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Supplementary Table from Epigenetic Activation of Plasmacytoid DCs Drives IFNAR-Dependent Therapeutic Differentiation of AML

Supplementary Figure from Epigenetic Activation of Plasmacytoid DCs Drives IFNAR-Dependent Therapeutic Differentiation of AML

Neural tube closure is a dynamic morphogenic event in early embryonic development. Perturbations of this process through either environmental or genetic factors induce the severe congenital malformations known collectively as neural tube defects (NTDs). Deficiencies in maternal folate intake have long been associated with NTDs, as have mutations in critical neurulation genes that include the Grainyhead-like 3 (Grhl3) gene. Mice lacking this gene exhibit fully penetrant thoraco-lumbo-sacral spina bifida and a low incidence of exencephaly. Previous studies have shown that exposure of pregnant mice carrying hypomorphic Grhl3 alleles to exogenous retinoic acid (RA) increases the incidence and severity of NTDs in their offspring. Here, we demonstrate that inhibition of RA signaling using a high affinity pan-RA receptor antagonist administered to pregnant mice at E7.5 induces fully penetrant exencephaly and more severe spina bifida in Grhl3-null mice. Later administration, although prior to neural tube closure has no effect. Similarly, blockade of RA in the context of reduced expression of Grhl2, a related gene known to induce NTDs, has no effect. Taken together, these findings provide new insights into the complexities of the interplay between RA signaling and Grhl3-induced neurulation.

Acute myeloid leukemia (AML) is a malignancy of immature progenitor cells. AML differentiation therapies trigger leukemia maturation and can induce remission, but relapse is prevalent and its cellular origin is unclear. Here we describe high resolution analysis of differentiation therapy response and relapse in a mouse AML model. Triggering leukemia differentiation in this model invariably produces two phenotypically distinct mature myeloid lineages in vivo. Leukemia-derived neutrophils dominate the initial wave of leukemia differentiation but clear rapidly and do not contribute to residual disease. In contrast, a therapy-induced population of mature AML-derived eosinophil-like cells persists during remission, often in extramedullary organs. Using genetic approaches we show that restricting therapy-induced leukemia maturation to the short-lived neutrophil lineage markedly reduces relapse rates and can yield cure. These results indicate that relapse can originate from therapy-resistant mature AML cells, and suggest differentiation therapy combined with targeted eradication of mature leukemia-derived lineages may improve disease outcome., Differentiation therapy induces the maturation and clearance of acute myeloid leukemia cells. Here, using a mouse model, the authors show that a specific lineage of mature leukemia-derived cells persists during remission and is responsible for disease relapse.

SummaryMouse hematopoietic tissues contain abundant and heterogeneous populations of tissue-resident macrophages attributed trophic functions in control of immunity, hematopoiesis and bone homeostasis. A systematic strategy to characterise macrophage subsets in mouse bone marrow (BM), spleen and lymph node, unexpectedly revealed macrophage surface marker staining typically emanated from membrane-bound subcellular remnants associated with unrelated cell types. Remnant-restricted macrophage-specific membrane markers, cytoplasmic fluorescent reporters and mRNA were all detected in non-macrophage cell populations including isolated stem and progenitor cells. The profile of macrophage remnant association reflects adhesive interactions between macrophages and other cell types in vivo. Applying this knowledge, reduced macrophage remnant attachment to BM granulocytes in Siglec1 deficient mice was associated with compromised emergency granulocytosis, revealing a function for Siglec1-dependent granulocyte-macrophage interactions. Analysis of published RNA-seq data for purified macrophage and non-macrophage populations indicates that macrophage fragmentation is a general phenomenon that confounds bulk and single cell analysis of disaggregated tissues.

Mouse hematopoietic tissues contain abundant tissue-resident macrophages that support immunity, hematopoiesis, and bone homeostasis. A systematic strategy to characterize macrophage subsets in mouse bone marrow (BM), spleen, and lymph node unexpectedly reveals that macrophage surface marker staining emanates from membrane-bound subcellular remnants associated with unrelated cells. Intact macrophages are not present within these cell preparations. The macrophage remnant binding profile reflects interactions between macrophages and other cell types in vivo. Depletion of CD169+ macrophages in vivo eliminates F4/80+ remnant attachment. Remnant-restricted macrophage-specific membrane markers, cytoplasmic fluorescent reporters, and mRNA are all detected in non-macrophage cells including isolated stem and progenitor cells. Analysis of RNA sequencing (RNA-seq) data, including publicly available datasets, indicates that macrophage fragmentation is a general phenomenon that confounds bulk and single-cell analysis of disaggregated hematopoietic tissues. Hematopoietic tissue macrophage fragmentation undermines the accuracy of macrophage ex vivo molecular profiling and creates opportunity for misattribution of macrophage-expressed genes to non-macrophage cells.

The classical myeloproliferative neoplasms (MPN) are uncommon clonal haematopoietic malignancies characterised by excessive production of mature blood cells. Clinically they are associated with thrombosis, haemorrhage, varying degrees of constitutional disturbance, and a risk of progression to myelofibrosis or acute myeloid leukaemia. Many of the disease manifestations may be ameliorated by treatment with interferon‐α (IFN) but its use in Australian MPN patients has been limited due to the inconvenience of frequent injections and side effects. The pegylated form of IFN is a long‐acting preparation which is better tolerated and its Pharmaceutical Benefits Scheme listing is likely to lead to increased usage. We review the literature on risks and benefits of IFN treatment for MPNs, suggest criteria for patient selection in each of these diseases, and discuss strategies to manage the side effects of pegylated IFN. Refereed/Peer-reviewed

In normoxia, hypoxia-inducible transcription factors (HIFs) are rapidly degraded within the cytoplasm as a consequence of their prolyl hydroxylation by oxygen-dependent prolyl hydroxylase domain (PHD) enzymes. We have previously shown that hematopoietic stem and progenitor cells (HSPCs) require HIF-1 for effective mobilization in response to granulocyte colony-stimulating factor (G-CSF) and CXCR4 antagonist AMD3100/plerixafor. Conversely, HIF PHD inhibitors that stabilize HIF-1 protein in vivo enhance HSPC mobilization in response to G-CSF or AMD3100 in a cell-intrinsic manner. We now show that extrinsic mechanisms involving vascular endothelial growth factor receptor-2 (VEGFR2), via bone marrow (BM) endothelial cells, are also at play. PTK787/vatalanib, a tyrosine kinase inhibitor selective for VEGFR1 and VEGFR2, and neutralizing anti-VEGFR2 monoclonal antibody DC101 blocked enhancement of HSPC mobilization by FG-4497. VEGFR2 was absent on mesenchymal and hematopoietic cells and was detected only in Sca1+ endothelial cells in the BM. We propose that HIF PHD inhibitor FG-4497 enhances HSPC mobilization by stabilizing HIF-1α in HSPCs as previously demonstrated, as well as by activating VEGFR2 signaling in BM endothelial cells, which facilitates HSPC egress from the BM into the circulation.

Hallmark features of myelofibrosis (MF) are cytopenias, constitutional symptoms and splenomegaly. Anemia and transfusion dependency are among the most important negative prognostic factors and are exacerbated by many JAK inhibitors (JAKi). Momelotinib (MMB) has been investigated in over 820 patients with MF and possesses a pharmacological and clinical profile differentiated from other JAKi by inhibition of JAK1, JAK2 and ACVR1. MMB is designed to address the complex drivers of iron-restricted anemia and chronic inflammation in MF and should improve constitutional symptoms and splenomegaly while maintaining or improving hemoglobin in JAKi-naive and previously JAKi-treated patients. The MOMENTUM Phase III study is designed to confirm and extend observations of safety and clinical activity of MMB.Lay abstract The most important features of myelofibrosis (MF) are low blood cell counts and symptoms including tiredness, night sweats and itching, along with increased size of the spleen, which may cause a feeling of fullness and pain. Low red blood cell counts (anemia) may mean regular blood transfusions are needed and this is one of the signs MF is getting worse. Drugs called JAK inhibitors (JAKi) are available to treat MF, but can have a side effect of making blood cell counts lower. Momelotinib (MMB) is a different type of JAKi to the ones currently available, and is an experimental drug for MF. MMB is designed to treat symptoms and spleen like other JAKi, but also to improve blood cell counts. MMB has already been given to more than 820 patients with MF in other clinical studies. Some of the patients in these studies had been treated with different JAKi before, and others got MMB as their first JAKi treatment. The MOMENTUM Phase III study is designed to collect more information on the safety and effectiveness of MMB in MF.

