Abstract
Abstract 540
Expression of the constitutively active tyrosine kinase BCR-ABL1 is the hallmark of two diseases with distinct pathologic and clinical features: chronic myeloid leukemia (CML), ...an expansion of relatively mature granulocytes that typically responds well to kinase inhibition, and pre-B cell acute lymphoblastic leukemia (ALL), an aggressive malignancy of lymphoid progenitors that has a dismal prognosis. The basis for this dichotomy has been poorly understood. Recent studies profiling genome-wide DNA copy number alterations in CML and ALL have identified common deletions of IKZF1 (encoding the lymphoid transcription factor IKAROS) in de novo BCR-ABL1 positive ALL, and at the progression of CML to lymphoid blast crisis, suggesting that perturbation of IKAROS activity is a key event in the pathogenesis of BCR-ABL1 lymphoid leukemia. The IKAROS alterations commonly involve coding exons 3–6, resulting in expression of a dominant negative IKAROS isoform, IK6. Moreover, the presence of IKZF1 alterations is associated with poor outcome in BCR-ABL1 ALL. We have previously shown in a retroviral bone marrow transplant model of BCR-ABL1 ALL that Ikzf1 loss results in increased penetrance of leukemia, but the role of IK6 in the pathogenesis of ALL has not been studied. Here, we have examined the effect of the expression of Ik6 in a retroviral bone marrow transplant model of murine BCR-ABL1 B-progenitor ALL. Unmanipulated marrow from C57BL/6 Arf null mice was transduced with MSCV retrovirus coexpressing p185 BCR-ABL1 and luciferase, plated for 8 days to derive pre-B cells, then transduced with MSCV retrovirus expressing either wildtype Ikaros (Ik1-RFP), Ik6-RFP, or empty vector. Expression of Ik1 was not tolerated and resulted in cell death and apoptosis. IK6 expression led to increased proliferation of p185+Arf null cells with reduced sensitivity to the BCR-ABL1 kinase inhibitor dasatinib compared to cells transduced with empty vector. Intracellular phosphosignaling analysis of Crkl phosphorylation demonstrated that this reduced sensitivity to dasatinib was independent of ABL1 inhibition. Gene expression profiling of p185+Arf null-Ik6 cells revealed a gene expression signature similar to that of human BCR-ABL1+ ALL with enrichment of hematopoietic stem cells genes as well as genes involved in B-cell receptor, Notch, and Jak-Stat signaling pathways. To test the role of Ik6 in leukemogenesis and treatment responsiveness in vivo, p185 BCR-ABL1-luciferase Arf null cells were transduced with MSCV retrovirus expressing GFP alone, Ik1-GFP, or Ik6-GFP then transplanted into lethally irradiated C57BL/6 recipients. Expression of Ik6 in vivo led to accelerated tumorigenesis and decreased survival with tumors uniformly of pre-B immunophenotype. Moreover, mice transplanted with Ik6-expressing marrow were less sensitive to dasatinib therapy (10mg/kg QD initiated 7 days post-BMT) compared to control mice (19d vs. 31.5d, p<0.001), suggesting that expression of the dominant-negative Ikaros isoform Ik6 may play a key role in resistance to therapy and poor outcome in human BCR-ABL1 positive ALL. These results indicate that perturbation of IKAROS activity is a key event in the pathogenesis of BCR-ABL1 positive ALL, and that expression of dominant negative IKZF1 isoforms influences tumor responsiveness.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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Introduction: BCR-ABL1-like, or Philadelphia-like acute lymphoblastic leukemia (Ph-like ALL), is characterized by a gene expression profile similar to BCR-ABL1-positive ALL, with a broad range of ...genetic alterations activating cytokine receptor and kinase signaling and poor outcome. We previously reported a rearrangement of EPOR, encoding the erythropoietin receptor, into the immunoglobulin heavy chain locus (IGH). The aims of this study were to define the frequency and genomic architecture of EPOR rearrangements in B-ALL and to examine their role in kinase signaling and lymphoid transformation.
