bims-tremyl Biomed News
on Therapy resistance biology in myeloid leukemia
Issue of 2021‒04‒25
33 papers selected by
Paolo Gallipoli
Barts Cancer Institute, Queen Mary University of London

  1. Blood Adv. 2021 Apr 27. 5(8): 2173-2183
      Spliceosome mutations (SRSF2, SF3B1, U2AF1, ZRSR2), are encountered in ∼50% of secondary acute myeloid leukemia cases (sAML) and define a molecular subgroup with outcomes similar to sAML in de novo AML patients treated with intensive chemotherapy. Outcomes in patients with spliceosome mutations treated with hypomethylating agents in combination with venetoclax (HMA+VEN) remains unknown. The primary objective was to compare outcomes in patients with spliceosome mutations vs wild-type patients treated with HMA+VEN. Secondary objectives included analysis of the mutational landscape of the spliceosome cohort and assessing the impact of co-occurring mutations. We performed a retrospective cohort analysis of patients treated with HMA+VEN-based regimens at The University of Texas MD Anderson Cancer Center. A total of 119 patients (spliceosome mutated n = 39 [SRSF2, n = 24; SF3B1, n = 8; U2AF1, n = 7]; wild-type, n = 80) were included. Similar responses were observed between spliceosome and wild-type cohorts for composite complete response (CRc; 79% vs 75%, P = .65), and measurable residual disease-negative CRc (48% vs 60%, P = .34). Median overall survival for spliceosome vs wild-type patients was 35 vs 14 months (P = .58), and was not reached; 35 months and 8 months for patients with SRSF2, SF3B1, and U2AF1 mutations, respectively. IDH2 mutations were enriched in patients with SRSF2 mutations and associated with favorable outcomes (1- and 2-year overall survival [OS] of 100% and 88%). RAS mutations were enriched in patients with U2AF1 mutations and associated with inferior outcomes (median OS, 8 months). Comparable outcomes were observed between patients with vs without spliceosome mutations treated with HMA+VEN regimens, with specific co-mutation pairs demonstrating favorable outcomes.
  2. Blood Adv. 2021 Apr 27. 5(8): 2087-2100
      Leukemia stem cells (LSCs) and therapy-resistant acute myeloid leukemia (AML) blasts contribute to the reinitiation of leukemia after remission, necessitating therapeutic interventions that target these populations. Autophagy is a prosurvival process that allows for cells to adapt to a variety of stressors. Blocking autophagy pharmacologically by using mechanistically distinct inhibitors induced apoptosis and prevented colony formation in primary human AML cells. The most effective inhibitor, bafilomycin A1 (Baf A1), also prevented the in vivo maintenance of AML LSCs in NSG mice. To understand why Baf A1 exerted the most dramatic effects on LSC survival, we evaluated mitochondrial function. Baf A1 reduced mitochondrial respiration and stabilized PTEN-induced kinase-1 (PINK-1), which initiates autophagy of mitochondria (mitophagy). Interestingly, with the autophagy inhibitor chloroquine, levels of enhanced cell death and reduced mitochondrial respiration phenocopied the effects of Baf A1 only when cultured in hypoxic conditions that mimic the marrow microenvironment (1% O2). This indicates that increased efficacy of autophagy inhibitors in inducing AML cell death can be achieved by concurrently inducing mitochondrial damage and mitophagy (pharmacologically or by hypoxic induction) and blocking mitochondrial degradation. In addition, prolonged exposure of AML cells to hypoxia induced autophagic flux and reduced chemosensitivity to cytarabine (Ara-C), which was reversed by autophagy inhibition. The combination of Ara-C with Baf A1 also decreased tumor burden in vivo. These findings demonstrate that autophagy is critical for mitochondrial homeostasis and survival of AML cells in hypoxia and support the development of autophagy inhibitors as novel therapeutic agents for AML.
  3. Nat Cancer. 2020 Dec;1(12): 1176-1187
      Venetoclax with azacitidine (ven/aza) has emerged as a promising regimen for acute myeloid leukemia (AML), with a high percentage of clinical remissions in newly diagnosed patients. However, approximately 30% of newly diagnosed and the majority of relapsed patients do not achieve remission with ven/aza. We previously reported that ven/aza efficacy is based on eradication of AML stem cells through a mechanism involving inhibition of amino acid metabolism, a process which is required in primitive AML cells to drive oxidative phosphorylation. Herein we demonstrate that resistance to ven/aza occurs via up-regulation of fatty acid oxidation (FAO), which occurs due to RAS pathway mutations, or as a compensatory adaptation in relapsed disease. Utilization of FAO obviates the need for amino acid metabolism, thereby rendering ven/aza ineffective. Pharmacological inhibition of FAO restores sensitivity to ven/aza in drug resistant AML cells. We propose inhibition of FAO as a therapeutic strategy to address ven/aza resistance.
