Development Of Myeloid Malignancies Research Articles

Thrombosis in Myeloid Malignancies, from CHIP to AML.

The development of myeloid malignancies is a multi-step process starting from pre-malignant stages. Large-scale studies on clonal hematopoiesis of indeterminate potential (CHIP) identified this condition as a risk factor for developing hematologic malignancies, in particular myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). In parallel, CHIP was found to confer an enhanced thrombotic risk, in particular for cardiovascular diseases. In a similar fashion, in recent years, alongside their life-threatening features, increasing attention has been drawn toward thrombotic complications in myeloid malignancies. The purpose of this review is to gather growing body of evidence on incidence, pathogenesis and clinical impact of thrombosis in myeloid malignancies at every step of malignant progression, from CHIP to AML.

Age-specific induction of mutant p53 drives clonal hematopoiesis and acute myeloid leukemia in adult mice

The investigation of the mechanisms behind p53 mutations in acute myeloid leukemia (AML) has been limited by the lack of suitable mouse models, which historically have resulted in lymphoma rather than leukemia. This study introduces two new AML mouse models. One model induces mutant p53 and Mdm2 haploinsufficiency in early development, showing the role of Mdm2 in myeloid-biased hematopoiesis and AML predisposition, independent of p53. The second model mimics clonal hematopoiesis by inducing mutant p53 in adult hematopoietic stem cells, demonstrating that the timing of p53 mutation determines AML vs. lymphoma development. In this context, age-related changes in hematopoietic stem cells (HSCs) collaborate with mutant p53 to predispose toward myeloid transformation rather than lymphoma development. Our study unveils new insights into the cooperative impact of HSC age, Trp53 mutations, and Mdm2 haploinsufficiency on clonal hematopoiesis and the development of myeloid malignancies.

Exploring the intricate cross-talk between clonal expansion and the bone marrow niche

Haematopoietic stem cells (HSCs) reside within an intricate network of cells in the bone marrow (BM) niche. HSC crosstalk with niche compartments influences lineage determination and blood cell production, while independent niche interactions are essential for the maintenance of HSC quiescence. How different niche components influence the genetic diversity of HSCs represents an expanding field of investigation. As such, we will summarise the current knowledge of the contribution to the Darwinian evolution of mutant HSCs of both haematopoietic and non-haematopoietic cells residing in the BM. In this review, we will disentangle how somatic evolution associates with the niche at two stages: from (1) the stage of preleukaemic HSC expansion and clonal haematopoiesis (CH) to (2) leukaemia-initiating cells (LICs) and the development of myeloid malignancies with acute myeloid leukaemia (AML) being the most prevalent. We will finally describe current challenges such as limitations in models used in the field or the difficulty in studying specific genetic clones in isolation.

Pathogenic Mechanisms of DDX41 Mutations in the Development of Myeloid Malignancies

DDX41 is a newly identified leukemia predisposition gene encoding an RNA helicase, whose germline mutations are tightly associated with late-onset myeloid malignancies. Importantly, germline DDX41 mutations were also found in as many as ~7 % of sporadic cases of high-risk MDS, conferring the largest germline risk for myeloid malignancies. In typical cases, a germline loss-of-function allele (most commonly p.A500fs or p.D140fs, depending on the ethnicity) is compounded by a somatic missense mutation affecting the helicase domain in the remaining allele (p.R525H). However, the molecular mechanism by which DDX41 mutations lead to myeloid neoplasms have not fully been elucidated. To clarify the role of these distinct DDX41 alleles, we generated mice models carrying either or both of conditional/constitutive Ddx41 knock-out (KO) and conditional R525H knock-in (KI) alleles. Vav1-Cre mediated homozygous deletion of Ddx41 resulted in embryonic lethality, suggesting that Ddx41 is indispensable for normal hematopoiesis. Next, by crossing these mice and further breeding with Rosa26-CreERT2 transgenic mice, we engineered mice that were wild-type for Ddx41 ( Ddx41 +/+), heterozygous Ddx41 KO( Ddx41 +/-), homozygous Ddx41 KO( Ddx41 -/-), heterozygous for the Ddx41 R525H mutation ( Ddx41 R525H/+), or hemizygous for the Ddx41 R525H mutation( Ddx41 R525H/-), in which expression of the mutant allele was induced by tamoxifen administration. First, we assessed cell intrinsic effects of these Ddx41 alleles, using noncompetitive transplantation experiments. Shortly after tamoxifen administration, most of the recipient mice that were transplanted with BM from Ddx41 -/- or Ddx41 R525H/- mice died within a month after CreERT2 induction due to severe BM failure (BMF), which was not observed in mice transplanted with BM from Ddx41 +/+, Ddx41 +/- or Ddx41 R525H/+ mice. By contrast, the mice transplanted with Ddx41 +/- or Ddx41 R525H/+ BM showed significantly reduced WBC counts and anemia in long-term observation in both primary and serial transplantations. Some of the Ddx41 +/- or Ddx41 R525H/+ BM-transplanted mice exhibited MDS-like phenotypes, showing ineffective hematopoiesis with evidence of erythroid dysplasia. Transcriptome analysis revealed that stem cells (Kit +Sca-1 -Lin low cells) derived from Ddx41 R525H/- BM-transplanted mice exhibited a significant upregulation of genes involved in innate immunity, including interferon stimulated genes, compared with stem cells derived from Ddx41 +/+ BM-transplanted mice. In addition, snoRNA and ribosomal genes were significantly deregulated in stem cells from Ddx41 -/- and Ddx41 R525H/- BM-transplanted mice, which could result in abnormal ribosome biogenesis and protein synthesis in Ddx41 mutant cells. We also assessed the reconstitution capacity of whole BM cells from different Ddx41 mutant mice in competitive transplantation experiments. The donor chimerism of Ddx41 -/- and Ddx41 R525H/- BM-transplanted mice in PB was markedly reduced compared to Ddx41 +/+ BM-transplanted mice. In contrast, Ddx41 +/- and Ddx41 R525H/+ BM-transplanted micedid not show significant changes in competitive bone marrow reconstitution compared to Ddx41 +/+ BM-transplanted mice. Given that the MDS clones bearing DDX41 R525H somatic alleles are typically observed as a small subclone in patients, we next co-transplanted Ddx41 +/+- and Ddx41 525H/--derived BM cells with Ddx41 +/+- or Ddx41 +/--derived BM cells at the ratio of 1:9. Recipient mice showed significantly reduced WBC counts when Ddx41 +/+- or Ddx41 +/- were co-transplanted with Ddx41 525H/- -derived BM, suggesting that Ddx41 525H/--derived hematopoietic cells have negative effect on normal hematopoiesis. In summary, compound biallelic loss-of function and R525 alleles led to severe BM failure. Monoallelic Ddx41 loss-of function and R525H knock-in alleles, by contrast, are compatible with hematopoiesis but associated with an impairment of hematopoiesis and the development of MDS with ageing, where activated innate immunity, impaired RNA metabolism and ribosome functions may play important roles.

