Acute Megakaryoblastic Leukemia Research Articles

3093 – SUBTYPE-SPECIFIC INDUCTION OF MITOCHONDRIAL APOPTOSIS AS A NOVEL THERAPEUTIC OPTION IN HIGH-FATALITY PEDIATRIC LEUKEMIA

A rare subtype of acute myeloid leukemia (AML) is acute megakaryoblastic leukemia (AMKL). Recurrent and mutually exclusive oncogenic fusions are detected in AMKL and are considered the transforming event in this disease. AMKL usually affects children below 3 years of age and is associated with less than 40% cure rates. In addition, the development of genotype tailored therapies is urgently needed in AMKL but greatly limited by the paucity of primary sample material. Our research group has established synthetic human models of high-fatality pediatric AMKL, driven by distinct oncogenic fusions, which phenocopy the disease in a patho-physiological context in mice. Inducers of mitochondria-mediated apoptosis, so called BH3 mimetics, recently entered the therapeutic arena in pediatric leukemia with promising results. Therefore, we set out to investigate the potential of Venetoclax (inhibitor of BCL-2) and Navitoclax (inhibitor of BCL-2, BCL-XL and BCL-W) as novel therapeutic options as a bridge to curative bone marrow transplantation in this high-fatality infant leukemia. Our research demonstrates that genetic and pharmacological inhibition of the pro-survival BCL-2 family member BCL-XL results in significant induction of apoptosis in our models of AMKL. In contrast, inhibition of BCL-2 does not induce apoptosis in our models, which is currently the most investigated BCL-family member in the clinic for other subtypes of AML (Venetoclax). In addition, Navitoclax showed promising in vivo activity with a significant decrease in infiltrating leukemic cells in bone-marrow and spleen after drug treatment in comparison to vehicle-only controls. In summary, this project will bring mechanistic insight into the role of apoptotic pathways in AMKL and greatly accelerate the identification of novel therapeutic options in high-fatality infant AML. A rare subtype of acute myeloid leukemia (AML) is acute megakaryoblastic leukemia (AMKL). Recurrent and mutually exclusive oncogenic fusions are detected in AMKL and are considered the transforming event in this disease. AMKL usually affects children below 3 years of age and is associated with less than 40% cure rates. In addition, the development of genotype tailored therapies is urgently needed in AMKL but greatly limited by the paucity of primary sample material. Our research group has established synthetic human models of high-fatality pediatric AMKL, driven by distinct oncogenic fusions, which phenocopy the disease in a patho-physiological context in mice. Inducers of mitochondria-mediated apoptosis, so called BH3 mimetics, recently entered the therapeutic arena in pediatric leukemia with promising results. Therefore, we set out to investigate the potential of Venetoclax (inhibitor of BCL-2) and Navitoclax (inhibitor of BCL-2, BCL-XL and BCL-W) as novel therapeutic options as a bridge to curative bone marrow transplantation in this high-fatality infant leukemia. Our research demonstrates that genetic and pharmacological inhibition of the pro-survival BCL-2 family member BCL-XL results in significant induction of apoptosis in our models of AMKL. In contrast, inhibition of BCL-2 does not induce apoptosis in our models, which is currently the most investigated BCL-family member in the clinic for other subtypes of AML (Venetoclax). In addition, Navitoclax showed promising in vivo activity with a significant decrease in infiltrating leukemic cells in bone-marrow and spleen after drug treatment in comparison to vehicle-only controls. In summary, this project will bring mechanistic insight into the role of apoptotic pathways in AMKL and greatly accelerate the identification of novel therapeutic options in high-fatality infant AML.

3173 – HUMAN MODELS OF PEDIATRIC CBFA2T3-GLIS2 ACUTE MEGAKARYOBLASTIC LEUKEMIA CONTRIBUTE TO UNCOVER THERAPEUTIC VULNERABILITIES

Acute megakaryoblastic leukemia (AMKL) is a poor prognostic subtype of AML afflicting children mostly under 3 years of age. Chromosomal translocations generating chimeric fusion genes are considered critical transforming events and are present in a high proportion of cases. Among them, the CBFA2T3-GLIS2 (CG2) fusion is associated with a high risk of relapse and accounts for ∼15% of pediatric AMKL cases. Using overexpression of CG2 in human cord blood CD34+ stem /progenitor cells (hHSPC) followed by xenotransplantation in immunodeficient mice, we are reporting the generation of multiple synthetic AMKL models that phenocopy the human disease in term of immunophenotype, morphology and gene expression. CG2 models revealed a stable genomic landscape with few copy number anomalies and lack of recurrent cooperating mutations. Leveraging from local and published transcriptomic datasets of CG2 AMKL samples (14 patients, 10 models), non-CG2 pediatric AMKL (n=66), NUP98-KDM5A synthetic models (n=5) and normal hHSPC (n=4), we have determined a robust gene expression signature defining CG2 AMKL. Gene set enrichment analysis of CG2 AMKL expression profile identified the JAK2-STAT5 axis as a potential pathway that is upregulated in CG2 leukemia, confirmed by downstream STAT5 phosphorylation in CG2 cells. Cell surface proteomic analysis by LC-MS identified multiple membrane proteins upstream of JAK-STAT signaling in CG2 model leukemia compared to normal hHSPC. Single-agent dose-response curves conducted with multiple FDA-approved drugs targeting JAK2 showed specific grow inhibition of CG2 AMKL models compared to normal hHSPC and non-AMKL cell line. Progress in leukemia research is hampered by the paucity of patient samples and the generated AMKL models pave the way toward a better understanding of leukemogenesis and development of targeted therapy. Acute megakaryoblastic leukemia (AMKL) is a poor prognostic subtype of AML afflicting children mostly under 3 years of age. Chromosomal translocations generating chimeric fusion genes are considered critical transforming events and are present in a high proportion of cases. Among them, the CBFA2T3-GLIS2 (CG2) fusion is associated with a high risk of relapse and accounts for ∼15% of pediatric AMKL cases. Using overexpression of CG2 in human cord blood CD34+ stem /progenitor cells (hHSPC) followed by xenotransplantation in immunodeficient mice, we are reporting the generation of multiple synthetic AMKL models that phenocopy the human disease in term of immunophenotype, morphology and gene expression. CG2 models revealed a stable genomic landscape with few copy number anomalies and lack of recurrent cooperating mutations. Leveraging from local and published transcriptomic datasets of CG2 AMKL samples (14 patients, 10 models), non-CG2 pediatric AMKL (n=66), NUP98-KDM5A synthetic models (n=5) and normal hHSPC (n=4), we have determined a robust gene expression signature defining CG2 AMKL. Gene set enrichment analysis of CG2 AMKL expression profile identified the JAK2-STAT5 axis as a potential pathway that is upregulated in CG2 leukemia, confirmed by downstream STAT5 phosphorylation in CG2 cells. Cell surface proteomic analysis by LC-MS identified multiple membrane proteins upstream of JAK-STAT signaling in CG2 model leukemia compared to normal hHSPC. Single-agent dose-response curves conducted with multiple FDA-approved drugs targeting JAK2 showed specific grow inhibition of CG2 AMKL models compared to normal hHSPC and non-AMKL cell line. Progress in leukemia research is hampered by the paucity of patient samples and the generated AMKL models pave the way toward a better understanding of leukemogenesis and development of targeted therapy.

