Double-mutant Acute Myeloid Leukemia Research Articles

Clinical Value of Translocator Protein Gene in Evaluating the Efficacy of FLT3-ITD/DNMT3A R882 Double-Mutated Acute Myeloid Leukemia

To observe the clinical significance of translocator proteins (TSPO) gene in the treatment of FLT3-ITD/DNMT3A R882 double-mutated acute myeloid leukemia (AML). Seventy-six patients with AML hospitalized in the Department of Hematology of the Affiliated People's Hospital of Ningbo University from June 2018 to June 2020 were selected, including 34 patients with FLT3-ITD mutation, 27 patients with DNMT3A R882 mutation, 15 patients with FLT3-ITD/DNMT3A R882 double mutation, as well as 19 patients with immune thrombocytopenia (ITP) hospitalized during the same period as control group. RNA was routinely extracted from 3 ml bone marrow retained during bone puncture, and TSPO gene expression was detected by transcriptome sequencing (using 2-deltadeltaCt calculation). The expression of TSPO gene in FLT3-ITD group and DNMT3A R882 group at first diagnosis was 2.02±1.04 and 1.85±0.76, respectively, which were both higher than 1.00±0.06 in control group, but the differences were not statistically significant (P=0.671, P=0.821). The expression of TSPO gene in the FLT3-ITD/DNMT3A R882 group was 3.98±1.07, wich was significantly higher than that in the FLT3-ITD group and DNMT3A R882 group, the differences were statistically significant (P=0.032, P=0.021). The expression of TSPO gene in patients who achieved complete response after chemotherapy in the FLT3-ITD/DNMT3A R882 group was 1.19±0.87, which was significantly lower than that at first diagnosis, and the difference was statistically significant (P=0.011). TSPO gene may be used as an indicator of efficacy in FLT3-ITD /DNMT3A R882 double-mutated AML.

Differential Implications of CSF3R Mutations in t(8;21) and CEBPA Double Mutated Acute Myeloid Leukemia

BackgroundFew data are available exploring mutations of the colony-stimulating factor 3 receptor (CSF3R) in acute myeloid leukemia (AML) in an all-round and systematic manner. The purpose of this study was to analyze the CSF3R mutations (CSF3Rmut) in AML with recurrent genetic abnormalities for potential synergistic pathomechanism. Patients and MethodsWe retrospectively screened 1102 adult de novo AML patients with available next-generation sequencing (NGS) information on 132 genes related to hematologic disorders. The χ2, Mann-Whitney U tests were used to analyze their associations with clinicopathologic characteristics, and a propensity score matching (PSM) followed by Kaplan-Meier method was applied to measure their prognostic effects. ResultsOverall, CSF3Rmut were detected in 40 (3.6%) of 1102 patients with adult de novo AML. CSF3Rmut were predominantly enriched in AML with the CEBPA double mutations (CEBPAdm) (16/122, 13.1%), t(8;21) (12/186, 6.5%) and mutated RUNX1 (3/50, 6.0%), respectively. The CSF3Rmut loci and types differed according to AML subtypes, with frameshift-indels and premature stop confined in the t(8;21) AML [10/12 (83.3%)], and missense recurrently aggregated in the CEBPAdm AML [16/16 (100%)]. Cases with CSF3Rmut had a lower WBC count versus those with CSF3R wild-type (CSF3Rwt) in the t(8;21) AML cohort, with a borderline significance [median 5.45 (range 0.94-20.30) × 109/L) vs. 8.80 (range 0.96-155.00) × 109/L, P = .046]. CSF3Rmut were non-significantly associated with higher WBC counts [median 33.6 (range 6.8-287.6) × 109/L vs. 18.1 (range 1.7-196.0) × 109/L, P = .156] and significantly with lower immunophenotypic CD15 positivity [0/8 (0%) vs. 44/80 (55%), P = .009] as compared to CSF3Rwt in the CEBPAdm AML cohort. After propensity score matching followed by Kaplan-Meier analysis, CSF3Rmut cases had comparable disease-free survival (DFS) and overall survival (OS) to those with CSF3Rwt (P = .607 and P = .842, respectively) in the t(8;21) AML cohort. By contrast, CSF3Rmut showed an inclination towards inferior DFS compared to CSF3Rwt in the CEBPAdm AML cohort [median DFS 19.8 (95%CI 3.1-36.5) months vs. not reached (NR), P = .086]. No significant difference was found for OS between CSF3Rmut and CSF3Rwt cases (P = .943). ConclusionWe concluded that CSF3Rmut were frequently enriched in patients with t(8;21) and CEBPAdm subtypes among AML, but showed divergent clinicopathologic features, mutation loci and types and differing prognostic aspects.

