Jan-Henning Klusmann

Developmental stage–selective effect of somatically mutated leukemogenic transcription factor GATA1

Acquired mutations in the hematopoietic transcription factor GATA binding protein-1 (GATA1) are found in megakaryoblasts from nearly all individuals with Down syndrome with transient myeloproliferative disorder (TMD, also called transient leukemia) and the related acute megakaryoblastic leukemia (DS-AMKL, also called DS-AML M7). These mutations lead to production of a variant GATA1 protein (GATA1s) that is truncated at its N terminus. To understand the biological properties of GATA1s and its relation to DS-AMKL and TMD, we used gene targeting to generate Gata1 alleles that express GATA1s in mice. We show that the dominant action of GATA1s leads to hyperproliferation of a unique, previously unrecognized yolk sac and fetal liver progenitor, which we propose accounts for the transient nature of TMD and the restriction of DS-AMKL to infants. Our observations raise the possibility that the target cells in other leukemias of infancy and early childhood are distinct from those in adult leukemias and underscore the interplay between specific oncoproteins and potential target cells.

miR-125b-2 is a potential oncomiR on human chromosome 21 in megakaryoblastic leukemia.

Children with trisomy 21/Down syndrome (DS) are at high risk to develop acute megakaryoblastic leukemia (DS-AMKL) and the related transient leukemia (DS-TL). The factors on human chromosome 21 (Hsa21) that confer this predisposing effect, especially in synergy with consistently mutated transcription factor GATA1 (GATA1s), remain poorly understood. Here, we investigated the role of Hsa21-encoded miR-125b-2, a microRNA (miRNA) overexpressed in DS-AMKL/TL, in hematopoiesis and leukemogenesis. We identified a function of miR-125b-2 in increasing proliferation and self-renewal of human and mouse megakaryocytic progenitors (MPs) and megakaryocytic/erythroid progenitors (MEPs). miR-125b-2 overexpression did not affect megakaryocytic and erythroid differentiation, but severely perturbed myeloid differentiation. The proproliferative effect of miR-125b-2 on MEPs accentuated the Gata1s mutation, whereas growth of DS-AMKL/TL cells was impaired upon miR-125b repression, suggesting synergism during leukemic transformation in GATA1s-mutated DS-AMKL/TL. Integrative transcriptome analysis of hematopoietic cells upon modulation of miR-125b expression levels uncovered a set of miR-125b target genes, including DICER1 and ST18 as direct targets. Gene Set Enrichment Analysis revealed that this target gene set is down-regulated in DS-AMKL patients highly expressing miR-125b. Thus, we propose miR-125b-2 as a positive regulator of megakaryopoiesis and an oncomiR involved in the pathogenesis of trisomy 21-associated megakaryoblastic leukemia.

Treatment and prognostic impact of transient leukemia in neonates with Down syndrome

Approximately 10% of the neonates with Down syndrome (DS) exhibit a unique transient leukemia (TL). Though TL resolves spontaneously in most patients, early death and development of myeloid leukemia (ML-DS) may occur. Prognostic factors as well as treatment indication are currently uncertain. To resolve that issue, we prospectively collected clinical, biologic, and treatment data of 146 patients with TL. The 5-year overall survival (OS) and event-free survival (EFS) were 85% plus or minus 3% and 63% plus or minus 4%, respectively. Multivariate analysis revealed a correlation between high white blood cell (WBC) count, ascites, preterm delivery, bleeding diatheses, failure of spontaneous remission, and the occurrence of early death. Treatment with cytarabine (0.5-1.5 mg/kg) was administered to 28 patients with high WBC count, thrombocytopenia, or liver dysfunction. The therapy had a beneficial effect on the outcome of those children with risk factors for early death (5-year EFS, 52% +/- 12% vs 28% +/- 11% [no treatment]; P = .02). Multivariate analysis demonstrated its favorable prognostic impact. A total of 29 (23%) patients with TL subsequently developed ML-DS. Patients with ML-DS with a history of TL had a significantly better 5-year EFS (91% +/- 5%) than those without documented TL (70% +/- 4%), primarily due to a lower relapse rate. A history of TL may therefore define a lower-risk ML-DS subgroup. This study was registered at www.clinicaltrials.gov as no. NCT 00111345.