Myeloproliferative neoplasms are characterised by somatic mutations in pathways that regulate cell proliferation, epigenetic modifications, RNA splicing or DNA repair. Assessment of the mutational profile assists diagnosis and classification, but also aids assessment of prognosis, and may guide the use of emerging targeted therapies. The most practical way to provide information on numerous genetic variants is by using massively parallel sequencing, commonly in the form of disease specific next generation sequencing (NGS) panels. This review summarises the diagnostic and prognostic value of somatic mutation testing in Philadelphia-negative myeloproliferative neoplasms: polycythaemia vera, essential thrombocythaemia, primary myelofibrosis, chronic neutrophilic leukaemia, systemic mastocytosis, and chronic eosinophilic leukaemia. NGS panel testing is increasing in routine practice and promises to improve the accuracy and efficiency of pathological diagnosis and prognosis. Refereed/Peer-reviewed

Pharmacologic inhibition of epigenetic enzymes can have therapeutic benefit against hematologic malignancies. In addition to affecting tumor cell growth and proliferation, these epigenetic agents may induce antitumor immunity. Here, we discovered a novel immunoregulatory mechanism through inhibition of histone deacetylases (HDAC). In models of acute myeloid leukemia (AML), leukemia cell differentiation and therapeutic benefit mediated by the HDAC inhibitor (HDACi) panobinostat required activation of the type I interferon (IFN) pathway. Plasmacytoid dendritic cells (pDC) produced type I IFN after panobinostat treatment, through transcriptional activation of IFN genes concomitant with increased H3K27 acetylation at these loci. Depletion of pDCs abrogated panobinostat-mediated induction of type I IFN signaling in leukemia cells and impaired therapeutic efficacy, whereas combined treatment with panobinostat and IFNα improved outcomes in preclinical models. These discoveries offer a new therapeutic approach for AML and demonstrate that epigenetic rewiring of pDCs enhances antitumor immunity, opening the possibility of exploiting this approach for immunotherapies. Significance: We demonstrate that HDACis induce terminal differentiation of AML through epigenetic remodeling of pDCs, resulting in production of type I IFN that is important for the therapeutic effects of HDACis. The study demonstrates the important functional interplay between the immune system and leukemias in response to HDAC inhibition. This article is highlighted in the In This Issue feature, p. 1397

The caudal-related homeobox transcription factor CDX2 is expressed in leukemic cells but not during normal blood formation. Retroviral overexpression of Cdx2 induces AML in mice, however the developmental stage at which CDX2 exerts its effect is unknown. We developed a conditionally inducible Cdx2 mouse model to determine the effects of in vivo, inducible Cdx2 expression in hematopoietic stem and progenitor cells (HSPCs). Cdx2-transgenic mice develop myelodysplastic syndrome with progression to acute leukemia associated with acquisition of additional driver mutations. Cdx2-expressing HSPCs demonstrate enrichment of hematopoietic-specific enhancers associated with pro-differentiation transcription factors. Furthermore, treatment of Cdx2 AML with azacitidine decreases leukemic burden. Extended scheduling of low-dose azacitidine shows greater efficacy in comparison to intermittent higher-dose azacitidine, linked to more specific epigenetic modulation. Conditional Cdx2 expression in HSPCs is an inducible model of de novo leukemic transformation and can be used to optimize treatment in high-risk AML., The caudal-related homeobox transcription factor CDX2 is expressed in leukemic cells in the majority of patients with leukemia but not during normal blood formation. Here, the authors report a mouse model with conditional Cdx2 expression showing de novo leukemic transformation, and use it to optimize treatment in high-risk AML.

KLF1 is an essential transcriptional activator that drives erythropoiesis. KLF1 variants can result in the Inhibitor of Lutheran, or In(Lu), phenotype where red blood cells (RBCs) have reduced BCAM (LU) and CD44 (IN). Other RBC surface molecules also have changed expression; however, there is controversy in the literature regarding which are truly impacted. We aimed to investigate KLF1 variants in the Australian population. In(Lu) samples were sourced through screening and through the RBC reference laboratory. Blood donor samples (8036) were screened to identify weakened/absent Lu antigen. Samples were genotyped by massively parallel sequencing, while surface carbohydrates and blood group molecules were assessed by flow cytometry. Hemoglobin (Hb) types were analyzed by high-performance liquid chromatography. Four of 8036 donors were identified to be In(Lu), and two previously identified In(Lu) samples were provided from the RBC reference laboratory. Five different KLF1 variants were identified; two were novel: c.954G>C/p.Trp318Cys and c.421C>T/p.Arg141*. BCAM and CD44 were reduced in all samples, consistent with previous reports. As a group, In(Lu) RBCs had reduced CD35 (KN), ICAM4 (LW), and CD147 (OK), and demonstrated increased binding of lectins ECA and SNAI. One In(Lu) sample had elevated HbF and another elevated HbA2. Different KLF1 variants may potentially produce variable phenotypes. A framework for investigating KLF1 variants and their phenotypic impact has been provided. In the future, given available international databases, further testing algorithms (as advocated here) will allow for correlation of phenotype with genotype and therefore accurately document this variability between KLF1 variants.