Chromatin Accessibility Analysis Reveals Epigenetic Evolution Is a Common Mechanism of Relapse in Acute Myeloid Leukemia

Introduction: Acute myeloid leukemia (AML) is associated with a poor prognosis and high rates of relapse despite aggressive treatments including high dose chemotherapy. To understand the clonal dynamics and genetic evolution of relapsed AML, we analyzed a cohort of 142 previously published genotyped and paired diagnosis-relapse AML samples. 40% of queried cases exhibited no major changes in somatic mutations upon relapse, and genetically stable clonal structure correlated with increased relapse probability. Thus, we hypothesized epigenetic reprogramming plays a role in these cases and AML relapse in general. Here, we examine the epigenetic landscape of relapsed AML and characterize the cis and trans regulatory elements that correlate with AML relapse in the presence or absence of genetic evolution.Methods: We identified 27 viable cryopreserved paired diagnosis and relapse samples from the same patient treated at Stanford with high-dose chemotherapy. Leukemic blasts and (when possible) leukemia stem cell (LSC) enriched populations were FACS purified and prepared for genotyping with a myeloid malignancy targeted sequencing panel as well as ATAC-seq for chromatin accessibility profiling. Single-cell ATAC-seq was further performed on select samples to investigate regulatory reprogramming in cell subpopulations. We then performed integrative analysis to uncover the interplay between genetic lesions, epigenetic regulatory programs, and gene accessibility in relapsed AML.Results: Genotyping analysis of these AML specimens revealed that 40% of samples exhibited no changes in AML-related genetic alterations upon relapse (hereby referred to as “stable” samples). Chromatin accessibility analysis revealed these stable samples had a distinct epigenetic signature, modulating similar gene accessibility programs and sharing enhancer loci that become accessible across all stable relapse samples. These sequences included genes involved in chromatin organization and compaction, as well as those involved in transcriptional control of hematopoietic differentiation and myeloid cell maturation. We also observed several regulatory signatures present at relapse specific for AML subtypes, including NPM1/FLT3 double mutant AML and those with mutations in transcription factors such as CEBPA or RUNX1.We then performed single-cell ATAC-seq on genetically stable samples to further characterize the sub-clonal epigenetic dynamics between the diagnosis and relapse cells. Several samples exhibited regulatory heterogeneity in multiple cell subpopulations that changed significantly at relapse. One subpopulation of interest was characterized by increased GATA and RUNX family transcription factor motif accessibility at relapse, indicating a shift toward a less differentiated progenitor cell phenotype. In addition, we identified a subpopulation of cells at diagnosis that were epigenetically similar to the major epigenetic states present at relapse, indicating that selection for specific epigenetic subclones may occur in AML patients during therapy in the absence of additional genetic lesions.Finally, given the critical role of LSCs in AML pathogenesis and their possible role as a reservoir for AML relapse, we analyzed LSC-enriched subpopulations in a subset of our cohort. ATAC-seq analysis indicated these cells shared several LSC-specific epigenetic features between samples, are distinguished from leukemia blasts by distinct regulatory programs, and undergo epigenetic remodeling between initial diagnosis and relapse. Gene accessibility analysis also revealed a shared LSC gene expression signature that also shifted at relapse. These data indicate a specific, distinct epigenomic signature for LSC enriched cell populations, and that epigenetic evolution at relapse occurs intracellularly, rather than reflecting heterogeneity in cellular subpopulations upon AML relapse.Conclusion: This study reveals that epigenetic remodeling in the absence of genetic evolution is a mechanism through which AML relapse occurs. We show that chromatin reorganization of genes and regulatory sequences occurs in these AML cells, leading to a permissive cell state that might be resistant to conventional treatment. Ongoing work includes dissecting the subclonal structure of these AML cells and identifying the relationship between gene regulatory networks that contribute to relapse. DisclosuresEdiriwickrema: Nanosive SAS: Patents & Royalties. Majeti: BeyondSpring Inc.: Membership on an entity's Board of Directors or advisory committees; CircBio Inc.: Membership on an entity's Board of Directors or advisory committees; Kodikaz Therapeutic Solutions Inc.: Membership on an entity's Board of Directors or advisory committees; Coherus Biosciences: Membership on an entity's Board of Directors or advisory committees; Acuta Capital Partners: Consultancy; Gilead: Patents & Royalties: inventor on a number of patents related to CD47 cancer immunotherapy licensed to Gilead Sciences, Inc..