Developmental stage-specific interplay of GATA1 and IGF signaling in fetal megakaryopoiesis and leukemogenesis

Oncogene-mediated transformation of hematopoietic cells has been studied extensively, but little is known about the molecular basis for restriction of oncogenes to certain target cells and differential cellular context-specific requirements for oncogenic transformation between infant and adult leukemias. Understanding cell type-specific interplay of signaling pathways and oncogenes is essential for developing targeted cancer therapies. Here, we address the vexing issue of how developmental restriction is achieved in Down syndrome acute megakaryoblastic leukemia (DS-AMKL), characterized by the triad of fetal origin, mutated GATA1 (GATA1s), and trisomy 21. We demonstrate overactivity of insulin-like growth factor (IGF) signaling in authentic human DS-AMKL and in a DS-AMKL mouse model generated through retroviral insertional mutagenesis. Fetal but not adult megakaryocytic progenitors are dependent on this pathway. GATA1 restricts IGF-mediated activation of the E2F transcription network to coordinate proliferation and differentiation. Failure of a direct GATA1-E2F interaction in mutated GATA1s converges with overactive IGF signaling to promote cellular transformation of DS fetal progenitors, revealing a complex, fetal stage-specific regulatory network. Our study underscores context-dependent requirements during oncogenesis, and explains resistance to transformation of ostensibly similar adult progenitors.

Next-generation sequencing for minimal residual disease monitoring in acute myeloid leukemia patients with FLT3-ITD or NPM1 mutations.

Systematic assessment of minimal residual disease (MRD) in acute myeloid leukemia (AML) patients has been hampered by lack of a reliable, uniform MRD marker applicable to all patients. We evaluated next‐generation sequencing (NGS) for MRD assessment in AML patients (n = 80 samples). The ability of NGS technologies to generate thousands of clonal sequences makes it possible to determine the allelic ratio of sequence variants. Using NGS, we were able to determine the allelic ratio of different FLT3‐internal tandem duplication (ITD) clones within one patient sample, in addition to resolution of FLT3‐ITD insertion site, length, and sequence in a single analysis. Furthermore, NGS allowed us to study emergence of clonal dominance. Parallel assessment of MRD by NGS and quantitative real‐time polymerase chain reaction in NPM1 mutated patients was concordant in 95% of analyzed samples (n = 38). The frequency of mutated alleles was linearly quantified by NGS. As NGS sensitivity is scalable depending on sequence coverage, it reflects a highly flexible and reliable tool to assess MRD in leukemia patients.

miR-99a/100~125b tricistrons regulate hematopoietic stem and progenitor cell homeostasis by shifting the balance between TGFβ and Wnt signaling.

Although regulation of stem cell homeostasis by microRNAs (miRNAs) is well studied, it is unclear how individual miRNAs genomically encoded within an organized polycistron can interact to induce an integrated phenotype. miR-99a/100, let-7, and miR-125b paralogs are encoded in two tricistrons on human chromosomes 11 and 21. They are highly expressed in hematopoietic stem cells (HSCs) and acute megakaryoblastic leukemia (AMKL), an aggressive form of leukemia with poor prognosis. Here, we show that miR-99a/100∼125b tricistrons are transcribed as a polycistronic message transactivated by the homeobox transcription factor HOXA10. Integrative analysis of global gene expression profiling, miRNA target prediction, and pathway architecture revealed that miR-99a/100, let-7, and miR-125b functionally converge at the combinatorial block of the transforming growth factor β (TGFβ) pathway by targeting four receptor subunits and two SMAD signaling transducers. In addition, down-regulation of tumor suppressor genes adenomatous polyposis coli (APC)/APC2 stabilizes active β-catenin and enhances Wnt signaling. By switching the balance between Wnt and TGFβ signaling, the concerted action of these tricistronic miRNAs promoted sustained expansion of murine and human HSCs in vitro or in vivo while favoring megakaryocytic differentiation. Hence, our study explains the high phylogenetic conservation of the miR-99a/100∼125b tricistrons controlling stem cell homeostasis, the deregulation of which contributes to the development of AMKL.

Histone deacetylase inhibitors induce apoptosis in myeloid leukemia by suppressing autophagy

Histone deacetylase (HDAC) inhibitors (HDACis) are well-characterized anti-cancer agents with promising results in clinical trials. However, mechanistically little is known regarding their selectivity in killing malignant cells while sparing normal cells. Gene expression-based chemical genomics identified HDACis as being particularly potent against Down syndrome-associated myeloid leukemia (DS-AMKL) blasts. Investigating the antileukemic function of HDACis revealed their transcriptional and post-translational regulation of key autophagic proteins, including ATG7. This leads to suppression of autophagy, a lysosomal degradation process that can protect cells against damaged or unnecessary organelles and protein aggregates. DS-AMKL cells exhibit low baseline autophagy due to mammalian target of rapamycin (mTOR) activation. Consequently, HDAC inhibition repressed autophagy below a critical threshold, which resulted in accumulation of mitochondria, production of reactive oxygen species, DNA damage and apoptosis. Those HDACi-mediated effects could be reverted upon autophagy activation or aggravated upon further pharmacological or genetic inhibition. Our findings were further extended to other major acute myeloid leukemia subgroups with low basal level autophagy. The constitutive suppression of autophagy due to mTOR activation represents an inherent difference between cancer and normal cells. Thus, via autophagy suppression, HDACis deprive cells of an essential pro-survival mechanism, which translates into an attractive strategy to specifically target cancer cells.