Therapy-related acute megakaryoblastic leukemia with severe myelofibrosis.

Therapy-related acute megakaryoblastic leukemia with severe myelofibrosis.

Germline GATA1s-generating mutations predispose to leukemia with acquired trisomy 21 and Down syndrome-like phenotype

AbstractIndividuals with Down syndrome are at increased risk of myeloid leukemia in early childhood, which is associated with acquisition of GATA1 mutations that generate a short GATA1 isoform called GATA1s. Germline GATA1s-generating mutations result in congenital anemia in males. We report on 2 unrelated families that harbor germline GATA1s-generating mutations in which several members developed acute megakaryoblastic leukemia in early childhood. All evaluable leukemias had acquired trisomy 21 or tetrasomy 21. The leukemia characteristics overlapped with those of myeloid leukemia associated with Down syndrome, including age of onset at younger than 4 years, unique immunophenotype, complex karyotype, gene expression patterns, and drug sensitivity. These findings demonstrate that the combination of trisomy 21 and GATA1s-generating mutations results in a unique myeloid leukemia independent of whether the GATA1 mutation or trisomy 21 is the primary or secondary event and suggest that there is a unique functional cooperation between GATA1s and trisomy 21 in leukemogenesis. The family histories also indicate that germline GATA1s-generating mutations should be included among those associated with familial predisposition for myelodysplastic syndrome and leukemia.

Sensitive detection of GATA1 mutations using complementary DNA-based analysis for transient abnormal myelopoiesis associated with the Down syndrome.

GATA1 mutation plays an important role in initiating transient abnormal myelopoiesis (TAM) and in the clonal evolution towards acute megakaryoblastic leukaemia (AMKL) associated with Down syndrome (DS). This study aimed to develop and validate the clinical utility of a complementary DNA (cDNA) analysis in parallel with the conventional genomic DNA (gDNA) Sanger sequencing (Ss), as an initial screening test for GATA1 mutations. GATA1 mutations were evaluated using both gDNA and cDNA in 14 DS patients using Ss and fragment analysis (FA), respectively. The detection sensitivity of conventional gDNA sequencing was limited in low blast percentage TAM (LBP-TAM); however, cDNA-based Ss readily detected all the pathognomonic GATA1 mutations. The cDNA-based FA readily detected GATA1 frameshift mutation with a reliable sensitivity ranging from 0.005% to 0.01% of clonal cells. GATA1 mutations are heterogeneous; therefore, we would like to propose a dual cDNA and gDNA analysis as a standard diagnostic approach, especially for LBP-TAM. cDNA-based FA promises an excellent sensitivity for detecting frameshift GATA1 mutations in the longitudinal clonal evolution towards AMKL without using a patient specific primer.

Prognostic impact of homeobox and PR domain containing protein 16 genes expressions in patients with acute myeloid leukemia

BackgroundThe functions of the HOXA 5, HOXA 9, and PRDM16 are concerned with embryonic growth and the regulation of adult hematopoietic cells differentiation. The HOXA5, HOXA9, and PRDM16 are expressed in the majority of solid cancers and several hematological malignancies, including myeloproliferative disease and acute leukemia. The function and prognostic values of HOXA5, HOXA9, and PRDM16 quantitative PCR expression in novel patients with acute myeloblastic leukemia (AML) were to be studied. MethodsThis prospective case-control study was performed on 60 newly diagnosed AML patients and 40 healthy subjects acting as a control group. The patients underwent CBC, BM analysis, HOXA5, HOXA9, and PRDM16 expression by qRT-PCR testing. ResultsHigh expressions of HOXA5, HOXA9, and PRDM16 were significantly prevalent in patients compared with the control. The highest incidence of expression was found in AML patients with minimal maturation and acute megakaryoblastic leukemia (M1/M7). Interestingly, high levels of HOXA5, HOXA9, and PRDM16 expressions were correlated with older age and hepatosplenomegaly associated with poor clinical outcome, shorter overall and disease-free survival than low levels of HOXA5, HOXA9, and PRDM16 expressions. ConclusionHigh HOXA and PRDM16 expressions predict bad outcomes and are associated with weak prognostic factors which can promote new therapeutic trends for AML.

