ineffective erythropoiesis and associated co-morbidities in β-thalassemia. We investigated the efficacy of RAP-536 (murine ortholog of ACE-536) in a mouse model of β-thalassemia intermedia (Hbbth1/th1). β-thalassemic mice were severely anemic and had significantly decreased RBC (−31.6% p<0.001), hemoglobin (−35.0% p<0.001) and hematocrit (−34.8% p<0.001) compared to wild type littermates. β-thalassemic mice were treated subcutaneously twice a week with RAP-536 (1 mg/kg) or TBS vehicle (VEH) control for two months (N=7 per treatment group). Wild-type littermates were dosed with VEH or RAP-536 (1 mg/kg) and used as controls (N=13 per treatment group). Following two months of treatment, RAP-536 treated β-thalassemic mice had significantly increased RBC (+32.9%, p<0.01), hemoglobin (+17.4%, p<0.01) hematocrit (+11.0%, p<0.01) and displayed reduced reticulocytosis (−30.07%, p<0.05) compared to VEH treated β-thalassemic mice. Terminal erythroid differentiation analyses of bone marrow and spleen from β-thalassemic mice treated with RAP-536 revealed significant decreases in basophilic erythroblasts while increasing late stage orthochromatic erythroblasts. RAP-536 treated β-thalassemic mice had significantly decreased serum EPO levels (639.7±111 vs. 1769.7± 517 pg/mL, p<0.05), bone marrow erythroid precursors and spleen weights (418.3± 28 vs. 677.1± 65 mgs, p<0.01) compared to VEH treatment indicating decreased erythroid hyperplasia and extramedullary erythropoiesis. RAP-536 treatment also restored bone mineral density in β-thalassemic mice to levels observed in wild type mice. Furthermore, RAP-536 treatment resulted in decreased splenic, liver and kidney iron levels by Perl's Prussian blue staining indicating decreased iron overloading. Interestingly, serum bilirubin (0.41± 0.01 vs. 0.72± 0.09 mg/dL, p<0.05) and lactate dehydrogenase levels (334.6± 33 vs. 424.6± 76 IU/mL) were lower in β-thalassemic mice treated with RAP-536 compared to VEH treated mice demonstrating decreased hemolysis. Morphological assessment of blood smears also displayed decreased hemolysis, reduced α-globin inclusions and poikilocytosis compared to VEH treatment. RAP-536 treatment also extended RBC life span in β-thalassemic mice compared to VEH treated mice. In summary, these data demonstrate that RAP-536 attenuates ineffective erythropoiesis, ameliorates anemia and improved associated co-morbidities in a murine model of β-thalassemia. ACE-536 represents a novel potential therapy for patients with β-thalassemia and these preclinical data provide a rationale for clinical studies of ACE-536 in β-thalassemia patients. Disclosures: Suragani: Acceleron Pharma Inc: Employment, Equity Ownership. Li:Acceleron Pharma Inc: Employment, Equity Ownership. Cawley:Acceleron Pharma Inc: Employment. Rivella:Novartis Pharmaceuticals: Consultancy; Biomarin: Consultancy; Merganser Biotech: Consultancy, Equity Ownership, Research Funding; Isis Pharma: Consultancy, Research Funding. Pearsall:Acceleron Pharma Inc: Employment, Equity Ownership. Kumar:Acceleron Pharma Inc: Employment, Equity Ownership.

Sotatercept Promotes Differentiation and Survival Of Erythroid Progenitors By Blocking Inhibitory Effects Of TGFβ Superfamily Members

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 944-944
Author(s):  
Soraya Carrancio ◽  
Jennifer A. Markovics ◽  
Piu Wong ◽  
Carla Heise ◽  
Tom O. Daniel ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Cell Proliferation ◽  
Late Stage ◽  
Erythroid Differentiation ◽  
Activin A ◽  
Employment Equity ◽  
Cell Divisions ◽  
Equity Ownership ◽  
Negative Growth ◽  
Tgfβ Superfamily