Introduction Patients (pts) with MF who discontinue ruxolitinib due to resistance or progression have a poor prognosis (median OS, 14 months; Kuykendall et al. Ann Hematol. 2018). Available therapies provide symptom control and reduce spleen volumes, but do not address the underlying pathophysiology of disease, underscoring a need for disease-modifying treatments. Murine double minute 2 (MDM2), a key negative regulator of the tumor suppressor protein p53, is overexpressed in CD34+ cells in MF. Elevated MDM2 attenuates p53 activity resulting in proliferation of malignant CD34+ cells. Navtemadlin (KRT-232), a potent, selective, orally available MDM2 inhibitor, restores p53 function and mediates apoptosis of malignant cells, suggesting a potential for disease-modification. As previously reported in relapsed/refractory (R/R) MF, once-daily navtemadlin at 240 mg (Day 1-7/28-day cycle) yielded a best spleen volume reduction (SVR) ≥35% by central review in 16% of pts, best total symptom score (TSS) response >50% in 30% of pts, and an 87% reduction of peripheral CD34+ cells at Week 24 (Al-Ali et al. EHA 2020). Aims To evaluate the correlations between changes in biomarkers of disease burden (variant allele frequency [VAF] of driver mutation and high-molecular risk (HMR) genes, peripheral blood CD34+ cells, serum cytokine levels, and bone marrow fibrosis) and clinical benefits (spleen volume reduction and symptom response). Methods Pts with R/R MF were treated in a phase 2 trial with different doses/schedules of navtemadlin (NCT03662126). Peripheral blood samples were collected at baseline and after 12 and 24 weeks of navtemadlin. Analysis of driver and HMR mutations (ASXL1, EZH2, SRSF2, IDH1/2, U2AF1) and VAF measurements from peripheral blood were determined by next-generation sequencing. Serum TNFα was analyzed by ELISA. Bone marrow biopsies were collected at baseline and after 24 weeks of treatment; fibrosis was assessed by a central pathology review. Correlations were investigated by calculating Spearman's rank-correlation coefficients. Results As of April 15, 2021, of 113 pts treated with navtemadlin, 111 were evaluable for mutation analyses. At baseline, 108 pts had ≥1 driver mutation and 75 pts had ≥1 mutation in an HMR gene Driver mutations in JAK2, CALR, or MPL were reported in 81 (73%), 22 (19%) and 13 (12%) of pts, respectively; 28 (25%) carried mutations in ≥2 HMR genes. Of 65 pts evaluable for driver gene or HMR VAF reductions, a best driver gene reduction ≥20% after navtemadlin was observed in 22 (34%) pts and 19 (29%) showed a complete VAF reduction (below the limit of detection) in HMR or driver genes (Fig 1). Reduction in driver allele VAF at any time on study significantly correlated with SVR (Fig 2A); SVR responses were noted in more pts with ≥20% vs Reductions in circulating CD34+ cells in peripheral blood observed with navtemadlin treatment correlated significantly with best SVR (Fig 2B). Navtemadlin induced reductions in serum TNFα with a median best decrease from baseline of 41%. Reductions in TNFα correlated with best SVR and TSS responses (Fig 2C and 2D). Of 45 pts who had bone marrow biopsies at baseline and Week 24, 41 (91%) had baseline fibrosis scores ≥1, with 31 (69%) and 4 (9%) having Grade 2 and 3 fibrosis, respectively. After navtemadlin treatment, 12 (27%) showed improved fibrosis scores of ≥1 grade and 23 (51%) had stable fibrosis scores. Among responders, fibrosis scores were improved or stable in 67% of pts with SVR ≥35% and 100% of pts with TSS improvement ≥50%. Fibrosis scores were also associated with improvements in mutation burden; of 14 patients with VAF reductions ≥20% and bone marrow assessments, 4 (29%) showed improvements in fibrosis and 8 (57%) had stable fibrosis scores. Conclusion Among pts with R/R MF treated with navtemadlin, spleen responses correlated with reductions of MPN-driver mutation burden, decreased peripheral CD34+ cell counts, improvements in bone marrow fibrosis scores, and reduction in inflammatory cytokine, TNFα. Improvement in symptom burden significantly correlated with reductions in TNFα. The reduction in mutation burden and CD34+ cells, together with an improvement in bone marrow fibrosis, suggest that navtemadlin has a disease-modifying effect in MF. These correlations will be explored further in BOREAS, a global phase 3 study in MF that is R/R to JAK inhibitors (NCT03662126). Figure 1 Figure 1. Disclosures Vachani: Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees. Delgado: Novartis: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding, Speakers Bureau; Abbvie: Consultancy. Al-Ali: Incyte: Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Takeda: Consultancy; Pfizer: Consultancy; AbbVie: Consultancy, Honoraria. Hernández-Rivas: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene/BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Kiladjian: Incyte Corporation: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Taiho Oncology, Inc.: Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Other: Personal fees; AOP Orphan: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees. Vannucchi: BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees. Perkins: Novartis: Consultancy, Honoraria, Speakers Bureau; Celgene: Consultancy; Abbvie: Honoraria, Speakers Bureau. Valmeekam: Telios Pharmaceuticals: Current Employment, Current holder of stock options in a privately-held company, Other: travel, accommodations, expenses. Krejsa: Seattle Genetics: Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months; Kartos Therapeutics: Current Employment, Current holder of stock options in a privately-held company, Other: travel, accommodations, expenses; AstraZeneca: Current equity holder in publicly-traded company; Acerta Pharma: Current holder of individual stocks in a privately-held company. Uyei: Kartos Therapeutics: Current Employment, Current holder of individual stocks in a privately-held company; Genentech/Roche: Ended employment in the past 24 months; Gilead Sciences: Current equity holder in publicly-traded company; Telios Pharma: Current holder of individual stocks in a privately-held company. McGreivy: Kartos Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Rothbaum: Quogue Capital: Current Employment; Iovance Biotherapeutics: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations, expenses; Acerta Pharma/Astra Zeneca: Current equity holder in publicly-traded company; Kartos Therapeutics: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations, expenses, Patents & Royalties; Telios Pharma: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations, expenses, Patents & Royalties; Quogue IP Holdings: Patents & Royalties. Mascarenhas: PharmaEssentia: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Forbius: Research Funding; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech/Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; Promedior: Consultancy, Membership on an entity's Board of Directors or advisory committees; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy, Research Funding; Constellation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merus: Research Funding; Geron: Consultancy; Galecto: Consultancy; Prelude: Consultancy. Verstovsek: CTI BioPharma: Research Funding; Blueprint Medicines Corp: Research Funding; Roche: Research Funding; Ital Pharma: Research Funding; Promedior: Research Funding; PharmaEssentia: Research Funding; Protagonist Therapeutics: Research Funding; NS Pharma: Research Funding; Celgene: Consultancy, Research Funding; Genentech: Research Funding; Gilead: Research Funding; Incyte Corporation: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; AstraZeneca: Research Funding; Novartis: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. OffLabel Disclosure: Navtemadlin (KRT-232) is an investigational agent that is being evaluated in a clinical trial setting.

Introduction Despite the advent of targeted therapy for FLT3-mutated AML, unmet need still exists for patients unfit for intensive chemotherapy, with no evidence that overall survival (OS) can be improved by combining either venetoclax (Konopleva et al., ASH 2020) or gilteritinib (Astellas press release, December 2020) with azacitidine. Although gilteritinib has been shown to improve median OS from 5.5 to 9.8 months, the majority will relapse (Perl et al., 2019). Adaptive on-target gilteritinib resistance may be due to the FLT3-F691L gatekeeper mutation, whereas off-target resistance may be due to loss-of-function variants in CBL, which encodes an E3 ubiquitin-protein ligase that negatively regulates FLT3 (McMahon et al, 2019). Ponatinib is a type-1 FLT3 inhibitor that is active in vitro against FLT3 F691L (Smith et al., 2013) and had an overall response rate (ORR) of 43% in a small pilot phase-I study (Talpaz et al., 2011). Combination of a FLT3 inhibitor with azacitidine may antagonize the synergistic hypermethylation reported for FLT3-ITD in association with epigenetic mutations (Shih et al., 2015). CBL loss-of-function mutations may also enhance responsiveness to FLT3 inhibitors (Taylor et al, 2015). We thus hypothesize that the combination of ponatinib and azacitidine could mitigate the rapid evolution of drug resistance typical of more selective FLT3 inhibitors used as single agents. Methods A phase-Ib study was conducted with the primary objective safety and key secondary objective preliminary efficacy of azacitidine in combination with ponatinib in patients with FLT3-ITD AML failing prior therapy or unfit for intensive chemotherapy. Exploratory objectives included mechanisms of ponatinib resistance and responsiveness of CBL-mutant AML to FLT3 inhibition. At dose level 1 (DL1), patients received azacitidine 60 mg/m 2 on days 1-5 and 8-9 and ponatinib 30 mg daily on days 5-25 of each cycle. In patients not achieving CR or CRi after cycle 1, the ponatinib dose was increased to 45 mg during cycle 2. For dose level 2 (DL2), the dose of azacitidine was increased to 75 mg/m 2. Results Thirty-one patients were evaluable for response. Median age was 67 years (range, 26-87). Frequency of prior lines of therapy was 0 (15%), 1 (46%), 2 (23%) or 3 (8%). Four patients had a history of prior allogeneic hematopoietic cell transplant and one had previously received a FLT3 inhibitor. FLT3-ITD was present in 28 patients (median VAF 0.33; range, 0.009-17.95) and 3 had inactivating CBL mutations. A total of 20 patients were treated at DL1 and 12 patients at DL2. There were two grade-4 DLTs (raised AST/ALT [DL1] and tubulointerstitial nephritis [DL2]). Three grade-2 thromboembolic events were observed (two cannula-related DVTs and a distal lower-limb DVT). There were two grade-5 AEs (infection and cardiac failure), which were not considered drug related. The most common grade-3-4 AEs were febrile neutropenia (57%), neutropenia (47%), infections (47%), thrombocytopenia (40%) and anaemia (27%). Cardiac arrhythmias (atrial fibrillation/flutter, bradycardia, sinus tachycardia and ventricular tachycardia [1 patient]) were observed in 30% of patients. Of these, 80% were grade 1 or 2 and only one was considered by the investigator to be related to study treatment. Response was evaluable in 23 of 31 patients. Nine patients (39%) achieved CR or CRi, 3 (13%) achieved a PR and 8 (35%) achieved SD (ORR 52%). ORR at DL1 and DL2 was 43% and 66%, respectively. Median time to best response was 1.4 months (range 1.0-11.9). Median duration of best response was 12.9 months at both dose levels. Median OS for DL1 was 6.5 months and not reached for DL2. Despite shorter follow-up, DL2 patients experienced better OS than DL1 patients (p = 0.015). Responses were seen in 2 of 4 patients with post-allograft relapse. Two of three patients with a CBL mutation responded (1 CR and 1 CRi). Eradication of the CBL mutation was seen in one patient, who remains on therapy after 15 cycles. Molecular studies to investigate dynamic changes in molecular architecture are ongoing. Conclusions The recommended phase-II dose of ponatinib is 30 mg on days 5-25 and that of azacitidine is 75 mg/m 2 for seven doses each cycle. The ORR was 52% and durable disease control was observed, especially in patients receiving DL2. Preliminary efficacy was observed in CBL-mutated patients. Further clinical investigation of this regimen is warranted in patients with FLT3- or CBL-mutant AML. Figure 1 Figure 1. Disclosures Kipp: Novartis: Honoraria. Perkins: Celgene: Consultancy; Novartis: Consultancy, Honoraria, Speakers Bureau; Abbvie: Honoraria, Speakers Bureau. Lane: Novartis: Consultancy; Geron: Consultancy; BMS: Consultancy, Research Funding; Abbvie: Honoraria; Astellas: Membership on an entity's Board of Directors or advisory committees. Enjeti: Sanofi: Honoraria; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Honoraria; Roche: Speakers Bureau; Astra Zeneca: Honoraria. Bajel: Abbvie, Amgen, Novartis, Pfizer: Honoraria; Amgen: Speakers Bureau. Reynolds: Novartis AG: Current equity holder in publicly-traded company; Abbvie: Research Funding; Alcon: Current equity holder in publicly-traded company. Wei: Abbvie, Amgen, Astellas, AstraZeneca, Celgene/BMS, Genentech, Janssen, MacroGenics, Novartis, Pfizer, and Servier: Membership on an entity's Board of Directors or advisory committees; Novartis, Abbvie, Celgene/BMS: Speakers Bureau; Former employee of Walter and Eliza Hall Institute: Patents & Royalties: Prof. Andrew Wei is a former employee of the Walter and Eliza Hall Institute and is eligible for a fraction of the royalty stream related to Venetoclax; Abbvie, Amgen, Astellas, AstraZeneca, Celgene/BMS, Genentech, Janssen, MacroGenics, Novartis, Pfizer, and Servier: Honoraria; Servier: Consultancy; Abbvie, Amgen, AstraZeneca, Celgene/BMS, Novartis, Servier and F. Hoffmann-La Roche: Research Funding. OffLabel Disclosure: Ponatinib - used as an experimental therapy for AML in combination with azacitidine