A Novel Humanized Murine Model to Identify Neoantigen-Specific T Cells in CBFA2T3-GLIS2 Positive Acute Megakaryoblastic Leukemia

CBFA2T3-GLIS2 is an oncogenic fusion gene that acts as the driver mutation in ~18% of pediatric patients with acute megakaryoblastic leukemia (AMKL) that do not have Down syndrome. CBFA2T3-GLIS2 driven leukemia carries the worst prognosis among all pediatric acute myeloid (AML) subtypes, with event free and overall survival probabilities of 8% and 14% respectively. Chemotherapy and stem cell transplantation fail to cure this disease, thus innovative treatment approaches are needed. While monoclonal antibody and chimeric antigen receptor T-cell (CAR-T) therapies have proven successful in acute lymphoblastic leukemia (ALL), similar successes haven't been realized in AML due to the lack of targetable antigens that eradicate leukemia cells while minimizing off target toxicities such as depletion of normal myeloid cells which can lead to prolonged neutropenia. An alternative is T cell receptor engineered T cell (TCR-T) immunotherapy which use heterodimers consisting of alpha and beta peptide chains to recognize polypeptide fragments presented by MHC molecules on the tumor cells. An advantage of this approach is the ability to recognize intracellular tumor specific and tumor associated antigen fragments in addition to extracellular proteins which results in a wider range of targets. To investigate the immunogenicity of CBFA2T3-GLIS2 positive AMKL cells, we established a humanized patient derived xenograft (PDX) murine model by conditioning 15 immunodeficient NSG-SGM3 mice with 200 rads 24 hours prior to transplantation of 3.5 million CBFA2T3-GLIS2 positive PDX cells derived from an individual female patient. After 20 days of engraftment, 2.5 million HLA class I matched PBMCs from an unrelated female donor were introduced. Experimental mice (engrafted with both PDX cells and PBMCs), leukemia only control mice, and PBMC only control mice were sacrificed at days 30, 35, and 40. Flow cytometry analysis at day 40 showed dramatic reduction of leukemic blasts (huCD45lo, huCD34+) when exposed to PBMCs compared to the leukemia only control (1.48% and 93.7%, respectively). Circulating human Granzyme A was elevated at day 40 in the PDX mice with PBMCs compared to the PBMC only control (9665.4 pg/ml vs. 789.7 pg/ml, p<0.001), indicating a potential leukemia-directed cytokine lymphocyte response. Single cell TCR repertoire analysis of CD8+ T cells from day 40 revealed a decrease in alpha beta TCR diversity when exposed to PDX cells compared to the PBMC only control, consistent with a clonal expansion of neoantigen-directed TCRs. Single TCR expressing stable cell lines have been generated for the top expanded clones. In ongoing experiments, we are utilizing these cell lines to assess leukemia clearance in our model and measuring specificity and functionality for the putative neoantigens through tetramer staining and peptide stimulation assays, respectively. For the latter studies, we have taken two approaches for the identification of potential neoantigens that may be directing this observed clonal expansion. First, to interrogate potential neoantigens spanning the fusion junction we used the algorithm from NetMHCcons which identified two peptides with intermediate binding affinity (defined by an IC50 of 150 - 500 nM). Second, we utilized immunopeptidomics to identify HLA class I presented peptides on the surface of the PDX cells. One of our top significant hits was a peptide that corresponds to the 5‘ untranslated region (UTR) of bone morphogenetic protein 2 (BMP2). This peptide fragment was not present in the human Uniprot database, suggesting the 5‘ UTR is not expressed in normal tissues. Although its role in leukemia is not well described, BMP2 is aberrantly upregulated in CBFA2T3-GLIS2 positive AMKL and required for serial replating in colony formation unit assays; therefore, this peptide is of great interest as a candidate leukemia-associated antigen. In summary, our novel humanized PDX model sheds light on the immunogenicity of CBFA2T3-GLIS2 mediated AMKL and the potential for TCR-T immunotherapy in the setting of minimal residual disease for this chemotherapy resistant malignancy. Studies are ongoing to identify the TCR clone(s) responsible for the anti-leukemic response seen in our model and the leukemia-associated antigens that are mediating this response. DisclosuresGruber: Kura Oncology: Consultancy.

Epigenetically Enhanced MED12L in ETO2-GLIS2 Positive Pediatric Acute Megakaryoblastic Leukemia Is Associated with Resistance to the CDK8 Inhibitors