Methods: Whole genome and/or transcriptome sequencing was performed on 154 Ph-like ALL cases. Sanger sequencing and fluorescent in situ hybridization were used to confirm and map the EPOR rearrangements. Wild-type or EPOR rearranged alleles were expressed in interleukin-3 (IL-3)-dependent mouse hematopoietic Ba/F3 cells and interleukin-7 (IL-7)-dependent pre-B cells harboring alterations of Arf and/or the dominant negative IKZF1 allele IK6 observed in EPOR-rearranged ALL. Proliferation and signaling were examined in the absence or presence of erythropoietin (EPO). EPOR expression and signaling in cell lines and primary leukemic cells were examined by immunofluorescence, flow cytometry and immunoblotting. Epor-/- fetal liver cells were transduced with empty vector, EPOR wild-type or rearranged alleles and used for erythroid colony forming unit (CFU-E) and erythroid burst-forming unit (BFU-E) assays. Luciferase-marked xenografts of human EPOR-rearranged ALL were established in NOD-SCID-IL2R gamma (NSG) null mice, and signaling, EPO-dependent proliferation and sensitivity to the JAK inhibitor ruxolitinib were assessed ex vivo and in vivo.
Results: Eight cases (5.2% of Ph-like ALL) harbored rearrangements of EPOR into either the IGH or immunoglobulin kappa light chain (IGK) loci with two consequences: i) inversion and insertion of EPOR 5’ untranscribed region into the the promoter and enhancer region of IGH/IGK; ii) truncation of the last coding exon of EPOR. Such rearrangements resulted in overexpression of a C-terminal truncated receptor that retained the phosphorylation site required for STAT5 activation, but lacked multiple intracytoplasmic tyrosine residues whose phosphorylation is required for normal negative regulation of the receptor. Notably, the locations of the truncation sites overlap with those arising from inherited mutations in primary familial congenital polycythemia, in which frameshift and nonsense mutations truncate the receptor. A real-time quantitative PCR assay was established to provide a diagnostic tool and to confirm that primary leukemia cells with these EPOR rearrangements overexpress N-terminal exons but lack expression of C-terminal truncated exon eight. The truncated alleles were expressed at higher levels than wild-type EPOR in IL-3-dependent Ba/F3 and IL-7-dependent Arf-/- mouse pre-B cells, and sustained cell proliferation and increased STAT5 phosphorylation following stimulation with exogenous EPO. Expression of wild-type or truncated EPOR in Epor-/- fetal liver cells promoted erythroid differentiation with formation of CFU-E and BFU-E colonies, indicating that truncated receptors sustain erythroid development. Xenografted EPOR-rearranged leukemic cells exhibited high levels of mutant EPOR on the cell surface, constitutive STAT5 phosphorylation and sensitivity to the JAK2 inhibitor ruxolitinib ex vivo and in vivo.
Conclusions: We have identified a subset of Ph-like ALL cases characterized by rearrangements of truncated EPOR into the IGH/IGK chain loci. This represents an entirely new mechanism of EPOR deregulation and unexpectedly implicates EPOR signaling as an important factor influencing B-lymphoid malignancies that are amenable to JAK-STAT5 inhibition. Clinical trials testing ruxolitinib in ALL patients with EPOR rearrangements are warranted.
No relevant conflicts of interest to declare.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Introduction. Prior studies have described a subset of B-progenitor ALL cases with a distinct gene expression profile and/or deletions involving ERG (encoding the ETS family member v-ets avian ...erythroblastosis virus E26 oncogene), however the relationship of these alterations and their role in leukemogenesis are poorly understood. We performed integrated genomic and epigenetic analyses, biochemical studies and leukemogenesis assays to define the genetic basis of this form of ALL.
Methods. We studied 1674 childhood, adolescent and young adult B-progenitor ALL cases with microarray gene expression profiling and/or RNA-sequencing data to enable the identification of ERG ALL by unsupervised clustering and predictive analysis of microarrays. Detailed genomic analysis was performed for 144 ERG ALL cases, including whole genome (N=38), exome (n=46) and/or RNA-sequencing (n=57) cases, and single nucleotide polymorphism array analysis. Epigenetic profiling, including whole genome bisulfite sequencing, chromatin immunoprecipitation and sequencing for ERG and histone modifications and ATAC-sequencing were performed for a subset of 8 xenografted ERG tumors and reference cell lines. ERG transcript expression was measured by analysis of RNA-seq analysis and quantitative RT-PCR assays, and by interrogation of TCGA and PCGP RNA-seq data. The function of ERG isoforms was evaluated by EMSA and transcriptional reporter assays, immunofluoresence, colony forming assays and retroviral bone marrow transplant assays.
