NUP98-HOXD13 Research Articles

Comparative analysis of immunological changes following realgar and arsenic trioxide treatments in a murine model of myelodysplastic syndrome

Background Myelodysplastic syndrome (MDS) is a prevalent hematological neoplastic disorder in clinics and its immunopathogenesis has garnered growing interest. Oral and intravenous arsenic agents have long been used to treat hematological malignancies. The main component of oral arsenic is realgar (arsenic disulfide), while arsenic trioxide is the main component of intravenous arsenic. Methods This study aimed to assess the effects of ATO and Realgar on the enhancement of peripheral blood, drug safety, and T cell immune status in the NUP98-HOXD13 (NHD13) mice model of MDS, specifically in the peripheral blood, spleen, and liver. Results The study findings indicate that realgar and arsenic trioxide (ATO) can improve peripheral hemogram in mice, whereas realgar promotes higher peripheral blood cell production than ATO. Furthermore, the clinical administration method and dose did not cause significant toxicity or side effects and thus can be considered safe. Coexistence and interconversion of hyperimmune function and immunosuppression in mice were also observed in this study. In addition, there were interactions between immune cells in the peripheral blood, spleen, and liver to regulate the immune balance of the body and activate immunity via T-cell activation. Conclusion In summary, oral and intravenous arsenic agents are beneficial in improving peripheral hemogram and immunity in mice.

Abstract 624: Ptpn1 deficiency collaborates with a NUP98::HOXD13 fusion gene to generate B cell precursor acute lymphoblastic leukemia

Abstract Background: Acute lymphoid leukemia is characterized by inherited or acquired mutations that effect critical differentiation and proliferation pathways. We have shown that Mcm2 deficient mice developed T cell acute lymphoblastic leukemia, due to copy number variations, most commonly interstitial deletions throughout the genome. When crossed with mice that expressed a NUP98::HOXD13 (NHD13) fusion gene, Mcm2−/−NHD13 mice developed B cell precursor ALL (BCP-ALL). A majority of these BCP-ALL had acquired homozygous deletions of Ptpn1, a protein tyrosine phosphatase, leading to the hypothesis that Ptpn1 deficiency combined with NHD13 expression leads to BCP ALL. Objective: To investigate the role of Ptpn1 deletion in BCP-ALL development using mouse models. Methods: Mice expressing an NHD13 fusion gene were crossed with Ptpn1 knockout mice, generating 6 possible genotypes. Mice were followed for 18 months. Mice with signs of leukemia were characterized by clinical evaluation, CBC, flow cytometry, and IHC. Primary BCP-ALL and derived BCP-ALL cell lines were also evaluated with RNA-seq and molecular pathway analysis. Results: NHD13+Ptpn1-/- mice developed BCP-ALL with 65% penetrance, characterized by hyperleukocytosis, anemia, thrombocytopenia, and invasion of non-hematopoietic tissues. Similar to human BCP-ALL, NHD13+Ptpn1-/- BCP-ALL had clonal IGH as well as clonal Tcrd gene rearrangements. Flow cytometry revealed CD19 and/or B220 expression. NHD13+Ptpn1+/- mice with BCP-ALL frequently lost the wild-type (WT) Ptpn1 allele in leukemic cells, reinforcing the hypothesis that Ptpn1 can function as a classic tumor suppressor gene in this context. Whole exome sequencing revealed acquired mutations in B-cell differentiation genes (Pax5 or Bcor) and activating mutations in tyrosine kinase genes (Jak1/3 and Flt3). Transcription signature analysis showed significant upregulation of Hoxa/b gene clusters, RNase12 and LncRNAs subsets. Conclusion: This study demonstrates that Ptpn1 loss combined with expression of NHD13 fusion gene leads to highly penetrant BCP-ALL in mice, suggesting a role for Ptpn1 in preventing malignant transformation. These findings present a collaborative model for BCP-ALL in which the NHD13 transgene leads to increased stem cell self-renewal, somatic Bcor or Pax5 mutations block normal B cell differentiation, and somatic signaling mutations (Jak1/3,Flt3) lead to hyperproliferation, which is potentiated by Ptpn1 deficiency. Citation Format: Nupur Nigam, Toshihiro Matsukawa, Ryan Bertoli, Michel L. Tremblay, Mianmian Yin, Peter D. Aplan. Ptpn1 deficiency collaborates with a NUP98::HOXD13 fusion gene to generate B cell precursor acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 624.

Abstract 1484: 5-Aza-4'-thio-2'-deoxycytidine induces C to G transversions in a specific trinucleotide context and leads to acute lymphoid leukemia

Abstract Myelodysplastic syndromes (MDS) are a diverse group of blood cancers characterized by peripheral blood cytopenias and dysplastic blood cell morphology. Up to 40% of patients with high risk MDS will transform to acute myeloid leukemia (AML), an aggressive blood cancer with significant morbidity and an overall 5-year survival of less than 35%. Both MDS and AML have been linked to hypermethylation of cytosine residues. Hypermethylation in the 5’ regulatory region can result in epigenetic downregulation of gene expression, and it has been speculated that hypermethylation of tumor suppressor genes can contribute to malignant transformation. DNA methyltransferase inhibitors (DNMTi), most commonly cytidine analogs, are compounds that are used clinically to decrease 5’-cytosine methylation, with the aim of inducing the re-expression of tumor suppressor genes resulting in a halt of tumor progression. 5-Aza-4’-thio-2’-deoxycytidine (Aza-TdCyd or ATC) is a cytidine analog that incorporates an aza modification (nitrogen in place of carbon) of the cytosine base and a thioether modification of the deoxyribose sugar. ATC is a promising new DNMT1i that has demonstrated efficacy in preclinical studies of solid tumors. Based on these prior studies, we sought to characterize the potential therapeutic effect of ATC in MDS.Mice that express a NUP98::HOXD13 (NHD13) transgene develop an MDS that closely recapitulates all of the key features of human MDS, including pancytopenia, dysplastic morphology, and transformation to AML. We transplanted NHD13 and wild-type (WT) hematopoietic stem and progenitor cells into WT recipients, and used this model of MDS to investigate the therapeutic potential of ATC. We found that ATC treatment led to both T and B lineage lymphoid leukemia (ALL) originating from the NHD13 cells. Surprisingly, ATC treatment also led to T and B lineage ALL in the WT cells, and further experiments demonstrated that non-transplanted, healthy WT mice developed T and B cell ALL after treatment with ATC. In sum, all mice that received at least 8 cycles of ATC therapy at the 1.0 mg/kg dose developed leukemia. Whole exome sequencing of tumors revealed thousands of acquired mutations, almost all of which were C>G transversions in a previously unrecognized, specific 5’-NCG-3’ context. These mutations involved a number of genes well-known to be involved in human lymphoid leukemia, such as Notch1, Pten, Pax5, Trp53, and Nf1. Treatment of the human U937 and CEM cell lines in vitro showed thousands of acquired C>G transversions in a similar context. Taken together, these findings demonstrate that ATC can be a potent mutagen in human and mouse cells, both in vitro and in vivo. Citation Format: Ryan Matthew Bertoli, Yang Jo Chung, Michael Difilippantonio, Anthony Wokasch, Madison R. Marasco, Haley Klimaszewski, Susannah Garber, Yuelin Jack Zhu, Robert L. Walker, Dengchao Cao, James Doroshow, Paul Meltzer, Peter D. Aplan. 5-Aza-4'-thio-2'-deoxycytidine induces C to G transversions in a specific trinucleotide context and leads to acute lymphoid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1484.