Introduction. ETO2-GLIS2 (aka CBFA2T3-GLIS2) is the most common (30%) alteration in pediatric de novo acute megakaryoblastic leukemia (AMKL). These patients have poor response to induction therapy, a high incidence of relapse (~90%), and dismal 5-year survival rates (<20%). Previous studies suggest that ETO2-GLIS2 induces leukemia through abnormal enhancer formation as a single oncogenic “hit”. Because ETO2-GLIS2 expression induces formation of leukemia-specific neo-superenhancer (SE) elements, we hypothesize that mediator (MED) proteins are involved in linking neo-SE elements to distal gene expression, and thus could be a therapeutic target. Here, we analyzed expression of MED-family genes in ETO2-GLIS2 positive AMKL patients in combination with enhancer-histone marks, and evaluated impact of MED-kinase inhibition with selective CDK8 inhibitors (CDKi) against cell viability.Methods. To address our hypothesis, we analyzed published RNA sequencing dataset (Smith et al. 2020) for human MED-genes expression from a pan-pediatric AML cohort (N=1476). The cohort consisted of subgroups expressing fusions of ETO2-GLIS2 (N=40), CBFB-MYH11 (N=174), DEK-NUP214 (N=49), KMT2A-ELL (N=50), KMT2A-MLLT10 (N=86), KMT2A-MLLT3 (N=114), KMT2A-MLLT4 (N=49), NUP98-NSD1 (N=107), RUNX1-RUNX1T1 (N=210) and no detectable fusions (N=526), compared to normal bone marrow (NBM) samples (N=71). Enrichment of histone marks overlapping MED-genes was analyzed from published chromatin immunoprecipitation (ChIP) sequencing in ETO2-GLIS2 positive M-07e AMKL line (Thirant et al. 2017). We tested efficacy of CDK8 inhibition with BI-1347 and CCT251545 against M-07e cells to determine their activity in the context of marked MED12L overexpression.Results. We examined expression of 29 MED-genes comprising the 4 major (head, middle, tail, and kinase) MED-modules. MED gene expression was variable across AML subtypes and NBM. However, MED genes were more commonly over-expressed in the ETO2-GLIS2 group, in particular MED 17, MED1, MED10, MED27, and MED12L (paralog of MED12) were upregulated in the subgroup. Most notably, we noted exceptional upregulation of MED12L (FC 4.9, log2), compared to NBM (Figure 1). Because MED12/12L plays an intrinsic biological role in establishing oncogenic enhancer-expression loops in hematopoietic stem or leukemic cells, we investigated the overlap of enhancer bound histones such as H3K27ac and H3K4me1 to MED12L in M-07e cells, compared to umbilical cord blood-derived normal megakaryoblasts (MK) (S004BT; Blueprint epigenome database). We found enrichment of H3K4me1 at MED12L transcription start site (TSS) and upstream promoter both in MK and M-07e cells. In addition, we observed a large region of H3K27ac enrichment spanning 89 Kb (16 kb upstream and 73 kb downstream) across MED12L TSS in M-07e cells, suggesting neo-enhancer activity at this locus. Considering the dependency of MED12 on CDK8 for MED-kinase activities (Klatt et al. 2020), we treated M-07e cells with CDK8i(s), to test our hypothesis if perturbation of epigenetically enhanced MED12L expression can impact leukemic growth. However, we observed a poor correlation between M-07e cell viability and IC 50 of BI-1347 (IC 50: 0.87 µM, R 2: 0.36) or CCT251545 (IC 50: 0.4 µM, R 2: 0.48). In contrast, ETO2-GLIS2 negative MV4-11 AML cells were susceptible to both BI-1347 (IC 50: 0.44 µM, R 2: 0.88) and CCT251545 (IC 50: 0.12 µM, R 2: 0.87). Given the inefficacy of CDK8i against M-07e, and cooperativity of bromodomain extra-terminal (BET)-BRD4 and MED12/12L in forming enhancer complexes, we tested possible inhibitory impact of BRD4 inhibitor JQ1 on MED12L expression and leukemic growth in target cells. We observed effective reduction in M-07e cell viability (IC 50:0.3 µM, R 2: 0.93) with concomitant reduction not only in BRD4 protein-expression, but diminished MED12L protein expression at IC 50 and higher doses of JQ1.Conclusion. Our findings revealed that MED12L is highly overexpressed and overlapped with strong neo-enhancer chromatin-marks in ETO2-GLIS2 positive cells, while maintaining resistance to CDK8i. Future studies will contribute to deeper insights into the preferential recruitment and role of MED12L in ETO2-GLIS2 bound enhancers and potential mechanisms of resistance to CDK8 inhibition in the disease. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Cytokine Analysis in 154 Patients with Transient Abnormal Myelopoiesis: Jccg JPLSG TAM-10 Clinical Study

Introduction:Transient abnormal myelopoiesis (TAM), also known as transient leukemia or transient myeloproliferative disorder, is a unique clonal myeloproliferation characterized by immature megakaryoblasts occurring in 10% of neonates with Down syndrome. Although most patients show spontaneously resolution of TAM without therapeutic interventions, approximately 20% of TAM cases result in early deaths, i.e., within 9 months, and approximately 20% of the survivors develop acute megakaryoblastic leukemia (AMKL) within 4 years. A somatic GATA1 gene mutation that leads to the exclusive expression of a truncated GATA1 protein is shared by both TAM and AMKL cells. According to previous reports, cytokine levels are associated with liver failure, which is a cause of early death. Here, we analyzed 154 DS patients with TAM enrolled in the TAM-10 prospective observational study conducted by the Japan Pediatric Leukemia/Lymphoma Study Group to determine the association between clinical characteristics and cytokine levels in such patients.Patients and Methods:A total of 167 neonates (89 boys and 78 girls) diagnosed with TAM were prospectively registered in the TAM-10 study between May 2011 and February 2014. We analyzed cytokine levels in 154 of the 167 enrolled patients whose samples were available. Somatic GATA1 gene mutations were confirmed in 151 (98%) of 154 patients using Sanger and/or next-generation sequencing. Using the Bio-Prex cytokine assay, serum concentrations of the following 27 cytokines were measured: interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), vascular endothelial growth factor (VEGF), platelet-derived growth factor-BB (PDGF-BB), basic fibroblast growth factor (bFGF), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory proteins alpha and beta (MIP-1α and MIP-1β), eotaxin, interferon gamma-induced protein (IP-10), regulated upon activation, normal T-cell expressed and secreted, interleukin I receptor agonist (IL-RA), and 13 different interleukins (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL-12, IL-13, IL-15, and IL-17). For all analyses, P values were two-tailed and a P value of <0.05 was considered statistically significant. Mann-Whitney test were used as appropriate for comparisons between groups. Moreover, the cumulative incidence for competing events was compared with the Gray test.Results:The median (range) white blood cell (WBC) count at diagnosis was 37.2 (2.4-478.7) × 10 9 cells/L. Forty-seven (31%) of 154 patients received low-dose cytarabine. When we compared 29 patients with a high WBC count (≥100 × 10 9 cells/L, known as a poor prognostic factor in TAM patients) to 125 patients without a high WBC count for 27 cytokine levels, the levels of 16 cytokines (IL-1b, IL-1ra, IL-6, IL-7, IL-8, IL-9, IL-10, IL-13, Eotaxin, PDGF-bb, basic FGF, G-CSF, GM-CSF, MCP-1b, and VEGF) were significantly higher in patients with a high WBC group. Early death occurred in 14 (9%) of 154 patients. Cytokine levels were compared between the early death group (n = 14) and remaining patients (n = 140) and it was observed that the levels of 10 cytokines (IL-1b [p = 0.016], IL-1ra [p < 0.001], IL-6 [p < 0.001], IL-7 [p = 0.009], IL-8 [p < 0.001], IL-10 [p = 0.014], IL-13 [p = 0.002], MCP-1 [p = 0.030], MIP-1b [p = 0.024], and TNF-α [p = 0.008]) were significantly higher in the early death group. When the patients were divided in two groups according to the median IL-1β concentration showing the lowest p-value, the early death rate in the IL-1β high group was significantly higher than that in the IL-1β low group (16% vs. 3%, p < 0.001). IL-1, IL-6, IL-8, and TNF-α are proinflammatory cytokines induced by MCP-1 and MIP1-b. Early death was strongly associated with hypercytokinemia, suggesting that therapeutic interventions (e.g., systemic steroid therapy) may be effective in patients with hypercytokinemia. However, there was no relation between the levels of 27 cytokines and leukemia development.Conclusion:Our findings suggested that measurement of cytokine levels may be a useful marker for predicting early death and an indicator of therapeutic interventions required in TAM patients. DisclosuresNo relevant conflicts of interest to declare.