Sickle cell disease (SCD) affects millions of people worldwide and represents the most common monogenic disease of mankind (1). It is due to a homozygous T to A transversion in the β-globin gene that results in an amino acid variant - G6V - and production of HbS, which polymerises in red blood cells (RBCs) under hypoxic conditions. This generates irreversibly sickled cells that fail to traverse the microcirculation, resulting in micro-infarcts, hypoxia and pain, or 'sickle cell crises'. During gestation RBCs utilise different sets of globin genes to produce embryonic and fetal hemoglobins (HbF), so it is not until after birth when adult hemoglobin (HbA) is first produced that the first signs of SCD become apparent. This process termed 'hemoglobin switching' has been the focus of research efforts for decades because it offers an opportunity to reactivate HbF in adult cells of patients with hemoglobinopathies. A number of transcription factors, including Krüppel-like factor 1 (KLF1), play critical roles in hemoglobin switching. KLF1 is an essential erythroid transcription factor that co-ordinates the expression of more than a thousand genes critical to the formation of adult RBCs. KLF1 directly binds the β-globin gene promoter to up regulate its expression, whilst regulating the expression of additional factors like BCL11A and LRF that directly repress γ-globin expression (HbF). Heterozygosity for loss of function mutations in KLF1 leads to a significant increase in HbF that is beneficial to patients with β-thalassemia. We propose this can be recreated by advanced gene editing techniques to provide an effective therapy for SCD. We have employed CRISPR-based gene editing to knockout the expression of KLF1 in human cells. We designed two separate sgRNAs with corresponding HDR templates to target the second exon of KLF1 and ablate its function. We optimised transfection protocols and tested the on-target specificity of our sgRNAs achieving >90% efficacy in all cell types assayed. Using HUDEP-2 cells (2), a conditionally immortalised erythroid cell line which harbors three copies of KLF1 (3), we have demonstrated that these cells require at least one copy (>1/3) for survival; heterozygous cells (+/-/- or +/+/-) proliferate at a reduced rate, but are able to differentiate normally. Using RNA-seq, we identified some genes, including ICAM-4 and BCAM, which are down-regulated accordingly in a KLF1 gene dosage-dependent manner. ICAM-4 and BCAM are cellular adhesion molecules implicated in triggering vaso-occlusive episodes (4; 5), so it is anticipated their reduced expression may provide additional benefit in treating SCD. Gamma-globin is upregulated 10-fold, BCL11A down-regulated 3-fold, and HbF+ RBCs generated at ~20% of total RBCs in KLF1 +/-/- HUDEP-2 cell lines. We also engineered the ablation of KLF1 in CD34+ cells harvested from the peripheral blood of SCD patients undergoing exchange transfusions. Following transfection of the two guides, we performed directed differentiation using an erythroid differentiation medium and analysed the levels of HbF. We observed HbF at levels of between 40-60% of total Hb by HPLC, and HbF+ cells of ~50% by FACS. There was no measurable block in erythroid differentiation by FACS. We documented the types of gene editing using a high throughout NGS assay (6). We compared efficiencies of CRISPR repair of the HbS mutation with CRIPSR damage of the KLF1 gene. Lastly, we transplanted gene-edited CD34 cells into NSGW41 mice (where human erythropoiesis is established) to determine the efficiency and safety of editing long term HSCs from SCD patients. We will report on the results of these xenotransplantation assays. Taken together these results reveal the potential utility in targeting KLF1 to cure SCD. References: Wastnedge, E. et al..J Glob Health 8, 021103 (2018). Kurita, R. et al.PLoS One 8, e59890 (2013). Vinjamur, D. S. & Bauer, D. E. Methods Mol Biol 1698, 275-284 (2018). Bartolucci, P. et al..Blood 116, 2152-9 (2010). Zhang, J., et al. PLoS One 14, e0216467 (2019). Bell, C. C., et al. BMC Genomics 15, 1002 (2014). Perkins, A. et al..Blood 127, 1856-62 (2016). Disclosures Kaplan: Celgene: Honoraria; Novartis: Honoraria. Perkins:Novartis Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees.