Tasquinimod Improves Erythropoiesis and Mitigates Bone Loss in Myelodysplastic Mice

Myelodysplastic neoplasms (MDS) are characterized by ineffective hematopoiesis, peripheral cytopenia, and a risk of transforming into acute myeloid leukemia (AML). Interestingly, MDS is also associated with an increased prevalence of osteoporosis. Studies have suggested that dysregulated innate immune responses and a proinflammatory bone marrow (BM) microenvironment play significant roles in the pathogenesis of MDS. Targeting inflammatory pathways, especially in low-risk MDS patients, presents a potential strategy to modulate the progression of the disease. One such candidate is Tasquinimod (TASQ, ABR-215050, Active Biotech AB), a small-molecule oral inhibitor and second-generation quinoline-3-carboxamide compound. TASQ binds to the inflammatory protein S100A9 and inhibits its interaction with the proinflammatory toll-like receptor 4, thereby displaying both immunomodulatory and antitumor properties. Our in vitro data provided evidence for a rescuing effect of TASQ on inflammatory signal-primed MDS stromal cells, leading to enhanced hematopoietic support. This study aims to validate these findings using a transgenic MDS mouse model expressing the NUP98/HOXD13 (NHD13) fusion protein in hematopoietic cells. NHD13 mice, generated on a C57BL/6J background, were obtained from Jackson Laboratory. TASQ was administered orally by adding it to the drinking water at a dose of 30 mg/kg. Both transgenic and littermate control (WT) mice (12 weeks old, n=5-10 per group) were treated with or without TASQ for 12 weeks. Throughout the experiment, peripheral blood cell counts were measured every 4 weeks using Sysmex analysis. In the final analysis, primary BM cells were isolated from the femora, and the number of lineage-negative, sca-1-positive, and c-kit-positive (LSK) cells, as well as erythroid differentiation, were assessed using flow cytometry. Additionally, bone volume, trabecular number, and thickness were analyzed in femora using µCT. Transgenic NHD13 mice displayed MDS-like characteristics, including peripheral cytopenias, dysplasia in blood and BM cells, and microstructural abnormalities in the bone microenvironment. As expected, hemoglobin levels (Hb) and red blood cell (RBC) counts were lower in NHD13 mice compared to WT mice [Hb: 8.9 vs. 9.5 mmol/L; RBC: 9.5 vs. 10.3x1012/L] and showed a consistent decrease in the untreated group from 12 to 24 weeks. Notably, treatment with TASQ significantly improved red blood cell counts in NHD13 mice [+14%; p<0.01] after 24 weeks, while having no effect on WT mice. White blood cells were significantly decreased in WT mice after 4 weeks of TASQ treatment [-19%; p<0.001] until the end of the experiment [-36%; p<0.001]. In contrast, in transgenic mice, the lower white blood cell counts [-76%; p<0.001] were not further diminished. Interestingly, TASQ led to an elevation in neutrophil counts. The platelet count was not affected by the treatment in both transgenic and WT mice. Using flow cytometry, an increase in the total number of LSK cells was detected in the BM of WT mice after TASQ treatment. However, no increase was observed in NHD13 mice, which already had lower LSK numbers compared to WT controls. Late-stage erythropoiesis was slightly increased in both WT and transgenic mice after TASQ treatment, whereas early erythroid differentiation was unaffected or even decreased by TASQ. Moreover, BM cells were used for colony-forming assays ex vivo. NHD13 mice had a lower erythroid differentiation potential compared to WT mice, which was improved after TASQ treatment. To assess the potential influence of the microenvironment, adherent BM cells were assayed for their CFU-F forming capacity. BM cells of transgenic mice exhibited a slightly lower CFU-F forming capacity compared to WT mice, which was partially reversed by TASQ treatment. Finally, the bone microarchitecture was analyzed. NHD13 mice showed a lower bone volume [-43%; p<0.01] compared to WT mice. Notably, treatment with TASQ abolished the bone loss in NHD13 mice by increasing the trabecular number [+35% p<0.001], whereas the trabecular thickness was not affected. In conclusion, this study provides the first evidence for an in vivo effect of TASQ in a murine model of MDS, suggesting improved erythropoiesis and positive effects on the bone phenotype. These results warrant further investigations of TASQ in human trials, particularly in MDS patients in whom anemia and bone loss often coexist.

AG-946, an Activator of Pyruvate Kinase, Improves Ineffective Erythropoiesis in the Bone Marrow of Mouse Models of Myelodysplastic Syndromes

Background: Myelodysplastic syndromes (MDS) are a heterogeneous group of hematologic malignancies characterized by ineffective erythropoiesis. Anemia is the most common cytopenia and major clinical problem in MDS. Acquired pyruvate kinase (PK) deficiency has been observed in MDS, and a direct impact on the glycolytic pathway in the pathogenesis of anemia associated with MDS has been demonstrated. AG-946 is an investigational, small-molecule, allosteric activator of PK that has the potential to enhance red blood cell (RBC) functionality and survival by increasing glycolysis and adenosine triphosphate (ATP) production, and improve differentiation of erythroid cells in bone marrow, potentially improving anemia caused by ineffective erythropoiesis in MDS. Previous findings showed that RBCs from patients with MDS treated ex-vivo with AG-946, led to an increase in PK activity. Here, we used two MDS-related mouse models to evaluate the effects of the PK activator AG-946 in this mechanism of anemia. Aim: Evaluate the effect of AG-946 treatment on impaired erythropoiesis in the bone marrow of two mouse models of MDS. Methods:NUP98-HOXD13 (NHD13) is a fusion gene mutation observed in some patients with MDS. Mouse models with this mutation develop key characteristics of MDS such as impaired erythropoiesis and progressive anemia leading to malignant leukemia around 12 months of age. Male and female NHD13 and C57BL/6J mice were placed on 0.006% AG-946 (approximate dose 10 mg/kg/day) formulated diet starting at 10 months given ad libitum and continuing for 3 months. Numbers of animals for wild type (WT) Control, WT AG-946, NHD13 Control, NHD13 AG-946 were 10, 10, 13, and 11, respectively.Polg D257A (Polg) mouse model, while not a mutation observed in patients with MDS, does display many key features of MDS, such as impaired erythropoiesis and progressive anemia. Male and female Polg mice were placed on 0.006% AG-946 (approximate dose 10 mg/kg/day) formulated diet starting at 4 months given ad libitum and continuing for 8 months. Numbers of animals for WT Control, WT AG-946, Polg Control, Polg AG-946 were 10, 10, 19, and 18, respectively. Bone marrow from 1 femur per mouse was collected and analyzed by flow cytometry. Bone marrow cell pellets were washed and treated with ACK lysing buffer prior to staining. Samples with fewer than 1000 Ter119+ events were removed from analysis due to insufficient cell count. Bone marrow erythroblast populations were gated using Single Cells/Live/B220-/Ter119+/CD44 vs FSC, which were then gated into three populations: basophilic erythroblasts (BasoE), polychromatic erythroblasts (PolyE), and orthochromatic erythroblasts and reticulocytes (OrthoE + Retic). Results:No differences in any erythroblast populations were observed between untreated WT and NHD13 mice. No changes in the BasoE population were observed in WT or NHD13 mice. The PolyE population in NHD13 mice treated with AG-946 was significantly decreased compared with both the NHD13 and WT untreated mice (p=0.0021 and 0.0003, respectively). NHD13 mice treated with AG-946 showed significant increases in the OrthoE + Retic populations over the untreated NHD13 mice (p=0.0275).No differences in BasoE or OrthoE + Retic populations were observed between untreated WT and Polg mice while the PolyE population was significantly decreased in Polg mice compared with WT (p<0.0001). The BasoE population was significantly decreased in Polg mice treated with AG-946 compared with untreated Polg (p=0.0002). No difference in PolyE population was observed in Polg mice with AG-946. OrthoE + Retic population was significantly increased in Polg mice treated with AG-946 compared with WT and Polg untreated mice (p=0.0001 and 0.0304, respectively). Data graphed as average +/- SEM. Conclusions: Our data suggest AG-946 treatment improves erythroblast maturation in two MDS mouse models as demonstrated by a reduction in early-stage erythroblasts (BasoE, PolyE) coupled with an increase in late-stage erythroblast populations (OrthoE + Retic). These data are the first to suggest that PK activation by AG-946 could improve ineffective erythropoiesis in MDS.