The Role of ETO and CtBP1 in CBFA2T3-GLIS2 Mediated Transcriptional Regulation and Leukemogenesis

CBFA2T3-GLIS2 is the most prevalent fusion oncogene in pediatric acute megakaryoblastic leukemia patients without Down syndrome and is associated with an event free survival of only 8%. A cryptic inversion event on chromosome 16 joins the three nervy homology regions (NHR) of CBFA2T3 to the five zinc fingers of GLIS2. This configuration enables the encoded chimeric transcription factor to bind GLIS2 consensus sequences throughout the genome and recruit transcriptional activators and repressors to alter gene expression and enhance self-renewal capability. Few cooperating mutations have been identified in patients harboring this fusion which suggests it is the sole oncogenic driver. The molecular mechanism by which CBFA2T3-GLIS2 drives leukemogenesis is not fully understood. Identification of components critical to the transcriptional complex and their role in gene regulation may reveal novel therapeutic targets to improve patient outcomes. Studies on the wild type CBFA2T3 and GLIS2 proteins have demonstrated interactions with the transcriptional regulators ETO and CtBP1 respectively. Further p300 has been shown to play a role in transcriptional regulation imparted by both transcription factors. We therefore hypothesize the fusion promotes transcriptional activation when the histone acetyltransferase p300 and the transcription factor ETO are recruited through NHR1 and NHR2, respectively. When the co-repressor CtBP1 is recruited through the PXDLS motif, located in the GLIS2 portion of the fusion, transcriptional repression predominates. Association of these co-factors with the fusion was confirmed through co-immunoprecipitations. Site-directed mutagenesis was then used to systematically delete NHR1 and NHR2 and mutate the PXDLS motif to evaluate the resultant effects on transcriptional regulation, self-renewal, and leukemogenesis imparted by the fusion. A luciferase reporter assay was used to assess transcriptional activation of the BMP2 promoter, a gene which is known to be upregulated by the CBFA2T3-GLIS2 fusion. Loss of NHR1, NHR2, or NHR3 did not alter the ability of the fusion to activate transcription. In contrast, loss of NHR1 and NHR2 in combination (NHR1-2Δ) and mutation of the PXDLS domain decreased transcriptional activation compared to the wild type fusion. The effect of the mutations on self-renewal capability was then evaluated through colony formation assays. Consistent with the luciferase reporter assay, NHR1-2Δ and PXDLS mutants decreased the number of colonies at week six compared to the unmanipulated fusion. Next, we investigated the effect of these mutations on leukemogenesis. Murine models harboring the CBFA2T3-GLIS2 fusion without cooperating mutations have been unsuccessful and patient-derived xenograft models are limited and difficult to manipulate. Therefore, we developed a novel in vivo model of CBFA2T3-GLIS2 driven leukemia. CD34+ stem cells were isolated from human cord blood and transduced with a lentivirus construct encoding the fusion and a GFP reporter. The cells were then differentiated to megakaryoblasts using human TPO and IL1-beta and sorted for purity prior to injection into immunodeficient NSG-SGM3 recipient mice. The fusion positive human primary megakaryoblasts induced a serially transplantable leukemia within 180 days that recapitulates CBFA2T3-GLIS2 positive patient specimens on a transcriptional and protein level. In contrast to our in vitro studies where NHR2 deletion alone did not alter transcriptional activation and self-renewal, the loss of this domain abrogated leukemogenesis in vivo, suggesting a dependency on the association of ETO with the fusion. Mice that received PXDLS mutant cells, however, developed leukemia at a normal latency suggesting that CtBP1 is not required. This study confirms the CBFA2T3-GLIS2 fusion is sufficient for oncogenic transformation of human CD34+ stem cells. We demonstrate that disruption of ETO, p300, and CtBP1 recruitment to the transcriptional complex decreases transcriptional regulation and self-renewal imparted by the fusion. The loss of ETO was the most detrimental to leukemogenesis in our murine model, uncovering a potential new pathway for the development of targeted therapies. Ongoing studies include CUT&RUN sequencing for the fusion, ETO, and CtBP1 to determine co-occupancy of target genes to further understand those that are critical in transformation. DisclosuresGruber: Kura Oncology: Consultancy.

ACUTE MEGACARYOBLASTIC LEUKEMIA IN CHILDREN: DIAGNOSTICS AND MRD MONITORING

Acute megakaryoblastic leukemia (AMKL) is a rare subtype of acute myeloid leukemia (AML) associated with poor prognosis for all patients except children with t(1;22) or Down syndrome. The frequency of complete remission in case of AMKL is comparable to the frequency of it in other variants of AML but the median survival is much lower. This determines the necessity of more thorough evaluation of treatment effect using flow cytometry accessment of minimal residual disease (MRD). The clinical and immunological profile of 8 girls and 9 boys with de novo AMKL between the ages of 3 months–11 years old was analyzed. The primary leucocytosis median was 10,25; only one patient had hyperleukocytosis (53х109/l) at presentation.The measurement of MRD was performed in 6 patients using multiparameter flow cytometry. The measurement of MRD performed after induction therapy on the basis of megakaryocytic markers, weak CD45 expression using the initial iimmunophenotype patterns. Adequate measurement of the level of MRD had required extensive diagnostic immunophenotyping in order to determine the aberration of megakaryoblasts. CD9(83,3%), CD33(75%), CD34(60%), CD13(50%) apart from megakaryocyte markers (100%) were most common for blast cells in case of AMKL. The expression of CD7 antigen was as frequent as of CD117-40%. The MRD level ranged from completely negative (0%; 0.006%) to evident (1.05%). The detection of residual tumor megakaryoblasts in AML M7 using flow cytometry is a promising method for assessing the effect of therapy. Adequate measurement of MRD requires detailed immunophenotyping in the diagnosis to determine the aberrations of megacaryoblasts immunophenotype.