Abstract Erythropoiesis, the process of cell proliferation and differentiation that produces erythrocytes, is a tightly regulated process, but apart from early progenitor development and the EPO-dependent response, very little is known about other molecular signals which control cellular fate during RBC production. Members of the transforming growth factor beta (TGFβ) superfamily have been studied as potential regulators of erythropoiesis, iron regulation and globin expression. Sotatercept, an ActRIIA ligand trap, binds to and inhibits activin and other members of the TGFβ superfamily to induce a rapid increase in red cell number and hemoglobin in healthy volunteers. Pharmacological findings demonstrate that RAP-011, a murine ortholog of sotatercept, stimulates RBC parameters in mice through a mechanism distinct from EPO. We conducted the current study to evaluate if RAP-011 may stimulate expansion of a late-stage erythroblast population that is not normally expanded and/or may induce faster differentiation of erythroid precursors. In order to determine if RAP-011 promotes proliferation or differentiation during erythropoiesis, the number of cell divisions was quantified by CFSE staining. During in vitro erythroid differentiation, RAP-011 did not appear to alter the number of cell divisions; however, the percentage of cells that underwent the last division was higher in cultures treated with RAP-011, suggesting that the drug induced faster cellular maturation/differentiation. We also analyzed cell viability of GPA+ cells at the end of the differentiation process and observed that the percentage of apoptotic death was higher in control vs. RAP-011-treated cells. This suggests that RAP-011 may promote survival of late-stage precursors. To assess potential candidates which may mediate the erythropoietic effects of RAP-011, we selected three high affinity RAP-011 ligands, Activin A, Activin B and GDF-11, and proceeded to evaluate their effects on Smad signaling and on erythroid differentiation of human bone marrow progenitors. First, we observed that RAP-011 blocked ligand-induced Smad2/3 phosphorylation in the bone marrow-derived cells. Secondly, RAP-011 rescued activin A-induced inhibition of BFU-E colony formation. Finally, when mature CD36+ cells were differentiated in liquid media containing each of the three ligands, RAP-011 was able to reverse GDF-11- and Activin A-induced inhibition of of erythroid cell proliferation. GDF-11 and Activin A also significantly decreased the percentage of GPA-positive cells in culture, while significantly increasing the percentage of CD45-positive cells. Consistent with proliferation results, RAP-011 blocked these ligand effects. Treatment of CD36+ cells with Activin B did not alter growth or differentiation. These data suggest that GDF-11 and Activin A may contribute, in part, to the erythropoietic stimulatory effects of RAP-011. Several members of the TGFβ superfamily of ligands have been implicated as negative growth regulators, or “chalones”, functioning in homeostasis to maintain specific, mature tissue size. The results from our studies using the ActRIIA-Fc ligand trap, RAP-011, suggest that GDF-11 and Activin A, as well as other sotatercept ligands, may also be “chalones” for the blood, specifically regulating homeostasis of mature RBCs. We suggest that sotatercept increases red blood cell maturation and survival by blocking the negative growth regulation by TGFβ members. In pathologic states such as ineffective erythropoiesis, sotatercept may have an even greater impact than in the healthy, homeostatically-balanced environment. Disclosures: Carrancio: Celgene Corp.: Employment. Markovics:Celgene Corp.: Employment. Wong:Celgene Corp.: Employment. Heise:Celgene: Employment, Equity Ownership. Daniel:Celgene Corp.: Employment, Equity Ownership. Chopra:Celgene: Employment, Equity Ownership. Sung:Celgene Corp.: Employment.

Modified Activin Receptor Type IIb-Fc Fusion Protein (RAP-536) Decreases Anemia In a Murine Model Of Myelodysplastic Syndrome and Improves Overall Survival

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 749-749
Author(s):  
Rajasekhar NVS Suragani ◽  
Robert Li ◽  
Sharon Cawley ◽  
R. Scott Pearsall ◽  
Ravi Kumar
Keyword(s):  
Bone Marrow ◽  
Overall Survival ◽  
Fusion Protein ◽  
Murine Model ◽  
Wild Type ◽  
Ineffective Erythropoiesis ◽  
Employment Equity ◽  
Fc Fusion Protein ◽  
Erythroid Precursors ◽  
Equity Ownership