Results. One hundred and forty four cases (8.6%) of B-ALL cases exhibited a distinct gene expression profile and lacked known chromosomal rearrangements (ERG ALL). Such cases had favorable outcome. Eighty cases (55.6%) had focal deletions of ERG with no evidence of oncogenic or chimeric ERG fusions. The deletions were most commonly heterozygous and involving exons 3-7 (n=27) or 3-9 (n=22) of 10 coding exons, and less commonly involving exon 1, or a larger region of the gene. No ERG deletions were identified in non-ERG ALL. Two cases harbored missense mutations in the ETS domain. Analysis of whole genome and exome sequencing data of 71 cases identified a high frequency of alterations of lymphoid transcription factors (46.5%; IKZF1 36.7%, PAX5 11.3%); mutation of transcription factors otherwise uncommon in ALL (21%; MYC, MYCBP2, MGA, ZEB2, GATA3); activation of signaling pathways, most commonly NRAS or KRAS (35.2%); cell cycle regulation (22.5%); and epigenetic modifiers (56.3%), most commonly KMT2D, SETD2, ARID2 and NCOR1. Notably, the five year event-free survival of ERG ALL cases with IKZF1 alterations exceeded 85% in both St Jude and Children's Oncology Group cohorts.
We observed striking transcriptional deregulation at the ERG locus. Most (51/56) ERG- deleted cases expressed an ERG isoform encoded by a novel exon in intron 6 that splices in frame to distal exons, resulting in expression of a truncated C-terminal ERG protein that lacks the pointed and central regulatory domains, but retains the ETS and transactivation domain (ERGalt). ERGalt was also present in most (36/44) cases lacking an ERG deletion, and was strongly associated with presence of ERGalt protein in leukemic cells. We also identified expression of an Antisense Long non-coding RNA associated with the ERG locus (ALE) in ERG ALL. ERGalt and ALE were absent, or uncommonly expressed at very low levels in non-ERG ALL. ERGalt was absent, and ALE rarely expressed in non-ALL PCGP and TCGA samples.
ERGalt and point mutant ERG were retained in the nucleus, bound DNA targets and acted as competitive inhibitors of wild type (WT) ERG in transcriptional reporter assays. Lineage-negative Arf -null bone marrow cells transduced with ERG WT induced an aggressive erythro-megakaryoblastic leukemia; in contrast ERGalt induced an immature lymphoid progenitor leukemia.
Conclusions. Genomic alterations drive aberrant transcription of ERG, resulting on expression of a truncated, C-terminal oncogenic ERG protein. This represents a novel mechanism of transcription factor deregulation in leukemia. As a subset of ERG ALL cases lack ERG deletion, and as IKZF1 alterations are not associated with inferior outcome in this form of ALL, diagnostic approaches must incorporate gene expression profiling in addition to identification of ERG and IKZF1 alterations to accurately identify this form of leukemia.
Evans:Prometheus Labs: Patents & Royalties: Royalties from licensing TPMT genotyping. Stock:Gilead: Membership on an entity's Board of Directors or advisory committees. Voorhees:Oncopeptides: Consultancy; Onyx Pharmaceuticals: Research Funding; GSK: Consultancy; Oncopeptides: Research Funding; Janssen: Research Funding; A Takeda Oncology Company: Consultancy, Research Funding; Celgene: Consultancy; Millennium Pharmaceuticals: Consultancy, Research Funding; Acetylon Pharmaceuticals, Inc.: Research Funding; Novartis: Consultancy; Array BioPharma: Consultancy; GSK: Research Funding; Celgene: Research Funding. Hunger:Spectrum Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Consultancy; Sigma Tau: Consultancy; Merck: Equity Ownership. Mullighan:Incyte: Consultancy; Amgen: Honoraria.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Acute lymphoblastic leukemia (ALL) in adolescents and young adults (AYA) is characterized by distinct presenting features and inferior prognosis compared to pediatric ALL. Age, as a continuous ...variable, is negatively correlated with prognosis, in spite of risk-adapted combination chemotherapy. To better understand the etiology of ALL in this age group, we performed the first genome-wide association study (GWAS) to comprehensively examine germline single nucleotide polymorphisms (SNPs) for their association with susceptibility to B-ALL in AYAs.
