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Scribble complex proteins can influence cell fate decisions and self-renewal capacity of hematopoietic cells. While specific cellular functions of Scribble complex members are conserved in mammalian hematopoiesis, they appear to be highly context dependent. Using CRISPR/Cas9-based genetic screening, we have identified Scribble complex-related liabilities in AML including LLGL1. Despite its reported suppressive function in HSC self-renewal, inactivation of LLGL1in AML confirms its relevant role for proliferative capacity and development of AML. Its function was conserved in human and murine models of AML and across various genetic backgrounds. Inactivation of LLGL1results in loss of stemness-associated gene-expression including HoxA-genes and induces a GMP-like phenotype in the leukemia stem cell compartment. Re-expression of HoxA9facilitates functional and phenotypic rescue. Collectively, these data establish LLGL1as a specific dependency and putative target in AML and emphasizes its cell-type specific functions.

Hintergrund: Die Myelofibrose kann sowohl primär als eigenständiger Subtyp der myeloproliferativen Neoplasien (primäre Myelofibrose, PMF) als auch als Spätphase einer Polycythaemia vera oder essenziellen Thrombozythämie auftreten. Ziel der Arbeit: In der vorliegenden Übersicht wird auf die PMF und deren Diagnostik, Klinik und Therapieoptionen fokussiert eingegangen. Ergebnisse: Die frühe Phase der PMF geht mit einer megakaryozytären und granulozytären Proliferationssteigerung einher. Im weiteren Verlauf kann eine Knochenmarkfibrose, begleitet von progredienter Splenomegalie und Panzytopenie, im Vordergrund stehen. In der aktuellen Klassifikation gemäß Weltgesundheitsorganisation (WHO) wird die präfibrotische Phase von der fibrotischen „overten“ Myelofibrose unterschieden. Die Diagnosekriterien beinhalten u. a. die histopathologischen Charakteristika des Knochenmarks, den molekularen Nachweis von Treibermutationen sowie den Ausschluss anderer myeloischer Neoplasien. Die Therapiestrategien in der Behandlung der PMF richten sich nach dem Progressionsrisiko und der Symptomlast. Neben dynamischen Risikoscores mit Betonung klinischer und hämatologischer Parameter nimmt aktuell die Stellung von molekular und zytogenetisch getriebenen Prädiktoren an Relevanz zu, um v. a. jüngeren Patienten eine verlässliche Risikostratifizierung zu ermöglichen. Gerade für jüngere Patienten mit PMF und ohne relevante Komorbiditäten wird bei Intermediär-2- oder Hochrisikokonstellation die kurative Option einer allogenen Stammzelltransplantation empfohlen. Hier ist eine Vorbehandlung mit JAK-Inhibitoren vorteilhaft, insbesondere für Patienten mit Splenomegalie und Symptombelastung. Bei fehlender Indikation oder fehlender Verfügbarkeit einer allogenen Stammzelltransplantation sind eine symptomorientierte Behandlung mit JAK-Inhibitoren oder experimentelle Therapieverfahren im Rahmen von klinischen Studien möglich.

Murine models offer a valuable tool to recapitulate genetically defined subtypes of AML, and to assess the potential of compound mutations and clonal evolution during disease progression. This is of particular importance for difficult to treat leukemias such as FLT3 internal tandem duplication (ITD) positive AML. While conditional gene targeting by Cre recombinase is a powerful technology that has revolutionized biomedical research, consequences of Cre expression such as lack of fidelity, toxicity or off-target effects need to be taken into consideration. We report on a transgenic murine model of FLT3-ITD induced disease, where Cre recombinase expression alone, and in the absence of a conditional allele, gives rise to an aggressive leukemia phenotype. Here, expression of various Cre recombinases leads to polyclonal expansion of FLT3ITD/ITDprogenitor cells, induction of a differentiation block and activation of Myc-dependent gene expression programs. Our report is intended to alert the scientific community of potential risks associated with using this specific mouse model and of unexpected effects of Cre expression when investigating cooperative oncogenic mutations in murine models of cancer.