Abstract Myelodysplastic syndromes (MDS) are caused due to abnormal proliferation and differentiation of pluripotent hematopoietic stem cells leading to peripheral cytopenias including anemia and an increased risk of progression to acute myelogenous leukemia (AML). The mainstay of anemia treatments for majority of non-del (5q) patients are frequent transfusions but often leads to iron overloading and enhanced progression to AML, causing a negative impact on overall survival (OS). Therefore, alternative therapies that promote effective erythropoiesis, decrease anemia, and improve OS, are needed. Members of the TGF-β superfamily are known regulators of erythropoiesis. ACE-536 is a modified soluble activin receptor type IIB-Fc fusion protein that acts as a ligand trap for certain TGF-β family ligands and prevents Smad 2/3 signaling. ACE-536 has shown a robust increase in RBCs in mice, rats and monkeys. In normal mice, ACE-536 promotes maturation but not proliferation of late stage erythroid precursors. Additionally, we have shown that RAP-536 (murine ortholog of ACE-536) corrected anemia in the NUP98-HOXD13 (NHD13) murine model of MDS. In this study, we evaluated the progression of MDS disease and OS of NHD13 mice administered RAP-536. NHD13 mice begin to develop anemia, neutropenia and lymphopenia at four months of age. NHD13 mice die by 14 months due to severe pancytopenia or progression to AML. In this study, 4-month old NHD13 mice (N=12-16/group) were dosed with RAP-536 (10 mg/kg) or vehicle (VEH) twice per week for 5 or 10 months. Age matched wild type mice were used as controls. At each time point, blood samples were collected for CBCs. Bone marrow and splenic hematopoietic precursors of various cell lineages were immuno-stained and analyzed by flow cytometry (FCM). Spleen sections, blood and bone marrow smears were also analyzed for histopathological changes. After 5 months of treatment, VEH treated NHD13 mice had decreased RBC (-19.6%, P<0.001), WBC (-30.8%, P<0.001), lymphocytes (-63.2%, P<0.001) and increased platelet counts (+89.2%, P<0.05) compared to wild type mice. Treatment with RAP-536 increased RBC (+7.2%, P<0.05) and reduced platelet counts compared to VEH control. No significant changes in other blood lineages were observed following RAP-536 treatment, demonstrating that RAP-536 is selective of the erythroid lineage. After 10 months of treatment, VEH treated NHD13 mice had severely decreased RBC (-32.9%) and hemoglobin (-21.8%) compared to wild-type mice. RAP-536 treatment increased RBC (+21.4%) and hemoglobin (+16.6%) compared to VEH treatment. FCM evaluation of erythroid precursors from bone marrow of NHD13 mice demonstrated increased immature CD71+Ter119+ erythroblasts (from 13.1% to 18.3%), and decreased mature CD71-Ter119+ erythroblasts (from 13.2% to 3.8%) compared to wild-type mice. Treatment with RAP-536 increased mature erythroblasts (from 3.8% to 9.6%) consistent with improved RBC parameters, indicating the stimulation of erythroid differentiation. Additionally, bone marrow from NHD13 mice had significantly elevated Gr1+ & CD11b+ (from 33.6% to 62.6%) and CD4+ & CD8+(from 19.1% to 32.3%) precursors, while peripheral blood displayed a concomitant decreases in granulocytes (-22.5%), WBC (-37.5%) and lymphocytes (-45%) compared to wild type mice, demonstrating ineffective hematopoiesis. Treatment with RAP-536 displayed a non-statistical decrease in these precursors in bone marrow and a similar increase in peripheral blood compared to VEH control. No changes in platelets were observed after ten months of treatment. These data suggests that the effect of RAP-536 on other hematopoietic lineages is likely secondary to its effect on erythropoiesis. Importantly, histopathological findings revealed no indication of increased leukemic progression in RAP-536 treated NHD13 mice compared to VEH treated mice. Furthermore, RAP-536 treated NHD13 mice demonstrated a trend for increased median survival compared to VEH treated mice, from 238 days to 277 days (P=0.08). Together, these data demonstrate that RAP-536 corrects anemia associated with ineffective erythropoiesis in NHD13 mouse model of MDS. RAP-536 does not enhance progression to AML, and may increase overall survival of NHD13 mice. ACE-536 is currently being evaluated for the treatment of anemia in patients with MDS and β-thalassemia, conditions characterized by ineffective erythropoiesis. Disclosures: Suragani: Acceleron Pharma Inc: Employment, Equity Ownership. Li:Acceleron Pharma Inc: Employment, Equity Ownership. Cawley:Acceleron Pharma Inc: Employment, Equity Ownership. Pearsall:Acceleron Pharma Inc: Employment, Equity Ownership. Kumar:Acceleron Pharma Inc: Employment, Equity Ownership.

Down-regulation of GATA1 uncouples STAT5-induced erythroid differentiation from stem/progenitor cell proliferation

Blood ◽  
2010 ◽  
Vol 115 (22) ◽  
pp. 4367-4376 ◽  
Author(s):  
Albertus T. J. Wierenga ◽  
Edo Vellenga ◽  
Jan Jacob Schuringa
Keyword(s):  
Progenitor Cells ◽  
Progenitor Cell ◽  
Target Genes ◽  
Lentiviral Vector ◽  
Erythroid Differentiation ◽  
Down Regulation ◽  
Hematopoietic Stem ◽  
Progenitor Cell Proliferation ◽  
Cord Blood Cells

Abstract Previously, we have shown that overexpression of an activated mutant of signal transducer and activator of transcription-5 (STAT5) induces erythropoiesis, impaired myelopoiesis, and an increase in long-term proliferation of human hematopoietic stem/progenitor cells. Because GATA1 is a key transcription factor involved in erythropoiesis, the involvement of GATA1 in STAT5-induced phenotypes was studied by shRNA-mediated knockdown of GATA1. CD34+ cord blood cells were double transduced with a conditionally active STAT5 mutant and a lentiviral vector expressing a short hairpin against GATA1. Erythropoiesis was completely abolished in the absence of GATA1, indicating that STAT5-induced erythropoiesis is GATA1-dependent. Furthermore, the impaired myelopoiesis in STAT5-transduced cells was restored by GATA1 knockdown. Interestingly, early cobblestone formation was only modestly affected, and long-term growth of STAT5-positive cells was increased in the absence of GATA1, whereby high progenitor numbers were maintained. Thus, GATA1 down-regulation allowed the dissection of STAT5-induced differentiation phenotypes from the effects on long-term expansion of stem/progenitor cells. Gene expression profiling allowed the identification of GATA1-dependent and GATA1-independent STAT5 target genes, and these studies revealed that several proliferation-related genes were up-regulated by STAT5 independent of GATA1, whereas several erythroid differentiation-related genes were found to be GATA1 as well as STAT5 dependent.