Abstract 5026: Protein tyrosine phosphatase Ptpn1 knockout in mouse models drives B-cell hematological malignancies

Abstract Background: Ptpn1 is a member of Protein Tyrosine Phosphatase family that dephosphorylates tyrosine residues. We previously reported that an Mcm2 hypomorphic mouse (designated Mcm Cre/Cre) develops T cell acute lymphoblastic leukemia (T-ALL), due to acquisition of 100-1000 kb interstitial deletions involving tumor suppressor genes. When crossed to mice that express a NUP98-HOXD13 (NHD13) fusion gene, NHD13+;Mcm2Cre/Cre mice develop B-cell precursor ALL (BCP-ALL). Sparse whole genome sequencing revealed somatic copy number variants (CNV) involving Pax5 and Ptpn1. The role of Pax5 in B-cell development, differentiation, and leukemia has been widely studied. However, little is known about deletions of Ptpn1 and its role in BCP-ALL. Objective: The principal objective is to investigate how deletion of Ptpn1 impacts BCP-ALL development in mouse models. Methods: Mice expressing NHD13 fusion (NHD13+) were crossed with Ptpn1 knockout mice. The F2 cross generated 6 genotypes that were positive or negative for NHD13 and wild type/heterozygous/homozygous for Ptpn1. Mice were studied for incidence of BCP-ALL, which was characterized by whole-exome sequencing, molecular pathway analysis and transcriptome-sequencing. Results: NHD13+;Ptpn1-/- mice developed BCP-ALL, characterized by hyperleukocytosis, variable anemia and thrombocytopenia, expression of B220 and/or CD19, and invasion of non-hematopoietic tissues (liver, kidney, lung). In addition, NHD13+;Ptpn1+/- mice that developed BCP-ALL lost the wild-type (WT) Ptpn1 allele in the leukemic cells. Similar to human BCP-ALL, NHD13+;Ptpn1-/- mice that developed BCP-ALL showed presence of clonal TCR-delta rearrangements as well as IGH rearrangements in the leukemic cells. Whole exome sequencing showed presence of acquired mutations in genes known to be involved in B-cell differentiation, such as Pax5 or Bcor, as well as genes involved in B cell signaling pathways, such as Jak3, Jak1 and Flt3 and Western blots demonstrated accumulation of phosphorylated STAT3 protein. Conclusion: This study demonstrates that Ptpn1 loss along with expression of an NHD13 fusion gene leads to a highly penetrant BCP ALL in mice, suggesting a role for Ptpn1 in preventing malignant transformation. Taken together, these findings are consistent with a collaborative model for BCP ALL in which the NHD13 transgene leads to increased stem cell self-renewal, somatic Bcor or Pax5 mutations block normal B cell differentiation, and somatic signaling mutations (Jak1/3, Flt3) lead to hyperproliferation, which is potentiated by Ptpn1 deficiency. Citation Format: Toshihiro Matsukawa, Nupur Nigam, Ryan Bertoli, Michel L. Tremblay, Mianmian Yin, Peter D. Aplan. Protein tyrosine phosphatase Ptpn1 knockout in mouse models drives B-cell hematological malignancies. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5026.

A murine model for human early/immature T-cell precursor acute lymphoblastic leukemia (EITP ALL).

Early/immature T cell precursor acute lymphoblastic leukemia (EITP ALL) represents a subset of human leukemias distinct from other T-ALL, and associated with poor prognosis. Clinical studies have identified chromosomal translocations involving the NUP98 gene and point mutations of IDH genes as recurrent mutations in patients with EITP-ALL. In a recent study using genetically engineered mice, we demonstrated that cooperation of an Idh2R140Q mutation with a NUP98-HOXD13 (NHD13) fusion gene resulted in EITP-ALL. Highlights of this double transgenic mouse model included the similarity of the immunophenotypic, mutational and gene expression landscape with human EITP-ALL. Additional studies showed that the Idh2R140Q /NHD13 EITP-ALL are sensitive to selective mutant IDH2 inhibitors in vitro, leading to the possibility that these mice can serve as a useful model for the study of EITP ALL development and therapy.

Abstract 2641: Examining the potential therapeutic efficacy of the CDK inhibitor alvocidib in a pre-clinical model of myelodysplastic syndrome

