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Patients treated with cytotoxic therapies, including autologous stem cell transplantation, are at risk for developing therapy-related myeloid neoplasms (tMN). Pre-leukemic clones (i.e., clonal hematopoiesis; CH) are detectable years before the development of these aggressive malignancies, though the genomic events leading to transformation and expansion are not well-defined. Here, leveraging distinctive chemotherapy-associated mutational signatures from whole-genome sequencing data and targeted sequencing of pre-chemotherapy samples, we reconstruct the evolutionary life-history of 39 therapy-related myeloid malignancies. A dichotomy is revealed, in which neoplasms with evidence of chemotherapy-induced mutagenesis from platinum and melphalan are hypermutated and enriched for complex structural variants (i.e., chromothripsis) while neoplasms with non-mutagenic chemotherapy exposures are genomically similar to de novo acute myeloid leukemia. Using chemotherapy-associated mutational signatures as temporal barcodes linked to a discrete clinical exposure in each patient's life, we estimate that several complex events and genomic drivers are acquired after chemotherapy is administered. For patients with prior multiple myeloma who were treated with high-dose melphalan and autologous stem cell transplantation, we demonstrate that tMN can develop from either a reinfused CH clone that escapes melphalan exposure and is selected following reinfusion, or from TP53-mutant CH that survives direct myeloablative conditioning and acquires melphalan-induced DNA-damage. Overall, we reveal a novel mode of tMN progression that is not reliant on direct mutagenesis or even exposure to chemotherapy. Conversely, for tMN that evolve under the influence of chemotherapy-induced mutagenesis, distinct chemotherapies not only select pre-existing CH, but also promote the acquisition of recurrent genomic drivers.

ObjectivesPatient education resources that address barriers to health literacy to improve understanding and outcomes in myelodysplastic syndromes (MDS) are limited. The aim of this study was to evaluate the impact and outcomes benefits of An Animated Patient's Guide to Myelodysplastic Syndromes (MDS) cancer educational modules (which includes the 'You and MDS' website and YouTube hosted resources) related to MDS education, awareness, understanding and health outcomes.MethodsThis was a retrospective study of learner feedback, metrics, and utilization data from July 2018 to August 2021. We evaluated audience reach (number of visit sessions, unique visitors, page views) and calculated top views by media type (animation, expert video, patient video, and slide show) and top retention videos from the modules. We also assessed the educational impact and utilization through learner feedback surveys.ResultsDuring the study period, 'You and MDS' had 233,743 views worldwide of which 104,214 were unique visitors and 78,161 (or 76% unique visitors) were from the United States. Of these, 61% were patients; 29% family members or caregivers; 5% were healthcare providers and 5% represented other groups. Most popular topics viewed among the animations were "Understanding Myelodysplastic Syndromes (MDS)" (40,219 views), "Managing and Treating MDS" (19,240 views), "Understanding Erythropoiesis" (17,564 views.) The most popular expert videos viewed were "What is iron overload, and how it is treated?" (20,310 views), "How serious a cancer is MDS? What is the prognosis for MDS?" (8,327 views), "What is MDS?" (3,157 views). Of participants who completed the online feedback survey, ≥ 95% reported improved knowledge gains and commitments to change.ConclusionsMDS patients using 'You and MDS - An Animated Patient's Guide to MDS' and its visual formats of learning represented a wide U.S. and global learner audience. This MDS educational resource had a significant impact on improved understanding among patients, families, and caregivers. Continued efforts should be made to provide patient-effective resources that address health literacy, improve patient understanding, and address educational needs that respond to the concerns of patients to achieve better quality of life and improved health outcomes in MDS.

Myelodysplastic syndromes (MDS) are hematopoietic stem and progenitor cell (HSPC) malignancies characterized by ineffective hematopoiesis and an increased risk of leukemia transformation. Epigenetic regulators are recurrently mutated in MDS, directly implicating epigenetic dysregulation in MDS pathogenesis. Here, we identified a tumor suppressor role of the acetyltransferase p300 in clinically relevant MDS models driven by mutations in the epigenetic regulators TET2, ASXL1, and SRSF2. The loss of p300 enhanced the proliferation and self-renewal capacity of Tet2-deficient HSPCs, resulting in an increased HSPC pool and leukemogenicity in primary and transplantation mouse models. Mechanistically, the loss of p300 in Tet2-deficient HSPCs altered enhancer accessibility and the expression of genes associated with differentiation, proliferation, and leukemia development. Particularly, p300 loss led to an increased expression of Myb, and the depletion of Myb attenuated the proliferation of HSPCs and improved the survival of leukemia-bearing mice. Additionally, we show that chemical inhibition of p300 acetyltransferase activity phenocopied Ep300 deletion in Tet2-deficient HSPCs, whereas activation of p300 activity with a small molecule impaired the self-renewal and leukemogenicity of Tet2-deficient cells. This suggests a potential therapeutic application of p300 activators in the treatment of MDS with TET2 inactivating mutations.

The germinal center (GC) reaction plays an important role in generating humoral immunity and is believed to give rise to most B-cell lymphomas. GC entry and exit are tightly regulated processes, controlled by the actions of transcription factors such as BCL6. Herein, we demonstrate that protein arginine methyltransferase 5 (PRMT5), a symmetric dimethyl arginine methyltransferase, is also necessary for GC formation and affinity maturation. PRMT5 contributes to GC formation and affinity maturation at least in part through its direct interaction with and methylation of BCL6 at arginine 305 (R305), a modification necessary for the full transcriptional repressive effects of BCL6. Inhibition of PRMT5 in B-cell lymphoma lines led to significant upregulation of BCL6 target genes, and the concomitant inhibition of both BCL6 and PRMT5 exhibited synergistic killing of BCL6-expressing lymphoma cells. Our studies identify PRMT5 as a novel regulator of the GC reaction and highlight the mechanistic rationale of cotargeting PRMT5 and BCL6 in lymphoma.

HOX gene dysregulation is a common feature of acute myeloid leukemia (AML). The molecular mechanisms underlying aberrant HOX gene expression and associated AML pathogenesis remain unclear. The nuclear protein CCCTC-binding factor (CTCF), when bound to insulator sequences, constrains temporal HOX gene-expression patterns within confined chromatin domains for normal development. Here, we used targeted pooled CRISPR-Cas9-knockout library screening to interrogate the function of CTCF boundaries in the HOX gene loci. We discovered that the CTCF binding site located between HOXA7 and HOXA9 genes (CBS7/9) is critical for establishing and maintaining aberrant HOXA9-HOXA13 gene expression in AML. Disruption of the CBS7/9 boundary resulted in spreading of repressive H3K27me3 into the posterior active HOXA chromatin domain that subsequently impaired enhancer/promoter chromatin accessibility and disrupted ectopic long-range interactions among the posterior HOXA genes. Consistent with the role of the CBS7/9 boundary in HOXA locus chromatin organization, attenuation of the CBS7/9 boundary function reduced posterior HOXA gene expression and altered myeloid-specific transcriptome profiles important for pathogenesis of myeloid malignancies. Furthermore, heterozygous deletion of the CBS7/9 chromatin boundary in the HOXA locus reduced human leukemic blast burden and enhanced survival of transplanted AML cell xenograft and patient-derived xenograft mouse models. Thus, the CTCF boundary constrains the normal gene-expression program, as well as plays a role in maintaining the oncogenic transcription program for leukemic transformation. The CTCF boundaries may serve as novel therapeutic targets for the treatment of myeloid malignancies.

Additional Sex Combs-Like 1 (ASXL1) is mutated at a high frequency in all forms of myeloid malignancies associated with poor prognosis. We generated a Vav1 promoter-driven Flag-Asxl1Y588X transgenic mouse model, Asxl1Y588X Tg, to express a truncated FLAG-ASXL1aa1-587 protein in the hematopoietic system. The Asxl1Y588X Tg mice had an enlarged hematopoietic stem cell (HSC) pool, shortened survival, and predisposition to a spectrum of myeloid malignancies, thereby recapitulating the characteristics of myeloid malignancy patients with ASXL1 mutations. ATAC- and RNA-sequencing analyses revealed that the ASXL1aa1-587 truncating protein expression results in more open chromatin in cKit+ cells compared with wild-type cells, accompanied by dysregulated expression of genes critical for HSC self-renewal and differentiation. Liquid chromatography-tandem mass spectrometry and coimmunoprecipitation experiments showed that ASXL1aa1-587 acquired an interaction with BRD4. An epigenetic drug screening demonstrated a hypersensitivity of Asxl1Y588X Tg bone marrow cells to BET bromodomain inhibitors. This study demonstrates that ASXL1aa1-587 plays a gain-of-function role in promoting myeloid malignancies. Our model provides a powerful platform to test therapeutic approaches of targeting the ASXL1 truncation mutations in myeloid malignancies.