  4. Cancer Discov. 2021 Apr 23. pii: candisc.1542.2020. [Epub ahead of print]
      Hundreds of genes become aberrantly silenced in acute myeloid leukemia (AML), with most of these epigenetic changes being of unknown functional consequence. Here, we demonstrate how gene silencing can lead to an acquired dependency on the DNA repair machinery in AML. We make this observation by profiling the essentiality of the ubiquitination machinery in cancer cell lines using domain-focused CRISPR screening, which revealed Fanconi anemia (FA) proteins UBE2T and FANCL as unique dependencies in AML. We demonstrate that these dependencies are due to a synthetic lethal interaction between FA proteins and Aldehyde Dehydrogenase 2 (ALDH2), which function in parallel pathways to counteract the genotoxicity of endogenous aldehydes. We show that DNA hypermethylation and silencing of ALDH2 occur in a recurrent manner in human AML, which is sufficient to confer FA pathway dependency. Our study suggests that targeting of the ubiquitination reaction catalyzed by FA proteins can eliminate ALDH2-deficient AML.
  5. Blood Adv. 2021 Apr 27. 5(8): 2156-2164
      In patients with acute myeloid leukemia evolving from myeloproliferative neoplasms (post-MPN-AML), the clinical activity of the B-cell lymphoma 2 inhibitor venetoclax remains to be determined. We review our experience with venetoclax-based regimens in 14 newly diagnosed (frontline [FL]) and 17 relapsed/refractory (R/R) post-MPN-AML patients. Venetoclax was used in combination with hypomethylating agents in 58% of cases and in 19% with intensive chemotherapy (treatment including cytarabine ≥1 g/m2 or CPX-351); the remaining patients received cladribine and low-dose cytarabine or isocitrate dehydrogenase 1/2 inhibitors. The median dose of venetoclax during the initial cycle was 100 mg in all patients (range, 50-800 mg) and 200 mg (range, 100-800 mg) for FL patients. The venetoclax dose was adjusted when used concomitantly with azole antifungal agents. In FL patients, complete remission with and without count recovery in 6 patients (median duration of 6.4 months) and partial remission in 1 patient was noted, with a median overall survival of 7 months. In R/R patients, no formal responses were seen, with a median overall survival of 3 months. Hematologic toxicities and adverse events were frequent; 83% of patients developed grade 3 or higher infection during the initial cycle. Severe hemorrhagic complications were observed in 14 patients, including 6 cases of intracranial and subdural hemorrhage. Overall 4-week and 8-week mortality were 10% and 32%, respectively. Given the substantial treatment-associated hematologic toxicity and mortality, and modest short-lived responses only in newly diagnosed patients with venetoclax-based regimens, additional treatment options are urgently needed for these patients.
  6. Cancer Lett. 2021 Apr 16. pii: S0304-3835(21)00166-X. [Epub ahead of print]
      Aberrant activation of cytokine and growth factor signal transduction pathways confers enhanced survival and proliferation properties to acute myeloid leukemia (AML) cells. However, the mechanisms underlying the deregulation of signaling pathways in leukemia cells are unclear. To identify genes capable of independently supporting cytokine-independent growth, we employed a genome-wide CRISPR/Cas9-mediated loss-of-function screen in GM-CSF-dependent human AML TF-1 cells. More than 182 genes (p < 0.01) were found to suppress the cytokine-independent growth of TF-1 cells. Among the top hits, genes encoding key factors involved in sialylation biosynthesis were identified; these included CMAS, SLC35A1, NANS, and GNE. Knockout of either CMAS or SLC35A1 enabled cytokine-independent proliferation and survival of AML cells. Furthermore, NSG (NOD/SCID/IL2Rγ-/-) mice injected with CMAS or SLC35A1-knockout TF-1 cells exhibited a shorter survival than mice injected with wild-type cells. Mechanistically, abrogation of sialylation biosynthesis in TF-1 cells induced a strong activation of ERK signaling, which sensitized cells to MEK inhibitors but conferred resistance to JAK inhibitors. Further, the surface level of α2,3-linked sialic acids was negatively correlated with the sensitivity of AML cell lines to MEK/ERK inhibitors. We also found that sialylation modulated the expression and stability of the CSF2 receptor. Together, these results demonstrate a novel role of sialylation in regulating oncogenic transformation and drug resistance development in leukemia. We propose that altered sialylation could serve as a biomarker for targeted anti-leukemic therapy.
    Keywords:  AML; CMAS; Loss of function screening; SLC35A1; Sialylation
  7. Cancer Metab. 2021 Apr 21. 9(1): 17
      Acute myeloid leukemias (AML) are a group of aggressive hematologic malignancies resulting from acquired genetic mutations in hematopoietic stem cells that affect patients of all ages. Despite decades of research, standard chemotherapy still remains ineffective for some AML subtypes and is often inappropriate for older patients or those with comorbidities. Recently, a number of studies have identified unique mitochondrial alterations that lead to metabolic vulnerabilities in AML cells that may present viable treatment targets. These include mtDNA, dependency on oxidative phosphorylation, mitochondrial metabolism, and pro-survival signaling, as well as reactive oxygen species generation and mitochondrial dynamics. Moreover, some mitochondria-targeting chemotherapeutics and their combinations with other compounds have been FDA-approved for AML treatment. Here, we review recent studies that illuminate the effects of drugs and synergistic drug combinations that target diverse biomolecules and metabolic pathways related to mitochondria and their promise in experimental studies, clinical trials, and existing chemotherapeutic regimens.