Abstract Myelodysplastic Syndrome (MDS) represents a group of hematologic malignancies characterized by pancytopenia and dysplastic morphology. High risk MDS is invariably fatal due to either severe cytopenia, or transformation to acute myeloid leukemia (AML). Inhibitors of transcription offer promising potential for new therapies. Modulation of CDK9 activity, which plays a critical role in controlling gene transcription through phosphorylation of RNA polymerase II, has been proposed as a novel therapeutic approach. In this study, we examined the efficacy of alvocidib, a broad spectrum CDK inhibitor with highest potency against CDK9, which is hypothesized to slow transcription via inhibition of CDK9, leading to stalled RNA Polymerase II and cell death. We employed a previously characterized pre-clinical model of MDS based on the NUP98-HOXD13 (NHD13) fusion gene, which induces MDS that progresses to AML in mice. In addition to alvocidib, we evaluated the in vitro efficacy of 5-Azacytidine (5-Aza) and Decitabine (DAC), which are hypomethylating agents used in treatment of MDS. The in vitro assays demonstrated a potent effect of alvocidib on cell lines that expressed the NHD13 fusion gene. Alvocidib induced a clear cytostatic effect and showed increasing cytotoxic effects with time, peaking at 70% cell death after 72 hours. Annexin-V staining further supported these results, revealing that most cells were apoptotic by 72 hours. Neither 5-Aza nor DAC treatment matched these effects in vitro. The in vivo assays were based on treatment of chimeric mice with both wild type (WT) and MDS hematopoiesis, generated by allogeneic hematopoietic stem cell transplant with bone marrow from WT and NHD13 mice. Four treatment groups (saline, 5-Aza, Alvocidib, and 5-Aza+Alvocidib) were assessed by serial flow cytometry and complete blood counts. In contrast to in vitro studies, in vivo results did not show a clear survival benefit from either group receiving alvocidib, whereas 5-Aza treatment demonstrated statistically significant survival. However, this study revealed several “exceptional responder” mice, defined as mice that demonstrated a ≥75% reduction in WBC count and a ≥50% reduction in NHD13 engraftment levels following transformation to AML; these exceptional responses were observed only in mice receiving alvocidib. This type of dramatic response has not previously been observed in over 20 prior chimeric transplant experiments employing the NHD13 mouse model. Ongoing efforts include follow-up studies to evaluate the frequency of exceptional responders, as well as identification of acquired mutations which collaborate with the initiating mutation (NHD13) to generate AML. Citation Format: Ryan M. Bertoli, Yang Jo Chung, Jason M. Foulks, Anthony S. Wokasch, Peter D. Aplan. Examining the potential therapeutic efficacy of the CDK inhibitor alvocidib in a pre-clinical model of myelodysplastic syndrome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2641.

Interleukin-1/Toll-like Receptor Inhibition Can Restore the Disrupted Bone Marrow Microenvironment in Mouse Model of Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) are myeloid neoplasms characterized by bone marrow (BM) failure and associated with aging. We have previously shown that reversal of BM microenvironment (BMME) dysfunction in MDS mitigates MDS associated marrow failure and delays progression to acute leukemia. However, the exact mechanisms driving BMME dysfunction in MDS remain unknown. We recently reported that interleukin-1 (IL1) Receptor Type1 (IL1R1) signaling is a driver in myeloid bias via disruption of BMME in aging. In addition, we have found that IL1R1 signaling is involved in disease progression of AML. Therefore, to assess the role of IL1R1 signaling in MDS associated BMME dysfunction and marrow failure, we employed an age appropriate murine transplant model for MDS utilizing NUP98-HOXD13 (NHD13) transgenic mice.Methods: BM cells (NHD13 transgenic or wild type (WT), 7 weeks) and competitor cells were transplanted into irradiated aged recipients (WT or IL1R1 KO, 60 weeks), and subsequently monitored for development of marrow failure. When marrow failure developed, mice were euthanized and peripheral blood, BM, BM extracellular fluid (BMEF), and collagenase-1 digested bone associated cells were analyzed including flow cytometry, colony forming units (CFU) assay, and cytokine analyses. Next, BM from NHD13 (8-10 weeks) and competitor cells were transplanted into lethally irradiated aged recipients (WT, 50-60 weeks). At onset of marrow failure, mice were treated with inhibitors of IL1/Toll-like receptor signaling (IL1R antagonist, MCC950, or IL1R-associated kinase 4 protein (IRAK4) inhibitor) for fourteen days, and then euthanized and analyzed as above. Finally, we evaluated cytokine profile in the BM serum from the patients with MDS and normal donors.Results: Transplant of NHD13 BM cells into aged IL1R1 wt recipients (NHD13→IL1R1 wt) was not associated with a significant difference in survival rates or levels of NHD13 engraftment compared to NHD13 into IL1R1 ko recipients (NHD13→IL1R1 ko). IL1R1 wt developed macrocytic anemia compared to IL1R1 ko recipient (Hb 11.3±0.57 v.s 13.1±0.42 g/dL, n=12 and 9, p<0.05). In CFU-C assays, NHD13→IL1R1 wt and NHD13→IL1R1 ko demonstrated similar levels of CFU-activity whereas CFU-fibroblast (CFU-F) assays of IL1R1 wt recipients demonstrated lower numbers of large colonies (reported to contain highly proliferative mesenchymal stem cells (MSC)). Flow cytometry analysis of hematopoietic stem and progenitor cells (HSPC) population in IL1R1 wt recipients showed increased myeloid progenitors and decreased long-term HSC (LT-HSC) compared to IL1R1 ko recipients. Cytokine/chemokine profiles revealed that the inflammatory cytokines (IL-6 and TNFα) and macrophage activating cytokines (MCP-1 and M-CSF) were significantly decreased in NHD13→IL1R1 ko compared to NHD13→IL1R1 wt. Next, we treated MDS model mice with inhibitors. The pharmacological targeting of IL1R1 signaling in vivo was associated with decreased NHD13 cell burden and improvement of macrocytic anemia. CFU-C assays demonstrated some decreases in NHD13 CFU capacity post-treatment. Interestingly, non-NHD13 HSPCs assessed by CFU capacity increased in IRAK4 inhibitor treated mice. Consistent with this, flow cytometric analyses of HSPC pools demonstrated decreased NHD13 HSPCs (LT-HSC and granulocyte-monocyte progenitor cells) and increased non-NHD13 HSCs and myeloid progenitors compared to vehicle group. BMME cell populations showed that arteriolar endothelial cells and MSCs were also affected by drug treatment and both IL1R antagonist and MCC950 increased the number of large CFU-F colonies. Analysis of BMEF revealed the decreased IFNγ and IL-18 and upregulated M-CSF in MCC950 treated group. The cytokines of human BM serum revealed higher concentrations of soluble formed IL1R1, IL-18, CXCL1, and osteopontin in MDS compared to young or aged normal donors.Conclusions: Collectively, our findings demonstrate that IL1R1 signaling alters the BMME and contributes to the disease phenotype of MDS and that the effects of targeting IL1R1 pharmacologically have differing effects based on the modality of inhibition as well as the cell population. IL1R1 signaling can be a promising target to alleviate the complexity of MDS via improving inflammatory status in BMME. DisclosuresNo relevant conflicts of interest to declare.

FLT3 ITD and NUP98 translocations Cooperate to Induce Type I Interferon Signaling That Impedes Hematopoietic Progenitor Differentiation