Different niches for stem cells carrying the same oncogenic driver affect pathogenesis and therapy response in myeloproliferative neoplasms

Aging facilitates the expansion of hematopoietic stem cells (HSCs) carrying clonal hematopoiesis-related somatic mutations and the development of myeloid malignancies, such as myeloproliferative neoplasms (MPNs). While cooperating mutations can cause transformation, it is unclear whether distinct bone marrow (BM) HSC-niches can influence the growth and therapy response of HSCs carrying the same oncogenic driver. Here we found different BM niches for HSCs in MPN subtypes. JAK–STAT signaling differentially regulates CDC42-dependent HSC polarity, niche interaction and mutant cell expansion. Asymmetric HSC distribution causes differential BM niche remodeling: sinusoidal dilation in polycythemia vera and endosteal niche expansion in essential thrombocythemia. MPN development accelerates in a prematurely aged BM microenvironment, suggesting that the specialized niche can modulate mutant cell expansion. Finally, dissimilar HSC-niche interactions underpin variable clinical response to JAK inhibitor. Therefore, HSC-niche interactions influence the expansion rate and therapy response of cells carrying the same clonal hematopoiesis oncogenic driver.

Epigenetic regulation by ASXL1 in myeloid malignancies.

Myeloid malignancies areclonal hematopoietic disorders that are comprised of a spectrum of genetically heterogeneous disorders, including myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), chronic myelomonocytic leukemia (CMML), and acute myeloid leukemia (AML). Myeloid malignancies are characterized by excessive proliferation, abnormal self-renewal, and/or differentiation defects of hematopoietic stem cells (HSCs) and myeloid progenitor cells hematopoietic stem/progenitor cells (HSPCs). Myeloid malignancies can be caused by genetic and epigenetic alterations that provoke key cellular functions, such as self-renewal, proliferation, biased lineage commitment, and differentiation. Advances in next-generation sequencing led to the identification of multiple mutations in myeloid neoplasms, and many new gene mutations were identified as key factors in driving the pathogenesis of myeloid malignancies. The polycomb protein ASXL1 was identified to be frequently mutated in all forms of myeloid malignancies, with mutational frequencies of 20%, 43%, 10%, and 20% in MDS, CMML, MPN, and AML, respectively. Significantly, ASXL1 mutations are associated with a poor prognosis in all forms of myeloid malignancies. The fact that ASXL1 mutations are associated with poor prognosis in patients with CMML, MDS, and AML, points to the possibility that ASXL1 mutation is a key factor in the development of myeloid malignancies. This review summarizes the recent advances in understanding myeloid malignancies with a specific focus on ASXL1 mutations.

Characteristics of Germline CHEK2 Mutated Patients in a Large Cohort of 2322 Myeloid Malignancies

Background Checkpoint kinase 2 (CHEK2) is a critical mediator of the DNA damage response and plays a role in DNA double strand break-induced apoptosis and cell cycle arrest (Bartek, 2003). Deleterious germline CHEK2 variants (CHEK2germ) have been associated with an increased risk for breast, colon, prostate, thyroid and kidney cancers (Cybulski, 2004). Early studies suggested that germline CHEK2 variants also predispose to myeloid malignancies, including myelodysplastic syndromes (MDS) (Janiszewska, 2018). Recently, CHEK2 was identified as the most frequent germline mutated gene in a cohort of 391 adult patients with AML (Yang, 2022). However, more data is warranted to clarify the role of germline CHEK2 mutations in the development of myeloid malignancies. Here we analyzed the prevalence of germline CHEK2 variants in a large series of unselected patients diagnosed with myeloid malignancies and describe their clinical features. Methods Between February 2018 and June 2022, 2322 consecutive adult patients diagnosed at Saint-Louis hospital, Paris with a myeloid malignancy were included in the study. DNA obtained from bone marrow or peripheral blood cells was subjected to capture-based next-generation sequencing of genes recurrently mutated in myeloid malignancies, including CHEK2. In selected patients, germline mutation testing was performed using Sanger sequencing of DNA obtained from skin fibroblasts or sorted CD3-positive cells from peripheral blood. Results We identified a CHEK2 variant in 38 out of 2322 (1.6%) unrelated patients. We focused on the 24 patients with a variant allele frequency (VAF) equal or higher than 40%, highly suggestive of a germline origin, which was subsequently confirmed in all patients with available germline DNA. Of these, 16 variants (Fig1 A) were considered as pathogenic/likely pathogenic (P/LP) according to the American College of Medical Genetics as well as 3 missense variants which were semi-functional in an in-vivo, yeast-based, functional assay (Delimitsou, 2019). The 5 remaining variants were considered of unknown significance (VUS). Finally, 19 CHEK2germ variants were considered causal for the myeloid malignancy representing a frequency of 0.8% (19/2322). Noteworthy, two out of them (10.5%) had a second somatic hit in CHEK2. (Fig1 B) The median age of the 19 CHEK2germ patients was 75 years (42-87) at diagnosis of the hematological disease. According to the revised WHO classification, there were 7 (37%) MDS-MLD, 2 (11% ) MDS-RS, 4 (21%) MDS-EB, 3 (16%) MPN, 2 (11%) AML, and 1 (5%) ICUS. Karyotype was normal in 7 patients (39%), 8 patients had an isolated abnormality, 3 patients had a complex karyotype and one had cytogenetic failure. Additional driver mutations (Fig 1 B) were identified in most patients (18/19, 95%), however no particular association was noticed. Seven patients (37%) had a personal history of cancer (prostate n=4, breast n=1, thyroid n=1, colon n=1). Five patients (26%) had a family history of hematologic disorders (MPN, n=2, multiple myeloma n=2, ICUS n=1) and 7 patients (37%) of non-hematological cancer (breast n=2, brain n=2, lung n=1, ovary n=1, intestinal n=1). Eleven patients were classified as low-risk MDS according to the IPSS classification with a median survival of 5.6 years. They mainly received ESA (N=2) or lenalidomide (N=2). Among the 3 high-risk MDS patients 2 received hypomethylating agent with a survival of 5 and 1.7 years, the remaining one is still alive after sequential bone marrow transplant. One AML patient is still receiving hypomethylating agent with BCL2-inhibitor in complete remission with a follow up of 1.1 year, while the other AML patient died of relapse after 2 sequential bone marrow transplants. Regarding the 3 MPN patients, 1 is still alive after 1.3 year and the 2 others died 11.5 and 3.8 years after diagnosis. Conclusion This is the largest study addressing the frequency (0.8%) and characteristics of carriers of germline CHEK2 pathogenic variants within patients with myeloid disorders. Their presentation is rather heterogenous with a majority of low-risk MDS. They did not appear to have a more complex karyotype or a poorer prognosis and seems to be less frequent than previously suggested. Compared to more frequent genetic predisposition to myeloid malignancies like DDX41, CHEK2germ hematological malignancies did not seem to represent a specific entity, in line with recent debate on CHEK2germ solid cancer. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Alemtuzumab and Eltrombopag Combination for Patients with Refractory or Relapsed Severe Aplastic Anemia