    Keywords:  Acute myeloid leukemia (AML); Drug combinations; Leukemia stem cells; Mitocans; Mitochondria; Mitochondrial abnormalities/alterations; Mitochondrial metabolism; Synergy
  8. Acta Haematol. 2021 Apr 21. 1-16
      BACKGROUND: Myeloproliferative neoplasms (MPNs) can transform into blast phase MPN (leukemic transformation; MPN-BP), typically via accelerated phase MPN (MPN-AP), in ∼20-25% of the cases. MPN-AP and MPN-BP are characterized by 10-19% and ≥20% blasts, respectively. MPN-AP/BP portend a dismal prognosis with no established conventional treatment. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the sole modality associated with long-term survival.SUMMARY: MPN-AP/BP has a markedly different mutational profile from de novo acute myeloid leukemia (AML). In MPN-AP/BP, TP53 and IDH1/2 are more frequent, whereas FLT3 and DNMT3A are rare. Higher incidence of leukemic transformation has been associated with the most aggressive MPN subtype, myelofibrosis (MF); other risk factors for leukemic transformation include rising blast counts above 3-5%, advanced age, severe anemia, thrombocytopenia, leukocytosis, increasing bone marrow fibrosis, type 1 CALR-unmutated status, lack of driver mutations (negative for JAK2, CALR, or MPL genes), adverse cytogenetics, and acquisition of ≥2 high-molecular risk mutations (ASXL1, EZH2, IDH1/2, SRSF2, and U2AF1Q157). The aforementioned factors have been incorporated in several novel prognostic scoring systems for MF. Currently, elderly/unfit patients with MPN-AP/BP are treated with hypomethylating agents with/without ruxolitinib; these regimens appear to confer comparable benefit to intensive chemotherapy but with lower toxicity. Retrospective studies in patients who acquired actionable mutations during MPN-AP/BP showed positive outcomes with targeted AML treatments, such as IDH1/2 inhibitors, and require further evaluation in clinical trials. Key Messages: Therapy for MPN-AP patients represents an unmet medical need. MF patients, in particular, should be appropriately stratified regarding their prognosis and the risk for transformation. Higher-risk patients should be monitored regularly and treated prior to progression to MPN-BP. MPN-AP patients may be treated with hypomethylating agents alone or in combination with ruxolitinib; also, patients can be provided with the option to enroll in rationally designed clinical trials exploring combination regimens, including novel targeted drugs, with an ultimate goal to transition to transplant.
    Keywords:  Accelerated phase myeloproliferative neoplasms; Blast phase myeloproliferative neoplasms; Myelofibrosis; Myeloproliferative neoplasms; Post-myeloproliferative neoplasm acute myeloid leukemia
  9. Proc Natl Acad Sci U S A. 2021 Apr 13. pii: e2014967118. [Epub ahead of print]118(15):
      Most genes associated with acute myeloid leukemia (AML) are mutated in less than 10% of patients, suggesting that alternative mechanisms of gene disruption contribute to this disease. Here, we find a set of splicing events that alter the expression of a subset of AML-associated genes independent of known somatic mutations. In particular, aberrant splicing triples the number of patients with reduced functional EZH2 compared with that predicted by somatic mutation alone. In addition, we unexpectedly find that the nonsense-mediated decay factor DHX34 exhibits widespread alternative splicing in sporadic AML, resulting in a premature stop codon that phenocopies the loss-of-function germline mutations observed in familial AML. Together, these results demonstrate that classical mutation analysis underestimates the burden of functional gene disruption in AML and highlight the importance of assessing the contribution of alternative splicing to gene dysregulation in human disease.
    Keywords:  AML; DHX34; EZH2; alternative splicing; cancer
  10. Blood Adv. 2021 Apr 27. 5(8): 2184-2195
      Calreticulin (CALR), an endoplasmic reticulum-associated chaperone, is frequently mutated in myeloproliferative neoplasms (MPNs). Mutated CALR promotes downstream JAK2/STAT5 signaling through interaction with, and activation of, the thrombopoietin receptor (MPL). Here, we provide evidence of a novel mechanism contributing to CALR-mutated MPNs, represented by abnormal activation of the interleukin 6 (IL-6)-signaling pathway. We found that UT7 and UT7/mpl cells, engineered by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to express the CALR type 1-like (DEL) mutation, acquired cytokine independence and were primed to the megakaryocyte (Mk) lineage. Levels of IL-6 messenger RNA (mRNA), extracellular-released IL-6, membrane-associated glycoprotein 130 (gp130), and IL-6 receptor (IL-6R), phosphorylated JAK1 and STAT3 (p-JAK1 and p-STAT3), and IL-6 promoter region occupancy by STAT3 all resulted in increased CALR DEL cells in the absence of MPL stimulation. Wild-type, but not mutated, CALR physically interacted with gp130 and IL-6R, downregulating their expression on the cell membrane. Agents targeting gp130 (SC-144), IL-6R (tocilizumab [TCZ]), and cell-released IL-6 reduced proliferation of CALR DEL as well as CALR knockout cells, supporting a mutated CALR loss-of-function model. CD34+ cells from CALR-mutated patients showed increased levels of IL-6 mRNA and p-STAT3, and colony-forming unit-Mk growth was inhibited by either SC144 or TCZ, as well as an IL-6 antibody, supporting cell-autonomous activation of the IL-6 pathway. Targeting IL-6 signaling also reduced colony formation by CD34+ cells of JAK2V617F-mutated patients. The combination of TCZ and ruxolitinib was synergistic at very low nanomolar concentrations. Overall, our results suggest that target inhibition of IL-6 signaling may have therapeutic potential in CALR, and possibly JAK2V617F, mutated MPNs.