Background: Patients treated with cytotoxic chemotherapies and/or autologous stem-cell transplantation (ASCT) are at risk for therapy-related myeloid neoplasms (tMN). As these agents yield increased mutation burden in relapsed malignancies and leave evidence of exposure via mutational signatures, we studied the genomic and temporal relationship between chemo exposure and progression of clonal hematopoiesis (CH) to tMN. Methods: We analyzed 32 tMN whole genomes (WG) from 31 patients [27 acute myeloid leukemias (AML), 4 myelodysplastic syndromes]. For 7 patients with tMN post-high-dose melphalan/ASCT, we investigated the presence of antecedent CH using targeted sequencing (MSK-IMPACT; Bolton et al. Nat Gen 2020) on pre-melphalan blood mononuclear cells, granulocytes, or CD34+ apheresis samples. Results: TMN was diagnosed a median of 4.2 years (IQR, 2.6-6.6) following primary treatment. When compared to data from 200 de novo AML from TCGA (NEJM, 2013), tMNs had fewer mutations in FLT3 (9.7% v 28.0%; p = 0.028) and NPM1 (3.2% v 27.0%; p = 0.003). TP53 loss was enriched in tMNs (25.8% v 10.5%; p = 0.035 ). Mutational signature analysis revealed 5 known single base substitution (SBS) signatures in tMN: the hematopoietic stem-cell (SBS-HSC), aging (SBS1), melphalan (SBS-MM1), and platinum signatures (E-SBS1, E-SBS20) (Rustad et al. Nat Comm 2020, Pich et al. Nat Gen 2019). Complex structural variants (SV), defined as ≥3 breakpoint pairs involved in simultaneous copy number changes (Rustad et al. Blood Can Disc 2020), were observed in 7 tMNs; including chromothripsis in 6 tumors (19.4%), chromoplexy in 2 (6.5%), templated insertion in 1 (3.2%), and unspecified complex SV in 2 (6.5%). Chromothripsis has not been previously reported in de novo AML and, in 4 cases, involved chromosome 19 with hyper-amplification of the SMARCA4 locus (≥5 copies). CH variants that became clonal in tumor were seen in 5/7 pre-melphalan/ASCT samples and included mutations in TP53, RUNX1, NCOR1, NF1, CREBBP, DNMT3A, and PPM1D. Chemotherapy introduces hundreds of mutations, leaving each exposed cell with a unique catalogue (i.e., barcode). In fact, TMNs with evidence of chemo signatures had a higher mutation burden (median 1574 single nucleotide variants) than those without (median 938; p = 0.004). Detection of chemo signatures in bulk genome sequencing relies on one cell, with its catalogue of mutations, to expand to clonal dominance (Fig 1a, Landau et al. Nat Comm 2020). Given the long latency between exposure and tMN diagnosis, this single-cell expansion model was expected for all samples exposed to melphalan or platinum-based regimens (i.e., agents with a measurable signature). Strikingly, all patients with pre-tMN platinum exposure (n=7) had evidence of platinum SBS signatures whereas only 2 of 7 patients with prior melphalan/ASCT had a melphalan signature (SBS-MM1). As all platinum-exposed tMN had mutational evidence of exposure, a CH clone must have existed prior to exposure, supporting a single-cell expansion model. Absence of a chemo signature for 5/7 post-melphalan/ASCT tumors despite exposure implies tumor progression driven either by multiple clones in parallel (Fig 1b) or by an unexposed clone. As latency largely excludes the former, this suggests pre-tMN CH clones were re-infused during SCT, thus avoiding chemo exposure (Fig 1c). This is supported by two lines of evidence: 1) tMNs from 2 patients exposed to sequential platinum and melphalan/ASCT had platinum but not melphalan signatures confirming single-cell expansion of the pre-tMN CH clone post-platinum but with escape from exposure to melphalan in the ASCT (Fig 1d); 2) targeted sequencing of pre-tMN samples from melphalan/ASCT patients identified tMN genomic mutations at the CH level in 5/7 cases, including in all 3 tested apheresis samples - one of which (TP53) expanded to dominance without a melphalan signature. Conclusion: WG sequencing identified novel features of tMN revealing the key driver role of complex SV. Mutational signature analyses and targeted sequencing of pre-tMN samples can increase our understanding of tMN pathogenesis and demonstrate that tMNs arising post-ASCT are often driven by CH clones that re-engraft after escaping melphalan exposure. This mode of expansion suggests that a permissive, immunosuppressed, post-transplant environment might play a more important role than chemotherapy-induced mutagenesis in tMN pathogenesis. Figure 1 Figure 1. Disclosures Diamond: Sanofi: Honoraria; Medscape: Honoraria. Watts: Rafael Pharmaceuticals: Consultancy; Genentech: Consultancy; Bristol Myers Squibb: Consultancy; Takeda: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy; Aptevo Therapeutices: Research Funding. Kazandjian: Arcellx: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees. Bradley: AbbVie: Consultancy, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Bolli: Amgen: Honoraria; Takeda: Honoraria; Janssen: Consultancy, Honoraria; Celgene/BMS: Consultancy, Honoraria. Papaemmanuil: Isabl Technologies: Divested equity in a private or publicly-traded company in the past 24 months; Kyowa Hakko Kirin Pharma: Consultancy. Scordo: Kite - A Gilead Company: Membership on an entity's Board of Directors or advisory committees; i3 Health: Other: Speaker; Omeros Corporation: Consultancy; Angiocrine Bioscience: Consultancy, Research Funding; McKinsey & Company: Consultancy. Lahoud: MorphoSys: Membership on an entity's Board of Directors or advisory committees. Stein: Jazz Pharmaceuticals: Consultancy; Foghorn Therapeutics: Consultancy; Blueprint Medicines: Consultancy; Gilead Sciences, Inc.: Consultancy; Abbvie: Consultancy; Janssen Pharmaceuticals: Consultancy; Genentech: Consultancy; Celgene: Consultancy; Bristol Myers Squibb: Consultancy; Agios Pharmaceuticals, Inc: Consultancy; Novartis: Consultancy; Astellas: Consultancy; Syndax Pharmaceuticals: Consultancy; PinotBio: Consultancy; Daiichi Sankyo: Consultancy; Syros Pharmaceuticals, Inc.: Consultancy. Sauter: Precision Biosciences: Consultancy; Kite/Gilead: Consultancy; Bristol-Myers Squibb: Research Funding; GSK: Consultancy; Gamida Cell: Consultancy; Celgene: Consultancy, Research Funding; Genmab: Consultancy; Novartis: Consultancy; Spectrum Pharmaceuticals: Consultancy; Juno Therapeutics: Consultancy, Research Funding; Sanofi-Genzyme: Consultancy, Research Funding. Hassoun: Celgene, Takeda, Janssen: Research Funding. Mailankody: Bristol Myers Squibb/Juno: Research Funding; Physician Education Resource: Honoraria; Plexus Communications: Honoraria; Takeda Oncology: Research Funding; Jansen Oncology: Research Funding; Fate Therapeutics: Research Funding; Allogene Therapeutics: Research Funding; Legend Biotech: Consultancy; Evicore: Consultancy. Korde: Medimmune: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding. Hultcrantz: Daiichi Sankyo: Research Funding; Intellisphere LLC: Consultancy; Curio Science LLC: Consultancy; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Research Funding. Shah: Bristol Myers Squibb: Research Funding; Janssen: Research Funding. Shah: Janssen Pharmaceutica: Research Funding; Amgen: Research Funding. Park: Servier: Consultancy; Affyimmune: Consultancy; Autolus: Consultancy; Minerva: Consultancy; PrecisionBio: Consultancy; BMS: Consultancy; Novartis: Consultancy; Kura Oncology: Consultancy; Curocel: Consultancy; Artiva: Consultancy; Innate Pharma: Consultancy; Intellia: Consultancy; Amgen: Consultancy; Kite Pharma: Consultancy. Landau: Genzyme: Honoraria; Takeda, Janssen, Caelum Biosciences, Celgene, Pfizer, Genzyme: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding. Sekeres: BMS: Membership on an entity's Board of Directors or advisory committees; Takeda/Millenium: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Ho: Blueprint Medicine: Membership on an entity's Board of Directors or advisory committees. Roshal: Celgene: Other: Provision of services; Auron Therapeutics: Other: Ownership / Equity interests; Provision of services; Physicians' Education Resource: Other: Provision of services. Lesokhin: pfizer: Consultancy, Research Funding; Janssen: Honoraria, Research Funding; Iteos: Consultancy; Serametrix, Inc: Patents & Royalties; Genetech: Research Funding; Trillium Therapeutics: Consultancy; bristol myers squibb: Research Funding; Behringer Ingelheim: Honoraria. Morgan: BMS: Membership on an entity's Board of Directors or advisory committees; Jansen: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees. Landgren: Janssen: Other: IDMC; Janssen: Research Funding; Amgen: Honoraria; Celgene: Research Funding; Janssen: Honoraria; Amgen: Research Funding; Takeda: Other: IDMC; GSK: Honoraria. Maura: OncLive: Honoraria; Medscape: Consultancy, Honoraria.