Background: Immune aplastic anemia (AA) results from cytotoxic T-lymphocyte-mediated destruction of hematopoietic stem cells. Although upfront immunosuppressive therapy (IST) is effective, patients, with relapsed and refractory disease need further treatment with a second round of IST or bone marrow transplantation (BMT). In this retrospective study, we assess the safety and efficacy of alemtuzumab combined with eltrombopag (EPAG) as second-line IST. Methods: Severe AA patients who relapsed after or were refractory to IST (horse anti-thymocyte globulin, cyclosporine and EPAG) were treated with alemtuzumab and EPAG in combination at the Clinical Center between 2017-2022. Alemtuzumab was given as previously reported in SAA: 10 mg/dose/day for 10 days as an intravenous infusion after a 1 mg test dose in adults and in children < 50Kg, 0.2mg/kg/day for 10 days (not to exceed 10 mg/day). EPAG was administered at 150 mg daily in adults and weight based for children as previously reported. Periodic blood counts and bone marrow evaluations were performed to assess for response and progression to myeloid malignancy. Toxicity was assessed based on the previous profile of the two drugs. Results: Six patients were included with a median age of 16 years (range 13- 39 years); half were children. Four of six had very severe disease at SAA presentation and the majority were refractory to initial IST. Two patients with relapsed SAA had achieved a response to IST at 6-month evaluation but then had declining blood counts at 60 and 49 days, respectively. All patients received alemtuzumab as second-line IST (Table 1). EPAG was subsequently added at a median of 60 days from alemtuzumab administration (range 26 days - 199 days) when there was no signs of response or when the counts declined further, .was performed at 3-months and 6-months from EPAG addition. Both patients with relapsed disease achieved a response at 6-month evaluationUPN3 showed early partial response (PR) at 3-months and then ultimately achieved a complete response (CR); at last follow-up, EPAG was being down-titrated with stable blood counts and no signs of evolution to myeloid malignancy. UPN4 achieved a PR at 6 months and at last follow-up maintained stable counts despite discontinuation of EPAG. Of the four refractory patients, only one (UPN1), responded to the addition of EPAG and continued treatment for 2 years. While the EPAG was reduced in dosage, evaluation for declining blood counts with a bone marrow biopsy revealed progression to acute myeloid leukemia, with monosomy 7 and an ASXL1 clone at 24% variant allele frequency. The patient achieved normal blood counts post BMT. Two of the non-responders (UPN2 and UPN5) died from SAA complications; UPN2 died shortly after BMT from refractory infection. UPN6 also had refractory disease; she is 5 months from alemtuzumab and 3 months from EPAG treatment without a response undergoing evaluation for BMT. Patients that responded (UPN1, UPN3, and UPN4) had a median hemoglobin baseline of 7 g/DL (range 6-7.6 g/DL) and increased to a median of 9.3 g/DL (range 8.4-11.6 g/DL), 6 months after EPAG. Responders had a median ANC baseline of 0.69 k/mcL (range 0.46-1.58 k/mcL) and increased to a median of 1.5 k/mcL(range 1.5-2.11). At baseline they also presented with a median platelet of 17 k/mcL at baseline (range 5-18 k/mcL) and increased to 23 k/mcL (range 23-37 k/mcL), 6 month,s after EPAG. None of the patients had toxicity, specifically liver function abnormalities, with the addition of EPAG. The median AST and ALT were 36 U/L (range 20-66 U/L) and 93 U/L (range 13-170 U/L) 6 months after EPAG, respectively. Patients had a median total bilirubin of 0.4 mg/DL (range 0.3-0.9 mg/DL). Conclusion: In absence of BMT, second-line IST is administered for relapsed and refractory SAA patients. The addition of EPAG to alemtuzumab after 1-3 months resulted in responses in relapsed patients but not in refractory cases. The combination was safe without increased toxicities, but prolonged use of EPAG in a single refractory patient associated with development of myeloid malignancy. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

A Circulating Microbial Metabolite Drives the Clonal Expansion of Pre-Leukemic Cells