  11. Mol Oncol. 2021 Apr 05.
      Recurrent somatic internal tandem duplications (ITD) in the FMS-like tyrosine kinase 3 (FLT3) gene characterise approximately one third of patients with acute myeloid leukaemia (AML), and FLT3-ITD mutation status guides risk-adapted treatment strategies. The aim of this work was to characterise FLT3-ITD variant distribution in relation to molecular and clinical features, and overall survival in adult AML patients. We performed two parallel retrospective cohort studies investigating FLT3-ITD length and expression by cDNA fragment analysis, followed by Sanger sequencing in a subset of samples. In the two cohorts, a total of 139 and 172 mutant alleles were identified in 111 and 123 patients, respectively, with 22% and 28% of patients presenting with more than one mutated allele. Further, 15% and 32% of samples had a FLT3-ITD total variant allele frequency (VAF) <0.3, while 24% and 16% had a total VAF ≥0.7. Most of the assessed clinical features did not significantly correlate to FLT3-ITD numerical variation nor VAF. Low VAF was, however, associated with lower white blood cell count, while increasing VAF correlated with inferior overall survival in one of the cohorts. In the other cohort, ITD length above 50bp was identified to correlate with inferior overall survival. Our report corroborates the poor prognostic association with high FLT3-ITD disease burden, as well as extensive inter- and intra-patient heterogeneity in the molecular features of FLT3-ITD. We suggest that future use of FLT3-targeted therapy could be accompanied with thorough molecular diagnostics and follow-up to better predict optimal therapy responders.
    Keywords:  Acute myeloid leukaemia; FLT3-ITD; length mutation; outcome; prognosis
  12. Blood. 2021 Feb 24. pii: blood.2020010165. [Epub ahead of print]
      IDH inhibitors are effective in AML, and trials evaluating frontline combinations with intensive chemotherapy (IC) are ongoing. Data on the prognostic significance of co-occurring genetic alterations and allogeneic hematopoietic stem cell transplantation (HSCT) are conflicting in each IDH-mutated subgroup treated by IC, while this information is important for trial design and results interpretation. We retrospectively analyzed 127 IDH1, 135 IDH2R140 and 57 IDH2R172 newly diagnosed AML patients treated with IC in three Acute Leukemia French Association (ALFA) prospective trials. We addressed in each IDH subgroup the prognostic impact of clinical and genetic covariates, and the role of HSCT in eligible patients. In IDH1 patients, presence of NPM1 mutations was the only variable predicting improved OS in multivariate analysis (p < 0.0001). In IDH2R140, normal karyotype (p= 0.008) and NPM1 mutations (p = 0.01) predicted better OS. NPM1 mutations were associated with better DFS (p = 0.0009) whereas presence of DNMT3A mutations was associated with shorter DFS (p = 0.0006). In IDH2R172, platelet count was the only variable retained in the multivariate model for OS (p = 0.002). Among non-favorable ELN-2010 eligible patients, 71 (36%) achieved an HSCT in first complete remission (CR1) and had longer OS (p = 0.03) and DFS (p = 0.02) than not-transplanted patients. Future clinical trial testing frontline IDH inhibitors combined with IC may consider stratification on NPM1 mutational status, the main prognostic factor in IDH1 and IDH2R140 mutated AML. HSCT improve OS of non-favorable IDH1/2-mutated AML and should be fully integrated in the treatment strategy.
  13. Blood. 2021 Apr 19. pii: blood.2020010510. [Epub ahead of print]
      Acute leukemias (AL) of ambiguous lineage are a heterogeneous group of high-risk leukemias characterized by co-expression of myeloid and lymphoid markers. In this study, we identified a distinct subgroup of immature acute leukemias characterized by a broadly variable phenotype, covering acute myeloid leukemia (AML M0 or M1), T/myeloid mixed phenotype acute leukemia (T/M MPAL), and early T-cell precursor acute lymphoblastic leukemia (ETP-ALL). Rearrangements at 14q32/BCL11B are the cytogenetic hallmark of this entity. In our screening of 915 hematological malignancies, there were 202 AML and 333 T-cell Acute Lymphoblastic Leukemia (T-ALL) (58 ETP, 178 non-ETP, 8 T/M MPAL, 89 not otherwise specified). We identified 20 cases of immature leukemias (4% of AML and 3,6% of T-ALL) harbouring four types of 14q32/BCL11B translocations: t(2,14)(q22.3;q32) (n=7), t(6;14)(q25.3;q32) (n=9), t(7;14)(q21.2;q32) (n=2) and t(8;14)(q24.2;q32) (n=2). The t(2;14) produced a ZEB2-BCL11B fusion transcript, while the other three rearrangements displaced transcriptionally active enhancer sequences close to BCL11B without producing fusion genes. All translocations resulted in the activation of BCL11B, a regulator of T-cell differentiation associated with transcriptional corepressor complexes in mammalian cells. The expression of BCL11B behaved as a disease biomarker, which was present at diagnosis but not in remission. Deregulation of BCL11B co-occurred with variants at FLT3 and at epigenetic modulators, most frequently DNMT3A, TET2 and/or WT1 gene. Transcriptome analysis identified a specific expression signature, with significant downregulation of BCL11B targets, and clearly separating BCL11B positive AL from AML, T-ALL, and ETP-ALL. Remarkably, ex-vivo drug sensitivity profile identified a panel of compounds with effective antileukemic activity.