Poly-ADP-ribose polymerase inhibitors (PARPi) are currently in clinical trial to determine their therapeutic efficacy for the treatment of acute myeloid leukemia (AML). We have shown that vitamin C (VitC), an essential micronutrient and co-factor of Ten-Eleven translocation (TET) proteins, enhances AML sensitivity to PARPi, potentially due to an increased dependency on base-excision repair (BER) enzymes needed to remove TET-catalyzed oxidized methylcytosine bases via active DNA demethylation. TET2 is the most frequently mutated TET gene in patients with AML, and vitamin C treatment can mimic genetic restoration of TET2 function, leading to DNA demethylation, differentiation, and leukemia cell death. Whether vitamin C efficacy in combination with PARPi depends on the level of TET2 functional alleles is not yet known and may stratify whether TET2 wild-type or mutant patients should be targeted by vitamin C adjuvant therapy. We have generated primary murine AML-ETO9a+ and MLL-AF9+ leukemia models with Tet2 +/+, Tet2 +/- and Tet2 -/- alleles to determine the Tet2-dependent efficacy of PARPi treatment when combined with vitamin C. Furthermore, we have performed CRISPR gene knockout and drug library screening in human AML cell lines in combination with vitamin C treatment, and tested a panel of 10 AML cell lines with titrating concentrations of PARPi (Olaparib, Talazoparib, Veliparib and Rucaparib) alone or in combination with vitamin C (L-ascorbic acid) mimicking physiological to pharmacological in vivo doses. Primary murine AML cells and human cell lines were assayed for colony-forming capacity, differentiation, cell cycling, viability and effects on DNA methylation, levels of oxidized 5-mC and gene expression upon combination treatment in vitro and in vivo. TET2 mutant PDX and primary murine AMLs treated in vivo with L-ascorbate (4g/kg) and Olaparib (50mg/kg) by daily IP injection were also monitored for disease burden, cellular differentiation and survival. Vitamin C is known to drive the TET-catalyzed iterative oxidation of 5-methylcytosine (5-mC) leading to the formation of 5-hydroxymethylcytosine (5-hmC), 5-formylcytosine (5-fC) and 5-carboxylcytosine (5-caC). We show that VitC-PARPi combination treatment causes an accumulation of oxidized 5-mC intermediates in the AML genome that correlates with increased yH2AX formation in mid-S phase and cell cycle stalling. Vitamin C reduces the IC 50 of Olaparib and Talazoparib by greater than 10-fold in human AML cells lines and primary murine leukemia cells, and treatment in combination promotes myeloid differentiation and blocks colony-forming capacity greater than either alone. In both our in vitro and in vivo studies, Tet2 +/- AML cells exhibit increased sensitivity to vitamin C treatment alone or in combination with PARPi compared to either Tet2 +/+ or Tet2 -/- cells, suggesting that patients with TET2 haploinsufficiency, which represents the majority of TET2 mutant cases, could benefit the most from combined treatment. Our findings confirm that vitamin C can act synergistically with PARPi to block AML cell viability, reduce colony-forming capacity, and decrease leukemia burden in PDX and primary murine leukemia models in a TET2 allelic dose-dependent manner. The combinatorial effect works at clinically relevant concentrations of PARPi, and low-pharmacological doses of vitamin C. These studies suggest that vitamin C can be used as a non-toxic therapeutic adjuvant to PARPi therapy for the treatment of AML. Disclosures Neel: Northern Biologics, LTD: Current equity holder in publicly-traded company, Other: Co- Founder; SAB: Other: Co-Founder; Navire Pharma: Consultancy, Current equity holder in publicly-traded company; Jengu Therapeutics: Consultancy, Current equity holder in publicly-traded company, Other: Co-Founder; Arvinas, Inc: Consultancy, Current equity holder in publicly-traded company; Recursion Pharma: Current equity holder in publicly-traded company.

The hematological malignancies classified as Mixed Lineage leukemias (MLL) harbor fusions of the MLL1 gene to partners that are members of transcriptional elongation complexes. MLL-rearranged leukemias are associated with extremely poor prognosis and response to conventional therapies and efforts to identify molecular targets are urgently needed. Using mouse models of MLL-rearranged acute myeloid leukemia (AML), here we show that genetic inactivation or small molecule inhibition of the protein arginine methyltransferase PRMT5 exhibit anti-tumoral activity in MLL-fusion protein driven transformation. Genome wide transcriptional analysis revealed that inhibition of PRMT5 methyltransferase activity overrides the differentiation block in leukemia cells without affecting the expression of MLL-fusion direct oncogenic targets. Furthermore, we find that this differentiation block is mediated by transcriptional silencing of the cyclin-dependent kinase inhibitor p21 (CDKN1a) gene in leukemia cells. Our study provides pre-clinical rationale for targeting PRMT5 using small molecule inhibitors in the treatment of leukemias harboring MLL-rearrangements.

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

To mount an effective immune response against infectious pathogens or tissue injury, hematopoietic stem cells (HSCs) increase their proliferation and production of myeloid cells, including macrophages, which destroy the pathogens and repair the damaged tissue. Proper resolution of inflammation is essential to restore hematopoietic homeostasis, as unrestrained inflammation can result in life-threatening pathologies such as sepsis, autoimmune disorders and cancer. The molecular mechanisms that control the resolution of inflammation, and how these contribute to disease phenotypes, are poorly understood. BAF (SWI/SNF) complexes are ATPase dependent chromatin-remodeling complexes that play fundamental roles in transcription. BAF complexes use the energy of ATP to modulate the accessibility of transcription factors to DNA and thus, orchestrate the gene expression programs that control proliferation and cellular identity. Genes encoding for BAF subunits are frequently mutated in cancer and developmental disorders. In hematopoietic malignancies, loss-of-function mutations and low expression of specific BAF subunits have been reported in patients with anemia and bone marrow failure. Work from our lab previously demonstrated that the hematopoietic-specific BAF complex subunit Dpf2 cooperates with the transcription factor Runx1 to regulate myeloid differentiation. Based on these studies, we generated a hematopoietic-specific Dpf2 knock-out mouse model and found that mice lacking Dpf2 develop pancytopenia, anemia and an uncontrolled inflammatory response that results in early death. Dpf2-/- peripheral blood samples showed dysplastic features including increased number of polychromatophilic blood cells and Howell-Jolly bodies in erythrocytes. Histopathological analyses revealed the presence of fibrosis and prominent infiltration of histiocytes in multiple organs, including lungs, liver and spleen. Detailed chemical profiling of plasma showed increased levels of multiple pro-inflammatory cytokines, indicative of systemic inflammation. Flow cytometry analyses and Mass cytometry profiling further revealed an expansion of myeloid lineages, specifically monocytes and macrophages, concomitant with severe defects in lymphoid and erythroid differentiation. We also found that Dpf2-/-HSCs had increased serial re-plating capacity and a marked myeloid differentiation bias. To identify the transcription factor networks underlying these phenotypes, we performed RNAseq and ATACseq on control and Dpf2-/- HSCs. Gene Set Enrichment Analyses indicated that Dpf2-/- HSCs have extensive gene expression alterations in immune signaling and interferon response pathways, as well as leukocyte and erythroid differentiation. We also found that Dpf2 loss results in pronounced changes in expression and genomic accessibility of specific transcription factors that control macrophage differentiation and proliferation. Together, our mechanistic studies support a model whereby the absence of Dpf2 results in misregulation of the transcription factor networks that establish macrophage cell identity, leading to a marked increase in macrophage infiltrations and shortened survival of the mice. Treatment of the Dpf2-/-mice with clodronate-containing liposomes, which deplete macrophages from bone marrow and spleen, prolonged survival of the mice. Our work uncovers a novel role of Dpf2 in restraining inflammatory responses by controlling macrophage proliferation and function. Moreover, we propose that, in addition to their tumor suppressive roles in cancer, BAF complexes may have a central role in the prevention of immunopathologies. Disclosures Kadoch: Foghorn Therapeutics: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Other: Scientific founder, fiduciary board of directors member, scientific advisory board member, shareholder, and consultant for Foghorn Therapeutics (Cambridge, MA). . Vega:NCI: Research Funding.