Inflammatory mediators, including cytokines and microbial ligands, are implicated in the development of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). A consequence of aging and various autoimmune and inflammatory conditions is loss of intestinal barrier integrity and translocation of microbial species and metabolites into circulation. More recent findings revealed that patients with inflammatory bowel disease (IBD) harbor mutant hematopoietic clones and often present with clinical manifestations of MDS/AML. Moreover, intestinal barrier dysfunction is commonly reported at diagnosis in patients with MDS and AML. These observations led us to speculate that microbial-derived signals may contribute to the expansion of pre-leukemic hematopoietic stem and progenitor cells (HSPCs) and development of myeloid malignancies. To determine if loss of intestinal barrier integrity contributes to the expansion of pre-leukemic DNMT3a-mutant HSPCs, we generated a model of IBD by inducing gut epithelial injury using dextran sulfate sodium (DSS). Upon gut epithelial injury, we observed a significant expansion of DNMT3a-mutant HSPCs, but not of wild-type (WT) HSPCs, in vivo. Unexpectedly, DNMT3a-mutant HSPCs do not exhibit a competitive advantage over WT cells in the absence of intestinal barrier dysfunction, such as following DSS or high-dose radiation. Fecal material from DSS-treated WT mice was sufficient to induce expansion of DNMT3a-mutant HSPCs and this expansion was prevented with broad-spectrum antibiotics. These findings indicate that the competitive advantage of DNMT3a-mutant HSPCs following gut epithelial injury was due to alterations in the microbiome. In parallel sequencing studies, we identified a significant enrichment of gram-negative bacterial phyla in stool samples from the IBD mouse model, IBD patients, and treatment-naive AML patients. All gram-negative bacteria uniquely generate a microbial intermediate, ADP-heptose, as part of the lipopolysaccharide biosynthesis pathway. ADP-heptose can enter the blood circulation and freely translocate into cells and activate the ALPK1-TIFA complex ("TIFAsome"). Alpha-protein kinase 1 (ALPK1) and tumor necrosis factor receptor-associated factor (TRAF)-interacting protein with an FHA domain (TIFA) are overexpressed in primary human MDS and AML HSPCs as compared to healthy donors and their expression is correlated with poor prognosis. Gram negative bacteria and corresponding ADP-heptose levels were also significantly increased in the plasma of individuals with intestinal barrier injury, such with IBD, MDS, or upon aging, as compared to young healthy individuals. The circulating levels of ADP-heptose from aged individuals and IBD or MDS patients were sufficient to induce the TIFAsome in leukemic cells. Moreover, administration of disease relevant levels of ADP-heptose resulted in expansion and enhanced function of mouse DNMT3a-mutant HSPCs and of human AML cell lines and primary MDS cells in vivo. Expansion of DNMT3a-mutant HSPCs and human MDS/AML cells was directly related to overexpression of ALPK1, as WT HSPCs or ALPK1-deficient AML cells did not respond to ADP-heptose. To gain deeper mechanistic insight, we examined global transcriptional and epigenetic changes in purified WT and DNTM3a-mutant HSCs treated with ADP-heptose. DNMT3a-mutant HSCs treated with ADP-heptose resulted in epigenetic changes and increased expression of gene programs related to non-canonical NF-kB, ERK/MAPK, cell cycle activation, cell survival, and stem cell function. Indeed, ADP-heptose caused increased cycling and self-renewal of DNMT3a-mutant HSPCs, but not WT HSPCs, via the TIFAsome in vitro and in vivo. Based on the enriched pathways in DNMT3a-mutant HSCs treated with ADP-heptose, we screened small molecule inhibitors of TIFAsome activation. We found that targeting UBE2N abrogated ADP-heptose-mediated signaling via the TIFAsome and expansion of patient-derived AML xenografts. In summary, we report that conditions leading to intestinal barrier dysfunction and circulating ADP-heptose from gram-negative bacteria induce expansion of pre-leukemic and MDS/AML cells via ALPK1-TIFA. Lastly, we provide a potential therapeutic strategy to prevent the competitive advantage of pre-leukemic cells prior to overt malignant transformation.

Micro-environment alterations through time leading to myeloid malignancies.

The micro-environment plays a critical role in haematopoietic stem cell (HSC) development, self-renewal, differentiation and maintenance by providing a supportive cellular framework and essential molecular cues to sustain homeostasis. In ageing and development of age-related clonal haematopoiesis, the combined contribution of intrinsic alterations in haematopoietic stem cells and their surrounding micro-environment can promote myeloid skewing and release of pro-inflammatory cytokines. A pro-inflammatory micro-environment is a common feature in the initiation and sustenance of several myeloid malignancies. Furthermore, remodelling of the micro-environment is recognized to potentiate the survival of malignant over normal cells. This review explores micro-environmental interactions in the haematopoietic system of adults, especially how the bone marrow micro-environment is impacted by ageing, the onset of age-related clonal haematopoiesis and the development of myeloid malignancies. In addition, we also discuss the possible role age-related clonal haematopoiesis and chronic inflammatory conditions play in altering the bone marrow micro-environment dynamics. Finally, we explore the importance of in vitro models that accurately mimic different aspects of the bone marrow micro-environment in order to study normal and malignant haematopoiesis. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

3044 – IP-10 LOSS MODULATES ERYTHROID CELL PRODUCTION IN MOUSE MODELS OF MYELOPROLIFERATIVE NEOPLASMS

The malignant transformation of hematopoietic stem cells (HSCs) is a multi-step process. In myeloproliferative neoplasms (MPNs), the JAK2 V617F missense mutation is found in most patients and loss of function TET2 mutations co-occur in approximately 10% of patients. Despite comprehensive genomic profiling, disease heterogeneity exists amongst individuals which cannot be solely resolved by genetic approaches. The microenvironment surrounding HSCs can be diverse and dynamic and deregulated cytokine levels have been implicated in the development of myeloid malignancies. One molecule in particular, IP-10/CXCL10, correlated strongly with disease severity and with JAK2 / TET2 mutational status with highest levels present in the serum of double-mutant patients and in JAK2/TET2 double-mutant mouse models compared to wild-type controls and to other MPN mouse models (e.g., CALRdel52) which recapitulate the MPN phenotype. To test the potential functional role of IP-10 in disease development and maintenance, we generated an allelic series of mutant mouse models carrying mutations in the JAK2, TET2 and IP10 genes. In transplantation experiments, JAK2/TET2 double mutant cells were slowed in their ability to drive an MPN in IP-10-/- animals, but eventually developed a strong disease phenotype, suggesting that the mutant clone itself eventually begins to produce IP-10. In double-mutant JAK2V617F/ V617F IP-10-/- models and triple mutant JAK2V617F/ V617F TET2-/- IP-10-/-, partial amelioration of disease phenotype in some animals as measured by serial monitoring of peripheral blood hemoglobin and hematocrit levels as well as erythroid differentiation assays. Together, these studies suggest that IP-10 may play a role in disease modulation at the red cell progenitor stage and set the stage for future studies exploring its reduction as a potential therapeutic modality in MPNs. The malignant transformation of hematopoietic stem cells (HSCs) is a multi-step process. In myeloproliferative neoplasms (MPNs), the JAK2 V617F missense mutation is found in most patients and loss of function TET2 mutations co-occur in approximately 10% of patients. Despite comprehensive genomic profiling, disease heterogeneity exists amongst individuals which cannot be solely resolved by genetic approaches. The microenvironment surrounding HSCs can be diverse and dynamic and deregulated cytokine levels have been implicated in the development of myeloid malignancies. One molecule in particular, IP-10/CXCL10, correlated strongly with disease severity and with JAK2 / TET2 mutational status with highest levels present in the serum of double-mutant patients and in JAK2/TET2 double-mutant mouse models compared to wild-type controls and to other MPN mouse models (e.g., CALRdel52) which recapitulate the MPN phenotype. To test the potential functional role of IP-10 in disease development and maintenance, we generated an allelic series of mutant mouse models carrying mutations in the JAK2, TET2 and IP10 genes. In transplantation experiments, JAK2/TET2 double mutant cells were slowed in their ability to drive an MPN in IP-10-/- animals, but eventually developed a strong disease phenotype, suggesting that the mutant clone itself eventually begins to produce IP-10. In double-mutant JAK2V617F/ V617F IP-10-/- models and triple mutant JAK2V617F/ V617F TET2-/- IP-10-/-, partial amelioration of disease phenotype in some animals as measured by serial monitoring of peripheral blood hemoglobin and hematocrit levels as well as erythroid differentiation assays. Together, these studies suggest that IP-10 may play a role in disease modulation at the red cell progenitor stage and set the stage for future studies exploring its reduction as a potential therapeutic modality in MPNs.