Ultrastructural alterations of megakaryocytes in thrombocytopenia: A review of 43 cases.

Thrombocytopenia is a frequent occurrence in a variety of hematopoietic diseases; however, the details of the mechanism leading to low platelet count remain elusive. Megakaryocytes are a series of progenitor cells responsible for the production of platelets. Alterations in megakaryocytes in the bone marrow are a causative factor resulting in thrombocytopenia in varied diseases. Based on ultrastructural analysis of incidentally encountered megakaryocytes in 43 patients with blood diseases marked by low platelet counts, electron micrographs demonstrated that aberrant megakaryocytes predominated in idiopathic thrombocytopenic purpura, aplastic anemia, and myelodysplastic syndrome; autophagy, apoptosis, and cellular damage in megakaryocytes were a prominent feature in aplastic anemia. On the other hand, poorly differentiated megakaryocytes predominated in acute megakaryoblastic leukemia (AMKL) although damaged megakaryocytes were seen in non-AMKL acute leukemia. This paper documents the ultrastructural alterations of megakaryocytes associated with thrombocytopenia and reveals distinctive features for particular blood diseases. A comment is made on future avenues of research emphasizing membrane fusion proteins.

Unusual CD34 positivity in acute myeloid leukaemia with myelodysplasia-related changes with megakaryoblastic differentiation.

Acute megakaryoblastic leukaemia is a rare entity with distinct immunophenotype profile and cytogenetic lesions. Herein, we report a case of acute myeloid leukaemia with myelodysplastic‐related changes with megakaryoblastic differentiation in absence of recurrent genomic lesions such as t(1;22), inv(3) and t(3;3).One of the peculiarities of this case is the positivity of CD34+ within the abnormal megakaryoblasts; CD61 immunohistochemistry highlights the heavily infiltration of bone marrow from abnormal megakaryoblasts.

The megakaryocytic transcription factor ARID3A suppresses leukemia pathogenesis

AbstractGiven the plasticity of hematopoietic stem and progenitor cells, multiple routes of differentiation must be blocked in the the pathogenesis of acute myeloid leukemia, the molecular basis of which is incompletely understood. We report that posttranscriptional repression of the transcription factor ARID3A by miR-125b is a key event in the pathogenesis of acute megakaryoblastic leukemia (AMKL). AMKL is frequently associated with trisomy 21 and GATA1 mutations (GATA1s), and children with Down syndrome are at a high risk of developing the disease. The results of our study showed that chromosome 21–encoded miR-125b synergizes with Gata1s to drive leukemogenesis in this context. Leveraging forward and reverse genetics, we uncovered Arid3a as the main miR-125b target behind this synergy. We demonstrated that, during normal hematopoiesis, this transcription factor promotes megakaryocytic differentiation in concert with GATA1 and mediates TGFβ-induced apoptosis and cell cycle arrest in complex with SMAD2/3. Although Gata1s mutations perturb erythroid differentiation and induce hyperproliferation of megakaryocytic progenitors, intact ARID3A expression assures their megakaryocytic differentiation and growth restriction. Upon knockdown, these tumor suppressive functions are revoked, causing a blockade of dual megakaryocytic/erythroid differentiation and subsequently of AMKL. Inversely, restoring ARID3A expression relieves the arrest of megakaryocytic differentiation in AMKL patient-derived xenografts. This work illustrates how mutations in lineage-determining transcription factors and perturbation of posttranscriptional gene regulation can interact to block multiple routes of hematopoietic differentiation and cause leukemia. In AMKL, surmounting this differentiation blockade through restoration of the tumor suppressor ARID3A represents a promising strategy for treating this lethal pediatric disease.

High EVI1 Expression Predicts Adverse Outcomes in Children With De Novo Acute Myeloid Leukemia

BackgroundA high ecotropic viral integration site 1 (EVI1) expression (EVI1 high) is an independent prognostic factor in adult acute myeloid leukemia (AML). However, little is known of the prognostic value of EVI1 high in pediatric AML. This study aimed to examine the biological and prognostic significance of EVI1 high in uniformly treated pediatric patients with AML from a large cohort of seven centers in China.MethodsA diagnostic assay was developed to determine the relative EVI1 expression using a single real-time quantitative polymerase chain reaction in 421 newly diagnosed pediatric AML patients younger than 14 years from seven centers in southern China. All patients were treated with a uniform protocol, but only 383 patients were evaluated for their treatment response. The survival data were included in the subsequent analysis (n = 35 for EVI1 high, n = 348 for EVI1 low).ResultsEVI1high was found in 9.0% of all 421 pediatric patients with de novo AML. EVI1 high was predominantly found in acute megakaryoblastic leukemia (FAB M7), MLL rearrangements, and unfavorable cytogenetic aberrance, whereas it was mutually exclusive with t (8; 21), inv (16)/t (16; 16), CEBPA, NPM1, or C-KIT mutations. In the univariate Cox regression analysis, EVI1 high had a significantly adverse 5-year event-free survival (EFS) and overall survival (OS) [hazard ratio (HR) = 1.821 and 2.401, p = 0.036 and 0.005, respectively]. In the multivariate Cox regression analysis, EVI1 high was an independent prognostic factor for the OS (HR = 2.447, p = 0.015) but not EFS (HR = 1.556, p = 0.174). Furthermore, EVI1 high was an independent adverse predictor of the OS and EFS of patients with MLL rearrangements (univariate analysis: HR = 9.921 and 7.253, both p < 0.001; multivariate analysis: HR = 7.186 and 7.315, p = 0.005 and 0.001, respectively). Hematopoietic stem cell transplantation (HSCT) in first complete remission (CR1) provided EVI1 high patients with a tendential survival benefit when compared with chemotherapy as a consolidation (5-year EFS: 68.4% vs. 50.8%, p = 0.26; 5-year OS: 65.9% vs. 54.8%, p = 0.45).ConclusionIt could be concluded that EVI1 high can be detected in approximately 10% of pediatric AML cases. It is predominantly present in unfavorable cytogenetic subtypes and predicts adverse outcomes. Whether pediatric patients with EVI1 high AML can benefit from HSCT in CR1 needs to be researched further.