FLT3-Internal Tandem Duplication (FLT3 ITD) mutations occur at similar frequencies in both childhood and adult acute myeloid leukemia (AML) patients, but they cooperate with different initiating mutations at different ages. In childhood AML, FLT3 ITD often cooperates with translocations that generate fusion proteins, such as NUP98 translocations (NUP98-t). In adult AML, FLT3 ITD often cooperates with mutations that inactivate RUNX1, DNMT3A, TET2 and other genes that regulate self-renewal and myeloid differentiation. This raises the question of whether FLT3 ITD induces similar, or distinct, changes in gene expression and cell fate when it arises in the setting of pediatric and adult driver mutations. To answer this question, we evaluated pre-leukemic changes in hematopoiesis and gene expression in neonatal and juvenile mice that carried pediatric-like FLT3 ITD/NUP98-HOXD13 and adult-like FLT3 ITD/Runx1 DEL/+ mutation profiles. Both NUP98-HOXD13 (NHD13) and Runx1 DEL/+ severely depleted phenotypic hematopoietic stem cells (HSCs) when coupled with FLT3 ITD. However, FLT3 ITD/NHD13 cooperated to enhancer ectopic self-renewal capacity in lineage committed hematopoietic progenitor cells (HPCs) whereas FLT3 ITD/Runx1 DEL/+ did not. FLT3 ITD/NHD13 and FLT3 ITD/Runx1 DEL/+ both induced changes in gene expression and enhancer activation that were not seen with either mutation alone. These cooperative changes were almost entirely non-overlapping. The most notable cooperative change in FLT3 ITD/NHD13 HPCs was activation of a type I Interferon target gene signature. By contrast, this signature was actively repressed in FLT3 ITD/Runx1 DEL/+ HPCs due to mir155 activation. Thus, FLT3 ITD/NHD13 and FLT3 ITD/Runx1 DEL/+ mutations have largely non-overlapping, cooperative effects on hematopoietic cell fate and gene expression.Interferon signaling sustained the FLT3 ITD/NHD13 HPC population by impeding differentiation into more committed myeloid progenitors. When we deleted the type I interferon receptor (Ifnar) on a FLT3 ITD/NHD13 background, the HPC population was virtually eliminated, yet the pre-granulocyte monocyte (pGM) and granulocyte-monocyte progenitor (GMP) populations expanded. HPC proliferation and death did not change in the absence of Ifnar. These findings suggest that type I interferon impedes HPC differentiation into pGMs during the neonatal and juvenile stages of life. Of note, ectopic interferon was insufficient to enhancer HPC numbers in setting of a sole NHD13 mutation. Thus, interferon is necessary to sustain FLT3 ITD/NHD13 HPCs, but not sufficient, and other signaling pathways downstream of FLT3 ITD must cooperate with NHD13 in parallel to drive HPC expansion. To our surprise, Ifnar deletion did not reduce repopulating activity in FLT3 ITD/NHD13 bone marrow - as measured by limiting dilution transplants - it simply shifted repopulating activity to more committed pGMs. Our raise two important conceptual points. First, we show that different initiating mutations can elicit completely different transcriptional responses downstream of FLT3 ITD. Precision medicine strategies must account for these differences as effective therapies for adult FLT3 ITD AML may not yield similar success in the pediatric population. Second, type I interferon shapes pre-leukemic hematopoiesis in the setting of FLT3 ITD/NUP98-t mutations. In doing so, the mutant cells may hijack a program that we recently identified as promoting normal perinatal HPC expansion. DisclosuresNo relevant conflicts of interest to declare.

Targeting miR-126 disrupts maintenance of myelodysplastic syndrome stem and progenitor cells.

BackgroundMyelodysplastic syndrome (MDS) arises from a rare population of aberrant hematopoietic stem and progenitor cells (HSPCs). These cells are relatively quiescent and therefore treatment resistant. Understanding mechanisms underlying their maintenance is critical for effective MDS treatment.MethodsWe evaluated microRNA‐126 (miR‐126) levels in MDS patients’ sample and in a NUP98‐HOXD13 (NHD13) murine MDS model along with their normal controls and defined its role in MDS HSPCs’ maintenance by inhibiting miR‐126 expression in vitro and in vivo. Identification of miR‐126 effectors was conducted using biotinylated miR‐126 pulldown coupled with transcriptome analysis. We also tested the therapeutic activity of our anti‐miR‐126 oligodeoxynucleotide (miRisten) in human MDS xenografts and murine MDS models.ResultsmiR‐126 levels were higher in bone marrow mononuclear cells from MDS patients and NHD13 mice relative to their respective normal controls (P < 0.001). Genetic deletion of miR‐126 in NHD13 mice decreased quiescence and self‐renewal capacity of MDS HSPCs, and alleviated MDS symptoms of NHD13 mice. Ex vivo exposure to miRisten increased cell cycling, reduced colony‐forming capacity, and enhanced apoptosis in human MDS HSPCs, but spared normal human HSPCs. In vivo miRisten administration partially reversed pancytopenia in NHD13 mice and blocked the leukemic transformation (combination group vs DAC group, P < 0.0001). Mechanistically, we identified the non‐coding RNA PTTG3P as a novel miR‐126 target. Lower PTTG3P levels were associated with a shorter overall survival in MDS patients.ConclusionsMiR‐126 plays crucial roles in MDS HSPC maintenance. Therapeutic targeting of miR‐126 is a potentially novel approach in MDS.

Cell-Extrinsic Differentiation Block Mediated by EphA3 in Pre-Leukaemic Thymus Contributes to Disease Progression.

Simple SummaryThe NUP98-HOXD13 (NHD13) mouse is a model of T-cell leukaemia (T-ALL) featuring a pre-leukemic phase, in which T-cell progenitors from the thymus of an NHD13 mouse can engraft into the thymus of a recipient mouse—an ability that normal T-cell progenitors do not possess. However, loss of this engraftment ability (by deletion of the Lyl1 gene) did not result in any loss of leukemogenesis activity, indicating the activity of redundant oncogenic pathways in this model. Having observed an overexpression of the EphA3 protein in the NHD13 thymocytes, we hypothesized that this gene might be involved in a redundant leukaemogenic pathway. Deletion of EphA3 did not affect the engraftment ability of the thymocytes, but did reduce the incidence of T-ALL. We thus uncovered a distinct mechanism of leukaemogenesis, which we believe operates in parallel to that mediated by Lyl1.We recently characterised the NUP98-HOXD13 (NHD13) mouse as a model of T-cell pre-leukaemia, featuring thymocytes that can engraft in recipient animals and progress to T-cell acute lymphoblastic leukaemia (T-ALL). However, loss of this engraftment ability by deletion of Lyl1 did not result in any loss of leukemogenesis activity. In the present study, we observe that NHD13 thymocytes overexpress EPHA3, and we characterise thymocyte behaviour in NHD13 mice with deletion of EphA3, which show a markedly reduced incidence of T-ALL. Deletion of EphA3 from the NHD13 mice does not prevent the abnormal accumulation or transplantation ability of these thymocytes. However, upon transplantation, these cells are unable to block the normal progression of recipient wild type (WT) progenitor cells through the normal developmental pathway. This is in contrast to the EphA3+/+ NHD13 thymocytes, which block the progression of incoming WT progenitors past the DN1 stage. Therefore, EphA3 is not critical for classical self-renewal, but is essential for mediating an interaction between the abnormally self-renewing cells and healthy progenitors—an interaction that results in a failure of the healthy cells to differentiate normally. We speculate that this may orchestrate a loss of healthy cell competition, which in itself has been demonstrated to be oncogenic, and that this may explain the decrease in T-ALL incidence in the absence of EphA3. We suggest that pre-leukaemic self-renewal in this model is a complex interplay of cell-intrinsic and -extrinsic factors, and that multiple redundant pathways to leukaemogenesis are active.