In an effort to identify novel drugs targeting fusion-oncogene–induced acute myeloid leukemia (AML), we performed high-resolution proteomic analysis. In AML1-ETO (AE)-driven AML, we uncovered a deregulation of phospholipase C (PLC) signaling. We identified PLCgamma 1 (PLCG1) as a specific target of the AE fusion protein that is induced after AE binding to intergenic regulatory DNA elements. Genetic inactivation of PLCG1 in murine and human AML inhibited AML1-ETO dependent self-renewal programs, leukemic proliferation, and leukemia maintenance in vivo. In contrast, PLCG1 was dispensable for normal hematopoietic stem and progenitor cell function. These findings are extended to and confirmed by pharmacologic perturbation of Ca++-signaling in AML1-ETO AML cells, indicating that the PLCG1 pathway poses an important therapeutic target for AML1-ETO+ leukemic stem cells.

Persistence of malignant clones is a major determinant of adverse outcome in patients with hematologic malignancies. Despite the fact that the majority of patients with acute myeloid leukemia (AML) achieve complete remission after chemotherapy, a large proportion of them relapse as a result of residual malignant cells. These persistent clones have a competitive advantage and can re-establish disease. Therefore, targeting strategies that specifically diminish cell competition of malignant cells while leaving normal cells unaffected are clearly warranted. Recently, our group identified YBX1 as a mediator of disease persistence in JAK2-mutated myeloproliferative neoplasms. The role of YBX1 in AML, however, remained so far elusive. Here, inactivation of YBX1confirms its role as an essential driver of leukemia development and maintenance. We identify its ability to amplify the translation of oncogenic transcripts, including MYC, by recruitment to polysomal chains. Genetic inactivation of YBX1disrupts this regulatory circuit and displaces oncogenic drivers from polysomes, with subsequent depletion of protein levels. As a consequence, leukemia cells show reduced proliferation and are out-competed in vitro and in vivo, while normal cells remain largely unaffected. Collectively, these data establish YBX1 as a specific dependency and therapeutic target in AML that is essential for oncogenic protein expression.

Die klassischen chronischen BCR::ABL1-negativen myeloproliferativen Neoplasien umfassen die Polycythaemia vera, die essenzielle Thrombozythämie und die primäre Myelofibrose. In den vergangenen Jahren haben signifikante Entwicklungen hinsichtlich der Therapiemöglichkeiten und Therapiestrategien stattgefunden, die neue Substanzen beinhalten. Interferone, Januskinase(JAK)-Inhibitoren und Kombinationstherapien zählen hier zu den klinischen Entwicklungen. Eine exakte Klassifizierung, Diagnosestellung und Risikostratifizierung ist für die Optimierung der Therapiestrategie und eine personalisierte Behandlung ausschlaggebend.

Mutations of the JAK2gene are frequent aberrations in the aging hematopoietic system and in myeloid neoplasms. While JAK-inhibitors efficiently reduce hyperinflammation induced by the constitutively active mutated JAK2 kinase, the malignant clone and abundance of mutated cells remains rather unaffected. Here, we sought to assess for genetic vulnerabilities of JAK2-mutated clones. We identified lysine-specific demethylase KDM4C as a selective genetic dependency that persists upon JAK-inhibitor treatment. Genetic inactivation of KDM4C in human and murine JAK2-mutated cells resulted in loss of cell competition and reduced proliferation. These findings led to reduced disease penetrance and improved survival in xenograft models of human JAK2-mutated cells. KDM4C deleted cells showed alterations in target histone residue methylation and target gene expression, resulting in induction of cellular senescence. In summary, these data establish KDM4C as a specific dependency and therapeutic target in JAK2-mutated cells that is essential for oncogenic signaling and prevents induction of senescence.