RNAi-Mediated Inhibition of Tmprss6 Ameliorates Anemia and Secondary Iron Overload in a Mouse Model of β-Thalassemia Intermedia and Decreases Iron Overload in Hfe−/− Mice

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1018-1018
Author(s):  
Paul J Schmidt ◽  
Anoop K Sendamarai ◽  
Ivanka Toudjarska ◽  
Tim Racie ◽  
Jim S Butler ◽  
...  
Keyword(s):  
Mouse Model ◽  
Iron Overload ◽  
Iron Absorption ◽  
Disease Phenotype ◽  
Ineffective Erythropoiesis ◽  
Employment Equity ◽  
Liver Iron ◽  
Secondary Iron Overload ◽  
Equity Ownership ◽  
Low Levels

Abstract Abstract 1018 β-Thalassemia intermedia (TI), an inherited hemoglobinopathy caused by partial loss of β-globin synthesis, is characterized by anemia, extramedullary hematopoiesis and ineffective erythropoiesis as well as secondary iron overload. Hereditary hemochromatosis (HH) is most frequently caused by mutations in HFE and is marked by excess uptake of dietary iron with concomitant tissue iron overload. In both diseases, increased iron absorption is due to inappropriately low levels of the liver hormone, hepcidin (encoded by Hamp1). The membrane serine protease Matriptase-2 (encoded by Tmprss6) attenuates BMP-mediated Hamp1 induction by cleaving the BMP co-receptor, hemojuvelin. Previously, it has been shown that elevating Hamp1 expression by genetic inactivation of Tmprss6 reduces disease severity in the Hbbth3/+ mouse model of TI and prevents iron overload in Hfe−/− mice. Therefore, a therapeutic approach comprising specific inhibition of Tmprss6 could prove efficacious in TI and HH. Here we show that systemic administration of a potent lipid nanoparticle (LNP) formulated siRNA directed against Tmprss6 leads to >80% inhibition of Tmprss6 mRNA in the livers of Hbbth3/+ and Hfe−/− mice with concomitant >2-fold elevation in Hamp1 expression. In the TI model, Tmprss6 silencing leads to ∼30% reductions in serum iron and non-heme liver iron. In Hfe−/− mice, serum iron and non-heme liver iron are similarly reduced, and Perls staining of peri-portal iron is diminished. Remarkably, the partial iron restriction induced by Tmprss6 inhibition in Hbbth3/+ mice leads to dramatic improvements in the hematological aspects of the disease phenotype: the severity of the anemia is decreased as evidenced by an approximately 1 g/dL increase in total hemoglobin and a 50% decrease in circulating erythropoietin levels. As in the human disease, Hbbth3/+ mice exhibit the hallmarks of ineffective erythropoiesis including splenomegaly, decreased erythrocyte survival and marked reticulocytosis. Treatment with LNP formulated Tmprss6 siRNA leads to a dramatic 2–3 fold decrease in spleen size, a 3–4 fold decrease in reticulocyte counts and a >7-day increase in RBC half-life. Histological analysis of spleens from Tmprss6 siRNA treated animals demonstrates restoration of normal splenic architecture, as well as a reduction in the number of Tfr1-positive erythrocyte precursors in the spleen. Furthermore, as evidenced by the near normalization of blood smears, the overall quality of erythropoiesis in treated animals is vastly improved. Taken together, these data demonstrate that RNAi-mediated silencing of liver Tmprss6 elevates Hamp1 expression and reduces iron overload in both TI and HH model mice. More significantly, Tmprss6 siRNA treatment ameliorates all aspects of the disease phenotype in the TI mouse model. These results support the development of an RNAi therapeutic targeting TMPRSS6 for the treatment of TI, HH and potentially other disorders characterized by excess iron absorption due to physiologically inappropriately low levels of hepcidin. Disclosures: Racie: Alnylam Pharmaceuticals: Employment. Butler:Alnylam Pharmaceuticals, Inc.: Employment, Equity Ownership. Bumcrot:Alnylam Pharmaceuticals, Inc.: Employment, Equity Ownership.