A Rare Pediatric Case Report With Review of Literature for the Diagnosis of Acute Megakaryoblastic Leukemia (FAB M7)

Acute megakaryoblastic leukemia (AMKL) is a subtype of acute myeloid leukemia (AML) accounting for 3%–10% of primary AML in childhood. Clinical manifestations of AML patients can include low grade of fever, diarrhea, easy bruising, failure to growth, and life-threatening clinical manifestations. Laboratory tests are very crucial to make a definitive diagnosis and treatment. We report here an uncommon case of AMKL in a 12-month-old boy who presented with general paleness and fatigue. Based on blood film investigation, bone marrow examination report, and immunophenotyping, he was diagnosed as a case of AMKL without Down syndrome.

Pathological and immunohistochemical aspects of acute megakaryoblastic leukaemia in a cat - Short communication.

An adult, mixed-breed, feline leukaemia virus (FeLV-) positive female cat was presented with mucosal jaundice and a history of anorexia and constipation for three days. Physical examination revealed splenomegaly, cachexia, and dehydration. Humane euthanasia was conducted, followed by postmortem examination. Grossly, the cat was icteric, and presented hepatomegaly with multifocal white spots and splenomegaly. Histologically, the bone marrow was nearly completely replaced by a proliferation of megakaryocytes and megakaryoblasts, and there was a proliferation of fibrous connective tissue. Similar neoplastic proliferation was observed infiltrating the liver, lymph nodes, spleen, kidney, skeletal muscle, and lungs. Immunohistochemistry was performed for von Willebrand Factor (VWF), CD79α, CD3, feline immunodeficiency virus, FeLV, and CD61. Marked cytoplasmic labelling was observed in the neoplastic cells for FeLV, VWF and CD61, corroborating the diagnosis of acute megakaryoblastic leukaemia.

Phenotypic and genetic analysis of acute megakaryoblastic leukemia in young children with WT1, MLL-PTD and EVI1 genes

To explore the phenotypic and genetic characteristics of acute megakaryoblastic leukemia (AMKL) in young children accompany by WT1, MLL-PTD and EVI1, in order to improve the diagnosis level of AMKL. EDTA-K2 anticoagulation venous blood was collected for blood routine and morphological analysis of blood cells; bone marrow was extracted for cell morphology, immunophenotype, chromosome karyotype and fusion gene analysis. White blood cell count was 12.3× 109/L, hemoglobin was 73 g/L, and platelet count was 13× 109/L. The morphological analysis of blood cells showed that the size of immature cells was like that of primitive immature lymphocytes, which was circular or irregular and part of them with obvious pseudopodia. The cytoplasm is basophilic with heterogeneous coloration and granules. Nuclear chromatin is fine and even, 1-3 nucleoli can be seen, these immature cells account for about 40%; the morphology of bone marrow cells was consistent with acute leukemia, negative for peroxidase staining, negative for AS-DNCE staining and alpha-NBE staining. Flow cytometry results showed that the protocells account for about 52% and significant expression of megakaryocytes related markers (cCD41+, CD61+, CD36+). Chromosome karyotype is 46, XX, der(3) add(3)(p21)add(3)(q25), add (9)(q22), -13, +mar [4]/46, XX, del(13)(q12q22) [3]/46, XX[3]. The fusion gene WT1 was overexpressed, MLL-PTD and EVI1 were positive. Acute megakaryocytic leukemia has unique and complex phenotypic and genetics characteristics.

The ETO2-GLIS2 Fusion Oncogene Alters Early Human Hematopoiesis in an Induced Pluripotent Stem Cells-Derived Model of Pediatric Acute Megakaryoblastic Leukemia

De novo pediatric acute megakaryoblastic leukemia (AMKL) is a genetically heterogeneous subtype of acute myeloid leukemia (AML) expressing fusion oncogenes, including CBFA2T3 - GLIS2 (a.k.a. ETO2-GLIS2) present in 15-25% of patients and associated with a poor prognosis because of a high risk of relapse or refractoriness to chemotherapy. To characterize the consequences of ETO2-GLIS2 on early stages of human hematopoiesis, we developed a model of ETO2-GLIS2 expression in induced pluripotent stem cells (iPSC) derived from healthy human CD34+ cells. To this end, we introduced the human ETO2-GLIS2 cDNA tagged with the green fluorescent protein (GFP) under the control of the human CD43 promoter in iPSC through ZFN-mediated recombination at the AAVS1 safe-harbor locus. After puromycin selection, 23 independent clones were confirmed by PCR and sequencing to bear a correct homozygous integration and were amplified. Three independent iPSC clones were subsequently differentiated into hematopoietic progenitors and then into megakaryocytes using a 2D co-culture system on matrix adapted from Chou S et al. (PNAS 2012) and compared to control iPSC. We demonstrated that ETO2-GLIS2 is expressed in CD43+ hematopoietic cells both at the transcript and protein levels and localizes in the nucleus. In addition, ETO2-GLIS2-expressing cells showed an increased expression of several recently characterized direct targets of the fusion including ERG as compared to control cells. Hematopoietic differentiation of iPSC was then assessed at day 13, 15 and 18 using flow cytometry analyses for progenitors and megakaryocytic markers. As early as day 13, ETO2-GLIS2-expressing cells showed an increased number of CD43+ hematopoietic cells composed of a higher percentage of CD41+CD42+ megakaryocytic cells compared to controls, indicating that ETO2-GLIS2 enhances early human megakaryocyte development. Importantly, we observed strong differentiation alterations, including a lower expression of CD61 on ETO2-GLIS2 megakaryocytes compared to controls at all time points and a progressive accumulation of an abnormal CD41lowCD42+ population never detected in control conditions. This CD41lowCD42+ population was also observed in AMKL patients. Finally, preliminary clonogenic assays in methylcellulose indicate that ETO2-GLIS2 enhances serial replating activity for several weeks. These data support the idea that expression of ETO2-GLIS2 in human hematopoietic cells obtained from iPSC recapitulates several cellular and molecular features of human pediatric AMKL, including transcriptional activation of target genes, enhanced self-renewal of progenitors and aberrant differentiation of megakaryocytic cells. This model will facilitate further cellular and preclinical studies on this rare pediatric cancer. DisclosuresNo relevant conflicts of interest to declare.