In the discovery GWAS, we compared genotype frequency at 635,297 SNPs between 308 AYA ALL cases (age 16-39 years, treated on the Children’s Oncology Group COG, the Alliance-Cancer and Leukemia Group B, Eastern Cooperative Oncology Group, MD Anderson Cancer Center, and St. Jude Children’s Research Hospital trials) vs. 6,661 non-ALL controls. The association between genotypes at each SNP and ALL susceptibility was tested by using a logistic regression model after adjusting for genetic ancestries to control for population stratification. SNPs that reached P≤ 5×10-8 in the discovery GWAS were tested in an independent cohort of 82 AYA ALL cases from the COG protocols and 5,755 non-ALL controls.
We identified a single genome-wide significant susceptibility locus on 10p14 signified by two SNPs within the GATA3 gene: rs3824662, P=2.8x10-10, odds ratio (OR)=1.77; rs3781093, P=3.2x10-9, OR=1.73, both of which were validated in the replication cohort (P=1.9x10-8 and P=4.3x10-5, respectively). We also examined the association signals in AYAs for susceptibility loci previously identified in pediatric ALL: ARID5B, IKZF1 and PIP4K2A variants were nominally significant in AYAs in the discovery GWAS and/or in the replication analysis, whereas CEBPE or CDKN2A/CDKN2B were not significant. These results imply both similarities and differences in genetic predisposition to ALL between children and AYAs.
At the GATA3 locus, rs3824662 risk variant was over-represented in Philadelphia chromosome (Ph)-like ALL in AYAs (P=0.02), confirming our previous report of Ph-like ALL susceptibility variants in GATA3 (Nat Genet 45:1494). Importantly, even after excluding Ph-like cases, rs3824662 remained associated with the risk of developing ALL in AYAs, suggesting that the influence of the GATA3risk variant on ALL susceptibility in AYAs extends beyond the predisposition to Ph-like subtype.
We next examined the relationship between GATA3 risk allele frequency and age at diagnosis in a cohort of unselected childhood and adolescent ALL cases enrolled in the COG P9900 protocols (N=1,827). Dividing patients into four consecutives age groups (<5, 5-10, 10-15 and >15 years), we observed a clear progressive increase in the risk allele frequency at rs3824662 (P=6.29×10-11) with increasing allelic odds ratio (i.e. relative risk of ALL conferred by each copy of the risk allele). This correlation between genotype and age was evident regardless of genetic ancestry, although the risk variant was more common among individuals with higher Native American ancestry. In contrast, the frequency of ALL susceptibility variant in ARID5B decreased progressively with increasing age at diagnosis (P=0.006), whereas PIP4K2A, CDKN2A/CDKN2B, IKZF1 and CEBPE variants were not related to age. Finally, we compared rs3824662 risk variant frequency by age in the COG P9900 protocols after stratifying the ALL cases into TCF3-PBX1, ETV6-RUNX1, hyperdiploid, MLL-rearranged and B-other. There was a trend that the risk allele was more frequent in cases older than 16 years compared to those below 16 in the five subtypes examined.
In conclusion, we have identified inherited GATA3 genetic variants that strongly influence ALL susceptibility in adolescent and young adults, indicating potential age-related differences in ALL biology.
No relevant conflicts of interest to declare.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
BCR-ABL1-like, or “Ph-like” B-progenitor acute lymphoblastic leukemia (B-ALL) constitutes up to 15% of childhood and 30% of adult ALL, and is characterized by a gene expression profile ...similar to BCR-ABL1 ALL, alteration of IKZF1, and poor outcome. A pilot next-generation sequencing study identified kinase activating alterations in 15 Ph-like ALL cases. The goals of this study were to define the genomic landscape of Ph-like ALL in children and young adults, and to examine the utility of tyrosine kinase inhibitors (TKIs) in patients harboring genetic alterations activating kinase signaling.
We studied 1665 B-ALL cases, including 309 childhood standard risk (10.8% Ph-like), 826 childhood high risk (14% Ph-like), 370 adolescent (16-21 years, 21% Ph-like) and 160 young adult (21-39 years; 26% Ph-like) cases. Approximately 50% of Ph-like cases harbored a CRLF2 rearrangement (IGH-CRLF2 or P2RY8-CRLF2). Next-generation sequencing was performed for 160 non-CRLF2 expressing Ph-like cases, including mRNA-seq (141 cases), whole genome sequencing (30 cases) and/or exome sequencing (12 cases). Fusion transcripts were identified using CICERO, a novel mRNA-seq assembly-based structural variation detection method.