  14. Leuk Lymphoma. 2021 Apr 21. 1-7
      The role of post allogeneic stem-cell transplantation (AlloSCT) FLT3 inhibition for acute myeloid leukemia in the real-world setting is unclear, especially in the era of widespread pre-transplant use of tyrosine kinase inhibitors (TKIs). In a multicenter nationwide study, we assessed 41 patients who were treated with post-transplant TKIs (sorafenib, n = 23, midostaurin, n = 18). The majority also received TKIs pre-transplant (n = 32, 79%). After a median follow up of 10 months post-transplant (range 3-53.6), 29 patients (71%) were alive and in complete remission. Similar results were seen in a subgroup analysis of pre-transplant TKI recipients (78%). In Univariate analysis, HCT-CI score < 4 and Type of TKI (sorafenib versus midostaurin) predicted longer overall survival. Seventeen patients (41%) suffered from side effects and seven patients (17%) stopped TKI therapy due to adverse events. Overall, our data suggest that post-transplant use of TKIs is safe and effective in an era of their widespread use prior to AlloSCT.
    Keywords:  Acute myeloid leukemia; FLT3 inhibitors; post-transplantation maintenance
  15. Cancer Discov. 2021 Apr 23.
      Deficiency of HUSH complex component MPP8 impaired myeloid leukemia cell growth in vitro and in vivo.
  16. Aging (Albany NY). 2021 Apr 23. 13
      Cancer cells-secreted extracellular vesicles (EVs) have emerged as important mediators of intercellular communication in local and distant microenvironment. Our initial GEO database analysis identified the presence of differentially-expressed microRNA-1246 (miR-1246) in acute myeloid leukemia (AML) cell-derived EVs. Consequently, the current study set out to investigate the role of AML-derived EVs-packaged miR-1246 in leukemia stem cells (LSCs) bioactivities. The predicted binding between miR-1246 and LRIG1 was verified using dual luciferase reporter assay. Then, gain- and loss-of-function assays were performed in LSCs, where LSCs were co-cultured with AML cell-derived EVs to characterize the effects of miR-1246-containing EVs, miR-1246, LRIG1 and STAT3 pathway in LSCs. Our findings revealed, in AML cell-derived EVs, miR-1246 was highly-expressed and directly-targeted LRIG1 to activate the STAT3 pathway. MiR-1246 inhibitor or EV-encapsulated miR-1246 inhibitor was found to suppress the viability and colony formation abilities but promoted the apoptosis and differentiation of LSCs through inactivation of STAT3 pathway by up-regulating LRIG1. In addition, the inhibitory effects of AML cell-derived EVs carrying miR-1246 inhibitor on LSCs were substantiated by in vivo experiments. Collectively, our findings reveal that the repression of AML cell-derived EVs containing miR-1246 inhibitor alters the survival of LSCs by inactivating the LRIG1-mediated STAT3 pathway.
    Keywords:  LRIG1; acute myeloid leukemia; extracellular vesicle; leukemia stem cells; microRNA-1246
  17. Leuk Res. 2021 Mar 31. pii: S0145-2126(21)00079-5. [Epub ahead of print]105 106578
      BACKGROUND: Molecular response (MR) 4.0 or 4.3 remains an indicator of treatment-free remission (TFR) in patients with chronic myeloid leukemia (CML) in countries that accept it as the criterion of undetectable minimal residual disease (UMRD) in clinical practice. We retrospectively analyzed the TFR outcomes to identify the clinical efficacy of MR4.0/4.3 as the UMRD criterion.PATIENTS AND METHODS: CML patients treated with tyrosine kinase inhibitors (TKIs) between March 2001 and May 2015 for >3 years and treatment cessation for over 6 months were included. TFR was analyzed using MR3.0 loss and UMRD loss as criteria. TFR failure-free survival was defined as the time from cessation of TKI therapy to MR loss or restarting TKI, and overall survival as the time from TKI cessation to death. The probability of regaining the MR was evaluated.
    RESULTS: In the 93 participants, the median duration of follow-up and TKI therapy were 17.3 (3.9-92.0) months and 7.4 (3.1-16.9) years, respectively. TFR at 5 years was 47.9 % and 44.4 %, for MR3.0 loss and UMRD loss, respectively. Among the 42 patients who restarted TKI, 41 regained MR3.0 (97.6 %). In multivariate analysis, the time to UMRD was ≤12 months, and the absence of prior TKI treatment (P = 0.018 and 0.044 in UMRD loss, respectively) was significantly correlated with TFR failure-free survival.
    CONCLUSION: Clinical outcomes were comparable to those of clinical trials. Our results suggest that the detection limit of MR4.3 can be used in clinical practice for TKI treatment cessation for TFR in CML patients.