Background Epigenetic dysregulation is a hallmark feature of myelodysplastic syndrome (MDS) as epigenetic regulator genes, such as ASXL1, TET2, and SRSF2, are highly mutated in MDS patients. Tet2 (ten-eleven translocation-2, a methylcytosine deoxygenase) mutations are found in ~20% of MDS patients; they are also seen in patients with acute myeloid leukemia (AML) and myeloproliferative neoplasms (MPN). Loss of Tet2 in hematopoietic cells leads hematopoietic defects including enhanced hematopoietic stem cell (HSC) self-renewal, myeloid expansion and an increased propensity to develop MDS or AML. The lysine acetyltransferase (KAT) p300 (encoded by the EP300 gene) plays pivotal roles in essential cellular functions including proliferation, differentiation and signal transduction. However, the function of p300 in hematopoietic malignancies is clearly cell-context dependent, as we have shown that p300 functions as an oncogene in AML1-ETO-driven AML, and a tumor suppressor gene in NUP98-HOXD13-driven MDS. The EP300 and the related CREBBP genes are infrequently mutated in MDS patients. Methods To investigate the role of p300 in MDS driven by lack of Tet2, we generated a mouse model carrying a hematopoietic-specific EP300 conditional knockout on a Tet2-null background and characterized the effect of p300 loss on HSC function and the pathogenesis of MDS and AML. We also explored the therapeutic potential of manipulating p300 KAT activity to affect the course of MDS driven by Tet2 loss. Results Compared to the Tet2-/- mice, the EP300Δ/ΔTet2-/- (DKO) mice had shortened survival and an accelerated onset of AML, with increased blasts in the bone marrow and peripheral blood, anemia, splenomegaly, and universal presence of granulocytic sarcomas, demonstrating that depletion of p300 enhances the leukemogenicity of Tet2-/- HSC. The DKO mice showed enhanced hematopoietic stem/progenitor cell (HSPC, defined as Lin-Sca1+Kit+ cell) proliferation and an increased HSPC pool only 2 weeks after p300 deletion, far in advance of the development of any disease manifestations. In contrast, deletion of p300 in wild type (wt) mice affected neither HSPC proliferation, nor pool size. To further define the mechanisms by which these two genetic events cooperate to drive the development of MDS/AML, we assessed the DNA methylation status and gene expression signatures of HSPCs isolated from wt, Tet2-/- and DKO mice. As expected, loss of Tet2 leads to a genome-wide decrease in 5-hmC, whereas loss of p300 does not change 5-hmC distribution across the genome. Interestingly, DKO HSPCs showed local gains of 5-hmC at a variety of genes (compared to Tet2-null HSPCs), including at the c-Myb gene, which is a known oncogenic driver of AML. Gene Set Enrichment Analysis (GSEA) revealed that p300 loss in Tet2-/- HSPCs interferes with leukocyte differentiation, enhances proliferation and inhibits apoptosis. ChIP-X Enrichment Analysis (ChEA) further also indicated that among the differentially expressed genes, between DKO HSPCs and Tet2-null HSPCs, are potential Myb target genes. Given this data and the RNA-Seq and Q-PCR results that showed elevated levels of Myb mRNA in the DKO HSPCs compared to the Tet2-/- HSPCs, we examined the biological effects of knocking down (KD) Myb. Myb KD reduced the colony-forming capacity of the DKO HSPCs, but not the Tet2 -/- HSPCs, identifying its potential role in mediating the effect of p300 on MDS prone HSPCs. These results indicate that loss of p300 in Tet2-null HSPCs enhances their leukemogenicity through elevated Myb expression and activity. To determine whether increasing p300 KAT activity could have an opposite effect on MDS cells, we utilized I-CBP112, which binds p300 and increases its KAT activity and ability to stimulate H3K18 acetylation. Exposure to I-CBP112 did in fact eliminate the indefinite self-renewal capacity of Tet2-/- HSPCs, as measured by serial replating assays, further highlighting the importance of p300 KAT activity in regulating the behavior of Tet2-/- HSPCs. Additional in vivo studies of the effects of I-CBP112 on the course of MDS/AML driven by the absence of Tet2 are ongoing. Conclusions This work clearly indicates that the EP300 gene can play a tumor suppressor role in MDS/AML driven by loss of Tet2- by repressing Myb expression and activity. It also suggests that the enhancement of p300's KAT activity by use of small molecules, could be an effective therapeutic strategy for MDS/AML. Disclosures Cole: Abbvie: Consultancy; Acylin Therapeutics: Equity Ownership.

AML1-ETO (AE), a fusion oncoprotein generated by t(8;21), can trigger acute myeloid leukemia (AML) in collaboration with mutations including c-Kit, ASXL1/2, FLT3, N-RAS, and K-RAS. Caspase-3, a key executor among its family, plays multiple roles in cellular processes, including hematopoietic development and leukemia progression. Caspase-3 was revealed to directly cleave AE in vitro, suggesting that AE may accumulate in a Caspase-3-compromised background and thereby accelerate leukemogenesis. Therefore, we developed a Caspase-3 knockout genetic mouse model of AML and found that loss of Caspase-3 actually delayed AML1-ETO9a (AE9a)-driven leukemogenesis, indicating that Caspase-3 may play distinct roles in the initiation and/or progression of AML. We report here that loss of Caspase-3 triggers a conserved, adaptive mechanism, namely autophagy (or macroautophagy), which acts to limit AE9a-driven leukemia. Furthermore, we identify ULK1 as a novel substrate of Caspase-3 and show that upregulation of ULK1 drives autophagy initiation in leukemia cells and that inhibition of ULK1 can rescue the phenotype induced by Caspase-3 deletion in vitro and in vivo. Collectively, these data highlight Caspase-3 as an important regulator of autophagy in AML and demonstrate that the balance and selectivity between its substrates can dictate the pace of disease.

Small molecule protein arginine methyltransferase inhibitors (PRMTi) are being actively pursued for the treatment of a variety of cancers; however, the mechanisms of response to PRMTi remain poorly understood. CARM1, also known as PRMT4, is significantly overexpressed in AML, as well as many solid tumors, and regulates myeloid differentiation. We have shown the dependency of AML cells, but not normal blood cells, on CARM1 activity, based on CARM1 knockout, CARM1 knockdown, and chemical inhibition (Greenblatt et al. Cancer Cell 2018). These experiments showed that CARM1 regulates essential processes in leukemia cells, and is critical for leukemic transformation. Although several small molecule inhibitors of CARM1 have been reported recently, many display a lack of selectivity for CARM1 or fail to produce a biological response. The recent discovery of potent and selective CARM1 inhibitors (Drew et al., 2017), has made it possible to investigate the implications of pharmacological inhibition of CARM1 in vitro and in vivo. In vitro, a selective CARM1 inhibitor, EPZ025654, reduced the methylation of a CARM1 substrate, BAF155, in a time and concentration-dependent manner, while the specific histone targets of CARM1 remained unchanged. Translocation (8;21) AML samples in the Eastern Cooperative Oncology Group cohort, have significantly higher CARM1 expression compared to normal CD34+ controls. This led us to hypothesize that CARM1 is a direct target of the AML1-ETO fusion protein. Therefore, we assessed whether EPZ025654 could inhibit AML1-ETO driven gene expression. AML1-ETO specific target genes showed significant changes in expression following EPZ025654 treatment. AML1-ETO positive patient samples also displayed decreased colony formation in methylcellulose and increased myeloid differentiation in response to CARM1 inhibition. We next evaluated EZM2302, a compound structurally related to EPZ025654, that is highly orally bioavailable and is well tolerated in mice (Drew et al., 2017). We generated AE9a-GFP primary transplantation mice and treated them with 100 mg/kg of EZM2302 or vehicle twice-daily (BID). The inhibitor treated mice showed significantly improved survival as well as fewer GFP+ cells in the peripheral blood over time. GFP+ AE9a bone marrow cells also showed decreased colony formation in vitro and induced macrophage differentiation in methylcellulose. GFP+ cells were isolated by FACS and submitted for RNA-sequencing. Flow cytometry analysis post-treatment revealed a significant downregulation of c-Kit and increased differentiation of hematopoietic stem and progenitor cells. Resistance to epigenetic targeted therapeutics has been observed, often through the induction of kinase signaling pathways. Therefore, we explored synergistic combinations with CARM1 inhibition using RNA-sequencing and proteomics analysis in leukemia cell lines. We used L1000 profiling (Subramanian et al., 2017) to simultaneously profile the transcriptional response of 18 AML cell line and CD34+ cells after 6 days of treatment. The AML1-ETO positive cell lines exhibited an IC50 in the 0.4-3 μM range, while CD34+ cells and several AML cell lines appeared to be resistant to CARM1 inhibition. While gene expression changes resulting from alterations in RNA stability were observed, the most significant differences between sensitive and resistant cell lines were genes associated with the regulation of cell cycle progression. Gene expression changes were evaluated over time in an AML1-ETO positive cell line, SKNO-1. SKNO-1 cell lines showed an upregulation of a gene expression signature associated with PI3K/AKT/mTOR signaling, with the most significant gene expression changes occurring 7-14 days post treatment. We simultaneously profiled these cells using multiplexed kinase inhibitor beads (MIBs) and quantitative mass spectrometry (MS) to compare kinase expression and activity in response to CARM1 inhibition over time. A comparison of this response to chemical perturbation signatures in the L1000 database, identified several chemical inhibitors of the PI3K/AKT/mTOR axis that could reverse the gene expression changes induced by CARM1 inhibition. This finding elucidated a response mechanism for CARM inhibition and a synergistic therapeutic strategy that has the potential to improve CARM1 directed therapy. Disclosures No relevant conflicts of interest to declare.