Over 100 chimeric in-frame fusions were identified, including 29 involving 12 tyrosine kinase or cytokine receptor genes, 15 of which were recurrent: JAK2 (10 partners), ABL1 (6), ABL2 (3), PDGFRB (3), CSF1R, TYK2, NTRK3, PTK2B, IL2RB (1 partner each), and rearrangements of EPOR into the IGH and IGK loci. Together, these rearrangements were present in ∼30% of Ph-like ALL cases. Additional sequence and structural alterations activating kinase signaling were identified in ∼10% of cases (e.g IL7R, FLT3, SH2B3).
Despite the diversity of kinase alterations, the majority are predicted to respond to a limited number of TKIs, but many are novel or have not been tested in suitable preclinical models of ALL. We show that expression of RCSD1-ABL1, RANBP2-ABL1, ZMIZ1-ABL1, RCSD1-ABL2, SSBP2-CFS1R and PAX5-JAK2 in Ba/F3 and primary mouse pre-B cultures induces cytokine-independent proliferation and constitutive activation of JAK/STAT signaling. Furthermore, the ABL1, ABL2 and CSF1R fusions were sensitive to dasatinib (IC50 range 1-2nM), whilst PAX5-JAK2 only responded to the JAK2 inhibitor, ruxolitinib. Notably, we show efficacy of dasatinib (20mg/kg/day p.o) in a xenograft model of ETV6-ABL1, with reduction of circulating human CD45+ cells (17.4 vs 88.2%; p<0.0001) and spleen weight (117 vs 321mg; p<0.0001) in dasatinib treated mice (n=5) compared to vehicle treated mice (n=5).
These data define the genomic landscape of Ph-like ALL and show that the majority of cases harbor genetic alterations that activate a limited number of kinase signaling pathways. These results provide the basis for prospective precision medicine clinical trials that identify and direct patients with Ph-like ALL to logical TKI therapy.
Citation Format: Kathryn G. Roberts, Yongjin Li, Debbie Payne-Turner, Jinghui Zhang, Richard C. Harvey, Yung-Li Yang, Guangchun Song, Jing Ma, Shann-Ching Chen, Jinjun Cheng, Natalia Santiago-Morales, Ilaria Iacobucci, Meenakshi Devidas, I-Ming Chen, Shalini Reshmi, Michael Rusch, Pankaj Gupta, Naomi J. Winick, William L. Carroll, Nyla A. Heerema, Andrew J. Carroll, Elizabeth A. Raetz, Guido Marcucci, Clara D. Bloomfield, Wendy Stock, Steven M. Kornblau, Elisabeth Paietta, Ching-Hon Pui, Sima Jeha, James Downing, Daniela S. Gerhard, Julie M. Gastier-Foster, Mignon L. Loh, Cheryl Willman, Stephen P. Hunger, Charles G. Mullighan. The genetic landscape of Ph-like acute lymphoblastic leukemia. abstract. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3083. doi:10.1158/1538-7445.AM2014-3083
The genetic basis underlying inferior outcome of adolescent and young adult acute lymphoblastic leukemia (AYA ALL) as compared to childhood cases is largely unknown. To comprehensively characterize ...the genetic landscape of AYA ALL we studied 423 adolescent (16-21 yrs; median 17.7±1.3 yrs) and 250 young adult (21-39 yrs; median 28.3±7.0 yrs) samples from the Children's Oncology Group high-risk trial AALL0232, St Jude Children's Research Hospital Total XV and XVI, Eastern Cooperative Oncology Group E2993, MD Anderson Cancer Center and the Alliance - CALGB trials. Single nucleotide polymorphism (SNP) microarray analysis and gene expression profiling were performed to identify copy number alterations and distinct genetic subgroups. Samples were also sub classified using hierarchical clustering, ROSE outlier and PAM analysis of gene expression profiling data. Sequence mutation analysis was performed on candidate genes known to be mutated in pediatric ALL (including IKZF1, PAX5, JAK1/2, NRAS, KRAS, FLT3, IL7R, SH2B3, TP53 and CREBBP), and mRNA-seq was performed on selected BCR-ABL1-like cases (n=41).