Analysis of GATA1 mutations in Down syndrome transient myeloproliferative disorder and myeloid leukemia

Children with Down syndrome (DS) up to the age of 4 years are at a 150-fold excess risk of developing myeloid leukemia (ML-DS). Approximately 4%-5% of newborns with DS develop transient myeloproliferative disorder (TMD). Blast cell structure and immunophenotype are similar in TMD and ML-DS. A mutation in the hematopoietic transcription factor GATA1 is present in almost all cases. Here, we show that simple techniques detect GATA1 mutations in the largest series of TMD (n = 134; 88%) and ML-DS (n = 103; 85%) cases tested. Furthermore, no significant difference in the mutational spectrum between the 2 disorders was seen. Thus, the type of GATA1 sequence mutation is not a reliable tool and is not prognostic of which patients with TMD are probable to develop ML-DS.

The role of matched sibling donor allogeneic stem cell transplantation in pediatric high-risk acute myeloid leukemia: results from the AML-BFM 98 study

Background The role of allogeneic stem cell transplantation in post-remission management of children with high-risk acute myeloid leukemia remains controversial. In the multi-center AML-BFM 98 study we prospectively evaluated the impact of allogeneic stem cell transplantation in children with high-risk acute myeloid leukemia in first complete remission. Design and Methods HLA-typed patients with high-risk acute myeloid leukemia, who achieved first complete remission (n=247), were included in this analysis. All patients received double induction and consolidation. Based on the availability of a matched-sibling donor, patients were allocated by genetic chance to allogeneic stem cell transplantation (n=61) or chemotherapy-only (i.e. intensification and maintenance therapy; n=186). The main analysis was done on an intention-to-treat basis according to this allocation. Results Intention-to-treat analysis did not show a significantly different 5-year disease-free survival (49±6% versus 45±4%, Plog rank=0.44) or overall survival (68±6% versus 57±4%, Plog rank=0.17) between the matched-sibling donor and no-matched-sibling donor groups, whereas late adverse effects occurred more frequently after allogeneic stem cell transplantation (72.5% versus 31.8%, PFischer<0.01). These results were confirmed by as-treated analysis corrected for the time until transplantation (5-year overall survival: 72±8% versus 60±4%, PMantel-Byar 0.21). Subgroup analysis demonstrated improved survival rates for patients with 11q23 aberrations allocated to allogeneic stem cell transplantation (5-year overall survival: 94±6% versus 52±7%, Plog-rank=0.01; n=18 versus 49) in contrast to patients without 11q23 aberrations (5-year overall survival: 58±8% versus 55±5%, Plog-rank=0.66). Conclusions Our analyses defined a genetic subgroup of children with high-risk acute myeloid leukemia who benefited from allogeneic stem cell transplantation in the prospective multi-center AML-BFM 98 study. For the remainder of the pediatric high-risk acute myeloid leukemia patients the prognosis was not improved by allogeneic stem cell transplantation, which was, however, associated with a higher rate of late sequelae.

Granulocyte Colony-Stimulating Factor (G-CSF) Treatment of Childhood Acute Myeloid Leukemias That Overexpress the Differentiation-Defective G-CSF Receptor Isoform IV Is Associated With a Higher Incidence of Relapse

PURPOSE This prospective, multicenter Acute Myeloid Leukemia Berlin-Frankfurt-Muenster (AML-BFM) 98 study randomly tested the ability of granulocyte colony-stimulating factor (G-CSF) to reduce infectious complications and to improve outcomes in children and adolescents with acute myeloid leukemia (AML). However, a trend toward an increased incidence of relapses in the standard-risk (SR) group after G-CSF treatment was observed. PATIENTS AND METHODS Of 154 SR patients in the AML-BFM 98 cohort, 50 patients were tested for G-CSF receptor (G-CSFR) RNA isoform I and IV expression, G-CSFR cell surface expression, and acquired mutations in the G-CSFR gene. RESULTS In patients randomly assigned to receive G-CSF after induction, 16 patients overexpressing the G-CSFR isoform IV showed an increased 5-year cumulative incidence of relapse (50% +/- 13%) compared with 14 patients with low-level isoform IV expression (14% +/- 10%; log-rank P = .04). The level of G-CSFR isoform IV had no significant effect in patients not receiving G-CSF (P = .19). Multivariate analyses of the G-CSF-treated subgroup, including the parameters G-CSFR isoform IV overexpression, sex, and favorable cytogenetics as covariables, revealed the prognostic relevance of G-CSFR isoform IV overexpression for 5-year event-free survival (P = .031) and the 5-year cumulative incidence of relapse (P = .049). CONCLUSION Our results demonstrate that children and adolescents with AMLs that overexpress the differentiation-defective G-CSFR isoform IV respond to G-CSF administration after induction, but with a significantly higher incidence of relapse.