The leukemogenic AML1-ETO fusion protein is produced by the t(8;21) translocation, which is one of the most common chromosomal abnormalities in acute myeloid leukemia (AML). In leukemic cells, AML1-ETO resides in and functions through a stable protein complex, AETFC, that contains multiple transcription factors and cofactors. Among these AETFC components, E2A (also known as TCF3) and HEB (also known as TCF12), two members of the ubiquitously expressed E proteins, directly interact with AML1-ETO, confer new DNA (E-box) binding capacity to AETFC, and are functionally essential for leukemogenesis. However, we find that the third E protein, E2-2 (also known as TCF4), is specifically silenced in AML1-ETO-expressing leukemic cells, suggesting E2-2 as a negative factor of leukemogenesis. Indeed, ectopic expression of E2-2 selectively inhibits the growth of AML1-ETO-expressing leukemic cells, and this inhibition requires the basic helix-loop-helix (bHLH) DNA-binding domain of E2-2. Gene expression profiling and ChIP-seq analysis reveal that, despite some overlap, the three E proteins differentially regulate many target genes. In particular, consistent with the fact that E2-2 is a critical transcription factor in dendritic cell (DC) development, our studies show that E2-2 both redistributes AETFC to, and activates, some genes associated with DC differentiation, and that restoration of E2-2 triggers a partial differentiation of the AML1-ETO-expressing leukemic cells into the DC lineage. Meanwhile, E2-2, but not E2A or HEB, represses MYC target genes, which may also contribute to leukemic cell differentiation and apoptosis. In AML patients, the expression of E2-2 is relatively lower in the t(8;21) subtype, and an E2-2 target gene, THPO, is identified as a potential predictor of relapse. In a mouse model of human t(8;21) leukemia, E2-2 suppression accelerates the development of leukemia. Taken together, these results reveal that, in contrast to HEB and E2A, which facilitate AML1-ETO-mediated leukemogenesis, E2-2 compromises the function of AETFC and negatively regulates leukemogenesis. The three E proteins thus define a molecular heterogeneity of AETFC, which merits further study in different t(8;21) AML patients, as well as in its potential regulation of cellular heterogeneity of AML. These studies should improve our understanding of the precise mechanism of leukemogenesis and assist development of diagnostic and therapeutic strategies. Disclosures No relevant conflicts of interest to declare.

Introduction: Additional sex combs-like 1 (ASXL1) is frequently mutated in a wide range of myeloid malignancies, including myelodysplastic syndrome (MDS), myeloproliferative neoplasm, chronic myelomonocytic leukemia, and acute myeloid leukemia (AML). Notably, ASXL1 mutations are generally associated with the poor clinical outcomes. We and others have established Asxl1 mouse models and demonstrated that loss of Asxl1 leads to MDS-like disease, which can transform to myeloid leukemia in aged mice. These studies suggest that additional mutations may cooperate with Asxl1 loss to induce the leukemia transformation. However, the molecular mechanisms underlying the leukemogenesis associated with ASXL1 and cooperating mutations remain to be elucidated. Methods: To identify cooperating events with ASXL1 mutations in myeloid malignancies, we recruited a cohort of 138 ASXL1 mutated patients and performed targeted exome sequencing. We then characterized the hematopoietic features using mouse models. A serial hematopoietic phenotypic analyses were used, including peripheral blood counts, flow cytometry, colony assay, morphology and transplantation assays. To decipher the molecular mechanisms by which loss of Asxl1 and Nf1 cooperate in promoting myeloid leukemia transformation, we performed RNA-seq and ChIP-seq to identify the differentially expressed genes and their associated histone modifications in four genotypes of mice, WT, Asxl1+/-, Nf1+/-, and Asxl1+/-;Nf1+/- mice. Finally, the leukemic mice were treated with pharmacologic inhibitors targeting both MAPK pathway and BET bromodomain in vivo as a proof-of-concept approach. Results: We analyzed the gene mutation profiles of 138 ASXL1 mutated patients based on targeted sequencing and found that 35 of these patients have gene mutations involving in RAS/MAPK signaling pathway, including NF1, NRAS, KRAS, PTPN11 or CBL. The incidence of AML was significantly higher in patients with RAS pathway mutations (48.6%) than in the cases without RAS pathway mutations (29.1%, p = 0.036, chi-square test). These data suggest that concomitant mutations of ASXL1 and RAS pathway genes associate with poor prognosis in myeloid malignancies. To validate the functional significance of cooperative mutations of ASXL1 and NF1, a negative regulator of the RAS signaling pathway, in the disease progression of myeloid leukemia, we generated Asxl1+/-;Nf1+/- and Mx1Cre;Asxl1fl/fl;Nf1fl/fl (Asxl1Δ/Δ;Nf1Δ/Δ) mice and performed hematopoietic phenotypic analyses. Asxl1 loss cooperates with haploinsufficiency of Nf1 to accelerate the development of myeloid leukemia in mice. Asxl1Δ/Δ;Nf1Δ/Δ mice displayed a rapid, progressive leukocytosis with severe anemia and thrombocytopenia 3-6 months after pIpC injection, indicative of aggressive myeloid leukemia with a 100% penetrance. Loss of Asxl1 and Nf1 in hematopoietic stem and progenitor cells lead to transcriptional activation of multiple pathways critical for leukemogenesis, such as MYC, NRAS, and BRD4. Convergent analysis of RNA-seq and ChIP-seq data reveal that the hyperactive MYC and BRD4 transcription program is correlated with elevated H3K4 tri-methylation at the promoter regions of genes involving these pathways. Importantly, pharmacological inhibition of both MAPK pathway and BET bromodomain prevents leukemia initiation and inhibits disease progression in Asxl1Δ/Δ;Nf1Δ/Δ mice, and significantly prolonged the survival of leukemic Asxl1+/-;Nf1+/- mice. Conclusion: This study sheds lights on the understanding of the cooperative effect between epigenetic alterations and signaling pathways in accelerating the progression of myeloid malignancies and provides a rationale therapeutic strategy for the treatment of myeloid malignancies with ASXL1 and RAS pathway gene mutations. Disclosures No relevant conflicts of interest to declare.