An important limitation of FLT3 tyrosine kinase inhibitors (TKIs) in FLT3-ITD positive AML is the development of resistance. To better understand resistance to FLT3 inhibition, we examined FLT3-ITD positive cell lines which had acquired resistance to midostaurin or sorafenib. In 6 out of 23 TKI resistant cell lines we were able to detect a JAK1 V658F mutation, a mutation that led to reactivation of the CSF2RB–STAT5 pathway. Knockdown of JAK1, or treatment with a JAK inhibitor, resensitized cells to FLT3 inhibition. Out of 136 patients with FLT3-ITD mutated AML and exposed to FLT3 inhibitor, we found seven different JAK family mutations in six of the cases (4.4%), including five bona fide, activating mutations. Except for one patient, the JAK mutations occurred de novo (n= 4) or displayed increasing variant allele frequency after exposure to FLT3 TKI (n= 1). In vitro each of the five activating variants were found to induce resistance to FLT3-ITD inhibition, which was then overcome by dual FLT3/JAK inhibition. In conclusion, our data characterize a novel mechanism of resistance to FLT3-ITD inhibition and may offer a potential therapy, using dual JAK and FLT3 inhibition.

Janus kinases (JAKs) mediate responses to cytokines, hormones and growth factors in haematopoietic cells1,2. The JAK gene JAK2is frequently mutated in the ageing haematopoietic system3,4and in haematopoietic cancers5. JAK2mutations constitutively activate downstream signalling and are drivers of myeloproliferative neoplasm (MPN). In clinical use, JAK inhibitors have mixed effects on the overall disease burden of JAK2-mutated clones6,7, prompting us to investigate the mechanism underlying disease persistence. Here, by in-depth phosphoproteome profiling, we identify proteins involved in mRNA processing as targets of mutant JAK2. We found that inactivation of YBX1, a post-translationally modified target of JAK2, sensitizes cells that persist despite treatment with JAK inhibitors to apoptosis and results in RNA mis-splicing, enrichment for retained introns and disruption of the transcriptional control of extracellular signal-regulated kinase (ERK) signalling. In combination with pharmacological JAK inhibition, YBX1 inactivation induces apoptosis in JAK2-dependent mouse and primary human cells, causing regression of the malignant clones in vivo, and inducing molecular remission. This identifies and validates a cell-intrinsic mechanism whereby differential protein phosphorylation causes splicing-dependent alterations of JAK2–ERK signalling and the maintenance of JAK2V617Fmalignant clones. Therapeutic targeting of YBX1-dependent ERK signalling in combination with JAK2 inhibition could thus eradicate cells harbouring mutations in JAK2.

Mutant KRAS modulates the metabolic plasticity of cancer cells to confer a growth advantage during hypoxia, but the molecular underpinnings are largely unknown. Using a lipidomic screen, we found that PLCγ1 is suppressed during hypoxia in KRAS-mutant human lung adenocarcinoma cancer cell lines. Suppression of PLCγ1 in hypoxia promotes a less oxidative cancer cell metabolism state, reduces the formation of mitochondrial reactive oxygen species and switches tumour bioenergetics towards glycolysis by impairing Ca2+entry into the mitochondria. This event prevents lipid peroxidation, antagonizes apoptosis and increases cancer cell proliferation. Accordingly, loss of function of Plcg1in a mouse model of KrasG12D-driven lung adenocarcinoma increased the expression of glycolytic genes, boosted tumour growth and reduced survival. In patients with KRAS-mutant lung adenocarcinomas, low PLCγ1 expression correlates with increased expression of hypoxia markers and predicts poor patient survival. Thus, our work reveals a mechanism of cancer cell adaptation to hypoxia with potential therapeutic value.