INTRODUCTION Myelofibrosis (MF) is a myeloproliferative neoplasm (MPN) characterized by megakaryocyte proliferation and progressive bone marrow fibrosis. Additional clinical features include splenomegaly due to extramedullary hematopoiesis, cytopenias resulting from bone marrow failure, and constitutional symptoms. MF can develop de novo (primary MF) or from the progression of antecedent MPNs, in particular polycythemia vera (PPV-MF) or essential thrombocythemia (PET-MF). At diagnosis, nearly one-quarter of patients (pts) are red blood cell transfusion dependent, and nearly 40% exhibit hemoglobin levels < 10 g/dL. Additionally, pts with MF have a shortened survival and reduced quality of life (QOL). Ruxolitinib (RUX), a first-in-class JAK1/JAK2 inhibitor, is the standard of care for MF and was approved on the basis of the COMFORT studies. In these studies, RUX demonstrated superiority over placebo (COMFORT-I) and best available therapy (COMFORT-II) in improving splenomegaly, MF-related symptoms, and QOL. An overall survival benefit was also observed with RUX (Harrison CN, et al. Leukemia. 2016). However, RUX is not a curative therapy and cytopenias remain a challenge in the management of MF. Additionally, not all pts respond to RUX, with some losing response while on treatment and some discontinuing treatment due to adverse events. RUX in combination with novel agents may offer superior disease control and transformative clinical benefits, including prolonged progression-free survival and improved cytopenias and QOL, and may reduce the malignant clone and bone marrow fibrosis. METHODS ADORE (NCT04097821) is a 3-part, open-label, multicenter, Phase 1/2 open-platform study that will assess the safety and efficacy of RUX in combination with ≥ 3 novel compounds (siremadlin [HDM2 inhibitor], crizanlizumab [P-selectin inhibitor], or sabatolimab [TIM-3 inhibitor]) for the treatment of MF (Figure). The study will include pts ≥ 18 years old who have primary MF, PPV-MF, or PET-MF, splenomegaly (a palpable spleen ≥ 5 cm from the left costal margin or spleen volume ≥ 450 cm3 by MRI or CT scan), hemoglobin level < 10 g/dL, and platelet count ≥ 75 × 109/L (≥ 50 × 109/L in Parts 2 and 3). Pts must have been treated with RUX for ≥ 24 weeks and have received a stable dose for ≥ 8 weeks prior to study entry. Key exclusion criteria include splenic irradiation within 6 months or blood platelet transfusion within 28 days of study start. Part 1 (Phase 1b) includes a Dose-escalation arm to determine the recommended Phase 2 dose (RP2D) for the combination of siremadlin and RUX, and 2 safety run-in arms to confirm the doses of crizanlizumab plus RUX and sabatolimab plus RUX combinations. RUX will be administered at the same stable dose used prior to study entry. A Bayesian logistic regression model will be used to identify the maximum tolerated dose and/or RP2D for the siremadlin and RUX combination. Pts will be treated for a planned duration of ≥ 6 cycles (24 weeks). The primary endpoint for Part 1 is the incidence of dose-limiting toxicities within the first 2 cycles. The combination treatments evaluated as safe and tolerable in Part 1 will proceed to Part 2. In Part 2 (Phase 2; early efficacy assessment, Selection), pts will be randomized with equal probability to 1 of the selected combination treatments or RUX monotherapy and treated for ≥ 12 cycles (48 weeks). After all Part 2 pts have completed 24 weeks of treatment, an interim analysis will be conducted to determine which treatment should be dropped for futility or considered in Part 3 (Phase 2; efficacy, Expansion). In Part 3, pts will be randomized 2:1:1 to the combination treatment arm, RUX cessation arm (novel agent monotherapy), or RUX monotherapy arm and treated for ≥ 12 cycles. Pts in the RUX cessation arm will be treated with RUX combination therapy for 12 weeks, followed by tapering of RUX. The primary endpoint for Parts 2 and 3 is the response rate for the composite endpoint of anemia improvement (increase in hemoglobin of ≥ 1.5 g/dL), no spleen volume progression, and no symptom worsening at the end of 6 treatment cycles (24 weeks). Secondary efficacy endpoints include hemoglobin improvement, change in spleen size, progression-free survival, change in symptoms, and bone marrow fibrosis improvement. The study will end 24 months after the last pt has initiated Part 3. Planned enrollment for the study with the current 3 combinations is 130 pts. Enrollment is currently ongoing. Disclosures Perkins: Novartis Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees. Lehmann:Novartis: Consultancy, Research Funding. Reiter:Incyte: Consultancy, Other: travel support ; AOP: Consultancy, Other: travel support ; Celgene,: Consultancy, Other: travel support ; Abbvie: Consultancy, Other: travel support ; Deciphera: Consultancy, Other: travel support ; Blueprint: Consultancy, Other: travel support ; Novartis: Consultancy, Honoraria, Other: travel support , Research Funding; Gilead: Other: travel support . Gupta:Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol MyersSquibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Incyte: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Harrison:Roche: Honoraria; Sierra Oncology: Honoraria; Promedior: Honoraria; AOP Orphan Pharmaceuticals: Honoraria; Celgene: Honoraria, Research Funding, Speakers Bureau; Shire: Honoraria, Speakers Bureau; CTI Biopharma Corp: Honoraria, Speakers Bureau; Gilead Sciences: Honoraria, Speakers Bureau; Incyte Corporation: Speakers Bureau; Janssen: Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau. Kiladjian:AOP Orphan: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Vannucchi:Incyte: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Blueprint: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Wondergem:Celgene: Other: Educational talks; Novartis: Other: Educational talks. Pack:Novartis Pharma AG: Current Employment. Wroclawska:Novartis Pharma AG: Current Employment. Wilke:Novartis Pharma AG: Current Employment, Other: Stock owner. Zhang:Novartis Pharma AG: Current Employment. Heidel:Novartis: Consultancy, Honoraria, Research Funding.

e19040 Background: Clinical trials investigating JAK1/JAK2 inhibitors for myelofibrosis (MF) subjects have measured symptom improvement as a minimum 50% reduction in total symptom score (TSS) at the end of a 24-week treatment period. This landmark analysis is based on post-baseline score changes from Weeks 21 (W21) to 24 and requires vastly different absolute TSS improvements for patients with very high or low baseline (BL) TSS to reach responder status. A phase 3 clinical study, SIMPLIFY-1, randomized 432 intermediate and high risk JAK inhibitor (JAKi) naive MF patients 1:1 to momelotinib (MMB) or ruxolitinib (RUX). Non-inferiority on the MPN-SAF TSS response rate endpoint at W24 was not met (MMB: 28% vs RUX: 42%); however, improvement in each of the 7 TSS items was similar for MMB vs RUX. To understand the discrepancy, we applied item analysis and mixed effect models for repeated measures (MMRM) to SIMPLIFY-1. Methods: Analyses were conducted in the intention-to-treat (ITT) population and in a symptomatic subset (selected as subjects with BL TSS ≥ 10). The distributions of TSS items were examined at BL and shift in scores at W24 (health state shifts) were assessed. GEE models were used to estimate item-level odds ratios using multiple predictive imputations for missing data. MMRM compared mean change in TSS from BL to W24 using data from all visits. The meaningful change threshold (MCT) was determined using Patient Global Impression of Change. Results: BL scores across items were heterogenous in the MMB and RUX groups; the proportion of subjects with no or mild symptoms (0–3 on a 0-10 point scale) ranged from 44% (tiredness) to 81% (itching). Distributions of BL scores were different across arms with 6 out of 7 items in the MMB arm reporting more severe or very severe symptoms (scores of 7-10) at BL. Despite the imbalance in BL scores, item-level health state shifts showed similar improvements for MMB and RUX. Categorical responder analysis showed no significant differences on any items. Odds ratios for each between-group comparison ranged from 0.74 to 1.20. MMRM mean TSS change at W24 was 6.35 (MMB) vs 7.87 (RUX) in the ITT and 8.80 (MMB) vs 10.46 (RUX) in the symptomatic subset. Mean TSS were near the within-subject MCT of 8 points in the ITT and exceeded the MCT in the symptomatic subset. The between-group difference was 1.52 (95% CI: (0.196, 2.847)) in the ITT and 1.67 (95% CI: -0.134, 3.468) in the symptomatic subset. Conclusions: Comparable item health state shifts at W24 and similar improvements in mean TSS as shown by MMRM, with a minimal between-group difference of 1.52 on the 70 point scale in context of an 8-point MCT suggest MMB provides clinically relevant and comparable symptom improvements to RUX; these analyses require further validation in independent data sets. Imbalance in BL symptom scores in MMB subjects may have contributed to the inability to demonstrate non-inferiority in TSS response rate at W24. Clinical trial information: NCT01969838.

TPS7057 Background: The prognosis for patients (pts) with MF who have primary resistance to or who have progressed after treatment with ruxolitinib (RUX) is poor (median OS is ̃13 months), highlighting the unmet need for novel treatments in this setting. MDM2 is a key negative regulator of the tumor suppressor protein p53 that is overexpressed in CD34+ cells in MF pts. Elevated MDM2 expression attenuates p53 activity, resulting in proliferation of malignant CD34+ cells. KRT-232 is a potent, selective, orally available MDM2 inhibitor that restores p53 function resulting in apoptosis of malignant stem and progenitor cells. KRT-232 has the potential to demonstrate disease-modifying effects in MF pts who are R/R to prior JAK inhibitor (JAKi) therapy. The FDA has granted KRT-232 Fast Track designation for the treatment of JAKi R/R MF. Clinical proof-of-concept for KRT-232 in R/R MF was established in phase 2 of this study. Once-daily dosing of KRT-232 at 240 mg (Day 1-7 of 28-day cycle) yielded a best spleen volume reduction (SVR) ≥35% by central review in 16% of pts, best total symptom score (TSS) response > 50% in 30% of pts, and 87% reduction of CD34+ cells in peripheral blood at Week 24. Spleen responses were superior in pts who were off RUX vs those on RUX at baseline imaging (best SVR ≥35%: 29% vs 0%). KRT-232 demonstrated a tolerable safety profile that included prophylaxis for nausea/vomiting (Al-Ali. EHA 2020). Methods: BOREAS is a randomized, controlled, open-label, global phase 3 study in MF pts (primary MF/post–polycythemia vera MF/post–essential thrombocythemia MF) who are R/R to JAKi. Pts aged ≥18 y with confirmed MF per WHO criteria, intermediate-1, 2, or high-risk disease (per DIPSS), ECOG performance status ≤2, adequate hematologic function (platelets ≥50 x 109/L), and wild-type p53 will be enrolled; pts with JAKi treatment = 28 d before baseline MRI/CT will be excluded. Pts will be randomized (2:1) to KRT-232 (240 mg on Day 1-7/28-day cycle; n = 188) or best available treatment (BAT; n = 94) and stratified by MF type (primary vs secondary) and baseline TSS (≤10 vs > 10). BAT options include hydroxyurea, chemotherapy, or supportive care (including; but not limited to: corticosteroids and androgens); treatment selection is at the discretion of the investigator. Pts in BAT arm with documented disease progression at any time (spleen volume increase ≥25% from baseline or confirmed leukemic transformation) or those who complete Week 24 assessments may crossover to the KRT-232 arm. Primary endpoint is rate of SVR ≥35% by MRI/CT at Week 24 (central review). Key secondary endpoints are ≥50% reduction in TSS rate at Week 24 (per MFSAF v4.0), PFS, OS, best overall SVR ≥35%, and duration of spleen response. Enrollment is planned at 137 sites in 21 countries in North and South America, Europe, and Asia-Pacific (ClinicalTrials.gov: NCT03662126). Clinical trial information: NCT03662126.