Aberrant expression of long non-coding RNAs (lncRNAs) might contribute to the development and progression of leukemia. However, functional studies on the actual role of lncRNAs during the development of leukemia remain scarce, and very few lncRNAs have been shown to be involved in leukemogenesis. HoxBlinc is an anterior HoxB gene-associated intergenic lncRNA. It is a cis-acting lncRNA and functions as an epigenetic regulator to coordinate anterior HoxB gene expression. Giving the dysregulation of HOXA/B genes is a dominant mechanism of leukemic transformation, HoxBlinc might be an oncogenic lncRNA of leukemia. To determine whether HOXBLINC lncRNA is aberrantly expressed in human AML samples, we performed RT-qPCR on bone marrow mononuclear cells (BMMNCs) from a cohort of 73 AML patients. A dramatic up-regulation of HOXBLINC was observed in over 60% of the patients. When TCGA-AML datasets of a cohort of 179 AML patients were analyzed for their HOXBLINC expression, a significant portion of these AML patients had high levels of HOXBLINC expression. Interestingly, AML patients with high HOXBLINC expression (the top thirty percentile of patients) had a significantly shortened survival as compared to patients with low HOXBLINC expression (the bottom thirty percentile). To investigate the impact of HoxBlinc overexpression on normal hematopoiesis and the pathogenesis of hematological malignancies in vivo, we generated a HoxBlinc transgenic(Tg) mouse model. Within 1 year of age, 67% of the HoxBlincTg mice (10 of 15) died or were sacrificed because of a moribund condition due to AML. We then assessed whether overexpression of HoxBlinc affects the pools of HSC/HPCs by flow cytometric analysis on the BM cells of young WT and HoxBlincTg mice (8-10 weeks of age). HoxBlincTg BM had a dramatically greater number of LT-HSC, ST-HSC, MPP cells, and a significantly higher percentage of GMP, but a lower percentage of MEP/CMP cell populations as compared to WT group. To determine the effect of HoxBlinc overexpression on the function of HSC/HPCs, we performed paired-daughter cell assay, replating assay and liquid culture on sorted LT-HSC, LSK or LK cells from young WT and HoxBlincTg mice, the results indicate that transgenic expression of HoxBlinc enhances HSC self-renewal and impairs HSC/HPC differentiation. To assess whether HoxBlinc overexpression-mediated changes in HSC/HPC function are cell-autonomous, we performed competitive transplantation assays to examine the repopulating capacity of HoxBlincTg BM cells. When the donor cell chimerism was analyzed kinetically in the PB of recipient mice, the CD45.2 cell population remained ~50% in mice receiving WT BM cells, whereas the CD45.2 chimerism in the recipients transplanted with HoxBlincTg BM cells steadily increased. Interestingly, mice receiving HoxBlincTg BM cells developed AML at 2-6 months after transplantation. Previous data reported that HoxBlinc can recruit the Setd1a/Mll1 histone H3K4 methyltransferase complex to mediate formation of the active topologically associated domain (TAD) in the anterior HoxB locus for transcription of the anterior HoxB genes. In this study, LSK or LK cells sorted from young WT and HoxBlincTg mice were analyzed by RNA-seq, ATAC-seq, H3K4me3 CHIP-seq and 4C analysis. Mechanistically, HoxBlinc overexpression alters HoxB locus chromatin three-dimensional organization to enhance enhancer/promoter chromatin accessibility and coordinate the expression of not only HoxB1-5 but also HoxA9, Runx1, Meis1 and so on, which are critical genes for HSC regulation and/or leukemogenesis. Our study provides novel insights into the HSC regulation by lncRNAs and identifies HOXBLINC, which coordinates to maintain an oncogenic transcription program for leukemic transformation, as a potent oncogenic lncRNA in leukemogenesis. Disclosures No relevant conflicts of interest to declare.

Histone-modifying enzymes have recently been shown to play a central role in the regulation of both normal and malignant hematopoiesis. Post-translational modifications of histones and non-histone proteins underlies a regulatory complexity affecting numerous processes including transcriptional regulation, RNA processing and DNA damage response. Insights into the functions of these enzymes as well as their role in the epigenetic alterations found in leukemia will guide the development of novel therapeutic approaches. This review discusses examples of the proteins that have been implicated in the pathogenesis of leukemia, that may serve as potential therapeutic targets.

Arginine methylation is an abundant covalent modification that regulates diverse cellular processes, including transcription, translation, DNA repair, and RNA processing. The enzymes that catalyze these marks are known as the protein arginine methyltransferases (PRMTs), and they can generate asymmetric dimethyl arginine (type I arginine methyltransferases), symmetric dimethylarginine (type II arginine methyltransferases), or monomethyarginine (type III arginine methyltransferases). The PRMTs are capable of modifying diverse substrates, from histone components to specific nuclear and cytoplasmic proteins. Additionally, the PRMTs can orchestrate chromatin remodeling by blocking the docking of other epigenetic modifying enzymes or by recruiting them to specific gene loci. In the hematopoietic system, PRMTs can regulate cell behavior, including the critical balance between stem cell self-renewal and differentiation, in at least two critical ways, via (i) the covalent modification of transcription factors and (ii) the regulation of histone modifications at promoters critical to cell fate determination. Given these important functions, it is not surprising that these processes are altered in hematopoietic malignancies, such as acute myeloid leukemia, where they promote increased self-renewal and impair hematopoietic stem and progenitor cell differentiation.

We retrospectively assessed morphologic and cytogenetic responses to 5-azacytidine and decitabine in a cohort of 42 adult therapy-related myelodysplastic syndromes (tMDS) patients treated at Memorial Sloan-Kettering Cancer Center and in 2 industry-sponsored decitabine trials (D0007 and DACO-020). The overall response rate (complete remission+marrow CR+hematologic improvement) was 38%, including 6 patients with complete remission (14%), 6 with marrow CR with or without hematologic improvement (14%), and 4 with hematologic improvement alone (10%). We conclude that DNA methyltransferase inhibitors showed activity in tMDS that is roughly comparable to that seen in de novo MDS.

Abstract 4621 Fusion protein AML1-ETO resulting from t(8;21) translocation is highly related to leukemia development. It has been demonstrated that full-length AML1-ETO blocks AML1 function and requires additional mutagenic events to promote leukemia. We have previously shown that the expression of AE9a, a splice isoform of AML1-ETO, can rapidly cause leukemia in mice. To understand how AML1-ETO is involved in leukemia development, we took advantage of our AE9a leukemia model and sought to identify its interacting proteins from primary leukemic cells. Here we report the discovery of a novel AE9a binding partner PRMT1 (protein arginine methyltransferase 1). PRMT1 not only interacts with but also weakly methylates Arginine 142 of AE9a. Knockdown of PRMT1 affects expression of a specific group of AE9a-activated genes. We also show that AE9a recruits PRMT1 to promoters of AE9a activated genes, resulting in enrichment of H4 Arg3 methylation, H3 Lys9/14 acetylation, and transcription activation. More importantly, knockdown of PRMT1 suppresses AE9a’s self-renewal capability, suggesting a potential role of PRMT1 in regulating leukemia development. Disclosures: No relevant conflicts of interest to declare.

Sodium salicylate is an inexpensive, readily available anti-inflammatory agent which inhibits NF-κB in in vitro models. We examined whether it was possible to safely achieve and maintain salicylate levels known to inhibit NF-κB in vitro in 11 patients with MDS or AML taking sodium salicylate. Most patients achieved the target blood salicylate level (20-30mg/dL) with acceptable toxicity, including reversible grade 1/2 elevations of hepatic transaminases (n=4) and ototoxicity (n=4). One patient had grade 3/4 elevations in AST/ALT. This study suggests that sodium salicylate may be safely combined with conventional chemotherapy regimens which are not associated with significant ototoxicity or hepatotoxicity.

Inhibitor of DNA binding 1 (Id1) functions as an E protein inhibitor, and overexpression of Id1 is seen in acute myeloid leukemia (AML) patients. To define the effects of Id1 on leukemogenesis, we expressed MLL-AF9 in fetal liver (FL) cells or bone marrow (BM) cells isolated from wild-type, Id1(-/-), p21(-/-), or Id1(-/-)p21(-/-) mice, and transplanted them into syngeneic recipient mice. We found that although mice receiving MLL-AF9-transduced FL or BM cells develop AML, loss of Id1 significantly prolonged the median survival of mice receiving FL cells but accelerated leukemogenesis in recipients of BM cells. Deletion of Cdkn1a (p21), an Id1 target gene, can rescue the effect of Id1 loss in both models, suggesting that Cdkn1a is a critical target of Id1 in leukemogenesis. It has been suggested that the FL transplant model mimics human fetal-origin (infant) MLL fusion protein (FP)-driven leukemia, whereas the BM transplantation model resembles postnatal MLL leukemia; in fact, the analysis of clinical samples from patients with MLL-FP(+) leukemia showed that Id1 expression is elevated in the former and reduced in the latter type of MLL-FP(+) AML. Our findings suggest that Id1 could be a potential therapeutic target for infant MLL-AF9-driven leukemia.