Clonal hematopoiesis is frequently observed in elderly people. To investigate the prevalence and dynamics of genetic alterations among healthy elderly individuals, a cohort of 50 people >80 years was genotyped for commonly mutated leukemia-associated genes by targeted deep next-generation sequencing. A total of 16 somatic mutations were identified in 13/50 (26%) individuals. Mutations occurred at low variant allele frequencies (median 11.7%) and remained virtually stable over 3 years without development of hematologic malignancies in affected individuals. With DNMT3Amutations most frequently detected, another cohort of 160 healthy people spanning all age groups was sequenced specifically for DNMT3Arevealing an overall mutation rate of 6.2% (13/210) and an age-dependent increase of mutation prevalence. A significant difference (p= 0.017) in the DNMT3Aexpression pattern was detected between younger and healthy elderly people as determined by qRT-PCR. To evaluate the selection of clonal hematopoietic stem cells (HSCs), bone marrow of two healthy individuals with mutant DNMT3Awas transplanted in a humanized mouse model. Xenografts displayed stable kinetics of DNMT3Amutations over 8 months. These findings indicate that the appearance of low-level clones with leukemia-associated mutations is a common age-associated phenomenon, but insufficient to initiate clonal selection and expansion without the additional influence of other factors.

Molecular alterations within the hematopoietic system influence cellular longevity and development of age-related myeloid stem-cell disorders like acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). A reduced SIRT7-expression in aged murine hematopoietic stem cells (HSC) resulted in reduced longevity and increased proliferation. In this study we investigated age-related changes of SIRT7-expression in healthy humans and relevant pathomechanisms in AML and CML. SIRT7-expression in leukocytes of healthy people decreased in an age-dependent manner. Low SIRT7 mRNA levels were also detected in AML and CML patients. With positive treatment response, SIRT7-expression increased, but showed reduction when patients progressed or relapsed. Pharmacologic inhibition of driver mutations in AML (FLT3-ITD) or CML (BCR-ABL) also restored SIRT7 levels in cell lines and patient samples. Furthermore, SIRT7-expression increased with time during PMA-mediated monocyte differentiation of THP-1 cells. SIRT7-overexpression in THP-1 cells resulted in increased expression of differentiation markers. BCR-ABL, FLT3-ITD, and differentiation-associated SIRT7-expression in general were positively regulated by C/EBPα, -β, and -ε binding to two different C/EBP-binding sites within the SIRT7 promoter. SIRT7 is important in human hematopoietic cell aging and longevity. It might act as tumor suppressor and could potentially serve as general biomarker for monitoring treatment response in myeloid stem-cell disorders.

JAK2V617F is the most common mutation in patients with BCR-ABL negative myeloproliferative neoplasms (MPNs). The eradication of JAK2V617F hematopoietic stem cells (HSCs) is critical for achieving molecular remissions and cure. We investigate the distinct effects of two therapies, ruxolitinib (JAK1/2 inhibitor) and interferon-alpha (IFN-α), on the disease-initiating HSC population. Whereas ruxolitinib inhibits Stat5 activation in erythroid progenitor populations, it fails to inhibit this same pathway in HSCs. In contrast, IFN-α has direct effects on HSCs. Furthermore, STAT1 phosphorylation and pathway activation is greater after IFN-α stimulation in Jak2V617F murine HSCs with increased induction of reactive oxygen species, DNA damage and reduction in quiescence after chronic IFN-α treatment. Interestingly, ruxolitinib does not block IFN-α induced reactive oxygen species and DNA damage in Jak2V617F murine HSCs in vivo. This work provides a mechanistic rationale informing how pegylated IFN-α reduces JAK2V617F allelic burden in the clinical setting and may inform future clinical efforts to combine ruxolitinib with pegylated IFN-α in patients with MPN.

To date, only one subtype of acute myeloid leukemia (AML), acute promyelocytic leukemia (APL) can be effectively treated by differentiation therapy utilizing all-trans retinoic acid (ATRA). Non-APL AMLs are resistant to ATRA. Here we demonstrate that the acetyltransferase GCN5 contributes to ATRA resistance in non-APL AML via aberrant acetylation of histone 3 lysine 9 (H3K9ac) residues maintaining the expression of stemness and leukemia associated genes. We show that inhibition of GCN5 unlocks an ATRA-driven therapeutic response. This response is potentiated by coinhibition of the lysine demethylase LSD1, leading to differentiation in most non-APL AML. Induction of differentiation was not correlated to a specific AML subtype, cytogenetic, or mutational status. Our study shows a previously uncharacterized role of GCN5 in maintaining the immature state of leukemic blasts and identifies GCN5 as a therapeutic target in AML. The high efficacy of the combined epigenetic treatment with GCN5 and LSD1 inhibitors may enable the use of ATRA for differentiation therapy of non-APL AML. Furthermore, it supports a strategy of combined targeting of epigenetic factors to improve treatment, a concept potentially applicable for a broad range of malignancies.