Spliceosomal Dysfunction Is a Critical Mediator of IDH2 Mutant Leukemogenesis

Mutations affecting RNA splicing factors are commonly found in leukemias and mutations in SF3B1, SRSF2, and U2AF1 impart specific changes to global splicing. We analyzed RNA-seq data from acute myeloid leukemia (AML) patients from The Cancer Genome Atlas (TCGA) to evaluate for spliceosomal alterations characteristic of mutant SRSF2, SF3B1, and U2AF1 . Although only 1 patient with an SRSF2 mutation was reported in the TCGA AML publication, we identified 19 additional patients to have the characteristic splicing changes of mutant SRSF2 . Mutational analysis of the RNA-seq data identified the SRSF2 proline 95 hotspot mutation in each of these 19 patients (19/178, 11%), making SRSF2 amongst the most commonly mutated genes in the AML TCGA dataset. Interestingly, 47% of SRSF2 mutant patients also had a co-existing IDH2 mutation (and conversely, 50% of IDH2 mutant patients had a co-existing SRSF2 mutation). These data are similar to recent observation that SRSF2 mutations were the most common accompanying mutation in IDH2 mutant myeloid leukemia patients treated on the phase I clinical trial of AG-221.We next sought to understand the functional contribution of SRSF2 mutations to co-existing IDH2 mutations. Overexpression of IDH2 R140Q and IDH2 R172K in Vav -cre Srsf2 P95H or Vav- cre Srsf2 wildtype(WT) backgrounds revealed a clear collaborative effect of mutant IDH2 and mutant Srsf2 (Figure A-B). As early as 4 weeks post-transplant, the peripheral blood of Srsf2 mutant mice transplanted with IDH2 R140Q or IDH2 R172K forms had a substantially greater percentage of GFP+ cells than seen in an Srsf2 WT background. Moreover, these mice exhibited significant myeloid skewing, macrocytic anemia, and thrombocytopenia of greater magnitude than seen with mutant IDH2 expressed in the SRSF2 WT background. IDH2 / Srsf2 double-mutant mice developed a lethal, mixed myelodysplastic/myeloproliferative neoplasm that was serially transplantable (Figure B). Effects from overexpression of mutant IDH2 were recapitulated in mice expressing Idh2 R140Q and Srsf2 P95H from endogenous loci(Mx1 -cre Idh2R140Q/+Srsf2P95H/+ double knock-in mice) (Figure C), providing the first model where spliceosomal gene mutations promote leukemogenesis in vivo .Given prior data identifying inhibition of TET2 as a mediator of IDH2 -mutant leukemogenesis, we evaluated if loss of TET2 might promote transformation of SRSF2 mutant cells. However, deletion of TET2 in an SRSF2 mutant background (Mx1 -cre Tet2fl/flSrsf2P95H/+) was insufficient to promote transformation (Figure D). We next analyzed RNA-seq data from the TCGA, Leucegene, and our own unpublished AML cohort using a novel analysis method to detect unannotated as well as complex splicing events that might explain the basis for the collaboration of mutant IDH2 and SRSF2 . This revealed that IDH2/SRSF2 double-mutant AML had increased aberrant splicing events compared to SRSF2 single-mutant AML and also that IDH2 -mutations are associated with a small but reproducible change in RNA splicing (Figure E). The vast majority of splicing changes affected by SRSF2 and/or IDH2 mutations were a change in cassette exon splicing with SRSF2 mutations promoting inclusion of C-rich containing mRNA sequences, regardless of the presence of concomitant IDH2 mutations (Figure F). One of the most robust mis-splicing events in IDH2/SRSF2 mutant AML was an intron retention event in INTS3 resulting in its reduced mRNA and protein expression (Figure G-H). INTS3 encodes a component of the integrator complex that participates in small nuclear RNA (snRNA) processing. Consistent with this, IDH2 / SRSF2 double-mutant cells exhibited alterations in processing of U2 and U4 snRNAs similar to that seen with direct INTS3 downregulation. Biologically, attenuation of INTS3 expression caused a blockade of myeloid differentiation in HL-60 cells upon ATRA treatment, an effect which was further enhanced in an IDH2 mutant background.These data uncover an important role for spliceosomal gene mutations in the pathogenesis of IDH2 mutant leukemogenesis and identify perturbations in the integrator complex as a novel mediator driving the transformation of IDH2 and SRSF2 mutant cells. The frequent coexistence of IDH2 and SRSF2 mutations underscores the enormous therapeutic potential for modulation of splicing in the ~50% of IDH2 -mutant leukemia patients who also harbor a spliceosomal gene mutation. [Display omitted] DisclosuresDe Botton:Servier: Honoraria; Agios: Honoraria, Research Funding; Celgene: Honoraria; Novartis: Honoraria; Pfizer: Honoraria. Stein:Pfizer: Consultancy, Other: Travel expenses; Novartis: Consultancy, Research Funding; Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Celgene Corporation: Consultancy, Other: Travel expenses, Research Funding; Seattle Genetics: Research Funding; GSK: Other: Advisory Board, Research Funding; Constellation Pharma: Research Funding. Peng:H3 Biomedicine Inc.: Employment. Buonamici:H3 Biomedicine Inc.: Employment. Palacino:H3 Biomedicine Inc.: Employment. Smith:H3 Biomedicine Inc.: Employment. Thompson:Merck: Membership on an entity's Board of Directors or advisory committees; Charles River Laboratories: Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Other: Founder. Levine:Roche: Research Funding; Roche: Research Funding; Qiagen: Equity Ownership; Qiagen: Equity Ownership; Celgene: Research Funding; Celgene: Research Funding.