Activation of SIRT1 Deacetylase As a Therapeutic Approach for Myelodysplastic Syndromes By Restoring TET2 Function

Myelodysplastic syndromes (MDS) which arise from a primitive CD34+ hematopoitic stem/progenitor cell (HSPC), are incurable by non-transplant therapy. Better understanding of MDS HSPC regulation is critical for developing targeted therapies against the fatal disease. Tet methylcytosine dioxygenase 2 (TET2), initiating DNA demethylation through converting 5-methylcytosine to 5-hydromethylcytosine (5hmC), is the most frequently mutated gene in MDS. TET2 alterations lead to DNA hypermethylation and dysregulated gene expression in HSPCs, resulting in enhanced self-renewal and skewed myeloid specific expansion. While TET2's biological function has been well studied, the knowledge of its regulation is limited. We had demonstrated the TET2 c-terminus acetylation was reversed by SIRT1 deacetylase which maintains normal HSPCs activity under stress. We also observed that SIRT1 protein in MDS CD34+CD38- was expressed below normal levels, and that knockdown (KD) of SIRT1 enhanced in vivo growth of MDS-L cells, a patient derived MDS cell line, is associated with TET2 acetylation (Blood. 2016;128:1053). These results indicate an important role for SIRT1 in MDS HSPCs maintenance.To further assess SIRT1 function in MDS, we ectopically expressed SIRT1 in primary MDS CD34+ cells enriched for HSPCs and MDS-L cells, respectively. Overexpression (OE) of SIRT1 resulted in inhibition of colony formation of MDS CD34+ cells (p<0.01, n=3) but not normal counterpart (p>0.05, n=3). SIRT1 OE also suppressed MDSL colony formation (p<0.01) and cell growth (p<0.01). SIRT1 OE significantly reduced MDS-L cell BM engraftment in NSGs mice relative to controls (human CD45+ cells: 5.7±0.8% of BM in SIRT1 OE group vs 31.4 ± 5.8% in control, p<0.01, n=7), resulting in delayed mortality of recipient mice (median survival: 52 days vs 35 days; p<0.05, n=5). Meanwhile, treatment of SIRT1 agonist SRT1720, reduced colony formation of primary MDS CD34+ cells in a dose dependent manner (p<0.01, n=9). Similar results were also achieved in SRT1720 treated MDS-L cells. Furthermore, TET2 was hyperacetylated in primary MDS cells (n=3) compared to normal counterpart (n=3). Next, we tested whether inhibition of MDS HSPCs following SIRT1 activation was related to TET2 activation via protein deacetylation. Indeed, enhanced TET2 activity marked by 5hmC was observed in MDS CD34+ cells upon SRT1720 treatment (P<0.05, n=3). TET2 KD diminished growth inhibition induced by SIRT1 OE or SRT1720, indicating a requirement of TET2 for SIRT1 function. Through mass spectrometry analysis, three conserved acetylated lysine residuals (K1472, K1473, K1478) were identified in TET2 catalytic domain (CD). Engineered lysines to glutamines (TET2 3KQ) mutant, mimicking acetylated TET2, produced lower 5hmC, and led to increased colony growth compared to MDS-L expressing TET2 WT (p<0.01). We further evaluated the effects of SRT1720 using NUP98-HOXD13 (NHD13)MDS mouse. This murine MDS is transferable and secondary recipients receiving primary NHD13 MDS cells succumb to MDS at 4 months, allowing generation of a cohort of MDS mice for preclinical studies of therapeutics against MDS. CD45.2+ BM cells from donor NHD13+ mice showed evidence of dysplasia were harvested, and transplanted into preconditioned congenic recipients expressing CD45.1. SRT1720 treatment (100mg/kg/day for 12 weeks, p.o.) resulted in partial reversal of MDS-like disease developed in recipients receiving MDS cells, including an increase in HGB, PLT, RBC and WBC (p<0.01,n=6). Importantly, significant reduction of NHD13+ CD45.2+ chimerism in LSK and other progenitors from BM were also observed (p<0.01, n=6). As expected, 5hmC level in lineage depleted cells from SRT1720 treated mice was increased (p<0.01). Secondary transplantation was performed to evaluate the effects of SRT1720 on MDS initiating cells. We observed that the mice receiving cells from SRT1720 treated donors showed reduced NHD13+ CD45.2+ cell long-term engraftment (p<0.01, n=5).In summary, we demonstrated that genetic overexpression or pharmacological activation of SIRT1 drastically inhibited MDS maintenance, and that TET2 function was required for the inhibitory effect of SIRT1. These results support the hypothesis that SIRT1 deficiency promotes MDS cell expansion through TET2 inactivation and support the rationale for exploring SIRT1 activation as a promising approach to selectively target MDS stem cells. DisclosuresNo relevant conflicts of interest to declare.

Aberrant Hedgehog Signaling in Myelodysplastic Syndrome Accelerates Leukemic Transformation Via Smoothened-Dependent and Smoothened-Independent Gli1 Activation

Introduction: Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders with increased risk of transformation to secondary acute myeloid leukemia (sAML) that carries uniformly dismal prognosis. The exact mechanisms driving this process remain obscure. Aberrant Hedgehog (Hh) signaling has been demonstrated in a number of solid tumors and hematologic malignancies. An emerging body of literature suggests the importance of Hh signaling in leukemic transformation of MDS. Moreover, a recent Phase II clinical trial using Smoothened (SMO) inhibitor with low-dose chemotherapy resulted in significant prolongation of overall survival (Lancet et al. Blood 2016). Thus, we sought to examine the clinical impact of aberrant Hh activation in MDS and further explore the mechanism of Hh-driven leukemic transformation.Methods/Results:To determine the pathway activity, we quantified the level of GLI1 in CD34+ cells from patients with MDS and healthy controls in published databases (N=17 and N=159, respectively; GSE58831) and while absent in controls, GLI1 was significantly upregulated in MDS patients (p<0.05). Analysis of serial samples revealed Hh activation at disease progression in 67% of patients (4/6). In addition, GLI1 levels were significantly higher in poor-risk AML with complex cytogenetics comparing to favorable risk disease (p<0.001, TCGA).To further evaluate the impact of of Hh activation in MDS progression, we crossed Nup98-HoxD13 (NHD13) mice with mice conditionally expressing the constitutively active mutant of Smoothened (SmoM2). Double transgenic NHD13/SmoM2 mice succumbed to aggressive myeloid leukemia (median survival of NHD13/SmoM2 and NHD13 controls, 3 months vs. 13 months, respectively, p<0.0001) characterized by leukocytosis (p<0.05), splenomegaly (p<0.0001) and significant expansion of immature myeloid progenitors in peripheral blood (p<0.0001) and bone marrow (p<0.0001). Analysis of hematopoietic stem/progenitor (HSPC) compartment revealed expansion of phenotypic granulocyte macrophage progenitors (GMP) (6244 vs. 131487 mean GMPs/femur , in NHD13 v. NHD13/SmoM2 respectively, p<0.05). To determine whether Hh activation resulted in aberrant self-renewal in GMP compartment, we carried out an in vivo repopulation assay. While NHD13 GMPs showed only transient engraftment, characteristic of non-self-renewing progenitors, NHD13/SmoM2 GMPs robustly engrafted and significantly expanded over time, and all recipient animals developed aggressive leukemia within 2-3 months. The engraftment was sustained through secondary transplantation. Our results suggest that Hh activation resulted in abnormal self-renewal in normally non-self-renewing progenitors.To delineate the mechanism leading to aberrant activation of self-renewal we compared the transcriptome of GMPs isolated from NHD13/SmoM2 and NHD13 controls. In addition to expected Hh activation, Gene Set Enrichment Analysis (GSEA) showed enrichment in gene signatures associated with other developmental pathways such as Wnt or TGF-β signaling as well as EWS/FLI1-protooncogen signature. Interestingly, these pathways have been found to act via direct activation of GLI1 .Using human AML (TF-1) and MDS (MDS-L) cell lines we confirmed that GLI1 may be activated in the absence of SMO. GLI1 knock-down and/or inhibition with GANT61 resulted in growth arrest (p<0.05, both) and significantly lower clonogenic potential in vitro (p<0.05, both) more so than upstream SMO inhibition.Conclusions: Our data suggest that aberrant Hh/GLI1 signaling is frequent in MDS and marks disease progression and leukemic transformation. In some cases, GLI1 can be activated in a SMO-independent manner and therapeutic strategies focused on targeting downstream Gli transcription factors may be more effective than currently used Smo inhibitors. DisclosuresNo relevant conflicts of interest to declare.