The transcription factor GATA1 is an essential regulator of erythroid cell gene expression and maturation and is also relevant for platelet biogenesis. GATA1-related thrombocytopenia (GATA1-RT) is a rare X-linked inherited platelet disorder (IPD) characterized by macrothrombocytopenia and dyserythropoiesis. Enlarged platelet size, reduced platelet granularity, and noticeable red blood cell anisopoikilocytosis are characteristic but unspecific morphological findings in GATA1-RT.

Introduction:Polycythemia vera (PV) is characterized by trilineage blood cell expansion, PV-associated symptoms, and the risk of thromboembolic complications, progression to post-PV myelofibrosis, and acute leukemia. Cytoreductive treatment with hydroxyurea (HU) or ropeginterferon-alpha is approved in EU for the treatment of high-risk patients (pts) with PV. In addition, ruxolitinib (RUX) is approved for HU-intolerant/-resistant PV. However, RUX vs. best available therapy (BAT) has not been investigated as first-line treatment of pts with untreated PV. We hypothesized that RUX may have higher efficacy in such early-line PV pts.

The Triggering Receptor Expressed on Myeloid Cells (TREM)-1 is a member of the Immunoglobulin superfamily and an activating receptor mainly expressed on myeloid cells. TREM-1 ligation leads to immediate activation of polymorphonuclear neutrophils (PMN) resulting in degranulation and release of reactive oxygen species as well as various effector molecules. Beyond its role in acute and chronic inflammatory processes, TREM-1 is also involved in cancer emergence and progression probably by alteration of the tumor associated neutrophils (TAN) and macrophages (TAM). Advanced information about the TREM-1 signaling cascade may reveal novel therapeutic approaches, as various kinases can specifically be targeted with kinase inhibitors. Therefore, we investigated the protein tyrosine kinome (PTK) and serine threonine kinome (STK) of human PMN after TREM-1 activation. To gain further insights beyond the signaling cascade, we performed RNAseq to validate the TREM-1 mediated activation and to reveal the TREM-1 mediated transcriptome.

Introduction

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare, acquired haematological stem cell disorder characterized by haemolysis, thrombophilia, and cytopenia. PNH is caused by a somatic mutation in the phosphatidylinositol glycan class A (PIG-A) gene at the level of pluripotent, hematopoietic stem cells leading to a lack of GPI anchored cell surface proteins, such as complement-inactivating proteins, (e.g., CD55, CD59) on stem cells, polymorphonuclear neutrophil granulocytes (PMN), erythrocytes, and platelets. Subsequently, uncontrolled complement overactivity leads to the systemic complications. Phenotypic mosaicism is a distinct characteristic of PNH. For diagnostic purposes, the absence of the GPI-anchor on granulocytes and monocytes in the flow cytometry is considered the gold standard. However, the exact consequences of GPI deficiency in PMNs and monocytes have not been studied sufficiently yet. Since the implementation of complement inhibitors, the primary cause of morbidity and mortality in PNH has been significantly reduced. Despite this, the tendency towards thrombosis, as well as the consequences of the deficiency of GPI-linked proteins on PMNs and monocytes, remain largely unclear.