Diagnostic Approach, Clinical Implications and Management of Clonal Cytopenia of Undetermined Significance

Due to demographic aging of the general population, cytopenia and especially anemia of unknown origin is on the rise, with an increasing need for a structured clinical assessment of these conditions. The advent of next-generation sequencing (NGS) in our clinical practice has facilitated the detection of clonal hematopoiesis (CH), which is present in more than 20−40% of individuals above 80 years of age. This poses unprecedented challenges as CH, especially clonal cytopenia of undetermined significance (CCUS), is associated with the development of myeloid malignancies, cardiovascular diseases and other chronic inflammatory-degenerative conditions. CH comprises an array of entities that are distinct from overt myeloid malignancies, but consensus recommendations are currently lacking for the management of affected patients. Many questions remain unsolved, such as which patients with unclear cytopenia should undergo molecular testing, what distinguishes age-associated CH from overt hematological malignancy, how CH impacts comorbidities and what might be the most appropriate treatment plan. In this review, we provide a structured approach to the assessment of unclear cytopenia and summarize the clinical implications of CH, as well as our current management of CCUS patients.

Functional Roles of DDX41 Mutations in the Development of Myeloid Malignancies

▪DDX41 is a newly identified leukemia predisposition gene encoding an RNA helicase, whose germline mutations are tightly associated with late-onset myeloid malignancies. Importantly, germline DDX41 mutations were also found in as many as ~7 % of sporadic cases of high-risk MDS, conferring the largest germline risk for myeloid malignancies. In typical cases, a germline loss-of-function allele (most commonly p.A500fs or p.D140fs, depending on the ethnicity) is compounded by a somatic missense mutation affecting the helicase domain in the remaining allele (p.R525H). However, little is known about the molecular mechanism by which DDX41 mutations lead to myeloid neoplasms.To clarify the role of these distinct DDX41 alleles, we generated mice models carrying either or both of conditional/constitutive Ddx41 knock-out (KO) and conditional R525H knock-in (KI) alleles. BM-specific biallelic Ddx41 deletion using Vav1-Cre resulted in embryonic lethality, suggesting that Ddx41 is indispensable for normal hematopoietic development. Next, by crossing these mice and further breeding with Rosa26-CreERT2 transgenic mice, we engineered mice that were wild-type for Ddx41 (Ddx41+/+), heterozygous Ddx41 KO (Ddx41+/-), homozygous Ddx41 KO (Ddx41-/-), heterozygous for the Ddx41 R525H mutation (Ddx41R525H/+), or hemizygous for the Ddx41 R525H mutation (Ddx41R525H/-), in which expression of the mutant allele was induced by tamoxifen administration.First, we assessed cell intrinsic effects of these Ddx41 alleles, using noncompetitive transplantation experiments. Shortly after tamoxifen administration, most of the recipient mice that were reconstituted with BM from Ddx41-/- or Ddx41R525H/- mice died within a month after CreERT2 induction due to severe BM failure (BMF). None of the mice transplanted with BM from Ddx41+/+, Ddx41+/- or Ddx41R525H/+ mice developed myeloid neoplasms.We also assessed the reconstitution capacity of whole BM cells from different Ddx41 mutant mice in competitive transplantation experiments. The donor chimerism of Ddx41-/- or Ddx41R525H/- mice-derived cells in PB was markedly reduced compared to that of cells derived from Ddx41+/+ mice. In contrast, Ddx41+/- or Ddx41R525H/+ mice-derived cells showed no significant changes in competitive bone marrow reconstitution compared to Ddx41+/+ mice-derived cells. Notably, about half of the recipient mice died due to BMF when Ddx41R525H/--derived BM cells were co-transplanted with Ddx41+/--derived BM cells but not with wild-type BM cells, suggesting some non-cell autonomous effect of Ddx41R525H/- cells on Ddx41+/- cells.Transcriptome analysis of stem cells (Kit +Sca-1 -Lin low cells) from different Ddx41 mutant mice revealed significant changes in gene expression and splicing patterns in many genes in stem cells from all the mutant mice, with larger changes for Ddx41R525H/- than Ddx41+/- or Ddx41R525H/+ cells. Notably, Ddx41R525H/- -derived stem cells exhibited a significant upregulation of genes involved in innate immunity, including an upregulation of cGAS-STING innate immunity pathways, as well as an enhanced Trp53 pathway, whereas there was a downregulation of genes related to RNA metabolism and ribosome biogenesis. Proteomics analysis confirmed the significant downregulation of ribosomal proteins in hematopoietic cells derived from Ddx41R525H/- mice.In summary, our results revealed an essential role of Ddx41 in normal hematopoiesis. While both heterozygous Ddx41 KO and heterozygous R525H knock-in did not develop myeloid neoplasm, compound biallelic loss-of function and R525 alleles led to a compromised function of hematopoietic stem cells, which was evident from reduced competitive repopulation capacity and impaired hematopoietic differentiation, where activated innate immunity and impaired ribosome functions may play important roles. Their roles in myeloid neoplasms need further evaluation. DisclosuresNakagawa: Sumitomo Dainippon Pharma Oncology, Inc.: Research Funding. Kataoka: Celgene: Honoraria; Eisai: Honoraria; Astellas Pharma: Honoraria; Novartis: Honoraria; Chugai Pharmaceutical: Honoraria; AstraZeneca: Honoraria; Sumitomo Dainippon Pharma: Honoraria; Kyowa Kirin: Honoraria; Janssen Pharmaceutical: Honoraria; MSD: Honoraria; Takeda Pharmaceutical: Honoraria; Otsuka Pharmaceutical: Honoraria; Asahi Genomics: Current equity holder in publicly-traded company; Otsuka Pharmaceutical: Research Funding; Chordia Therapeutics: Research Funding; Chugai Pharmaceutical: Research Funding; Takeda Pharmaceutical: Research Funding; Bristol-Myers Squibb: Research Funding; Eisai: Other: Scholarship; Otsuka Pharmaceutical: Other: Scholarship; Ono Pharmaceutical: Other: Scholarship; Kyowa Kirin: Other: Scholarship; Shionogi: Other: Scholarship; Takeda Pharmaceutical: Other: Scholarship; Summitomo Dainippon Pharma: Other: Scholarship; Chugai Pharmaceutical: Other: Scholarship; Teijn Pharma: Other: Scholarship; Japan Blood Products Organization: Other: Scholarship; Mochida Pharmaceutical: Other: Scholarship; JCR Pharmaceuticals: Other: Scholarship; Genetic Alterations: Patents & Royalties: PD-L1 abnormalties . Ogawa: Ashahi Genomics: Current holder of individual stocks in a privately-held company; Otsuka Pharmaceutical Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding; Kan Research Laboratory, Inc.: Consultancy, Research Funding; Dainippon-Sumitomo Pharmaceutical, Inc.: Research Funding; ChordiaTherapeutics, Inc.: Consultancy, Research Funding.