CD123 Is Consistently Expressed on NPM1-Mutated AML Cells.

Simple SummaryOne-third of adult acute myeloid leukemia (AML) harbors NPM1 mutations. A deep knowledge of the distribution of selected antigens on the surface of NPM1-mutated AML cells may help optimizing new therapies for this frequent AML subtype. CD123 is known to be expressed on leukemic cells but also on healthy hematopoietic and endothelial cells, although at lower levels. Differences in antigen densities between AML and healthy cells may enlighten therapeutic windows, where targeting CD123 could be effective without triggering “on-target off-tumor” toxicities. Here, we perform a thorough analysis of CD123 expression demonstrating high expression of this antigen on both NPM1-mutated bulk leukemic cells and CD34+CD38− cells.NPM1-mutated (NPM1mut) acute myeloid leukemia (AML) comprises about 30% of newly diagnosed AML in adults. Despite notable advances in the treatment of this frequent AML subtype, about 50% of NPM1mut AML patients treated with conventional treatment die due to disease progression. CD123 has been identified as potential target for immunotherapy in AML, and several anti-CD123 therapeutic approaches have been developed for AML resistant to conventional therapies. As this antigen has been previously reported to be expressed by NPM1mut cells, we performed a deep flow cytometry analysis of CD123 expression in a large cohort of NPM1mut and wild-type samples, examining the whole blastic population, as well as CD34+CD38− leukemic cells. We demonstrate that CD123 is highly expressed on NPM1mut cells, with particularly high expression levels showed by CD34+CD38− leukemic cells. Additionally, CD123 expression was further enhanced by FLT3 mutations, which frequently co-occur with NPM1 mutations. Our results identify NPM1-mutated and particularly NPM1/FLT3 double-mutated AML as disease subsets that may benefit from anti-CD123 targeted therapies.