Human embryonic stem cells (hESCs) can be used to study the early events in human development and, hopefully, to understand how to differentiate human pluripotent cells for clinical use. To define how L3MBTL1, a chromatin-associated polycomb group protein with transcriptional repressive activities, regulates early events in embryonic cell differentiation, we created hESC lines that constitutively express shRNAs directed against L3MBTL1. The L3MBTL1 knockdown (KD) hESCs maintained normal morphology, proliferation, cell cycle kinetics, cell surface markers, and karyotype after 40 passages. However, under conditions that promote spontaneous differentiation, the L3MBTL1 KD cells differentiated into a relatively homogeneous population of large, flat trophoblast-like cells, unlike the multilineage differentiation seen with the control cells. The differentiated L3MBTL1 KD cells expressed numerous trophoblast markers and secreted placental hormones. Although the L3MBTL1 KD cells could be induced to differentiate into various embryonic lineages, they adopted an exclusive trophoblast fate during spontaneous differentiation. Our data demonstrate that depletion of L3MBTL1 does not affect hESC self-renewal, rather it enhances differentiation toward extra-embryonic trophoblast tissues.

Relapse is the overwhelming cause of treatment failure after autologous transplantation for multiple myeloma (MM). For patients with a syngeneic donor, twin transplants provide a healthy graft that is free of myeloma. The relative impact of the graft on posttransplant relapse can be estimated by comparing risk of relapse after hematopoietic cell transplantation from genetically identical twins versus autotransplants because confounding differences in minor or major histocompatibility antigens are absent in the syngeneic transplant setting. Outcomes of 43 subjects who received twin transplants for MM were compared to 170 matched autotransplant recipients reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). Multivariate analysis was performed by fitting a Cox model stratified on matched pairs. The matched transplant patients studied were similar with respect to subject-, disease-, and transplant-related characteristics. Cumulative incidence of relapse/progression was significantly lower, and progression-free survival (PFS) was significantly higher following twin transplants. In multivariate analysis, the probability of relapse/progression was lower in twins (relative risk [RR] = 0.49, 95% confidence interval [CI] 0.28-0.86, P = .011). Twin transplants have a significantly lower relapse risk than autotransplants in MM, suggesting that graft composition may impact outcomes following high-dose chemotherapy.

Despite advances in therapy, many patients with systemic light-chain amyloidosis (AL) die within 3 years from diagnosis. The humanized 2B6 monoclonal antibody (MoAb) is specific for the low-affinity IgG Fc receptor CD32B and effective in a human CD32B+ B-cell lymphoma murine xenograft model. Because MoAb therapy could improve outcomes in AL, we studied CD32B expression by clonal plasma cells obtained from 48 patients with AL. Transcript profiling showed that expression of CD32B was significantly higher than expression of all other Fc receptor family members. Reverse-transcriptase polymerase chain reaction (RT-PCR) using double-enriched CD138+ plasma cells showed uniform expression of the stable cell surface CD32B1 isoform at diagnosis and relapse, and flow cytometry showed intense CD32B cell surface staining on 99% of CD138+ plasma cells at diagnosis and relapse. These data provide a rationale for the novel therapeutic targeting of CD32B using the humanized 2B6 MoAb in patients with systemic AL-amyloidosis.

We studied the role of HLA-matched sibling hematopoietic cell transplantation (HCT) in treating t(8;21) acute myelogenous leukemia (AML) in first remission. Outcomes of 118 patients receiving HCT and reported to the Center for International Blood and Marrow Transplant Research were compared with 132 similar patients receiving chemotherapy selected from 8 German AML Intergroup multicenter trials. Characteristics of the cohorts were similar except that chemotherapy recipients were significantly older. To adjust for time to treatment bias, outcomes were compared using left-truncated Cox regression models. Transplants were associated with higher treatment-related mortality (TRM; relative risk [RR] 6.76, 95% confidence interval [CI] 2.95-15.45, P < .001), lower relapse (RR 0.47, 95% CI 0.25-0.85, P = .01), and similar relapse-free survival (P = .2). Loss of sex chromosomes (LOS) in addition to t(8;21) had a negative impact on overall survival (OS) in patients receiving chemotherapy. Patients without LOS experienced shorter survival after HCT comparing to chemotherapy (RR 3.05, P = .02), whereas patients with LOS had similar survival regardless of postremission therapy. In both cohorts, white blood cell count (WBC) at diagnosis >25 × 109/L was associated with a higher relapse risk (RR = 2.09, P = .03), lower relapse-free (RR = 1.9, P = .008), and OS (RR = 1.91, P = .01). In this cohort of patients with t(8;21) AML, HCT did not improve OS, because reduction of relapse was offset by high TRM. In the group without LOS, survival after chemotherapy was far superior to HCT. These results suggest that patients with t(8;21) AML without poor prognostic factors have higher rates of survival after chemotherapy as a post remission therapy compared to HCT.

Despite the various abnormalities identified in the immune system or the bone marrow microenvironment in patients with myelodysplastic syndrome (MDS), most of the investigation of this disorder has centered on the hematopoietic stem/progenitor compartment. It is generally written that MDS is a stem cell disorder, and there is certainly evidence supporting this view. However, whether it occurs in a cell with only myeloid multipotentiality (i.e., that involves megakaryocytic, erythroid and granulocytic/monocytic lineages) or occurs in a true stem cell is open to debate. The absence of an assay for human stem cells necessitates the use of surrogate markers for such cells, such as gene expression profiles, or the identification of specific genetic or epigenetic abnormalities that are found in multiple lineages. Clearly, the common cytogenetic and genetic abnormalities found in MDS are most indicative of a clonal myeloid disease similar to AML, rather than a lymphoid disease, and the often tri-lineage ineffective hematopoiesis and dysplasia are generally not found within the lymphoid compartment. Recent studies, using modern molecular detection techniques, have identified new recurring molecular lesions in these disorders but have not really unraveled its pathogenesis.

High-dose melphalan (MEL) with autologous stem cell transplant (SCT) is an effective therapy for systemic AL amyloidosis (AL), but treatment-related mortality (TRM) has historically been high. We performed a phase II trial of risk-adapted SCT followed by adjuvant dexamethasone (dex) and thalidomide (thal) in an attempt to reduce TRM and improve response rates. Patients (n = 45) with newly diagnosed AL involving < or =2 organ systems were assigned to MEL 100, 140, or 200 mg/m(2) with SCT, based on age, renal function and cardiac involvement. Patients with persistent clonal plasma cell disease 3 months post-SCT received 9 months of adjuvant thal/dex (or dex if there was a history of deep vein thrombosis or neuropathy). Organ involvement was kidney (67%), heart (24%), liver/GI (22%) and peripheral nervous system (18%), with 31% having two organs involved. TRM was 4.4%. Thirty-one patients began adjuvant therapy, with 16 (52%) completing 9 months of treatment and 13 (42%) achieving an improvement in haematological response. By intention-to-treat, overall haematological response rate was 71% (36% complete response), with 44% having organ responses. With a median follow-up of 31 months, 2-year survival was 84% (95% confidence interval: 73%, 94%). Risk-adapted SCT with adjuvant thal/dex is feasible and results in low TRM and high haematological and organ response rates in AL patients.

Phosphoproteomic analysis identifies the M0-91 cell line as a cellular model for the study of TEL-TRKC fusion-associated leukemia

RUNX1 (previously termed AML1) is a frequent target of human leukaemia-associated gene aberrations, and it encodes the DNA-binding subunit of the Core-Binding Factor transcription factor complex. RUNX1 expression is essential for the initiation of definitive haematopoiesis, for steady-state thrombopoiesis, and for normal lymphocytes development. Recent studies revealed that protein arginine methyltransferase 1 (PRMT1), which accounts for the majority of the type I PRMT activity in cells, methylates two arginine residues in RUNX1 (R206 and R210), and these modifications inhibit corepressor-binding to RUNX1 thereby enhancing its transcriptional activity. In order to elucidate the biological significance of these methylations, we established novel knock-in mouse lines with non-methylable, double arginine-to-lysine (RTAMR-to-KTAMK) mutations in RUNX1. Homozygous Runx1(KTAMK) (/) (KTAMK) mice are born alive and appear normal during adulthood. However, Runx1(KTAMK) (/) (KTAMK) mice showed a reduction in CD3(+) T lymphoid cells and a decrease in CD4(+) T cells in peripheral lymphoid organs, in comparison to their wild-type littermates, leading to a reduction in the CD4(+) to CD8(+) T-cell ratio. These findings suggest that arginine-methylation of RUNX1 in the RTAMR-motif is dispensable for the development of definitive haematopoiesis and for steady-state platelet production, however this modification affects the role of RUNX1 in the maintenance of the peripheral CD4(+) T-cell population.