MLL-AF6 Mediated Transformation Is Dependent On the H3K79 Methyl-transferase Dot1l

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3502-3502
Author(s):  
Aniruddha J Deshpande ◽  
Liying Chen ◽  
Maurizio Fazio ◽  
Amit U. Sinha ◽  
Kathrin M Bernt ◽  
...  
Keyword(s):  
Cell Line ◽  
Target Genes ◽  
Fusion Gene ◽  
Histone Methyltransferase ◽  
Leukemia Cells ◽  
Transformed Cells ◽  
Employment Equity ◽  
Specific Antibodies ◽  
Equity Ownership ◽  
H3k79 Methylation

Abstract Abstract 3502 The t(6;11)(q27;q23) produces a chimeric MLL-AF6 oncogene, and is a recurrent chromosomal rearrangement observed in patients with diverse hematologic malignancies such as acute myelogenous leukemia (AML), as well as both B-cell and T-cell acute lymphoblastic leukemias (ALL). The presence of an MLL-AF6 translocation predicts a particularly poor prognosis. Of particular biological interest, the MLL-AF6 translocation is the most common fusion event in which MLL fuses to a predominantly cytoplasmic protein. Very little is known about the molecular mechanisms of transformation mediated by the MLL-AF6 fusion oncogene, forestalling the development of specific therapeutic strategies for t(6;11)(q27;q23) positive leukemias. Recent studies suggest that the histone methyltransferase DOT1L could be an important therapeutic target in MLL-rearranged leukemias. We sought to assess whether MLL-AF6 mediated transformation is also dependent on aberrant H3K79 methylation using genomic, genetic and pharmacological approaches. First, we performed chromatin immuno-precipitation using H3K79me2 specific antibodies followed by next generation sequencing (ChIP-seq) on murine MLL-AF6 leukemias as well as on ML2, the human myelomonocytic leukemia cell line bearing the MLL-AF6 fusion gene. We observed that in both murine and human MLL-AF6 leukemia cells, MLL-fusion target genes display markedly high levels of H3K79 dimethylation as compared to other highly expressed genes. We then investigated whether MLL-AF6-induced transformation was dependent on aberrant H3K79 methylation through genetic or pharmacologic inhibition of the Dot1l histone methyltransferase. Lineage negative/Sca-1 positive/Kit positive (LSK) cells from mice bearing homozygous Dot1l floxed alleles were immortalized by retroviral expression of the MLL-AF6 fusion gene. Cre-recombinase mediated excision of Dot1l from MLL-AF6 transformed bone marrow cells resulted in a significant reduction in H3K79 dimethylation at the promoters of the MLL-target genes Hoxa9, Hoxa10 and Meis1, with a concomitant decrease in their expression. Dot1l excision significantly diminished the clonogenic capacity, abrogated blast colony formation in methylcellulose based medium, and enhanced differentiation of MLL-AF6 transformed cells. We then sought to assess whether EPZ004777, a recently described specific small molecule inhibitor of DOT1L could show efficacy against murine and human MLL-AF6 transformed cells. Dot1l inhibition using EPZ004777 significantly diminished H3K79 dimethylation globally (as assessed by immunoblotting) as well as on MLL-target genes (as assessed by ChIP-qPCR) using H3K79me2 specific antibodies. Importantly, EPZ004777 treatment significantly impaired the proliferation of both murine MLL-AF6 transformed cells as well as the ML2 cell line, whereas the proliferation rates of Hoxa9-Meis1 transformed cells as well as the human MLL-germline cell line HL60 were unaffected despite a similar decrease in H3K79me2 levels. EPZ004777 treatment induced cell cycle arrest as well as increased apoptosis in MLL-AF6 positive, but not control leukemia cells, demonstrating a selective activity of the DOT1L inhibitor EPZ004777 on MLL-AF6 transformed cells. In summary, we demonstrate that the MLL-AF6 oncoprotein requires continued activity of the histone methyltransferase DOT1L for aberrant epigenetic activation of downstream target oncogenes. More studies are needed to understand the mechanisms by which DOT1L is recruited to MLL-target genes by the MLL-AF6 fusion, since AF6 is not believed to normally associate with DOT1L. Nevertheless, the demonstration that H3K79 methylation is important for MLL-AF6 mediated transformation indicates that patients bearing the t(6;11)(q27;q23) translocation may benefit from therapeutic agents targeting aberrant H3K79 methylation. Disclosures: Olhava: Epizyme: Employment. Daigle:Epizyme, Inc.: Employment. Richon:Epizyme, Inc.: Employment, Equity Ownership. Pollock:Epizyme Inc.: Employment, Equity Ownership. Armstrong:Epizyme: Consultancy.