Modeling Defective Erythropoiesis in Myelodysplastic Syndrome (MDS)

Anemia is a significant clinical component of MDS, which results from defective erythropoiesis. By 30 weeks of age, a murine model of MDS based on genetic defects in Nup98-HOXD13 (NHD13) recapitulates the peripheral cytopenias seen in patients, including macrocytic anemia (Balderman et al. 2016, Blood 127:616). We found that these defects in the peripheral blood were correlated with decreases in marrow erythropoiesis at the earliest erythroid-specific progenitor (BFU-E), as well as a decrease in the expansion of downstream erythroblast precursors. Along with a cell-intrinsic defect, erythropoiesis in MDS patients could also be influenced by bone marrow microenvironmental changes. To investigate potential cell-intrinsic and microenvironmental defects, we analyzed erythropoiesis in chimeric mice transplanted with both UBC-GFP+ wildtype bone marrow and either 1) cells from NHD13, or 2) another MDS model based on overexpression of Evi1, or 3) unlabeled wildtype cells, which served as controls. In the two chimeric MDS models, cytopenias were not observed until after 15 weeks post-transplantation. Yet as early as 6 weeks post-transplant, analysis of peripheral blood demonstrated that GFP+ wild-type cells contributed disproportionately to circulating red blood cell (RBCs) in both MDS models. In the bone marrow of chimeric mice with normal hematocrits, we found significant decreases in both MDS-derived and wildtype BFU-E. The maintenance of RBC numbers was achieved by extensive expansion of wildtype erythroid precursors. Concurrently, MDS-derived erythroid precursors failed to expand, as seen in the non-chimeric NHD13 model. At later time-points when cytopenias become evident in the periphery of the chimeric MDS mice, erythropoiesis was still provided by wildtype cells, but the bone marrow intermediates were no longer present in sufficient numbers to prevent anemia. The source(s) of this cell-extrinsic inhibition of erythropoiesis during MDS progression may include the expanding myeloid cell populations derived from the MDS clone, which we found both in the non-chimeric NHD13 model, as well as in both chimeric MDS models. Taken together, these data suggest that MDS leads to an intrinsic block in erythropoiesis and to a progressive expansion of myelopoiesis in the marrow. These changes initially lead to a compensatory increase in erythropoiesis from wild-type cells to preserve normal RBC output, which ultimately fails with continued disease progression. DisclosuresNo relevant conflicts of interest to declare.

DOCK2 Knockdown Mitigates Disease Progression in Murine Models Harboring a FLT3/ITD Mutation

Acute myeloid leukemia (AML) is an aggressive hematologic neoplasm characterized by clonal expansion of myeloid blasts in the bone marrow and other tissues. The FMS-like tyrosine kinase-3 (FLT3) receptor gene is the most commonly mutated gene in AML, and patients who harbor a FLT3/ITD mutation have a relatively poor prognosis.Previous work in the laboratory has demonstrated that FLT3/ITD interacts with Dedicator of Cytokinesis 2 (DOCK2), which is a guanine nucleotide exchange factor for Rac GTPases. Expression of DOCK2 is limited to hematopoietic cells, and it is also expressed in the leukemic blasts of patients with FLT3/ITD AML. Knockdown (KD) of DOCK2 results in reduced Rac1 activity, and leads to decreased survival of leukemic cells that carry a FLT3/ITD mutation. This effect is seen in both in vitro studies and a mouse xenograft model, and is enhanced by treatment with cytarabine. Initial studies have shown that the anti-leukemic effect of DOCK2 KD may, in part, be due to reduced expression of both FLT3 and key DNA Damage Response (DDR) factors. In order to further investigate the relationship between DOCK2 and FLT3/ITD in hematopoietic neoplasms, we utilized mice that harbor a spontaneous Dock2 mutation (Dock2/Hsd). This mutation results in a substantial reduction in Dock2 mRNA and protein expression in hematolymphoid cells.Flt3/ITD mice develop a myeloproliferative neoplasm (MPN) that includes greatly increased spleen size. In contrast, the spleens of progeny of Flt3/ITD mice bred with Dock2/Hsd mice were greatly reduced in size. Flow cytometric analysis of the bone marrow also demonstrated that DOCK2 KD results in at least a partial reversal of the Flt3/ITD phenotype. Flt3/ITD mice characteristically demonstrate an increased fraction of immature hematopoietic stem/progenitor cells (Lin-Sca-1+c-KIT+ cells or LSKs); however, the fraction of LSKs in Flt3/ITD-Dock2/Hsd mice is similar to that seen in the marrow of WT mice. While the Flt3/ITD-Dock2/Hsd mice continued to show a disruption in the early to late Pro-B transition similar to that described in Flt3/ITD mice, the Flt3/ITD-Dock2/Hsd mice had a small but significant increase in the late Pre-B cell population, suggesting a less stringent block in B-cell development. Additionally, as compared with Flt3/ITD mice, the bone marrow of Flt3/ITD-Dock2/Hsd mice exhibited a decreased fraction of Mac1+Gr-1+ myeloid cells with a concomitant increase in Ter119+CD41- erythroid precursors, to levels that are indistinguishable from WT mice. These findings indicate that DOCK2 KD mitigates the myeloproliferative phenotype of Flt3/ITD mice.Since experiments using FLT3/ITD cell lines have suggested that DOCK2 KD may act by reducing expression of the FLT3 protein itself and also by inhibiting the DNA Damage Response, we evaluated these factors in the Flt3/ITD-Dock2/Hsd mice. Quantitative PCR of mouse whole bone marrow revealed that the mRNA levels of the Flt3 transcription regulators Meis1 and c-Myb were decreased in the Flt3/ITD-Dock2/Hsd mice, compared with Flt3/ITD mice, and the expression of Flt3 itself was markedly decreased as well. Moreover, reduced expression of key DDR factors including Chk1, Wee1, Rad51, Pim1, MSH2, MSH6 and MLH1 was also observed in Flt3/ITD-Dock2/Hsd mice.Finally, to assess the role of DOCK2 in leukemogenesis and disease progression, the Dock2/Hsd mutation was introduced into a murine AML model that carries both Flt3/ITD and the Nup98-HoxD13 (NHD13) fusion gene. The Flt3/ITD-NHD13 mice develop AML with 100% penetrance and short latency; however, the expression of Dock2/Hsd in Flt3/ITD-NHD13 mice extended the median survival of these mice from approximately 110 days to over 155 days (and counting).These findings suggest that DOCK2 may cooperate with FLT3/ITD and play an important role in disease progression of FLT3/ITD leukemia. Thus, pharmacologic inhibition of DOCK2 may provide a novel and promising therapeutic target for FLT3/ITD AML. Additionally, since DOCK2 KD results in decreased expression of DDR factors, the addition of DDR inhibitors to conventional chemotherapy may be useful in the treatment of FLT3/ITD AML. DisclosuresNo relevant conflicts of interest to declare.