    Keywords:  Chronic myeloid leukemia; Molecular response 4.3; Real-world practice; Treatment-free remission
  18. Front Immunol. 2021 ;12 618710
      T cell immunoglobulin and mucin protein 3 (Tim-3) is an immune checkpoint and plays a vital role in immune responses during acute myeloid leukemia (AML). Targeting Tim-3 kills two birds with one stone by balancing the immune system and eliminating leukemia stem cells (LSCs) in AML. These functions make Tim-3 a potential target for curing AML. This review mainly discusses the roles of Tim-3 in the immune system in AML and as an AML LSC marker, which sheds new light on the role of Tim-3 in AML immunotherapy.
    Keywords:  AML; LSC; Tim-3; antibody; immunotherapy
  19. Curr Treat Options Oncol. 2021 Apr 17. 22(6): 49
      OPINION STATEMENT: ABL1 tyrosine kinase inhibitors (TKI) have dramatically improved the outcome for CML (chronic myeloid leukemia) patients. When TKI therapy is addressed appropriately, it can lead to an optimal molecular response in the majority of CML patients and a life expectancy that approaches that of the general population. However, lifelong TKI therapy may have consequences, including chronic, mostly low-grade, adverse events that can substantially impact patients' quality of life, adherence to therapy and, consequently, success of treatment. In the last few years, several groups have demonstrated that approximately 50% of chronic phase CML patients (CP-CML) who have achieved a stable deep molecular response (DMR) can stop therapy without suffering molecular relapse. Nowadays, treatment-free remission (TFR) has a significant role in the management of CML and should be considered in selected motivated patients that fulfill well-defined requirements to maximize the probability of successful discontinuation of TKI therapy.
    Keywords:  Chronic myeloid leukemia; TKI discontinuation; Treatment discontinuation; Treatment-free remission
  20. Leukemia. 2021 Apr 20.
      Mutations of Nucleophosmin (NPM1) are the most common genetic abnormalities in adult acute myeloid leukaemia (AML), accounting for about 30% of cases. NPM1-mutated AML has been recognized as distinct entity in the 2017 World Health Organization (WHO) classification of lympho-haematopoietic neoplasms. WHO criteria allow recognition of this leukaemia entity and its distinction from AML with myelodysplasia-related changes, AML with BCR-ABL1 rearrangement and AML with RUNX1 mutations. Nevertheless, controversial issues include the percentage of blasts required for the diagnosis of NPM1-mutated AML and whether cases of NPM1-mutated myelodysplasia and chronic myelomonocytic leukaemia do exist. Evaluation of NPM1 and FLT3 status represents a major pillar of the European LeukemiaNet (ELN) genetic-based risk stratification model. Moreover, NPM1 mutations are particularly suitable for assessing measurable residual disease (MRD) since they are frequent, stable at relapse and do not drive clonal haematopoiesis. Ideally, combining monitoring of MRD with the ELN prognostication model can help to guide therapeutic decisions. Here, we provide examples of instructive cases of NPM1-mutated AML, in order to provide criteria for the appropriate diagnosis and therapy of this frequent leukaemia entity.
  21. Cell Rep. 2021 Apr 20. pii: S2211-1247(21)00324-7. [Epub ahead of print]35(3): 109010
      Acute myeloid leukemia (AML) is caused by recurrent mutations in members of the gene regulatory and signaling machinery that control hematopoietic progenitor cell growth and differentiation. Here, we show that the transcription factor WT1 forms a major node in the rewired mutation-specific gene regulatory networks of multiple AML subtypes. WT1 is frequently either mutated or upregulated in AML, and its expression is predictive for relapse. The WT1 protein exists as multiple isoforms. For two main AML subtypes, we demonstrate that these isoforms exhibit differential patterns of binding and support contrasting biological activities, including enhanced proliferation. We also show that WT1 responds to oncogenic signaling and is part of a signaling-responsive transcription factor hub that controls AML growth. WT1 therefore plays a central and widespread role in AML biology.
    Keywords:  FLT3-ITD AML; WT1 binding motif; WT1 isoforms; Wilms tumour 1; acute myeloid leukemia; chromatin; early growth response factors; gene regulatory networks; oncogenic signaling; t(8;21) AML; transcription
  22. Mol Cell. 2021 Apr 10. pii: S1097-2765(21)00264-1. [Epub ahead of print]
      Even though SYK and ZAP70 kinases share high sequence homology and serve analogous functions, their expression in B and T cells is strictly segregated throughout evolution. Here, we identified aberrant ZAP70 expression as a common feature in a broad range of B cell malignancies. We validated SYK as the kinase that sets the thresholds for negative selection of autoreactive and premalignant clones. When aberrantly expressed in B cells, ZAP70 competes with SYK at the BCR signalosome and redirects SYK from negative selection to tonic PI3K signaling, thereby promoting B cell survival. In genetic mouse models for B-ALL and B-CLL, conditional expression of Zap70 accelerated disease onset, while genetic deletion impaired malignant transformation. Inducible activation of Zap70 during B cell development compromised negative selection of autoreactive B cells, resulting in pervasive autoantibody production. Strict segregation of the two kinases is critical for normal B cell selection and represents a central safeguard against the development of autoimmune disease and B cell malignancies.