Transcriptomic and Network Signatures of Cryptic Fusion CBFA2T3-GLIS2 in Pediatric AML Reveals Clinical Considerations and Implications

IntroductionA cryptic inv(16)(p13.3q24.3) encoding the CBFA2T3-GLIS2 fusion was initially reported in childhood acute megakaryoblastic leukemia (AMKL) and was shown to be associated with unfavorable outcomes. Although this fusion onco-protein is more prevalent in FAB M7 AML, it is reported in younger patients with all subtypes of AML. We present a comprehensive transcriptomic signature of an unselected cohort of children with CBFA2T3-GLIS2 fusion treated on COG AML trials.MethodsCBFA2T3-GLIS2 fusions were identified in 26 of 1042 (2.5%) patients enrolled in Children's Oncology Group (COG) studies AAML03P1 and AAML0531, with a prevalence of 8% in patients < 3 years of age. Whole transcriptome sequence data was available from 466 patients and 20 normal bone marrows (NBM) for expression profiling. Differentially expressed genes were identified using the Limma v.3.30.12 R package. Unsupervised hierarchal clustering was performed using Euclidean distance with the WPGMA linkage algorithm. Gene-set enrichment analysis was completed using the Broad Institute software v.2-2.2.4 with MSigDB C2 curated gene sets.ResultsOf 26 patients with CBFA2T3-GLIS2 fusions, 21 (81%) were < 5 years of age (Fig. 1A). KMT2A fusions co-occurred in only two patients, and none of the positive tumors carried core binding factor fusions. Few other variants accompanied CBFA2T3-GLIS2 fusions and overall, this subclass of AML had been categorized as cytogenetically normal (42% CN-AML, Fig. 1B). CBFA2T3-GLIS2 AML fared worse than the AML population as a whole; more than 75% of fusion-positive cases relapsed within two years (Fig. 1C, p = 0.001).Gene-set enrichment analysis between CBFA2T3-GLIS2 fusion and fusion-negative tumors revealed the top three positively enriched gene sets as 1) basal cell carcinoma (FDR = 0.003), 2) ECM receptor interactions (FDR = 0.006), and 3) hedgehog signaling pathways (FDR = 0.029). Consistent with previous reports, genes associated with WNT, hedgehog (HH), and BMP signaling were significantly up-regulated in CBFA2T3-GLIS2 tumors (Fig. 1D). CBFA2T3-GLIS2 fusions have been associated with induction of BMP signaling through downstream HH targets, BMP2 and BMP4 in pediatric AMKL. Moreover, concurrent dysregulation of WNT, BMP and HH signaling is a feature of CBFA2T3-GLIS2 AMKL (Gruber et al., 2015). Unsupervised hierarchical clustering of differentially expressed genes effectively clustered the fusion-positive samples, suggesting CBFA2T3-GLIS2 fusions drive a distinct transcriptional profile from other AML subtypes (Fig. 1E). CBFA2T3-GLIS2 tumors compared to NBM had upregulated expression of 4 cancer testes antigens (CTAs): CCNA1, PRAME, IGF2BP3, and KDM5B (fold-change > 2, adj. p < 0.001). CTAs are promising candidates for targeted T-cell therapies due their low expression in NBM and surrounding tissues, which could limit treatment related toxicity ( Ochsenreither et al., 2012) .We further performed unsupervised hierarchical clustering in 437 patients for whom flow cytometry data were available (Fig. 1F). Most fusion-positive tumors (7/10) clustered together by mean fluorescence intensity (MFI), indicating that CBFA2T3-GLIS2 tumors have highly distinctive immune profiles. Of particular interest, fusion-positive tumors expressed CD56 at high levels (median CD56 in CBFA2T3-GLIS2 : 1,505.0 MFI [range: 6.4 - 4,290.0] versus median CD56 in fusion-negative AML: 9.0 MFI [range: 2.4 - 3,360.0], p = 0.001). A novel immunophenotype in pediatric AML, termed RAM, has been associated with high CD56 expression and much lower event-free survival. A preponderance of CBFA2T3-GLIS2 AML displayed the RAM phenotype, with 70% of fusion-positive tumors identified as RAM compared to 0.23% (1/427) in the fusion-negative population (p < 0.001).ConclusionCBFA2T3-GLIS2 AML tends to have an aggressive disease pathology in much younger patients, who had been primarily classified as CN-AML. This suggests screening for CBFA2T3-GLIS2 in younger patients could be valuable as standard practice, though not yet recommended by the World Health Organization. Our associations with CBFA2T3-GLIS2 fusions provides a potential link between genomic and immunologic characteristics of a high-risk group of pediatric AMLs, which could be employed in the future for clinical screening through molecular or flow-cytometric methods. [Display omitted] DisclosuresBrodersen:Hematologics Inc: Employment. Loken:Hematologics Inc: Employment, Equity Ownership.