Pharmacological Inhibition Of Histone Deacetylase (HDAC) 1, 2 Or 3 Have Distinct Effects On Cellular Viability, Erythroid Differentiation, and Fetal Globin (HbG) Induction

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 564-564
Author(s):  
Jeffrey R Shearstone ◽  
John H van Duzer ◽  
Simon S Jones ◽  
Matthew Jarpe
Keyword(s):  
Bone Marrow ◽  
Cell Viability ◽  
Bone Marrow Cells ◽  
Fold Increase ◽  
Erythroid Differentiation ◽  
Employment Equity ◽  
Human Cd34 ◽  
Ic50 Values ◽  
Equity Ownership ◽  
Marrow Cells

Abstract Induction of HbG is an established therapeutic strategy for the treatment of sickle cell disease (SCD), and could also be effective in treating beta-thalassemia (bT). Genetic ablation of HDAC1 or HDAC2, but not HDAC3, results in the induction of HbG expression (Bradner JE, Proc Natl Acad Sci, 2010). Furthermore, we have previously shown that selective chemical inhibitors of HDAC1 and 2 elicit a dose and time dependent induction of HbG mRNA and fetal hemoglobin (HbF) protein in cultured human CD34+ bone marrow cells undergoing erythroid differentiation (Shearstone JS, ASH Annual Meeting Abstracts, 2012). While a variety of selective HDAC inhibitors have been used successfully to induce HbF, further clinical development has been limited by variable efficacy and concerns over off-target side-effects observed in clinical trials, potentially due to inhibition of HDAC3. Additionally, it remains to be determined if HDAC1 or HDAC2 is the preferred therapeutic target. In this work we present data that investigates the effects of selective inhibitors of HDAC1, 2, or 3 on cytotoxicity, erythroid differentiation, and HbG induction in cultured human CD34+ bone marrow cells. Acetylon Pharmaceuticals has generated a library of structurally distinct compounds with a range of selectivity for each of HDAC1, 2, or 3 (Class I HDAC) as determined in a biochemical assay platform. From our initial chemical series, we identified ACY-822 as a Class I HDAC inhibitor with IC50 values of 5, 5, and 8 nM against HDAC1, 2, and 3, respectively. In contrast, ACY-1112 is 30-fold selective for HDAC1 and 2, with IC50 values of 38, 34, and 1010 nM against HDAC1, 2, and 3, respectively. Treatment of cells for 4 days with ACY-822 (1 μM) resulted in a 20-fold decrease in cell viability, while ACY-1112 (1 μM) treatment resulted in a minimal reduction in viability (1.2-fold) and a 2-fold increase in the percentage of HbG relative to other beta-like globin transcripts. This result suggests that pharmacological inhibition of HDAC3 is cytotoxic and is consistent with the therapeutic rationale for the design selective inhibitors of HDAC1 and 2. To investigate if HDAC1 or HDAC2 is the preferred therapeutic target, we utilized a second series of structurally distinct compounds. We identified ACY-957 as an HDAC1/2 selective compound biased towards HDAC1 with IC50 values of 4, 15, and 114 nM for HDAC1, 2, and 3, respectively. In contrast ACY-1071 showed balanced HDAC1 and 2 selectivity with IC50 values of 27, 24, and 247 nM for HDAC1, 2, and 3, respectively. Treatment of cells for 6 days with 1 μM of ACY-957 or ACY-1071 resulted in a 3-fold increase in the percentage of HbG relative to other beta-like globin transcripts. However, we found that ACY-957 treatment resulted in an approximately 3-fold decrease in cell viability after 6 days of treatment, while ACY-1071 treatment resulted in a minimal reduction (1.2-fold) in cell viability. Decreased cell viability observed with ACY-957 was associated with a reduction of cells positive for the erythroid differentiation markers CD71 and glycophorinA. This result is consistent with the Mx-Cre mouse model where HDAC1KO; HDAC2het had reduced numbers of erythrocytes, thrombocytes, and total bone marrow cells, while the HDAC1het; HDAC2KO was unaffected (Wilting RH, EMBO Journal, 2010). Our results suggest that compounds with a pharmacological profile of increased selectivity towards HDAC2 inhibition versus HDAC1 may be less cytotoxic and minimize effects on differentiation, while still inducing HbG in human CD34+ bone marrow cells. Disclosures: Shearstone: Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. van Duzer:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. Jones:Acetylon Pharmaceuticals, Inc: Employment, Equity Ownership. Jarpe:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership.

TGFb1 Antagonist Inhibits Fibrosis in a Murine Model of Myelofibrosis

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 605-605 ◽  
Author(s):  
Rajasekhar NVS Suragani ◽  
Pedro A. Martinez ◽  
Sharon M Cawley ◽  
Robert Li ◽  
Robert Scott Pearsall ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Flow Cytometry ◽  
Murine Model ◽  
Jak2 V617f ◽  
Mutant Mice ◽  
Wild Type ◽  
Employment Equity ◽  
Bone Marrow Fibrosis ◽  
Equity Ownership ◽  
Marrow Fibrosis