Combined Targeting of Bcl-2 and XPO1 Overcomes Acquired Resistance to Tyrosine Kinase Inhibitors in the FLT3-ITD/TKD Double Mutant AML

FMS-like tyrosine kinase 3 with internal tandem duplication (FLT3-ITD), the most frequent mutation in acute myeloid leukemia (AML), results in the constitutive ligand-independent activation of FLT3 receptor downstream signaling. FLT3-targeted therapies using tyrosine kinase inhibitors (TKIs) demonstrate single agent activity in these patients but long-term efficacy is limited by emerging resistance in part due to acquired point mutations in the tyrosine kinase domains (TKD) of the FLT3 gene, most commonly found at D835 within the activation loop.Exportin 1 (XPO1) mediates the nucleo-cytoplasmic transport, and is overexpressed in AML cells with FLT3-ITD mutations (Kojima, Blood, 2013). We have reported that the clinically available XPO1 inhibitor selinexor effectively inhibits cell proliferation in both FLT3-ITD and FLT3-ITD/D835 mutated cells through upregulation of TP53 and blockade of c-Myc signaling (Tabe, ASH, 2017).In this study, we aimed at developing novel mechanism-based combination therapies for TKI-resistant FLT3-ITD cells with acquired TKD mutation. First we investigated the transcriptional changes associated with XPO1 and FLT3 inhibition in FLT3-ITD and FLT3-ITD/D835 mutated cells. We utilized paired isogenic FLT3-ITD or FLT3-ITD/D835Y transfected Ba/F3 cell lines and performed the cap analysis of gene expression (CAGE) that identifies and quantifies gene expression at the transcription start sites (TSS). FLT3-ITD cells are sensitive and FLT3-ITD/D835 cells are resistant to FLT3 inhibitor quizartinib. CAGE detected the shared upregulation of 3833 TSS genes induced by selinexor in FLT3-ITD and FLT3-ITD/D835 cells (FDR <0.05, EdgeR) with the most prominent upregulation of the negative regulator of BCL-2, Ddit3, and the tumor suppressing transcriptional activator Klf6. Selinexor downregulated 4196 shared TSS genes in FLT3-ITD and FLT3-ITD/D835 cells with the top 2 downregulated hits being the transcriptional activator Foxm1 and the cell cycle control transcription factor E2f. In contrast, quizartinib induced TSS gene expression changes only in FLT3-ITD cells (upregulated 7295, downregulated 6335) but not in FLT3-ITD/D835 cells; similar to selinexor, quizartinib upregulated Ddit3 and Klf6 and downregulated E2f in FLT3-ITD cells. The previously reported upstream activation of TP53 and CDKN2A and inhibition of Myc and estrogen receptor 1 were consistently observed in selinexor-treated FLT3-ITD and FLT3-ITD/D835 cells and in quizartinib-treated FLT3-ITD cells (Ingenuity Pathway Analysis). CAGE also demonstrated higher basic TSS transcription levels of Bcl-2 and Myc in FLT3-ITD/D835 cells than in FLT3-ITD cells, which were confirmed by Western blot.Based on these findings, we focused on Bcl-2 as a novel therapeutic target in FLT3-ITD/D835 cells, and investigated the anti-leukemia efficacy of combined inhibition of Bcl-2 and XPO1. We utilized the clinically available selective Bcl-2 inhibitor venetoclax and observed synergistic anti-proliferative and pro-apoptotic effects of venetoclax and selinexor in FLT3-ITD/D835 (Combination Index, CI: 0.39 and 0.45). Simultaneous inhibition of Bcl-2 by venetoclax and FLT3 by quizartinib showed no synergistic or additive effects in FLT3-ITD/D835 cells. Western blot analysis showed that the combination of venetoclax / selinexor reduced Bcl-2 and Mcl-1 in FLT3-ITD/D835 cells, and activated cleaved caspase3. In FLT3-ITD cells, the venetoclax / selinexor combination induced only small decrease of Bcl-2, did not change Mcl-1 and Bcl-xL, and increased cleaved caspase3. These changes were not observed in wt-FLT3 transfected Ba/F3 cells.Collectively, CAGE analysis of transcription start sites identified the primary mechanism underlying the synergistic activity of concomitant inhibition of Bcl-2 and XPO1 in FLT3-ITD/D835 cells as related to the regulation of Bcl-2, Mcl-1, Bcl-xL and c-Myc. These findings suggest that Bcl-2 inhibition by venetoclax combined with XPO1 inhibition by selinexor could be developed into a promising therapeutic strategy for TKI-resistant AML patients with FLT3-ITD and secondary acquired TKD mutations. DisclosuresKonopleva:Stemline Therapeutics: Research Funding. Andreeff:AstraZeneca: Research Funding.