Krüppel-like factors (KLFs) are a family of 17 transcription factors characterized by a conserved DNA-binding domain of three zinc fingers and a variable N-terminal domain responsible for recruiting cofactors. KLFs have diverse functions in stem cell biology, embryo patterning, and tissue homoeostasis. KLF1 and related family members function as transcriptional activators via recruitment of co-activators such as EP300, whereas KLF3 and related members act as transcriptional repressors via recruitment of C-terminal Binding Proteins. KLF1 directly activates the Klf3 gene via an erythroid-specific promoter. Herein, we show KLF1 and KLF3 bind common as well as unique sites within the erythroid cell genome by ChIP-seq. We show KLF3 can displace KLF1 from key erythroid gene promoters and enhancers in vivo. Using 4sU RNA labelling and RNA-seq, we show this competition results in reciprocal transcriptional outputs for >50 important genes. Furthermore, Klf3−/− mice displayed exaggerated recovery from anemic stress and persistent cell cycling consistent with a role for KLF3 in dampening KLF1-driven proliferation. We suggest this study provides a paradigm for how KLFs work in incoherent feed-forward loops or networks to fine-tune transcription and thereby control diverse biological processes such as cell proliferation.

Ruxolitinib is a dual janus kinase 1 (JAK1)/JAK2 inhibitor used to treat splenomegaly and symptoms associated with myelofibrosis (MF). Current therapeutic options for symptomatic MF include supportive care, myelosuppressive therapy (such as hydroxycarbamide) and janus kinase (JAK) inhibitors (in particular ruxolitinib). Allogeneic stem cell transplantation remains the only potentially curative treatment for MF, and younger transplant-eligible patients should still be considered for allogeneic stem cell transplantation; however, this is applicable only to a small proportion of patients. There is now increasing and extensive experience of the efficacy and safety of ruxolitinib in MF, both in clinical trials and in 'real-world' practice. The drug has been shown to be of benefit in intermediate-1 risk patients with symptomatic splenomegaly or other MF-related symptoms, and higher risk disease. Optimal use of the drug is required to maximise clinical benefit, requiring an understanding of the balance between dose-dependent responses and dose-limiting toxicities. There is also increasing experience in the use of ruxolitinib in the pre-transplantation setting. This paper aims to utilise several 'real-life' cases to illustrate several strategies that may help to optimise clinical practice.

Introduction A 74-year-old man presented to hospital with a headache, thrombocytopaenia and an acute deterioration in cognition on a background of acute monocytic leukaemia in remission. Method This is a case report with computed tomography (CT), magnetic resonance (MR) and histopathology imaging. Results Preoperative CT and limited MR demonstrated a subdural lesion with marked midline shift. Craniotomy performed for evacuation of the presumed subdural haematoma revealed a solid tumour-like lesion. Histopathology identified the presence of a myeloid sarcoma (chloroma). Postoperative MRI with contrast revealed the solid nature of the mass. Conclusion The use of contrast is critical in the assessment of intracranial lesions to distinguish myeloid sarcoma from subdural haematoma in the context of leukaemia and a neurologically deteriorating patient.

Summary Background Available therapies for myelofibrosis can exacerbate cytopenias and are not indicated for patients with severe thrombocytopenia. Pacritinib, which inhibits both JAK2 and FLT3, induced spleen responses with limited myelosuppression in phase 1/2 trials. We aimed to assess the efficacy and safety of pacritinib versus best available therapy in patients with myelofibrosis irrespective of baseline cytopenias. Methods This international, multicentre, randomised, phase 3 trial (PERSIST-1) was done at 67 sites in 12 countries. Patients with higher-risk myelofibrosis (with no exclusions for baseline anaemia or thrombocytopenia) were randomly assigned (2:1) to receive oral pacritinib 400 mg once daily or best available therapy (BAT) excluding JAK2 inhibitors until disease progression or unacceptable toxicity. Randomisation was stratified by risk category, platelet count, and region. Treatment assignments were known to investigators, site personnel, patients, clinical monitors, and pharmacovigilance personnel. The primary endpoint was spleen volume reduction (SVR) of 35% or more from baseline to week 24 in the intention-to-treat population as assessed by blinded, centrally reviewed MRI or CT. We did safety analyses in all randomised patients who received either treatment. Here we present the final data. This trial is registered with ClinicalTrials.gov, number NCT01773187. Findings Between Jan 8, 2013, and Aug 1, 2014, 327 patients were randomly assigned to pacritinib (n=220) or BAT (n=107). Median follow-up was 23·2 months (IQR 14·8–28·7). At week 24, the primary endpoint of SVR of 35% or more was achieved by 42 (19%) patients in the pacritinib group versus five (5%) patients in the BAT group (p=0·0003). 90 patients in the BAT group crossed over to receive pacritinib at a median of 6·3 months (IQR 5·8–6·7). The most common grade 3–4 adverse events through week 24 were anaemia (n=37 [17%]), thrombocytopenia (n=26 [12%]), and diarrhoea (n=11 [5%]) in the pacritinib group, and anaemia (n=16 [15%]), thrombocytopenia (n=12 [11%]), dyspnoea (n=3 [3%]), and hypotension (n=3 [3%]) in the BAT group. The most common serious adverse events that occurred through week 24 were anaemia (10 [5%]), cardiac failure (5 [2%]), pyrexia (4 [2%]), and pneumonia (4 [2%]) with pacritinib, and anaemia (5 [5%]), sepsis (2 [2%]), and dyspnoea (2 [2%]) with BAT. Deaths due to adverse events were observed in 27 (12%) patients in the pacritinib group and 14 (13%) patients in the BAT group throughout the duration of the study. Interpretation Pacritinib therapy was well tolerated and induced significant and sustained SVR and symptom reduction, even in patients with severe baseline cytopenias. Pacritinib could be a treatment option for patients with myelofibrosis, including those with baseline cytopenias for whom options are particularly limited. Funding CTI BioPharma Corp.

Background: Momelotinib (MMB) is a potent, orally bioavailable, small-molecule inhibitor of JAK1, JAK2, and ACVR1 with demonstrable clinical activity against the three hallmark features of myelofibrosis (MF), namely anemia, constitutional symptoms, and splenomegaly, across the continuum of intermediate-/high-risk MF patients whether JAKi-naive or previously JAKi-treated. Objective: To characterize the long-term safety of MMB in comparison to ruxolitinib (RUX). Methods: SIMPLIFY-1 was a double-blind, randomized, study of MMB vs RUX in intermediate-/high-risk JAKi-naive patients with MF (n=215 MMB, 217 RUX). SIMPLIFY-2 (S2) was a randomized study of MMB vs best available therapy (BAT; RUX in 88% of patients) in prior RUX-treated patients with hematological toxicity (n=104 MMB, 52 BAT). Randomized treatment (RT) for 24 weeks was followed by open-label MMB extended treatment in both studies. Data from RT were compared, and further long-term data were analyzed from 550 subjects receiving MMB, including 336 subjects on MMB for ≥48 weeks and 148 for ≥144 weeks. Results: Despite treatment duration exceeding 3.5 years for >90 subjects, the incidence of grade 3/4 hematological toxicity was very low. During the S1 RT period, grade 3/4 anemia occurred in only 6.1% of MMB subjects compared with -4-fold higher rate (22.7%) for RUX. Dose reductions due to thrombocytopenia were also 4-fold higher for RUX (24.5%) than MMB (6.1%). Subjects randomized to MMB in S1 experienced a rapid, sustained increase in hemoglobin, in contrast to significant hemoglobin decrease on RUX. Following crossover to MMB from RUX, hemoglobin increased rapidly to above baseline. Platelet values were also significantly higher compared to RUX. Similarly, in S2, hemoglobin and platelet values were maintained or improved on MMB. Importantly, no new safety signals and no cumulative toxicity were observed during extended MMB dosing. Rates of peripheral neuropathy remained low. Conclusions: MMB displays very favorable long-term tolerability, including an absence of significant rates of high-grade hematological and other toxicities or evidence of cumulative toxicity, consistent with its differentiated pharmacological and clinical profile. Notably, subjects switching from RUX also experienced favorable tolerability, despite their previous therapy.