Clonal hematopoiesis is an age-associated condition characterized by the expansion of hematopoietic stem cell (HSC) pools with somatic mutations, observed in 10-30% of individuals older than 70 years. This phenomenon is primarily driven by mutations in transcriptional regulators such as DNMT3A, TET2, and ASXL1. While the clonal expansion of mutated HSCs is ubiquitous with age, it appears largely benign in the absence of strong selective pressures. These benign clones might compensate for the loss of regenerative HSC capacity during aging, and skew differentiation towards the myeloid lineage. Telomere erosion plays a significant role in this process. Telomeres normally prevent the activation of the DNA damage response (DDR) machinery. However, with each cell division, telomeres shorten until they reach a critical length, eventually leading to apoptosis or senescence. Previous studies have suggested a potential involvement of telomere attrition in the development of clonal hematopoiesis (Hinds et al. Blood 2016; Zink et al. Blood 2017). Late generation telomerase deficient (Terc-/- G5) mice develop premature bone marrow failure and mortality, however earlier generation Terc-/- G3 (3 homozygous crosses) have shortened telomeres but appear relatively normal. Importantly, inhibitors of telomerase have recently entered clinical trials for haematological malignancies and therefore understanding the long-term effects of telomerase inhibition is important. By studying the interplay between telomere attrition, HSC aging, and the development of CHIP, we aim to gain insights into the mechanisms underlying age-associated hematopoietic changes and their potential clinical implications.

The receptor tyrosine kinase FLT3 is expressed in myeloid and lymphoid progenitor cells. Activating mutations in FLT3 occur in 25–30% of acute myeloid leukaemia (AML) patients. Most common are internal tandem duplications of sequence (ITD) leading to constitutive FLT3-ITD kinase activity with an altered signalling quality promoting leukaemic cell transformation. Here, we observed the attenuating role of the receptor-like protein tyrosine phosphatase (RPTP) CD45/Ptprc in FLT3 signalling in vivo. Low level expression of this abundant RPTP correlates with a poor prognosis of FLT3-ITD-positive AML patients. To get a further insight into the regulatory role of Ptprc in FLT3-ITD activity in vivo, Ptprcknock-out mice were bred with FLT3-ITD knock-in mice. Inactivation of the Ptprcgene in FLT3-ITD mice resulted in a drastically shortened life span and development of severe monocytosis, a block in B-cell development and anaemia. The myeloproliferative phenotype was associated with extramedullary haematopoiesis, splenohepatomegaly and severe alterations of organ structures. The phenotypic alterations were associated with increased transforming signalling of FLT3-ITD, including activation of its downstream target STAT5. These data reveal the capacity of Ptprc for the regulation of FLT3-ITD signalling activity in vivo. In addition, histopathology and computed tomography (CT) revealed an unexpected bone phenotype; the FLT3-ITD Ptprc-/-mice, but none of the controls, showed pronounced alterations in bone morphology and, in part, apparent features of osteoporosis. In the spleen, ectopic bone formation was observed. The observed bone phenotypes suggest a previously unappreciated capacity of FLT3-ITD (and presumably FLT3) to regulate bone development/remodelling, which is under negative control of CD45/Ptprc.

Glasdegib is a Hedgehog pathway inhibitor. This phase II, randomized, open-label, multicenter study (ClinicalTrials.gov, NCT01546038) evaluated the efficacy of glasdegib plus low-dose cytarabine (LDAC) in patients with acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome unsuitable for intensive chemotherapy. Glasdegib 100 mg (oral, QD) was administered continuously in 28-day cycles; LDAC 20 mg (subcutaneous, BID) was administered for 10 per 28 days. Patients (stratified by cytogenetic risk) were randomized (2:1) to receive glasdegib/LDAC or LDAC. The primary endpoint was overall survival. Eighty-eight and 44 patients were randomized to glasdegib/LDAC and LDAC, respectively. Median (80% confidence interval [CI]) overall survival was 8.8 (6.9–9.9) months with glasdegib/LDAC and 4.9 (3.5–6.0) months with LDAC (hazard ratio, 0.51; 80% CI, 0.39–0.67, P= 0.0004). Fifteen (17.0%) and 1 (2.3%) patients in the glasdegib/LDAC and LDAC arms, respectively, achieved complete remission (P< 0.05). Nonhematologic grade 3/4 all-causality adverse events included pneumonia (16.7%) and fatigue (14.3%) with glasdegib/LDAC and pneumonia (14.6%) with LDAC. Clinical efficacy was evident across patients with diverse mutational profiles. Glasdegib plus LDAC has a favorable benefit–risk profile and may be a promising option for AML patients unsuitable for intensive chemotherapy.