Functional Characterization of Compound DDX41 Germline and Somatic R525H Mutations in the Development of Myeloid Malignancies

DDX41 is a newly identified leukemia predisposition gene encoding an RNA helicase, whose germline mutations are tightly associated with late-onset myeloid malignancies. Importantly, germline DDX41 mutations were also found in as many as ~7 % of sporadic cases of high-risk MDS, conferring the largest germline risk for myeloid malignancies. In typical cases, a germline loss-of-function allele (most commonly p.A500fs or p.D140fs, depending on the ethnicity) is compounded by a somatic missense mutation affecting the helicase domain in the remaining allele (p.R525H). However, the molecular mechanism by which DDX41 mutations lead to myeloid neoplasms have not been elucidated. To clarify the role of these distinct DDX41 alleles, we generated mice models carrying either or both of conditional/constitutive Ddx41 knock-out (KO) and conditional R525H knock-in (KI) alleles. Vav1-Cre mediated homozygous deletion of Ddx41 resulted in embryonic lethality, suggesting that Ddx41 is indispensable for normal hematopoiesis. Next, by crossing these mice and further breeding with Rosa26-CreERT2 transgenic mice, we engineered mice that were wild-type for Ddx41 (Ddx41+/+), heterozygous Ddx41 KO (Ddx41+/-), heterozygous for the Ddx41 R525H mutation (Ddx41R525H/+), or hemizygous for the Ddx41 R525H mutation (Ddx41R525H/-), in which expression of the mutant allele was induced by tamoxifen administration. First, we assessed cell intrinsic effects of these Ddx41 alleles, using noncompetitive transplantation experiments. Shortly after tamoxifen administration, most of the recipient mice that were reconstituted with BM from Ddx41R525H/- mice died within a month after CreERT2 induction due to severe BM failure (BMF) with no development of myeloid neoplasms. However, about 20% of mice transplanted with BM derived from Ddx41R525H/- mice survived longer without showing BMF. These mice exhibited macrocytic anemia and increased platelet counts four months after tamoxifen-induction. In contrast, mice transplanted with BM from Ddx41+/- and Ddx41R525H/+ animals showed increased white blood cell counts compared to those with BM from Ddx41+/+ mice. In flow cytometry, Ddx41R525H/--derived BM-transplanted mice showed a significant increase in the number of long-term and short-term hematopoietic stem cells (HSCs), common myeloid progenitors (CMPs) and granulocyte/macrophage lineage-restricted progenitors (GMPs), compared to those transplanted with BM from Ddx41+/+, Ddx41+/- or Ddx41R525H/+ mice. Single cell RNA-seq of lineage negative cell fractions from these mice also revealed expanded stem cell fractions in mice transplanted with BM from Ddx41R525H/- mice, even though there was impaired formation of mature peripheral blood cells, which was suggestive of impaired HSPC differentiation. We also assessed the reconstitution capacity of whole BM cells from different Ddx41 mutant mice in competitive transplantation experiments. The donor chimerism of Ddx41R525H/- mice-derived cells in PB was reduced compared to that of cells derived from Ddx41+/+, Ddx41+/- or Ddx41R525H/+ mice. Transcriptome analysis of stem cells (Kit+Sca-1-Linlow cells) from different Ddx41 mutant mice revealed significant changes in gene expression and splicing patterns in many genes in stem cells from all the mutant mice, with larger changes for Ddx41R525H/- than Ddx41+/- or Ddx41 R525H/+ cells. Notably, Ddx41R525H/- cells exhibited a significant upregulation of genes involved in innate immunity, whereas there was a downregulation of genes related to RNA metabolism and ribosome biogenesis. Proteomics analysis confirmed the significant downregulation of ribosomal proteins in hematopoietic cells derived from Ddx41R525H/- mice. In summary, our results revealed an essential role of Ddx41 in normal hematopoiesis. While both heterozygous Ddx41 KO and heterozygous R525H knock-in did not develop myeloid neoplasm, compound biallelic loss-of function and R525 alleles led to a compromised function of hematopoietic stem cells, which was evident from reduced competitive repopulation capacity and impaired hematopoietic differentiation, where activated innate immunity and impaired ribosome functions may play important roles. Their roles in myeloid neoplasms need further evaluation. Disclosures Nakagawa: Sumitomo Dainippon Pharma Co., Ltd.: Research Funding. Inagaki:Sumitomo Dainippon Pharma Co., Ltd.: Current Employment. Kataoka:Takeda Pharmaceutical Company: Research Funding; Asahi Genomics: Current equity holder in private company; CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Otsuka Pharmaceutical: Research Funding. Ogawa:KAN Research Institute, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Chordia Therapeutics, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Eisai Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co., Ltd.: Research Funding; Asahi Genomics Co., Ltd.: Current equity holder in private company.

Relation between mutations in the 5′ UTR of ANKRD26 gene and inherited thrombocytopenia with predisposition to myeloid malignancies. An Egyptian study

Inherited thrombocytopenias are a heterogeneous group of diseases characterized by a reduced number of platelets and a bleeding tendency that ranges from very mild to life threatening especially in surgery. Mutations in the 5′ untranslated region (UTR) of Ankirin repeat domain 26 (ANKRD26) are responsible for autosomal-dominant form of thrombocytopenia, that is known as ANKRD26-related thrombocytopenia (ANKRD26 RT), characterized by a moderate thrombocytopenia with mild propensity to bleeding and predisposition to hematological malignancies including AML and MDS. We included 90 unrelated patients with inherited thrombocytopenia. In addition, we investigated 45 patients with ITP. Peripheral blood and bone marrow samples were collected and examined and molecular detection of mutations in the 5︡ UTR of ANKRD26 gene was performed for all the patients. Also, screening of the mutation and development of myeloid malignancies in the extended series of the affected subjects was done. ANKRD26 mutations were identified in 10% of the patients with inherited thrombocytopenia. The most common types were c.128 G > A and c.127A>T, while no mutations were found in the ITP group. In those affected, the median number of platelets was 69 x109/L (43–106) with normal MPV in most of the patients (9.4–11.6). There was a statistically significant increase in the unexpected high frequency of myeloid malignancies in the extended series of the mutated subjects compared with the ITP group-extended series (P < .001). So, we can conclude that ANKRD26 RT is associated with increased risk for developing myeloid malignancies and ANKRD26 mutations can represent a valuable tool for making therapeutic decisions.