The genetic subgroups were divided into ETV6-RUNX1, TCF3-PBX1, hyperdiploid (>50 chromosomes), MLL rearrangements, BCR-ABL1, BCR-ABL1-like, ERG and other (cases with no known lesions). As expected, ETV6-RUNX1 and hyperdiploid ALL were less frequent in adolescents (4% and 11%, respectively) and adults (2% for both) than in childhood ALL (<16 years; 25% for both). In contrast, the frequency of BCR-ABL1-like ALL, a recently described subgroup in 10-15% of pediatric ALL associated with kinase-activating lesions and a poor outcome, was very frequent and increased with age (21% in adolescent, 25% in young adults), similar to cases with the classic BCR-ABL1 translocation (6% in adolescent, 22% in young adults).
Notably, BCR-ABL1 and BCR-ABL1-like ALL patients presented with higher white blood counts at diagnosis compared to non BCR-ABL1-like ALL patients in both adolescents (117.6 and 76.8 vs 21.9 x109/L, p<0001), and young adults (72.6 and 94.1 vs 17.6 x109/L, p<0001). BCR-ABL1-like ALL patients were also more likely to be male compared to non BCR-ABL1-like ALL patients, with 74% vs 62% in adolescents (p<0.05; Fisher's exact test), and 81% vs 63% in young adults (p=0.07; Fisher's exact test). The outcome of BCR-ABL1 and BCR-ABL1-like ALL was markedly inferior to other ALL subtypes, with 5-year event free survival (EFS) rates of 53.7+18.3 and 40.0+7.1 vs 85.0±3.3 (p<0.0001) in adolescent cases, and 23.2±9.1 and 16.1±8.5 vs 57.9±8.0 (p=0.006) for young adults (Figure 1). IKZF1 alterations, a marker of poor outcome in pediatric ALL, were enriched in BCR-ABL1 and BCR-ABL1-like ALL cases (70% and 77%, respectively) compared to non BCR-ABL1-like patients (26%). Regardless of genetic subtype, the presence of an IKZF1 alteration correlated with inferior 5 year EFS in adolescent (60.3±6.0 vs 77.4±4.1; p=0.0015) and young adults (25.7±7.0 vs 52.7±6.4; p=0.0011).
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We then sought to characterize the alterations activating kinase signaling in AYA BCR-ABL1-like ALL cases. As observed in pediatric ALL, approximately 55% of these cases harbored CRLF2 rearrangements. Using mRNA-seq we identified a variety of additional rearrangements involving the tyrosine kinase or cytokine receptor genes ABL1, ABL2, CSF1R, JAK2, EPOR or PDGFRB, with a marked enrichment of fusions involving JAK2 (6 different fusions in 9/20 cases sequenced), thus providing a rationale for the investigation of targeted therapies directed against these alterations. Collectively, the kinase-activating BCR-ABL1 and BCR-ABL1-like subtypes are associated with poor outcome and make up ∼25% of adolescent and ∼50% of young adult ALL patients. The identification of these patients at diagnosis will provide an opportunity to incorporate tyrosine kinase inhibitor treatment to current chemotherapeutic regimens, and significantly improve the treatment outcome for AYA ALL.
Hunger:Bristol Myers Squibb: Consultancy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
BCR-ABL1-like B-progenitor acute lymphoblastic leukemia (B-ALL) accounts for 10-15% of childhood B-ALL and is characterized by alteration of IKZFI, a gene expression profile similar to BCR-ABL1 ALL ...and poor outcome. Using next-generation sequencing, we have shown that BCR-ABL1-like ALL patients harbor genetic alterations activating kinase pathways that are sensitive to tyrosine kinase inhibitors (TKIs), and have shown that refractory BCR-ABL1-like ALL is responsive to TKIs in vivo (Weston et al., J. Clin. Oncol 2013). Furthermore, the outcome of ALL in adolescent and young adult (AYA) patients is inferior to children, yet the genetic basis underlying treatment failure is poorly understood.
To define the frequency and genomic landscape of BCR-ABL1-like ALL in children, adolescents, and young adults we have extended our studies to include 665 high-risk childhood (<16 years, 14% BCR-ABL1-like), 370 adolescent (16-21 years, 21% BCR-ABL1-like) and 161 young adult (21-39 years; 26% BCR-ABL1-like) B-ALL cases from the Children's Oncology Group, St Jude Children's Research Hospital, Eastern Cooperative Oncology Group, MD Anderson Cancer Center and the Alliance - CALGB trials. Event-free survival (EFS) for BCR-ABL1-like cases was inferior to non BCR-ABL1-like cases with 5-year EFS rates of 40.0±7.1 vs 85.0±3.3 (p<0.0001) for adolescent cases and 16.1±8.5 vs 57.9±8.0 (p=0.006) for young adult cases. In each age group, 50-60% of BCR-ABL1-like cases harbored rearrangements of CRLF2 (IGH@-CRLF2 or P2RY8-CRLF2) (Fig. 1).