    Keywords:  Anergy; B cell selection; Kinases; Leukemia; NFAT; Tolerance
  23. Cancer Res. 2021 Apr 22.
      Inactivation of Polybromo 1 (PBRM1), a specific subunit of the PBAF chromatin remodeling complex, occurs frequently in cancer, including 40% of clear cell renal cell carcinomas (ccRCC). To identify novel therapeutic approaches to targeting PBRM1-defective cancers, we used a series of orthogonal functional genomic screens that identified PARP and ATR inhibitors as being synthetic lethal with PBRM1 deficiency. The PBRM1/PARP inhibitor synthetic lethality was recapitulated using several clinical PARP inhibitors in a series of in vitro model systems and in vivo in a xenograft model of ccRCC. In the absence of exogenous DNA damage, PBRM1-defective cells exhibited elevated levels of replication stress, micronuclei, and R-loops. PARP inhibitor exposure exacerbated these phenotypes. Quantitative mass spectrometry revealed that multiple R-loop processing factors were downregulated in PBRM1-defective tumor cells. Exogenous expression of the R-loop resolution enzyme RNase H1 reversed the sensitivity of PBRM1-deficient cells to PARP inhibitors, suggesting that excessive levels of R-loops could be a cause of this synthetic lethality. PARP and ATR inhibitors also induced cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) innate immune signaling in PBRM1-defective tumor cells. Overall, these findings provide the preclinical basis for using PARP inhibitors in PBRM1-defective cancers. SIGNIFICANCE: This study demonstrates that PARP and ATR inhibitors are synthetic lethal with the loss of PBRM1, a PBAF-specific subunit, thus providing the rationale for assessing these inhibitors in patients with PBRM1-defective cancer. GRAPHICAL ABSTRACT:
  24. Oncogene. 2021 Apr 22.
      Extramedullary infiltration (EMI), as a concomitant symptom of acute myeloid leukemia (AML), is associated with low complete remission and poor prognosis in AML. However, the mechanism of EMI remains indistinct. Clinical trials showed that increased miR-29s were associated with a poor overall survival in AML [14]. Nevertheless, they were proved to work as tumor suppressor genes by encouraging apoptosis and inhibiting proliferation in vitro. These contradictory results led us to the hypothesis that miR-29s may play a notable role in the prognosis of AML rather than leukemogenesis. Thus, we explored the specimens of AML patients and addressed this issue into miR-29c&b2 knockout mice. As a result, a poor overall survival and invasive blast cells were observed in high miR-29c&b2-expression patients, and the wildtype mice presented a shorter survival with heavier leukemia infiltration in extramedullary organs. Subsequently, we found that the miR-29c&b2 inside leukemia cells promoted EMI, but not the one in the microenvironment. The analysis of signal pathway revealed that miR-29c&b2 could target HMG-box transcription factor 1 (Hbp1) directly, then reduced Hbp1 bound to the promoter of non-muscle myosin IIB (Myh10) as a transcript inhibitor. Thus, increased Myh10 encouraged the migration of leukemia cells. Accordingly, AML patients with EMI were confirmed to have high miR-29c&b2 and MYH10 with low HBP1. Therefore, we identify that miR-29c&b2 contribute to the poor prognosis of AML patients by promoting EMI, and related genes analyses are prospectively feasible in assessment of AML outcome.
  25. Blood. 2021 Feb 24. pii: blood.2020007362. [Epub ahead of print]
      Total body irradiation (TBI) is commonly used in host conditioning regimens for human hematopoietic stem cell (HSC) transplantation to treat various hematological disorders. Exposure to TBI not only induces acute myelosuppression and immunosuppression but also impairs the various components of the HSC niche in recipients. Our previous study demonstrated that radiation-induced bystander effects (RIBE) of irradiated recipients decreased the long-term repopulating ability of transplanted mouse HSCs. However, RIBE on human HSCs have not been studied. Here, we report that RIBE on transplanted human hematopoietic cells impaired the long-term hematopoietic reconstitution of human HSCs as well as the colony-forming ability of human hematopoietic progenitor cells (HPCs). Our further studies found that the RIBE-affected human hematopoietic cells showed enhanced DNA damage responses, cell cycle arrest and p53-dependent apoptosis, mainly due to oxidative stress. Moreover, multiple antioxidants could mitigate these bystander effects, though at different efficacies both in vitro and in vivo. Taken together, these findings suggest that RIBE impairs human HSCs by oxidative DNA damage. This study provides definitive evidence for RIBE in transplanted human HSCs and further justifies the necessity for conducting clinical trials to assess the ability of multiple antioxidants to improve the efficacy of HSC transplantation for patients with hematological or non-hematological disorders.
  26. Blood. 2021 Apr 19. pii: blood.2020008955. [Epub ahead of print]
      T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy. Despite recent advances in treatments with intensified chemotherapy regimens, relapse rates and associated morbidities remain high. In this context, metabolic dependencies have emerged as a druggable opportunity for the treatment of leukemia. Here, we tested the antileukemic effects of MB1-47, a newly developed mitochondrial uncoupling compound. MB1-47 treatment in T-ALL cells robustly inhibited cell proliferation via both cytostatic and cytotoxic effects as a result of compromised mitochondrial energy and metabolite depletion, which severely impaired nucleotide biosynthesis. Mechanistically, acute treatment with MB1-47 in primary leukemias promoted AMPK activation and downregulation of mTOR signaling, stalling anabolic pathways that support leukemic cell survival. Indeed, MB1-47 treatment in mice harboring either murine NOTCH1-induced primary leukemias or human T-ALL PDXs led to potent antileukemic effects with a significant extension in survival without overlapping toxicities. Overall, our findings demonstrate a critical role for mitochondrial oxidative phosphorylation in T-ALL and uncover MB1-47-driven mitochondrial uncoupling as a novel therapeutic strategy for the treatment of this disease.