Recently, the myelofibrosis secondary to PV and ET prognostic model (MYSEC-PM) was introduced to assess prognosis in myelofibrosis (MF) secondary to polycythemia vera and essential thrombocythemia (post-PV and post-ET MF), replacing the International Prognostic Scoring System (IPSS) and/or Dynamic IPSS (DIPSS) that was applied for primary MF (PMF). In a cohort of 421 ruxolitinib (RUX)-treated patients (post-PV and post-ET MF: 44.2%), we evaluated the following: (1) disease phenotype, responses, and toxicity to RUX; and (2) performance of the MYSEC-PM in post-PV or post-ET MF. While the IPSS failed to correctly stratify post-PV or post-ET MF patients at diagnosis, the MYSEC-PM identified 4 risk categories projected at significantly different survival probability (P< .001). Additionally, the MYSEC-PM maintained a prognostic value in post-PV and post-ET MF also when used over time, at RUX start. Notably, the MYSEC-PM reclassified 41.8% and 13.6% of patients into a lower and higher risk category, respectively. Finally, patients at intermediate-1 risk had significantly higher spleen responses and lower hematological toxicities compared to higher risk patients. Compared to PMF, post-PV and post-ET MF presented a more hyperproliferative disease, with higher leukocyte and/or platelet count and hemoglobin levels both at diagnosis and at RUX start. Despite comparable response rates, post-PV and post-ET MF had lower rate of RUX-induced anemia and thrombocytopenia at 3 and 6 months. The study validates MYSEC-PM in post-PV and post-ET MF prognostication. Post-PV or post-ET MF represents a separate entity compared to PMF in terms of clinical manifestations and toxicity to RUX.

Cell fate determinants influence self-renewal potential of hematopoietic stem cells. Scribble and Llgl1 belong to the Scribble polarity complex and reveal tumor-suppressor function in drosophila. In hematopoietic cells, genetic inactivation of Llgl1 leads to expansion of the stem cell pool and increases self-renewal capacity without conferring malignant transformation. Here we show that genetic inactivation of its putative complex partner Scribble results in functional impairment of hematopoietic stem cells (HSC) over serial transplantation and during stress. Although loss of Scribble deregulates transcriptional downstream effectors involved in stem cell proliferation, cell signaling, and cell motility, these effectors do not overlap with transcriptional targets of Llgl1. Binding partner analysis of Scribble in hematopoietic cells using affinity purification followed by mass spectometry confirms its role in cell signaling and motility but not for binding to polarity modules described in drosophila. Finally, requirement of Scribble for self-renewal capacity also affects leukemia stem cell function. Thus, Scribble is a regulator of adult HSCs, essential for maintenance of HSCs during phases of cell stress.

Deregulated proliferation is key to tumor progression. Although unrestricted proliferation of solid tumor cells correlates with the cold-shock protein Y-box (YB)-binding protein-1 accumulation in the nuclei, little is known about its expression and function in hematopoietic malignancies, such as T-cell acute lymphoblastic leukemia (T-ALL). Here we show that YB-1 protein is highly enriched in the nuclei of activated T cells and malignant human T-ALL cell lines but not in resting T cells. YB-1 S102mutations that either mimic (S102D) or prevent phosphorylation (S102N) led to accumulation of YB-1 in the nucleus of T cells or strictly excluded it, respectively. Inactivation of ribosomal S6 kinase (RSK) was sufficient to abrogate T-cell and T-ALL cell proliferation, suggesting that RSK mediates cell-cycle progression, possibly dependent on YB-1-phosphorylation. Indeed, phosphomimetic YB-1S102Denhanced proliferation implying that S102phosphorylation is a prerequisite for malignant T-cell proliferation. At initial diagnosis of T-ALL, YB-1 localization was significantly altered in the nuclei of tumor blasts derived from bone marrow or peripheral blood. Our data show deregulated YB-1 in the nucleus as a yet unreported characteristic of T-ALL blasts and may refine strategies to restrict progression of hematopoietic tumors.