To characterize the full spectrum of kinase lesions in the remaining BCR-ABL1-like ALL cases we performed mRNA-seq on pediatric (n=39), adolescent (n=21) and young adult (n=22) cases, and whole genome (WGS; n=18) or exome sequencing (n=10) on cases with matched tumor and normal material. Fusion transcripts were identified using deFuse and CICERO, a novel assembly-based structural variation detection method specifically designed for mRNA-seq analysis. We identified 23 different kinase rearrangements involving 7 tyrosine kinase or cytokine receptor genes. These consist of 5 ABL1, 2 PDGFRB, 8 JAK2 fusions and 2 EPOR translocations to IGH@ and IGK@ loci, along with new fusions involving the tyrosine kinases ABL2 (n=3), CSF1R (n=1), AKT2 (n=1) and STAT5B (n=1). We performed frequency testing for 15 of these fusions on 555 cases from the COG AALL0232 trial of high-risk B-ALL. Several alterations were recurrent in BCR-ABL1-like ALL, including NUP214-ABL1, RCSD1-ABL2, SSBP2-CSF1R, PAX5-JAK2 and EPOR translocations. Notably, we did not identify any of these fusions in non BCR-ABL1-like cases. The frequency of ABL1/ABL2 and EPOR translocations was consistent across all age groups (∼16% and 7% of BCR-ABL1-like cases, respectively), while JAK2 rearrangements were more common in young adult than in pediatric and adolescent ALL (12%). Importantly, ∼10% of BCR-ABL1-like ALL cases lacked a kinase-activating alteration on analysis of mRNA-seq data. Notably, we identified two additional cases with IL7R or SH2B3 sequence mutations, indicating the requirement for complementary approaches such as WGS to fully define the genomic landscape of BCR-ABL1-like ALL.
Current functional studies include the development of experimental models using the Ba/F3 hematopoietic progenitor cell line, primary mouse pre-B cultures and the generation of xenografts to determine the role of these alterations in leukemogenesis, and to enable testing of targeted therapies. For example, we show that RCSD1-ABL1 and SSBP2-CSF1R confer factor-independent growth and constitutive activation of JAK/STAT pathways in Ba/F3 cells. Furthermore, RCSD1-ABL1 and SSBP2-CSF1R are both sensitive to the TKIs, imatinib (IC50 378nM and 327nM, respectively) and dasatinib (IC50 2.1nM and 2.5nM, respectively). Together, these complementary approaches will further define the genetic landscape of both pediatric and AYA ALL, and facilitate the development of diagnostic and therapeutic strategies to improve the treatment outcome for high-risk BCR-ABL1-like ALL patients. Display omitted
Hunger:Bristol Myers Squibb: Consultancy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Hypodiploid acute lymphoblastic leukemia (ALL) comprises up to 7% of pediatric ALL cases and is characterized by chromosomal loss and very poor outcome. Prognosis is associated with the ...severity of aneuploidy, with the worst outcome for cases with less than 32 chromosomes. To gain insights into the genetic basis of hypodiploid ALL, we performed a genome wide analysis of genetic alterations in 128 hypodiploid childhood ALL cases treated by the Children's Oncology Group and St Jude. This cohort comprised 51 near haploid cases (24-31 chr), 24 low hypodiploid cases (32-39 chr), 29 masked hypodiploid cases (with a doubled near haploid or low hypodiploid genome), 2 high hypodiploid cases (40-43 chr) and 22 cases with 44-45 chromosomes, the majority of which had a dicentric chromosome. DNA copy number alterations and loss of heterozygosity were examined using Affymetrix SNP 6.0 arrays, and candidate gene resequencing was performed for genes and pathways recurrently altered in ALL. We identified multiple recurring focal deletions, the nature and frequency of which were associated with degree of aneuploidy. The most common alteration was deletion of CDKN2A/B (encoding INK4/ARF) in hypodiploid ALL cases with 40-45 chromosomes (75% of cases) compared to 23% in the other hypodiploid ALL subgroups. The B-lymphoid transcription factor gene PAX5 was mutated more frequently in dicentric cases (59%) than in cases with less than 44 chromosomes (7%). We also observed recurring deletions in the histone loci at 6p22 and PAG1 (11% and 10%, respectively, of near haploid, low and masked hypodiploid cases). A striking novel finding was a high frequency of alterations targeting the IKAROS family members IKZF2 (encoding the lymphoid transcription factor HELIOS) and IKZF3 (AIOLOS) that