Abstract Introduction: Myelofibrosis (MF) is a clonal stem cell disorder that originates from acquired mutations in the hematopoietic stem cells leading to abnormal kinase signaling, cell proliferation, cytokine expression, and splenomegaly and ultimately bone marrow (BM) fibrosis. Primary myelofibrosis (PMF), post-polycythemia vera (PV) MF and post-essential thrombocythemia MF are categorized under MF with overlapping disease phenotypes including progression to BM fibrosis. A genetic mutation in Janus kinase 2 (V617F) was identified as causative in ~95% PV, and ~50% of ET and PMF patients. Currently, treatment of MF patients with a JAK2 inhibitor offers symptomatic benefit, but does not alter the natural history of the disease or improve BM fibrosis. It is known that TGFβ1 is a critical regulator of fibrosis in many disease states. Elevated TGFβ1 levels were reported to be important for fibrosis in patients with MF. We hypothesize that inhibition of TGFβ1 signaling may prevent fibrosis and help reduce secondary morbidities associated with disease in MF patients. Therefore, we evaluated this hypothesis using a TGFβ1 antagonist in a murine model of MF. Methods: Transgenic JAK2 (V617F) mutant mice (MF model) and age-matched wild-type controls were used in the studies. Mice were dosed twice weekly with TGFβ1 antagonist (10 mg/kg). Complete blood counts (CBC), serum TGFβ1, bone metabolism and inflammatory cytokines levels were determined at different ages (2-12 months) during disease progression. Bone marrow and spleen cells were analyzed for different cell lineages by flow cytometry. Tissue sections were stained with H&E and reticulin to determine cellularity or degree of fibrosis respectively. Results: To understand the onset and progression of MF disease in JAK2 (V617F) mice, we initially analyzed the CBC and degree of fibrosis at various ages (2, 3, 4, 5, 8, 10 and 12 months) and compared the data with wild-type mice. These data were then correlated with the levels of TGFβ1 and other cytokines. As expected, red blood cells (RBC) and platelets were elevated in JAK2 mutant mice at all ages compared to wild-type mice, although a trend towards a progressive increase was observed between 2 to 5 months followed by a decrease from 8 to 14 months. Bone marrow fibrosis was detected starting at 5 months and worsened with age. JAK2 mutant mice displayed splenomegaly that increased as the disease progressed. Interestingly, serum levels of TGFβ1, TGFβ3 and bone metabolism cytokines (OPG, OPN, aFGF and Trance) displayed an increase at earlier ages (2-5 months) compared to the latter ages, a trend similar to RBC levels. These levels peaked during the initiation of fibrosis at 5 months. In contrast, inflammatory cytokines (such as IL6, IL-1β, and TNFα) were elevated at later ages consistent with disease progression. We initiated treatment with TGFβ1 antagonist in JAK2 (V617F) mice (N=8/treatment group) at 4 months of age, the age corresponding to elevated serum TGFβ1 levels and prior to the onset of fibrosis (at 5 months of age). Following 6 months of treatment, vehicle (VEH) treated JAK2 mutant mice displayed elevated RBC (+37.1%, P<0.001), platelets (+74.5%, P<0.001) and spleen weights (+9.5 fold, P<0.001) compared to wild-type mice. BM and spleen sections from VEH treated JAK2 mutant mice revealed severe fibrosis. TGFβ1 antagonist treatment of JAK2 mice displayed moderate effect on RBC (-8.4%, N.S) without any effect on platelet counts compared to VEH treatment. Flow-cytometry identified a reduced proportion of Ter119+ erythroid precursors in BM and spleen (-15%, P<0.05) and no change in CD41+ megakaryocytes. TGFβ1 antagonist treated mice displayed reduced spleen weights (-29%, P<0.01), and marked reduction in fibrosis in bone marrow (Figure) and spleen sections compared to VEH. Consistent with the reduction in fibrosis, TGFβ1 antagonist treated JAK2 mice displayed reduced IL-6 levels (-48.9%, P<0.05) compared to VEH treatment. Conclusion: Together, these data demonstrated that TGFβ1 levels were correlated with bone marrow fibrosis in a murine model of MF disease, and its inhibition using TGFβ antagonist reduces fibrosis, splenomegaly and inflammation in this murine model of myelofibrosis. Figure 1. Figure 1. Disclosures Suragani: Acceleron Pharma Inc: Employment, Equity Ownership, Patents & Royalties: No royalties. Martinez:Acceleron Pharma: Employment. Cawley:Acceleron Pharma Inc: Employment. Li:Acceleron Pharma: Employment, Equity Ownership. Pearsall:Acceleron Pharma Inc: Employment, Equity Ownership, Patents & Royalties. Kumar:Acceleron Pharma: Employment, Equity Ownership, Patents & Royalties.

scholarly journals Pharmacological Inhibition of Histone Deacetylases 1 and 2 (HDAC1/2) Induces Fetal Hemoglobin (HbF) through Activation of Gata2