Variable outcome and methylation status according to CEBPA mutant type in double-mutated acute myeloid leukemia patients and the possible implications for treatment.

Although CEBPA double-mutated (CEBPADM) acute myeloid leukemia is considered to be a favorable-risk disease, relapse remains a major cause of treatment failure. Most CEBPADM patients have a classic biallelic mutant combination with an N-terminal mutation leading to production of p30 protein plus a C-terminal loss-of-function in-frame indel mutation (CEBPAClassic-DM), but approximately one-third of cases have one or more non-classic mutations, with diverse combinations reported, and there is little information on the consequences of such mutants. We evaluated outcome in a cohort of 104 CEBPADM patients, 79 CEBPAClassic-DM and 25 with non-classic mutants, and found that the latter may have poorer survival (5-year overall survival 64% vs. 46%; P=0.05), particularly post relapse (41% vs. 0%; P=0.02). However, for this analysis, all non-classic cases were grouped together, irrespective of mutant combination. As CEBPADM cases have been reported to be hypermethylated, we used methylation profiling to assess whether this could segregate the different mutants. We developed a CEBPAClassic-DM methylation signature from a preliminary cohort of 10 CEBPADM (including 8 CEBPAClassic-DM) and 30 CEBPA wild-type (CEBPAWT) samples, and independently validated the signature in 17 CEBPAClassic-DM cases. Assessment of the signature in 16 CEBPADM cases with different non-classic mutant combinations showed that only 31% had a methylation profile equivalent to CEBPAClassic-DM whereas for 69% the profile was either intermediate between CEBPAClassic-DM and CEBPAWT or equivalent to CEBPAWT. These results suggest that CEBPADM cases with non-classic mutants may be functionally different from those with CEBPAClassic-DM mutants, and should not automatically be included in the same prognostic group. (AML12 is registered under ISRCTN17833622 and AML15 under ISRCTN17161961).

CEBPA-double-mutated acute myeloid leukemia displays a unique phenotypic profile: a reliable screening method and insight into biological features.

Mutations in CCAAT/enhancer binding protein α (CEBPA) occur in 5–10% of cases of acute myeloid leukemia. CEBPA-double-mutated cases usually bear biallelic N- and C-terminal mutations and are associated with a favorable clinical outcome. Identification of CEBPA mutants is challenging because of the variety of mutations, intrinsic characteristics of the gene and technical issues. Several screening methods (fragment-length analysis, gene expression array) have been proposed especially for large-scale clinical use; although efficient, they are limited by specific concerns. We investigated the phenotypic profile of blast and maturing bone marrow cell compartments at diagnosis in 251 cases of acute myeloid leukemia. In this cohort, 16 (6.4%) patients had two CEBPA mutations, whereas ten (4.0%) had a single mutation. First, we highlighted that the CEBPA-double-mutated subset displays recurrent phenotypic abnormalities in all cell compartments. By mutational analysis after cell sorting, we demonstrated that this common phenotypic signature depends on CEBPA-double-mutated multi-lineage involvement. From a multidimensional study of phenotypic data, we developed a classifier including ten core and widely available parameters. The selected markers on blasts (CD34, CD117, CD7, CD15, CD65), neutrophil (SSC, CD64), monocytic (CD14, CD64) and erythroid (CD117) compartments were able to cluster CEBPA-double-mutated cases. In a validation set of 259 AML cases from three independent centers, our classifier showed excellent performance with 100% specificity and 100% sensitivity. We have, therefore, established a reliable screening method, based upon multidimensional analysis of widely available phenotypic parameters. This method provides early results and is suitable for large-scale detection of CEBPA-double-mutated status, allowing gene sequencing to be focused in selected cases.

Clinical Relevance of Concomitant Gene Mutations in CEBPA Double-Mutated Acute Myeloid Leukemia.