The rules of engagement between zinc finger transcription factors and DNA have been partly defined by in vitro DNA-binding and structural studies, but less is known about how these rules apply in vivo. Here, we demonstrate how a missense mutation in the second zinc finger of Krüppel-like factor-1 (KLF1) leads to degenerate DNA-binding specificity in vivo, resulting in ectopic transcription and anemia in the Nan mouse model. We employed ChIP-seq and 4sU-RNA-seq to identify aberrant DNA-binding events genome wide and ectopic transcriptional consequences of this binding. We confirmed novel sequence specificity of the mutant recombinant zinc finger domain by performing biophysical measurements of in vitro DNA-binding affinity. Together, these results shed new light on the mechanisms by which missense mutations in DNA-binding domains of transcription factors can lead to autosomal dominant diseases.

Fibroblast growth factor-1 (FGF-1) promotes differentiation of human preadipocytes into mature adipocytes via modulation of a BMP and Activin Membrane-Bound Inhibitor (BAMBI)/Peroxisome proliferator-activated receptor (PPARγ)-dependent network. Here, we combined transcriptomic and functional investigations to identify novel downstream effectors aligned with complementary analyses of gene expression in human adipose tissue to explore relationships with insulin sensitivity. RNA-Seq and qRT-PCR analysis revealed significant down-regulation of carboxypeptidase A4 (CPA4) following FGF-1 treatment or induction of differentiation of human preadipocytes in a BAMBI/PPARγ-independent manner. siRNA-mediated knockdown of CPA4 resulted in enhanced differentiation of human preadipocytes. Furthermore, expression of CPA4 in subcutaneous adipose tissue correlated negatively with indices of local and systemic (liver and muscle) insulin sensitivity. These results identify CPA4 as a negative regulator of adipogenesis that is down-regulated by FGF-1 and a putative deleterious modulator of local and systemic insulin sensitivity. Further investigations are required to define the molecular mechanism(s) involved and potential therapeutic opportunities.

Modulators of epithelial-to-mesenchymal transition (EMT) have recently emerged as novel players in the field of leukemia biology. The mechanisms by which EMT modulators contribute to leukemia pathogenesis, however, remain to be elucidated. Here we show that overexpression of SNAI1, a key modulator of EMT, is a pathologically relevant event in human acute myeloid leukemia (AML) that contributes to impaired differentiation, enhanced self-renewal, and proliferation of immature myeloid cells. We demonstrate that ectopic expression of Snai1 in hematopoietic cells predisposes mice to AML development. This effect is mediated by interaction with the histone demethylase KDM1A/LSD1. Our data shed new light on the role of SNAI1 in leukemia development and identify a novel mechanism of LSD1 corruption in cancer. This is particularly pertinent given the current interest surrounding the use of LSD1 inhibitors in the treatment of multiple different malignancies, including AML.

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Background Mutations in the transcription factor, KLF1, are common within certain populations of the world. Heterozygous missense mutations in KLF1 mostly lead to benign phenotypes, but a heterozygous mutation in a DNA-binding residue (E325K in human) results in severe Congenital Dyserythropoietic Anemia type IV (CDA IV); i.e. an autosomal-dominant disorder characterized by neonatal hemolysis. Results To investigate the biochemical and genetic mechanism of CDA IV, we generated murine erythroid cell lines that harbor tamoxifen-inducible (ER™) versions of wild type and mutant KLF1 on a Klf1−/− genetic background. Nuclear translocation of wild type KLF1 results in terminal erythroid differentiation, whereas mutant KLF1 results in hemolysis without differentiation. The E to K variant binds poorly to the canonical 9 bp recognition motif (NGG-GYG-KGG) genome-wide but binds at high affinity to a corrupted motif (NGG-GRG-KGG). We confirmed altered DNA-binding specificity by quantitative in vitro binding assays of recombinant zinc-finger domains. Our results are consistent with previously reported structural data of KLF-DNA interactions. We employed 4sU-RNA-seq to show that a corrupted transcriptome is a direct consequence of aberrant DNA binding. Conclusions Since all KLF/SP family proteins bind DNA in an identical fashion, these results are likely to be generally applicable to mutations in all family members. Importantly, they explain how certain mutations in the DNA-binding domain of transcription factors can generate neomorphic functions that result in autosomal dominant disease. Electronic supplementary material The online version of this article (10.1186/s12864-019-5805-z) contains supplementary material, which is available to authorized users.

Erythroid-specific Kruppel-like factor 1, or KLF1, is an integral transcriptional activator for erythropoiesis. Genetic variants within KLF1 can result in a range of erythropoietic clinical phenotypes from benign to significant. The In(Lu) phenotype refers to changes in the quantitative expression of blood group-associated red cell surface molecules due to KLF1 variants which are otherwise clinically benign. These clinically benign KLF1 variants are associated with a reduced expression of 1 or more red cell membrane proteins/carbohydrates that carry blood group antigens for the LU (Lutheran), IN (Indian), P1PK, LW (Landsteiner-Wiener), KN (Knops), OK, RAPH, and I blood group systems. This is of significance during routine serologic blood typing when expression falls below the test sensitivity and therefore impacts on the ability to accurately detect the presence of affected blood group antigens. This is of clinical importance because the transfusion requirements for individuals with the In(Lu) phenotype differ from those of individuals that have a true Lunull phenotype. With this review, we summarize the current body of knowledge with regard to the In(Lu) phenotype and associated KLF1 variants. Our review also highlights discordant reports and provides insights for future research and management strategies. Serological heterogeneity in blood group expression of In(Lu) individuals has been shown, but studies are limited by the low prevalence of the phenotype and therefore the small numbers of samples. They are further limited by availability and inconsistent application of serological reagents and varying test algorithms. With the advent of genome sequence-based testing, an increasing list of In(Lu)-associated KLF1 variants is being revealed. The spectrum of effects on blood group expression due to these variants warrants further attention, and a consistent methodological approach of studies in larger cohorts is required. We propose that a recently reported testing framework of standardized serological studies, flow cytometry, and variant analysis be adopted; and that the international databases be curated to document KLF1 variability and the resultant In(Lu) red cell blood group expression. This will provide better classification of KLF1 variants affecting blood group expression and allow for phenotype prediction from genotype, accurate typing of In(Lu) individuals, and better transfusion management of related challenging transfusion scenarios.