Allogeneic haematopoietic stem-cell transplantation is a potential curative therapy for otherwise fatal haematological diseases. This treatment modality is complex, burdensome, and can involve considerable or life-threatening adverse events requiring high-quality symptom control. In contrast to patients with solid tumours, the transition to end-of-life care can be abrupt if the underlying disease relapses or other severe transplantation-related complications occur. This Viewpoint elucidates the relationships between transplantation and palliative care teams and discusses why patients who have undergone transplantation might benefit considerably from early admittance to palliative care, even when the treatment goal is clearly curative. Close and early collaboration between transplantation teams and palliative care teams is clearly endorsed.

Up to 30% of patients with acute myeloid leukemia have constitutively activating internal tandem duplications (ITDs) of the FLT3 receptor tyrosine kinase. Such mutations are associated with a poor prognosis and a high propensity to relapse after remission. FLT3 inhibitors are being developed as targeted therapy for FLT3-ITD+ acute myeloid leukemia; however, their use is complicated by rapid development of resistance, which illustrates the need for additional therapeutic targets. We show that the US Food and Drug Administration–approved CDK4/6 kinase inhibitor palbociclib induces apoptosis of FLT3-ITD leukemic cells. The effect is specific for FLT3-mutant cells and is ascribed to the transcriptional activity of CDK6: CDK6 but not its functional homolog CDK4 is found at the promoters of the FLT3 and PIM1 genes, another important leukemogenic driver. There CDK6 regulates transcription in a kinase-dependent manner. Of potential clinical relevance, combined treatment with palbociclib and FLT3 inhibitors results in synergistic cytotoxicity. Simultaneously targeting two critical signaling nodes in leukemogenesis could represent a therapeutic breakthrough, leading to complete remission and overcoming resistance to FLT3 inhibitors.

Up to 30% of patients with acute myeloid leukemia have constitutively activating internal tandem duplications (ITDs) of the FLT3 receptor tyrosine kinase. Such mutations are associated with a poor prognosis and a high propensity to relapse after remission. FLT3 inhibitors are being developed as targeted therapy for FLT3-ITD+acute myeloid leukemia; however, their use is complicated by rapid development of resistance, which illustrates the need for additional therapeutic targets. We show that the US Food and Drug Administration–approved CDK4/6 kinase inhibitor palbociclib induces apoptosis of FLT3-ITD leukemic cells. The effect is specific for FLT3-mutant cells and is ascribed to the transcriptional activity of CDK6: CDK6 but not its functional homolog CDK4 is found at the promoters of the FLT3and PIM1genes, another important leukemogenic driver. There CDK6 regulates transcription in a kinase-dependent manner. Of potential clinical relevance, combined treatment with palbociclib and FLT3 inhibitors results in synergistic cytotoxicity. Simultaneously targeting two critical signaling nodes in leukemogenesis could represent a therapeutic breakthrough, leading to complete remission and overcoming resistance to FLT3 inhibitors.

Acute myeloid leukemia (AML) is an aggressive and lethal blood cancer maintained by rare populations of leukemia stem cells (LSCs). Selective targeting of LSCs is a promising approach for treating AML and preventing relapse following chemotherapy, and developing such therapeutic modalities is a key priority. Here, we show that targeting telomerase activity eradicates AML LSCs. Genetic deletion of the telomerase subunit Terc in a retroviral mouse AML model induces cell-cycle arrest and apoptosis of LSCs, and depletion of telomerase-deficient LSCs is partially rescued by p53 knockdown. Murine Terc−/−LSCs express a specific gene expression signature that can be identified in human AML patient cohorts and is positively correlated with patient survival following chemotherapy. In xenografts of primary human AML, genetic or pharmacological inhibition of telomerase targets LSCs, impairs leukemia progression, and delays relapse following chemotherapy. Altogether, these results establish telomerase inhibition as an effective strategy for eliminating AML LSCs.