only were present in near haploid, low and masked hypodiploid cases (IKZF2 21%; IKZF3 10%). Deletions of these genes are rare in other ALL subtypes. Conversely, alteration of IKZF1 (encoding IKAROS), found in up to 30% of non-hypodiploid ALL cases, was rare in hypodiploid ALL. Further, a high frequency of deletions and sequence mutations targeting the Ras signaling pathway (KRAS, NRAS, NF1, PTPN11 and FLT3) was observed in 45% of near haploid, low and masked hypodiploid ALL cases. Notably, the alterations of NF1 and IKZF2/3 were almost always mutually exclusive and mostly occurred in conjunction with loss of the other copy of the corresponding chromosome, resulting in biallelic deletion and/or inactivation of the involved gene. This study provides the first detailed genetic analysis of this high risk ALL subtype, and suggests that genetic alterations targeting Ras signaling and lymphoid development are central to the pathogenesis and poor prognosis of hypodiploid ALL. Moreover, these results suggest that therapeutic targeting of Ras signaling may be of clinical benefit in this very high risk ALL subtype.
Citation Format: {Authors}. {Abstract title} abstract. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4755. doi:10.1158/1538-7445.AM2011-4755
Abstract
Hypodiploid acute lymphoblastic leukemia (ALL) is an aggressive form of leukemia characterized by multiple whole chromosomal losses and very dismal outcome. Our previous genome wide study of ...hypodiploid childhood ALL cases treated by the Children's Oncology Group and St Jude, employed interrogation of DNA copy number alterations using Affymetrix SNP 6.0 microarrays, candidate gene resequencing and gene expression profiling using Affymetrix U133 Plus 2.0 microarrays. These analyses showed that this disease can be divided into multiple subtypes characterized by variation in the degree of aneuploidy, distinct submicroscopic deletions, sequence mutations and gene expression profile. Near haploid ALL (24-31 chromosomes) frequently harbors alterations of genes regulating Ras signaling (67.6%; NF1, NRAS, KRAS, PTPN11, FLT3, and PAG1), IKZF3 (encoding the lymphoid transcription factor AIOLOS; 13.2%), and a histone gene cluster at 6p22 (17.6%), while low hypodiploid ALL (32-39 chromosomes) is enriched for IKZF2 (HELIOS; 52.9%), TP53 (70.6%) and RB1 (41.2%) alterations. A striking finding was exclusivity of Ras signaling and IKZF2/3 alterations, and biochemical indications of Ras pathway activation in both near haploid and low hypodiploid ALL. To further interrogate the genomic changes of hypodiploid ALL, we performed next generation sequencing using either Illumina GAIIx or HiSeq3000 sequencers on both tumor and matched remission DNA. Whole genome sequencing to at least 30 fold haploid coverage was performed on 10 near haploid and 8 low hypodiploid cases, and whole exome sequencing (Agilent SureSelect Human All Exon 50Mb) on 5 near haploid and 1 low hypodiploid cases. The burden of single nucleotide variations (SNVs) and insertion/deletion (indel) mutations was in general low in this ALL subtype, with 0-5 indels and 9-95 SNVs in coding regions and untranslated leader regions in the whole genome sequenced cases, where the majority of cases had fewer than 30 SNVs. Further, the number of structural variations, including the ones too small to be identified by SNP microarray analysis, and structural rearrangements, were also low, with less than 25 structural variations identified in the whole genome sequenced cases. For the whole exomes, between 10 and 42 non-silent SNVs and 1-2 indels were identified per case. No recurrent alterations not previously identified in the hypodiploid cohort were found in these 24 cases, indicating that the initial genome wide study of this cohort identified the major recurrent alterations in hypodiploid ALL. However, the recurrence screening including the remaining 78 near haploid and low hypodiploid cases in our cohort on the alterations identified by the whole genome and exome sequencing study is ongoing. Altogether, these findings provide critical new insights into the genetic basis of hypodiploid ALL, and indicate that therapeutic targeting of the Ras pathway should be pursued in this disease.
Citation Format: {Authors}. {Abstract title} abstract. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4870. doi:1538-7445.AM2012-4870
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