CRISPR/Cas9-Targeted De Novo DNA Methylation Is Maintained and Impacts the Colony Forming Potential of Human Hematopoietic CD34+ Cells

Introduction The epigenome is significantly perturbed in hematological malignancies with global DNA hypomethylation and localized hypermethylation of gene promoter CpG islands. Whether specific gene promoter hypermethylation can contribute to the clonal expansion of hematopoietic stem and progenitor cells (HSPCs) in humans by affecting HSPC biology, independently of genetic mutations, has not previously been investigated due to the lack of appropriate tools. We show for the first time that it is possible to target de novo DNA methylation using CRISPR/Cas9 in human CD34+ cells isolated from cord blood (CB). DNA methylation targeted to key cell cycle control gene promoters, INK4b (p15) and ARF (p14), is permanently maintained after dCas9 3A3L degradation and inherited as cells differentiate; inhibiting gene expression and affecting the colony forming potential of CD34+ cells. This demonstrates that specific DNA hypermethylation events can permanently change HSPC biology and impact differentiation, potentially contributing to pre-malignant processes. Methods Human CD34+ HSPCs were isolated from human CB and maintained in liquid culture for 24 hours before nucleofection with mRNA encoding an adapted form of CRISPR/Cas9 which has no nuclease activity (dCas9) and is fused to the catalytic domain of DNA methyltransferase 3A (DNMT3A) and 3L (3A3L). The nucleofection cocktail contained dCas9 3A3L or dCas9 3A3L-mut (lacks methyltransferase activity) and 1 to 3 guide RNAs to target DNA methylation to combinations of the INK4a-ARF-INK4b locus. Cells were then seeded into methylcellulose for a primary colony forming assay (CFU). Colonies were scored after 14 days and cells were either harvested and pooled or individual colonies were picked for single-colony molecular analyses. The DNA was extracted and methylation at the INK4a-ARF-INK4b promoters was quantified using targeted bisulfite sequencing; target gene expression was measured using qPCR. The remaining cells from the primary CFU were re-plated a second (secondary CFU) and third (tertiary CFU) time and colonies were again scored after 14 days. Results and Conclusions Targeting DNA methylation to the INK4a-ARF-INK4b locus or INK4b individually in human CD34+ cells resulted in maintenance of hypermethylation at ARF and/or INK4b gene promoters in individual BFU-E (burst-forming unit-erythroid) and CFU-GM (granulocyte, macrophage) colonies as measured by single-colony targeted bisulfite sequencing after the primary CFU; causing heritable repression of INK4b gene expression in the differentiated cells. Some CpGs were up to 90% methylated, indicating that DNA methylation added at these gene promoters is highly stable as cells differentiate. Hypermethylation of ARF and INK4b was found in some colonies even after the tertiary CFU, demonstrating long-term maintenance of promoter hypermethylation. Unexpectedly, no DNA hypermethylation was detected at INK4a in differentiated cells, but whether this is the case for all subpopulations of HSPCs (i.e. HSCs or lymphoid progenitors) is under investigation. Hypermethylation of INK4b and ARF increased the colony forming potential of CD34+ cells in primary, secondary and tertiary CFUs, compared to the control. Conversely, methylation targeted to INK4b alone did not significantly affect the number of colonies in the first CFU, and decreased the number of colonies in the secondary CFU. This suggests a complex interplay between key cell cycle regulators ARF and INK4b in CD34+ cells and during differentiation which can be disrupted by DNA hypermethylation and gene repression. These findings demonstrate the novel insights we can gain by using CRISPR/Cas9 tools to target DNA methylation and these investigations will reveal how gene promoter hypermethylation can impact HSPC function. Furthermore, studying this locus may uncover an important role for DNA hypermethylation in the development of myeloid malignancies, since INK4b is frequently hypermethylated, but rarely mutated, in myeloid dysplastic/proliferative neoplasms and acute myeloid leukemia. Disclosures Gribben: Janssen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Acerta/Astra Zeneca: Consultancy, Honoraria, Research Funding.

Effect of TP53 contact and conformational mutations on cell survival and erythropoiesis of human hematopoietic stem cells in a long term culture model.

TP53 deficiencies characterize myeloid malignancies with a dismal prognosis. To unravel the pathomechanism of TP53 mutations in the development of myeloid malignancies, we analyzed the functional properties of TP53 conformational and contact mutations and TP53 loss in human CD34+ cells. We show for the first time that the analyzed conformational mutations lead to higher cell viability in human hematopoietic stem progenitor cells. In contrast to these conformational mutations, contact mutations interfered with efficient erythropoiesis.These findings show that not only the detection of a TP53 mutation is important, but also the specific mutation may play a role in malignant transformation and progression.

Frequency and Evolution of TP53 Mutant Clones in Shwachman Diamond Syndrome. a Cohort Study from the French Severe Chronic Neutropenia (SCN) Registry

Context: Shwachman Diamond disease (SDS) is caused by an SBDS mutation, is typically associated with neutropenia and exocrine pancreas deficiency. Pancytopenia, myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML), are life-threatening complications of SDS. To date, the sole risk factors identified for SDS are early symptoms (before age of 3 months) and mild chronic anemia or thrombocytopenia(1).Methods: To determine which mutations underlie clonal development and leukemic changes in SDS, we screened a series of patients with congenital neutropenias at various time points of follow-up. We used a consensus NGS panel of 41 genes involved in the development of myeloid malignancies (Haloplex® Agilent) (2, 3). Patients with SBDS mutations included in the French Severe Congenital Neutropenia registry or followed in the Leuwen University were screened when bone marrow samples were available as well as other subtypes of congenital neutropenia.Results: Among the 139 SDS patients, bone marrow samples of 23 patients were available for screening at various time points. We found isolated somatic TP53 mutations in 10 cases. In addition one patient had concomitant FLT3 TKD and TP53 mutations, and another patient had the recurrent IDH1 p.Arg132Cys variant. Strikingly, no TP53 mutations were observed when the screening was extended to 70 non-SDS neutropenia patients. None of the 11 SDS patients without any detectable mutations (with a threshold of detection of 0.5%) had any severe hematological expression nor presented any major hematological complications at time of sampling. By contrast, among the 12 SDS patients with somatic mutations, AML or MDS were observed in 3 cases, 1 with the IDH1 mutation (Variant allelic frequency (VAF): 42%), 1 with the recurrent TP53 p.Gly245Ser mutation (VAF:53%), 1 with two TP53 mutations (VAFs : 19% and 37%). Severe cytopenias without MDS or AML were found in 2 other cases, one with an isolated TP53 mutation at 24%, and one with both TP53 and FLT3 mutations around 45%. In the 7 remaining patients, allele frequencies of TP53 variants were found below 2% in four cases, and at 3%, 14%, and 37% in the 3 other patients. By sequential analysis in one patient we found a p.Val272Met variant (1.1% at 9 years) which was no more observed but was replaced by the recurrent p.Arg175His mutation (4% at 12 years and 14% at 15 years). Figure 1 depicts the allele frequencies of the variants with time among the 23 patients. The three patients with MDS / AML died despite hematopoietic stem cell transplantation (HSCT) in two of them. In contrast, the two patients with severe cytopenias and TP53 mutations who were transplanted are doing well three years after HSCT, and no TP53 mutation was detected one year after transplant.Conclusion: TP53 mutations are associated with hematological complications and specifically acquired in SDS when compared to other congenital neutropenias. This is in line with the frequency of complex karyotype MDS/AML in SDS(1). Routine evaluation of TP53 load in SDS patients may offer a powerful tool to screen SDS who may be susceptible to have severe hematological complications in a preemptive transplantation strategy setting.