Transcriptional regulators are recurrently altered through translocations, deletions, or aberrant expression in acute myeloid leukemia (AML). Although critically important in leukemogenesis, the underlying pathogenetic mechanisms they trigger remain largely unknown. Here, we identified that Id1 (inhibitor of DNA binding 1) plays a pivotal role in acute myeloid leukemogenesis. Using genetically modified mice, we found that loss of Id1 inhibited t(8;21) leukemia initiation and progression in vivo by abrogating protein kinase B (AKT)1 activation, and that Id1 interacted with AKT1 through its C terminus. An Id1 inhibitor impaired the in vitro growth of AML cells and, when combined with an AKT inhibitor, triggered even greater apoptosis and growth inhibition, whereas normal hematopoietic stem/progenitor cells were largely spared. We then performed in vivo experiments and found that the Id1 inhibitor significantly prolonged the survival of t(8;21)(+) leukemic mice, whereas overexpression of activated AKT1 promoted leukemogenesis. Thus, our results establish Id1/Akt1 signaling as a potential therapeutic target in t(8;21) leukemia.

Natural killer T (NKT) cells are CD1d-restricted glycolipid reactive innate lymphocytes that play an important role in protection from pathogens and tumors. Pharmacologic approaches to enhance NKT cell function will facilitate specific NKT targeting in the clinic. Here we show that lenalidomide (LEN), a novel thalidomide (Thal) analog, enhances antigen-specific expansion of NKT cells in response to the NKT ligand α-galactosylceramide (α-GalCer) in both healthy donors and patients with myeloma. NKT cells activated in the presence of LEN have greater ability to secrete interferon-γ. Antigen-dependent activation of NKT cells was greater in the presence of dexamethasone (DEX) plus LEN than with DEX alone. Therapy with LEN/Thal also led to an increase in NKT cells in vivo in patients with myeloma and del5q myelodysplastic syndrome. Together these data demonstrate that LEN and its analogues enhance CD1d-mediated presentation of glycolipid antigens and support combining these agents with NKT targeted approaches for protection against tumors.

Autologous transplantation (ASCT) is the standard of care for chemosensitive relapsed or primary refractory aggressive lymphoma, but little is known about its efficacy in the subset of patients with peripheral T-cell lymphoma (PTCL). We undertook a retrospective review of patients with PTCL who underwent ASCT for relapsed or refractory disease after responding to second-line therapy, excluding patients with indolent histologies and those with anaplastic lymphoma kinase (ALK) expressing anaplastic large cell lymphoma. The results of 24 patients with PTCL were compared with those of 86 consecutive patients with chemosensitive relapsed or primary refractory diffuse large B-cell lymphoma (DLBCL). With a median follow-up time of 6 years for surviving patients with PTCL and DLBCL, the 5-year progression-free survival (PFS) rates for PTCL and DLBCL patients were 24% and 34% respectively (P = 0.14); the corresponding overall survival (OS) rates were 33% and 39% respectively. There were no significant differences between the two groups with respect to time to disease progression or survival after progression. The second-line age-adjusted international prognostic index was the only variable prognostic for PFS and OS in a multivariate analysis. The outcome of ASCT for patients with chemosensitive relapsed or primary refractory PTCL is similar to that for patients with DLBCL.

Somatic mutations in IDH1/IDH2 and TET2 result in impaired TET2-mediated conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). The observation that WT1 inactivating mutations anticorrelate with TET2/IDH1/IDH2 mutations in acute myeloid leukemia (AML) led us to hypothesize that WT1 mutations may impact TET2 function. WT1 mutant AML patients have reduced 5hmC levels similar to TET2/IDH1/IDH2 mutant AML. These mutations are characterized by convergent, site-specific alterations in DNA hydroxymethylation, which drive differential gene expression more than alterations in DNA promoter methylation. WT1 overexpression increases global levels of 5hmC, and WT1 silencing reduced 5hmC levels. WT1 physically interacts with TET2 and TET3, and WT1 loss of function results in a similar hematopoietic differentiation phenotype as observed with TET2 deficiency. These data provide a role for WT1 in regulating DNA hydroxymethylation and suggest that TET2 IDH1/IDH2 and WT1 mutations define an AML subtype defined by dysregulated DNA hydroxymethylation., info:eu-repo/semantics/published

Autologous stem cell transplantation (SCT) with high-dose melphalan (HDM, 200 mg/m2) is the most effective therapy for multiple myeloma. To determine the feasibility of combining carmustine (300 mg/m2) with HDM, we enrolled 49 patients with previously treated Durie-Salmon stage II/III myeloma (32M/17W, median age 53) on a phase I/II trial involving escalating doses of melphalan (160, 180, 200 mg/m2). The median beta2-microglobulin was 2.5 (0-9.3); marrow karyotypes were normal in 88%. The phase I dose-limiting toxicity was > or =grade 2 pulmonary toxicity 2 months post-SCT. Other endpoints were response rate and progression-free survival (PFS). HDM was safely escalated to 200 mg/m2; treatment-related mortality was 2% and > or =grade 2 pulmonary toxicity 10%. The complete (CR) and near complete (nCR) response rate was 49%. With a median post-SCT follow-up of 2.9 years, the PFS and overall survival (OS) post-SCT were 2.3 and 4.7 years. PFS for those with CR or nCR was 3.1 years while for those with stable disease (SD) it was 1.3 years (P=0.06). We conclude that carmustine can be combined with HDM for myeloma with minimal pulmonary toxicity and a high response rate.

Multiple myeloma (MM) is an incurable hematologic malignancy for which autologous hematopoietic stem cell transplantation (HCT) is a standard therapy. The optimal method of stem cell mobilization is not defined. We evaluated intravenous melphalan (60 mg/m2), the most effective agent for MM, and G-CSF (10 microg/kg/day) for mobilization. End points were safety, adequacy of CD34+ collections, MM response, and contamination of stem cell components (SCC). In total, 32 patients were mobilized. There were no deaths or significant bleeding episodes; 14 patients (44%) required hospitalization for neutropenic fever. Median days of grade 3 or 4 neutropenia or thrombocytopenia were 7 (2-20) and 8 (3-17). Median mobilization days, CD34+ cells/kg and total leukaphereses were 16 (12-30), 12.1 million (2.6-52.8), and 2 (1-5) respectively. Four patients (12.5 %) failed to achieve the target of 4 million CD34+ cells/kg in five leukaphereses. Reduction in myeloma was seen in 11 patients (34%) with 3 (9%) achieving complete response; 15 (47%) maintained prior responses. Estimated MM contamination per SCC (N=48) was 0.0009% (range 0-0.1) and 0.21 x 10(4) cells per kg (range 0-41.2). Increased contamination was associated with increased patient age. This strategy for mobilization is feasible, frequently requires hospitalization and transfusion, and controls disease in most patients.

Prospective randomized studies have determined that high dose therapy and autologous stem cell transplantation (ASCT) is the standard treatment for patients with chemosensitive relapsed Hodgkin's disease (HD); however, the role of this approach in patients with primary refractory disease has been controversial. This report is an integrated analysis of 75 consecutive patients with biopsy-confirmed primary refractory HD, who were treated with high dose chemoradiotherapy (HDT) and ASCT at the Memorial Sloan Kettering Cancer Center. The patients underwent conventional dose cytoreductive chemotherapy followed by HDT and ASCT. At a median follow-up of 10 years for surviving patients, the event-free survival (EFS), progression-free survival (PFS) and overall survival (OS) rates were 45%, 49% and 48% respectively. Only chemosensitivity to standard-dose second-line chemotherapy (SDSC) predicted for a better survival, thus responding patients had an EFS, PFS and OS of 60%, 62% and 66%, respectively, versus 19%, 23% and 17% for patients who had a poor response to SDSC (P < 0.001). While patients with chemosensitive disease have an excellent outcome with HDT and ASCT, novel approaches are needed to cure HD patients who fail front-line and second-line chemotherapy.

Hematopoiesis is a complex process involving hematopoietic stem cell (HSC) self-renewal and lineage commitment decisions that must continue throughout life. Establishing a reproducible technique that allows for the long-term ex vivo expansion of human HSCs and maintains self-renewal and multipotential differentiation will allow us to better understand these processes, and we report the ability of the leukemia-associated AML1-ETO fusion protein to establish such a system. AML1-ETO-transduced human CD34+ hematopoietic cells routinely proliferate in liquid culture for more than 7 months, remain cytokine dependent for survival and proliferation, and demonstrate self-renewal of immature cells that retain both lymphoid and myeloid potential in vitro. These cells continue to express the CD34 cell surface marker and have ongoing telomerase activity with maintenance of telomere ends, however they do not cause leukemia in nonobese diabetic-severe combined immunodeficiency (NOD/SCID) mice. Identification of the signaling pathways that are modulated by AML1-ETO and lead to the self-renewal of immature human progenitor cells may assist in identifying compounds that can efficiently expand human stem and progenitor cells ex vivo. (Blood. 2003; 102:4369-4376)