Krüppel-like factors (KLFs) are a family of transcription factors that play essential roles in the development and differentiation of the hematopoietic system. These transcription factors possess highly conserved C-terminal zinc-finger motifs, which enable their binding to GC-rich, or CACC-box, motifs in promoter and enhancer regions of target genes. The N-terminal domains of these proteins are more varied and mediate the recruitment of various co-factors, which can form a complex with either activator or repressor function. Acting primarily as a gene repressor through its recruitment of CtBPs and histone deacetylases (HDACs) [1], we have recently shown that KLF3 competes with KLF1 bound sites in the genome to repress gene expression during erythropoiesis [2]. However, the function of Klf3 in other lineages has been less well studied. This widely expressed transcription factor has reported roles in the differentiation of marginal zone B cells, eosinophil function and inflammation [3]. We utilised the Klf3-null mouse model [4] to more closely examine the role of Klf3 in innate inflammatory cells. These mice exhibit elevated white cell counts, including monocytes (Figure 1A), and inflammation of the skin. Conditional knockout of Klf4 in myeloid cells leads to a deficiency of inflammatory macrophages [5]. To test our hypothesis KLF3 normally represses inflammation, perhaps by antagonising the action of KLF4, bone-marrow derived macrophages (BMDM) were generated from wild-type or Klf3-null mice and stimulated with the bacterial toxin lipopolysaccharide (LPS). In wild type BMDM, LPS induces Klf3 gene expression and activation then delayed repression of target genes such as Lgals3 (galectin-3) over a 21 hour time course (Figure 1B). Quantitative real-time PCR and mRNA-seq of WT v Klf3-null macrophages identified ~100 differentially expressed genes involved in proliferation, macrophage activation and inflammation. We transduced the monocyte cell line, RAW264.7 (that expresses Klf4, Klf3 and Klf2), with a retroviral vector expressing a tamoxifen-inducible KLF3-ER fusion construct. KLF3 induced cell cycle arrest and macrophage differentiation. We will report on KLF3-induced gene expression changes (repression and activation), and ChIP-seq for KLF3, in RAW cells. The results shed light on the mechanism by which KLF3 normally represses monocyte/macrophage responses to infection. This study highlights the importance of key transcriptional regulators that tightly control gene expression during inflammation. Loss of Klf3 leads to alterations in this process, resulting in hyper-activation of inflammatory macrophages, increased white cell counts and inflammation of the skin. A greater knowledge of the inflammatory process and how it is regulated is important for our understanding of acute infection and inflammatory disease. Further studies are planned to investigate the role of the KLF3 transcription factor in response to inflammation in vivo. References: 1. Pearson, R., et al., Kruppel-like transcription factors: A functional family. Int J Biochem Cell Biol, 2007. W2. Ilsley, M.D., et al., Kruppel-like factors compete for promoters and enhancers to fine-tune transcription. Nucleic Acids Res, 2017. 45(11): p. 6572-6588. W3. Knights, A.J., et al., Kruppel-like factor 3 (KLF3) suppresses NF-kappaB-driven inflammation in mice. J Biol Chem, 2020. 295(18): p. 6080-6091. W4. Sue, N., et al., Targeted disruption of the basic Kruppel-like factor gene (Klf3) reveals a role in adipogenesis. Mol Cell Biol, 2008. 28(12): p. 3967-78. W5. Alder, J.K., et al., Kruppel-like factor 4 is essential for inflammatory monocyte differentiation in vivo. J Immunol, 2008. 180(8): p. 5645-52. Figure 1: Elevated WCC (A) and inflammatory markers (B) in BMDM after LPS stimulation. 1. Total WCC in adult mice (3-6 months old) of the indicated genotypes. There is a statistically significant increase in the WCC in Klf3-/- v wild type mice (P Figure 1 Disclosures Perkins: Novartis Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Until recently our approach to analyzing human genetic diseases has been to accurately phenotype patients and sequence the genes known to be associated with those phenotypes; for example, in thalassemia, the globin loci are analyzed. Sequencing has become increasingly accessible, and thus a larger panel of genes can be analyzed and whole exome and/or whole genome sequencing can be used when no variants are found in the candidate genes. By using such approaches in patients with unexplained anemias, we have discovered that a broad range of hitherto unrelated human red cell disorders are caused by variants in KLF1, a master regulator of erythropoiesis, which were previously considered to be extremely rare causes of human genetic disease.

A direct interaction between the erythropoietin (EPOR) and the beta-common (βc) receptors to form an Innate Repair Receptor (IRR) is controversial. On one hand, studies have shown a functional link between EPOR and βc receptor in tissue protection while others have shown no involvement of the βc receptor in tissue repair. To date there is no biophysical evidence to confirm a direct association of the two receptors either in vitro or in vivo. We investigated the existence of an interaction between the extracellular regions of EPOR and the βc receptor in silico and in vitro (either in the presence or absence of EPO or EPO-derived peptide ARA290). Although a possible interaction between EPOR and βc was suggested by our computational and genomic studies, our in vitro biophysical analysis demonstrates that the extracellular regions of the two receptors do not specifically associate. We also explored the involvement of the βc receptor gene (Csf2rb) under anaemic stress conditions and found no requirement for the βc receptor in mice. In light of these studies, we conclude that the extracellular regions of the EPOR and the βc receptor do not directly interact and that the IRR is not involved in anaemic stress.

Anemic Nan mice carry a mutation (E339D) in the second zinc finger of erythroid transcription factor KLF1. Nan-KLF1 fails to bind a subset of normal KLF1 targets and ectopically binds a large set of genes not normally engaged by KLF1, resulting in a corrupted fetal liver transcriptome. Here, we performed RNAseq using flow cytometric-sorted spleen erythroid precursors from adult Nan and WT littermates rendered anemic by phlebotomy to identify global transcriptome changes specific to the Nan Klf1 mutation as opposed to anemia generally. Mutant Nan-KLF1 leads to extensive and progressive transcriptome corruption in adult spleen erythroid precursors such that stress erythropoiesis is severely compromised. Terminal erythroid differentiation is defective in the bone marrow as well. Principle component analysis reveals two major patterns of differential gene expression predicting that defects in basic cellular processes including translation, cell cycle, and DNA repair could contribute to disordered erythropoiesis and anemia in Nan. Significant erythroid precursor stage specific changes were identified in some of these processes in Nan. Remarkably, however, despite expression changes in large numbers of associated genes, most basic cellular processes were intact in Nan indicating that developing red cells display significant physiological resiliency and establish new homeostatic set points in vivo.

KLF1 is an essential transcriptional activator that drives erythropoiesis. KLF1 variants can result in the Inhibitor of Lutheran, or In(Lu), phenotype where red blood cells (RBCs) have reduced BCAM (LU) and CD44 (IN). Other RBC surface molecules also have changed expression; however, there is controversy in the literature regarding which are truly impacted. We aimed to investigate KLF1 variants in the Australian population.In(Lu) samples were sourced through screening and through the RBC reference laboratory. Blood donor samples (8036) were screened to identify weakened/absent LuFour of 8036 donors were identified to be In(Lu), and two previously identified In(Lu) samples were provided from the RBC reference laboratory. Five different KLF1 variants were identified; two were novel: c.954GC/p.Trp318Cys and c.421CT/p.Arg141*. BCAM and CD44 were reduced in all samples, consistent with previous reports. As a group, In(Lu) RBCs had reduced CD35 (KN), ICAM4 (LW), and CD147 (OK), and demonstrated increased binding of lectins ECA and SNAI. One In(Lu) sample had elevated HbF and another elevated HbA2.Different KLF1 variants may potentially produce variable phenotypes. A framework for investigating KLF1 variants and their phenotypic impact has been provided. In the future, given available international databases, further testing algorithms (as advocated here) will allow for correlation of phenotype with genotype and therefore accurately document this variability between KLF1 variants.

PURPOSE OF REVIEW The nature and function of macrophages at the center of erythroblastic islands is not fully understood. This review discusses novel findings on the phenotypic and molecular characterization of erythroblastic island macrophages, and their role in regulating normal and pathological erythropoiesis. RECENT FINDINGS The phenotype to prospectively isolate erythroblastic island macrophages from mouse bone marrow has been identified. In-vivo depletion of erythroblastic island macrophages causes blockade of erythroblast maturation and delays erythropoietic recovery following chemical insults. The cytokine granulocyte colony-stimulating factor arrests medullary erythropoiesis by depleting erythroblastic island macrophages from the bone marrow. In-vivo ablation of macrophages improves anemia associated with β-thalassemia and reduces red blood cell counts in the mouse model of polycythemia vera. The role of cell adhesion molecules regulating interactions between erythroblastic island macrophages and erythroblasts has been clarified, and mechanisms of pyrenocyte engulfment by erythroblastic island macrophages have been demonstrated to involve Mer tyrosine kinase receptor. SUMMARY Prospective isolation of mouse erythroblastic island macrophages together with new genetic mouse models to specifically target erythroblastic island macrophages will enable molecular studies to better define their role in controlling erythroblast maturation. These studies have revealed the key role of erythroblastic island macrophages in regulating normal erythropoiesis and could be interesting targets to treat β-thalassemia or polycythemia vera.