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 335-335
Author(s):  
Jeffrey R Shearstone ◽  
Olga Golonzhka ◽  
Apurva Chonkar ◽  
Matthew Jarpe
Keyword(s):  
Bone Marrow Cells ◽  
Fetal Hemoglobin ◽  
Fold Increase ◽  
Erythroid Differentiation ◽  
Beta Globin ◽  
Employment Equity ◽  
Regulatory Regions ◽  
Genetic Ablation ◽  
Equity Ownership ◽  
Highly Correlated

Abstract Induction of HbF is an established therapeutic strategy for the treatment of sickle cell disease, and could also be effective in treating beta-thalassemia. Genetic ablation of HDAC1 or HDAC2, but not HDAC3, results in the induction of the fetal beta-like globin gene (HbG) transcript (Bradner JE, Proc Natl Acad Sci, 2010). We have previously shown that selective chemical inhibitors of HDAC1/2 elicit a dose and time dependent induction of HbG mRNA and HbF protein in cultured human CD34+ bone marrow cells undergoing erythroid differentiation (Shearstone JS, ASH Annual Meeting Abstracts, 2012). In this work, we have utilized our proof of concept molecule ACY-957, a selective inhibitor of HDAC1/2, to discover a novel role for Gata2 in the activation of HbG. To identify genes affected by HDAC1/2 inhibition, CD34+ bone marrow cells undergoing erythroid differentiation were treated with ACY-957 or vehicle, followed by mRNA expression profiling. Among the genes differentially regulated by both pharmacological inhibition and genetic ablation of HDAC1/2 were Bcl11a and Sox6, known HbG repressors, and Gata2, a potential HbG activator. Quantitative real time PCR (QRT-PCR) time course experiments confirmed that ACY-957 treatment leads to a 2-fold and 10-fold decrease in Bcl11A and Sox6, respectively, and an 8-fold increase in Gata2 mRNA. Unlike Bcl11a and Sox6, Gata2 induction by ACY-957 was highly correlated with HbG induction, suggesting a possible role for this transcription factor in the direct activation of HbG. To investigate this possibility, lentiviral infection was utilized to overexpress full length Gata2 transcript in differentiating primary erythroblasts. After 5 days of differentiation, Gata2 overexpression resulted in a 2.5-fold increase in HbG mRNA, while the level of the major adult beta-like globin chain (HbB) mRNA was unaffected. HbG mRNA remained elevated by Gata2 overexpression at day 7 of differentiation, while HbB was reduced by 1.6-fold. Gata2 overexpression appeared to have minimal effect on cell differentiation, as determined by the cell surface markers CD71 and GlycophorinA, a finding consistent with observations in ACY-957 treated cells with elevated Gata2. Furthermore, lentiviral delivery of short hairpin RNA (shRNA) targeting Gata2, attenuated HbG induction by ACY-957. These data suggest that elevated levels of Gata2 resulting from HDAC1/2 inhibition is sufficient to induce HbG at early stages of erythroid cell differentiation. To understand how HDAC1/2 inhibition drives Gata2 activation, chromatin immunoprecipitation coupled with either next generation sequencing (ChIP-seq) or QRT-PCR was performed in ACY-957 and vehicle treated cells. HDAC1 and HDAC2 were present throughout the Gata2 gene body and promoter regions, and HDAC1/2 binding levels were highly correlated, suggesting co-occupancy of these enzymes at this locus. ACY-957 treatment led to elevated histone acetylation at previously described Gata2 gene regulatory regions (Bresnick et. al. 2010, J Biol Chem). Specifically, the -1.8 kb and -2.8 kb regulatory regions showed a 6-fold increase in histone H3K9 and H2BK5 acetylation, while the +9.5 kb and -3.9 kb regions showed a 3-fold increase. The Gata2 protein showed increased binding at these regulatory regions in response to ACY-957 treatment, with a maximum increase of 3-fold at the -1.8 kb region. This finding is consistent with the known positive autoregulation of the Gata2 gene. Taken together, these data suggest that selective inhibition of HDAC1/2 leads to elevated Gata2 through acetylation-induced activation of a positive autoregulatory loop. The tight temporal correlation between Gata2 and HbG activation following HDAC1/2 inhibition argues that Gata2 may affect the beta-globin locus directly. ChIP-seq data across the 70-kb beta-globin locus demonstrated that ACY-957 treatment altered Gata2 binding only at a single region, lying within the promoter for delta globin. This region is suspected in playing a role in switching from fetal to adult globin during development, as naturally occurring deletions of this region are associated with elevated fetal hemoglobin in adults (Sankaran et. al. 2011, NEJM). Whether the change in GATA2 binding to this region is responsible for the increased expression of HbG in cells treated with HDAC1/2-selective inhibitors is under investigation. Disclosures Shearstone: Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. Golonzhka:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. Chonkar:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. Jarpe:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership.

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