Increased FGF-23 levels are linked to ineffective erythropoiesis and impaired bone mineralization in myelodysplastic syndromes.

Myelodysplastic syndromes (MDS) are clonal malignant hematopoietic disorders in the elderly characterized by ineffective hematopoiesis. This is accompanied by an altered bone microenvironment, which contributes to MDS progression and higher bone fragility. The underlying mechanisms remain largely unexplored. Here, we show that myelodysplastic NUP98‑HOXD13 (NHD13) transgenic mice display an abnormally high number of osteoblasts, yet a higher fraction of nonmineralized bone, indicating delayed bone mineralization. This was accompanied by high fibroblast growth factor-23 (FGF-23) serum levels, a phosphaturic hormone that inhibits bone mineralization and erythropoiesis. While Fgf23 mRNA expression was low in bone, brain, and kidney of NHD13 mice, its expression was increased in erythroid precursors. Coculturing these precursors with WT osteoblasts induced osteoblast marker gene expression, which was inhibited by blocking FGF-23. Finally, antibody-based neutralization of FGF-23 in myelodysplastic NHD13 mice improved bone mineralization and bone microarchitecture, and it ameliorated anemia. Importantly, higher serum levels of FGF‑23 and an elevated amount of nonmineralized bone in patients with MDS validated the findings. C‑terminal FGF‑23 correlated negatively with hemoglobin levels and positively with the amount of nonmineralized bone. Thus, our study identifies FGF-23 as a link between altered bone structure and ineffective erythropoiesis in MDS with the prospects of a targeted therapeutic intervention.

TLR2/6 signaling promotes the expansion of premalignant hematopoietic stem and progenitor cells in the NUP98–HOXD13 mouse model of MDS

Toll-like receptor 2 (TLR2) expression is increased on hematopoietic stem and progenitor cells (HSPCs) of patients with myelodysplastic syndromes (MDS), and enhanced TLR2 signaling is thought to contribute to MDS pathogenesis. Notably, TLR2 heterodimerizes with TLR1 or TLR6, and while high TLR2 is associated with lower-risk disease, high TLR6, but not TLR1, correlates with higher-risk disease. This raises the possibility of heterodimer-specific effects of TLR2 signaling in MDS, and in the work described here, we tested the effects of specific modulation of TLR1/2 versus TLR2/6 signaling on premalignant HSPCs. Indeed, chronic stimulation of TLR2/6, but not TLR1/2, accelerates leukemic transformation in the NHD13 mouse model of MDS, and conversely, loss of TLR6, but not TLR1, slows this process. TLR2/6 stimulation expands premalignant HSPCs, and chimeric mouse studies revealed that cell-autonomous signaling contributes to this expansion. Finally, TLR2/6 stimulation is associated with an enrichment of Myc and mTORC1 activities. While Myc inhibition partially suppressed the TLR2/6 agonist-mediated expansion of premalignant HSPCs, inhibition of mTORC1 exacerbated it, suggesting that these pathways play opposite roles in regulating the effects of TLR2/6 ligation on HSPCs. Together, these data reveal heterodimer-specific effects of TLR2 signaling on premalignant HSPCs, with TLR2/6 signaling promoting their expansion and leukemic transformation.

SETD2 deficiency accelerates MDS-associated leukemogenesis via S100a9 in NHD13 mice and predicts poor prognosis in MDS

AbstractSETD2, the histone H3 lysine 36 methyltransferase, previously identified by us, plays an important role in the pathogenesis of hematologic malignancies, but its role in myelodysplastic syndromes (MDSs) has been unclear. In this study, low expression of SETD2 correlated with shortened survival in patients with MDS, and the SETD2 levels in CD34+ bone marrow cells of those patients were increased by decitabine. We knocked out Setd2 in NUP98-HOXD13 (NHD13) transgenic mice, which phenocopies human MDS, and found that loss of Setd2 accelerated the transformation of MDS into acute myeloid leukemia (AML). Loss of Setd2 enhanced the ability of NHD13+ hematopoietic stem and progenitor cells (HSPCs) to self-renew, with increased symmetric self-renewal division and decreased differentiation and cell death. The growth of MDS-associated leukemia cells was inhibited though increasing the H3K36me3 level by using epigenetic modifying drugs. Furthermore, Setd2 deficiency upregulated hematopoietic stem cell signaling and downregulated myeloid differentiation pathways in the NHD13+ HSPCs. Our RNA-seq and chromatin immunoprecipitation–seq analysis indicated that S100a9, the S100 calcium-binding protein, is a target gene of Setd2 and that the addition of recombinant S100a9 weakens the effect of Setd2 deficiency in the NHD13+ HSPCs. In contrast, downregulation of S100a9 leads to decreases of its downstream targets, including Ikba and Jnk, which influence the self-renewal and differentiation of HSPCs. Therefore, our results demonstrated that SETD2 deficiency predicts poor prognosis in MDS and promotes the transformation of MDS into AML, which provides a potential therapeutic target for MDS-associated acute leukemia.

A unique mutator phenotype reveals complementary oncogenic lesions leading to acute leukemia.

Mice homozygous for a hypomorphic allele of DNA replication factor minichromosome maintenance protein 2 (designated Mcm2cre/cre) develop precursor T cell lymphoblastic leukemia/lymphoma (pre-T LBL) with 4-32 small interstitial deletions per tumor. Mice that express a NUP98-HOXD13 (NHD13) transgene develop multiple types of leukemia, including myeloid and T and B lymphocyte. All Mcm2cre/cre NHD13+ mice develop pre-T LBL, and 26% develop an unrelated, concurrent B cell precursor acute lymphoblastic leukemia (BCP-ALL). Copy number alteration (CNA) analysis demonstrated that pre-T LBLs were characterized by homozygous deletions of Pten and Tcf3 and partial deletions of Notch1 leading to Notch1 activation. In contrast, BCP-ALLs were characterized by recurrent deletions involving Pax5 and Ptpn1 and copy number gain of Abl1 and Nup214 resulting in a Nup214-Abl1 fusion. We present a model in which Mcm2 deficiency leads to replicative stress, DNA double strand breaks (DSBs), and resultant CNAs due to errors in DNA DSB repair. CNAs that involve critical oncogenic pathways are then selected in vivo as malignant lymphoblasts because of a fitness advantage. Some CNAs, such as those involving Abl1 and Notch1, represent attractive targets for therapy.