  27. Cancer Discov. 2021 Apr 23.
      Loss of ZRSR2, frequently mutated in blood cancer, enhanced hematopoietic stem cell self-renewal.
  28. Blood. 2021 Apr 19. pii: blood.2020009729. [Epub ahead of print]
      We surveyed 16 published and unpublished data sets to determine whether a consistent pattern of transcriptional deregulation in aging murine hematopoietic stem cells (HSC) exists. Despite substantial heterogeneity between individual studies, we uncovered a core and robust HSC aging signature. We detected increased transcriptional activation in aged HSCs, further confirmed by chromatin accessibility analysis. Unexpectedly, using two independent computational approaches, we established that deregulated aging genes consist largely of membrane-associated transcripts, including many cell surface molecules previously not associated with HSC biology. We show that Selp, the most consistent deregulated gene, is not merely a marker for aged HSCs but is associated with HSC functional decline. Additionally, single-cell transcriptomics analysis revealed increased heterogeneity of the aged HSC pool. We identify the presence of transcriptionally "young-like" HSCs in aged bone marrow. We share our results as an online resource and demonstrate its utility by confirming that exposure to sympathomimetics, and deletion of Dnmt3a/b, molecularly resembles HSC rejuvenation or aging, respectively.
  29. Blood Adv. 2021 Apr 27. 5(8): 2115-2122
      Clonal hematopoiesis (CH), characterized by a fraction of peripheral blood cells carrying an acquired genetic variant, emerges with age. Although in general CH is associated with increased mortality and morbidity, no higher risk of death was observed for individuals ≥80 years. Here, we investigated CH in 621 individuals aged ≥80 years from the population-based LifeLines cohort. Sensitive error-corrected sequencing of 27 driver genes at a variant allele frequency ≥1% revealed CH in the majority (62%) of individuals, independent of gender. The observed mutational spectrum was dominated by DNMT3A and TET2 variants, which frequently (29%) displayed multiple mutations per gene. In line with previous results in individuals ≥80 years, the overall presence of CH did not associate with a higher risk of death (hazard ratio, 0.91; 95% confidence interval, 0.70-1.18; P = .48). Being able to assess the causes of death, we observed no difference between individuals with or without CH, except for deaths related to hematological malignancies. Interestingly, comparison of mutational spectra confined to DNMT3A and TET2 vs spectra containing other mutated genes, showed a higher risk of death when mutations other than DNMT3A or TET2 were present (hazard ratio, 1.48; 95% confidence interval, 1.06-2.08; P = .025). Surprisingly, no association of CH with cardiovascular morbidity was found, irrespective of clone size. Further, CH associated with chronic obstructive pulmonary disease. Data on estimated exposure to DNA damaging toxicities (ie, smoking, a history of cancer [as a proxy for previous genotoxic therapy], and job-related pesticide exposure) showed an association with spliceosome and ASXL1 variants, but not with DNMT3A and TET2 variants.
  30. Blood Adv. 2021 Apr 27. 5(8): 2216-2228
      Myelodysplastic syndromes (MDS) are heterogeneous hematopoietic stem cell malignancies that can phenotypically resemble other hematologic disorders. Thus, tools that may add to current diagnostic practices could aid in disease discrimination. Constitutive innate immune activation is a pathogenetic driver of ineffective hematopoiesis in MDS through Nod-like receptor protein 3 (NLRP3)-inflammasome-induced pyroptotic cell death. Oxidized mitochondrial DNA (ox-mtDNA) is released upon cytolysis, acts as a danger signal, and triggers inflammasome oligomerization via DNA sensors. By using immortalized bone marrow cells from murine models of common MDS somatic gene mutations and MDS primary samples, we demonstrate that ox-mtDNA is released upon pyroptosis. ox-mtDNA was significantly increased in MDS peripheral blood (PB) plasma compared with the plasma of healthy donors, and it was significantly higher in lower-risk MDS vs higher-risk MDS, consistent with the greater pyroptotic cell fraction in lower-risk patients. Furthermore, ox-mtDNA was significantly higher in MDS PB plasma compared with all other hematologic malignancies studied, with the exception of chronic lymphocytic leukemia (CLL). Receiver operating characteristic/area under the curve (ROC/AUC) analysis demonstrated that ox-mtDNA is a sensitive and specific biomarker for patients with MDS compared with healthy donors (AUC, 0.964), other hematologic malignancies excluding CLL (AUC, 0.893), and reactive conditions (AUC, 0.940). ox-mtDNA positively and significantly correlated with levels of known alarmins S100A9, S100A8, and apoptosis-associated speck-like protein containing caspase recruitment domain (CARD) specks, which provide an index of medullary pyroptosis. Collectively, these data indicate that quantifiable ox-mtDNA released into the extracellular space upon inflammasome activation serves as a biomarker for MDS and the magnitude of pyroptotic cell death.