Targeted Inhibition of STAT/TET1 Axis As a Potent Therapeutic Strategy for Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is one of the most common and fatal forms of hematopoietic malignancies. Over 70% of patients with AML cannot survive over 5 years. Many AML subtypes, such as the MLL -rearranged AMLs, are often associated with unfavorable outcome. Current treatment frequently involves intensive chemotherapy, which impairs the quality of life of the patients. While the incidence of AML is continually rising due to aging, most elder patients cannot bear intensive chemotherapy and are associated with very poor survival. Thus, improved therapeutic strategies with less intensive treatment but a higher cure rate are urgently needed.The Ten-eleven translocation (TET) proteins (including TET1/2/3) are known to be able to convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), leading to DNA demethylation. In contrast to the repression and tumor-suppressor role of TET2 observed in hematopoietic malignancies, we recently showed that TET1, the founding member of the TET family, was significantly up-regulated in MLL -rearranged AML and played an essential oncogenic role. An independent study by Zhao et al. confirmed the essential oncogenic role of Tet1 in the development of myeloid malignancies. Thus, TET1 is an attractive therapeutic target for AML.In order to identify chemical compounds that may target TET1 signaling, we searched the drug-sensitivity/gene expression database of a total of 20,602 chemical compounds in the NCI-60 collection of cancer cell samples. The expression levels of endogenous TET1 showed a significant positive correlation with the responsiveness of cancer cells across the NCI-60 panel to 953 compounds (r > 0.2; P <0.05). We selected the top 120 with the highest r values and tested their effects on cell viability of TET1 -high and TET1 -low AML cell lines. Finally we got two top candidate compounds, NSC-X1 and especially, NSC-X2, with the highest potency of inhibiting cell viability of TET1 -high AML cell, but not TET1 -low cells. Both compounds significantly suppressed cellular TET1 expression levels as well as 5hmC levels in TET1 -high AML cells.Further, secondary bone marrow transplantation followed by drug treatment was carried out to test the in vivo therapeutic effects of NSC-X1 and NSC-X2. Both candidate compounds significantly inhibited MLL-AF9 -induced AML, by prolonging the median survival from 49 days (control) to 94 (NSC-X1) or >200 (NSC-X2) days. Notably, 57% of the NSC-X2 treated mice were cured. In another AML model induced by AML-ETO9a (AE9a), NSC-X1 and NSC-X2 also exhibited remarkable therapeutic effects, with an elongated median survival from 46 days (control) to 95 (NSC-X1) and 122 (NSC-X2) days, respectively.To decipher the molecular mechanism by which NSC-X2 represses TET1 expression, we treated THP-1 AML cells with moderate to high concentration of NSC-X2 for over 100 days and then isolated a set of individual drug-resistant THP-1 single clones. Through RNA-seq of 6 of the NSC-X2-resistant clones, recurrent mutations were found in 14 genes, including JAK1 . Ingenuity pathway analysis (IPA) was used to analyze biological relationships amongst the 14 mutated genes. The top one network identified by IPA involving all of the 14 genes is closely associated with the JAK/STAT5 pathway. Results of chromatin immunoprecipitation (ChIP) assays showed TET1 is one of the direct downstream gene targets of STAT3 and STAT5. Through NMR chemical shift perturbation (CSP) and electrophoretic mobility shift assays (EMSAs), we showed a strong direct association between STAT3/5 DNA binding domain and the TET1 promoter, which could be severely interrupted by NSC-X2. Compared to currently available JAK/STAT inhibitors (e.g., Pacritinib, KW-2449, Stattic, and sc-355979), our compounds (NSC-370284 and UC-514321) exhibit a much higher selectivity and also a higher efficacy in targeting TET1 -high AML.Taken together, we identified chemical compounds NSC-X1 and especially, NSC-X2, as potent inhibitors that significantly and selectively suppress the viability of AML cells with high level of TET1 expression, and dramatically repress the progression of TET1 -high AML in mice. NSC-X2 directly binds STAT3/5 as STAT inhibitors and thereby suppress TET1 transcription and TET1 signaling, leading to potent anti-leukemic effects. Our results highlight the therapeutic potential of targeting the STAT/TET1 axis by selective inhibitors in AML treatment. DisclosuresNo relevant conflicts of interest to declare.

Role of SHP2 in hematopoiesis and leukemogenesis.

SH2 domain-containing tyrosine phosphatase 2 (SHP2), encoded by PTPN11 plays an important role in regulating signaling from cell surface receptor tyrosine kinases during normal development as well as oncogenesis. Herein we review recently discovered roles of SHP2 in normal and aberrant hematopoiesis along with novel strategies to target it. Cell autonomous role of SHP2 in normal hematopoiesis and leukemogenesis has long been recognized. The review will discuss the newly discovered role of SHP2 in lineage specific differentiation. Recently, a noncell autonomous role of oncogenic SHP2 has been reported in which activated SHP2 was shown to alter the bone marrow microenvironment resulting in transformation of donor derived normal hematopoietic cells and development of myeloid malignancy. From being considered as an 'undruggable' target, recent development of allosteric inhibitor has made it possible to specifically target SHP2 in receptor tyrosine kinase driven malignancies. SHP2 has emerged as an attractive target for therapeutic targeting in hematological malignancies for its cell autonomous and microenvironmental effects. However a better understanding of the role of SHP2 in different hematopoietic lineages and its crosstalk with signaling pathways activated by other genetic lesions is required before the promise is realized in the clinic.