Abstract 2400 Background:CEBPA mutations occur in 5–14% of patients with acute myeloid leukemia (AML). A difference in clinical outcome between single- (sm) and double-mutated (dm) cases has been reported, whereupon dm cases were shown to be associated with longer overall (OS) and event-free survival (EFS). Aims:1. Determine the frequency and clinical impact of CEBPA sm and dm in a large AML cohort. 2. Evaluate the spectrum of additional molecular mutations in CEBPA dm AML and their prognostic influence. Patients and Methods:First, we investigated CEBPA mutations in a cohort of 997 AML cases (462 female, 535 male; median age: 66.8 years) by 454 deep-sequencing (454 Life Sciences, Branford, CT). The cohort included: t(15;17)(q22;q12) n=33; t(8;21)(q22;q22) n=39; inv(16)(p13q22) n=31; normal karyotype (NK) n=447; complex karyotype (CK) (≥4 abnormalities) n=116; other abnormalities n=331. Second, we investigated an additional cohort of 111 AML dm CEBPA cases for mutations in ASXL1, DNMT3A, FLT3-ITD, FLT3-TKD, GATA2, IDH1/2, KRAS, MLL-PTD, NPM1, NRAS, RUNX1, TET2, TP53, and WT1 using 454 sequencing, Sanger sequencing, conventional PCR and melting curve analyses. This cohort was composed of 60 female and 51 male cases; median age: 62.3 years; 76 cases showed NK, 19 aberrant karyotype (n=4 n.a.). Survival data was available in 90/111 (81.1%) cases. Results:1. In total, CEBPA mutations were detected in 75/997 (7.5%) of cases (t(15;17)(q22;q12) n=2/33; NK n=52/447; CK n=1/116; other abnormalities n=20/331). Of the 75 patients with CEPBA mutations 31 (41.3%) were sm, while 44 (58.7%) were dm. Patients with dm CEPBA showed better outcome compared to sm cases (OS at 3 yrs: 78.9% vs 38.5%, P=0.014; EFS after 3 yrs: 53.9% vs 36.6%, P=0.108). OS and EFS of CEBPA sm cases were comparable to CEPBA wt cases (OS at 3 yrs: 38.5% and 43.6%, P=0.689, EFS at 3 yrs: 36.6% and 29.4%, P=0.678). OS of CEBPA dm cases was comparable to patients with t(15;17)(q22;q12) (OS after 3 yrs: 78.9% vs 86.1%, P=0.597).2. In the cohort of 111 patients we detected 227 CEBPA mutations. In 106 (95.5%) cases two mutations, and in 5 (4.5%) cases three mutations were detected. The median mutation load was 42% (range: 2–98%). The majority of mutations were frame-shift (n=135) and in-frame (n=66). Further, missense (n=19) and nonsense (n=7) mutations were observed. Most cases showed one N- and one C-terminal mutation (92/111, 82.8%), 10 (9.0%) cases harbored two N-terminal mutations, and 4 (3.6%) cases showed two C-terminal mutations. In addition, two cases showed one N- and two C-terminal mutations, two cases two N- and one C-terminal mutations, and one case harbored three N-terminal mutations.In 92/111 (82.9%) cases we observed at least one additional mutation (mean: 1.6 mutations; range: 1–4): TET2 39/109 (35.8%), ASXL1 20/111 (18.0%), GATA2 20/111 (18.0%), WT1 14/111 (12.6%), DNMT3A 11/109 (10.1%), IDH1/2 9/111 (8.1%) (IDH1 n=2, IDH2 n=7), NRAS 9/111 (8.1%), RUNX1 7/111 (6.3%), FLT3-ITD 7/111 (6.3%), KRAS 4/109 (3.7%), NPM1 3/111 (2.7%), FLT3-TKD 2/110 (1.8%), MLL-PTD 1/111 (1.0%), and TP53 1/110 (1.0%). With respect to clinical outcome we observed no differences in OS for concomitant mutations in DNMT3A, FLT3-ITD, IDH1/2, NRAS, TET2 and WT1. Cases with additional GATA2 mutations showed longer survival than wt cases (OS at 3 yrs: 100% versus 73.4%, P=0.026, EFS at 3 yrs: 67.5% versus 48.5%, P=0.137). In contrast, cases harboring additional ASXL1 or RUNX1 mutations were associated with worse outcome (ASXL1: OS at 3 yrs: 32.8% versus 85.7%, P<0.001, EFS at 3 yrs: 0% versus 57.9%, P=0.002; RUNX1: OS at 3 yrs: 0% versus 81.8%, P=0.001, EFS at 3 yeaers: 0% versus 53.8%, P=0.003). Since mutations in ASXL1 and RUNX1 frequently occurred concomitantly, they were grouped together (n=21). When then separating cases into (1) GATA2 mut, (2) GATA2 wt, ASXL1wt, RUNX1wt and (3) ASXL1mut and/or RUNX1mut we observed 3 distinct survival curves (OS at 3 yrs: 100% vs 81.2% vs 32.8, P<0.001, EFS at 3 yrs: 67.5% and 55.3% and 0%, P=0.005). No statistical analysis was performed for FLT3-TKD, KRAS, MLL-PTD, NPM1, TP53 due to the low number of mutations. Conclusions:1. In CEBPA dm cases a high frequency of concomitant mutations (82.9%) was observed. 2. Most common mutated genes were TET2 (35.8%), ASXL1 (18.0%), GATA2 (18.0%), WT1 (12.6%), DNMT3A (10.1%), and RUNX1 (6.3%). 3. In CEBPA dm cases GATA2 mutations were associated with longer OS, whereas OS was poor in ASXL1 and/or RUNX1 mutated cases. Disclosures:Grossmann:MLL Munich Leukemia Laboratory: Employment. Schnittger:MLL Munich Leukemia Laboratory: Equity Ownership. Nadarajah:MLL Munich Leukemia Laboratory: Employment. Weissmann:MLL Munich Leukemia Laboratory: Employment. Fasan:MLL Munich Leukemia Laboratory: Employment. Eder:MLL Munich Leukemia Laboratory: Employment. Stopp:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Equity Ownership. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Equity Ownership.

Characterization of CEBPA mutations and promoter hypermethylation in pediatric acute myeloid leukemia

Dysfunctioning of CCAAT/enhancer binding protein α (C/EBPα) in acute myeloid leukemia can be caused, amongst others, by mutations in the encoding gene (CEBPA) and by promoter hypermethylation. CEBPA-mutated acute myeloid leukemia is associated with a favorable outcome, but this may be restricted to the case of double mutations in CEBPA in adult acute myeloid leukemia. In pediatric acute myeloid leukemia, data on the impact of these mutations are limited to one series, and data on promoter hypermethylation are lacking. Our objective was to investigate the characteristics, gene expression profiles and prognostic impact of the different CEBPA aberrations in pediatric acute myeloid leukemia. We screened a large pediatric cohort (n=252) for CEBPA single and double mutations by direct sequencing, and for promoter hypermethylation by methylation-specific polymerase chain reaction. Furthermore, we determined the gene-expression profiles (Affymetrix HGU133 plus 2.0 arrays) of this cohort (n=237). Thirty-four mutations were identified in 20 out of the 252 cases (7.9%), including 14 double-mutant and 6 single-mutant cases. CEBPA double mutations conferred a significantly better 5-year overall survival compared with single mutations (79% versus 25%, respectively; P=0.04), and compared with CEBPA wild-type acute myeloid leukemia excluding core-binding factor cases (47%; P=0.07). Multivariate analysis confirmed that the double mutations were an independent favorable prognostic factor for survival (hazard ratio 0.23, P=0.04). The combination of screening for promoter hypermethylation and gene expression profiling identified five patients with silenced CEBPA, of whom four cases relapsed. All cases characteristically expressed T-lymphoid markers. Moreover, unsupervised clustering of gene expression profiles showed a clustering of CEBPA double-mutant and silenced cases, pointing towards a common hallmark of abrogated C/EBPα-functioning in these acute myeloid leukemias. We showed the independent favorable outcome of patients with CEBPA double-mutant acute myeloid leukemia in a large pediatric series. This molecular marker may, therefore, improve risk-group stratification in pediatric acute myeloid leukemia. For the first time, CEBPA-silenced cases are suggested to confer a poor outcome in pediatric acute myeloid leukemia, indicating that further investigation of this aberration is needed. Furthermore, clustering of gene expression profiles provided insight into the biological similarities and diversities of the different aberrations in CEBPA in pediatric acute myeloid leukemia.