Showing papers by "Brian J. P. Huntly published in 2011"

Inhibition of BET recruitment to chromatin as an effective treatment for MLL-fusion leukaemia

Abstract: Recurrent chromosomal translocations involving the mixed lineage leukaemia (MLL) gene initiate aggressive forms of leukaemia, which are often refractory to conventional therapies1. Many MLL-fusion partners are members of the super elongation complex (SEC), a critical regulator of transcriptional elongation, suggesting that aberrant control of this process has an important role in leukaemia induction2, 3. Here we use a global proteomic strategy to demonstrate that MLL fusions, as part of SEC2, 3 and the polymerase-associated factor complex (PAFc)4, 5, are associated with the BET family of acetyl-lysine recognizing, chromatin ‘adaptor’ proteins. These data provided the basis for therapeutic intervention in MLL-fusion leukaemia, via the displacement of the BET family of proteins from chromatin. We show that a novel small molecule inhibitor of the BET family, GSK1210151A (I-BET151), has profound efficacy against human and murine MLL-fusion leukaemic cell lines, through the induction of early cell cycle arrest and apoptosis. I-BET151 treatment in two human leukaemia cell lines with different MLL fusions alters the expression of a common set of genes whose function may account for these phenotypic changes. The mode of action of I-BET151 is, at least in part, due to the inhibition of transcription at key genes (BCL2, C-MYC and CDK6) through the displacement of BRD3/4, PAFc and SEC components from chromatin. In vivo studies indicate that I-BET151 has significant therapeutic value, providing survival benefit in two distinct mouse models of murine MLL–AF9 and human MLL–AF4 leukaemia. Finally, the efficacy of I-BET151 against human leukaemia stem cells is demonstrated, providing further evidence of its potent therapeutic potential. These findings establish the displacement of BET proteins from chromatin as a promising epigenetic therapy for these aggressive leukaemias.

Common and overlapping oncogenic pathways contribute to the evolution of acute myeloid leukemias

Abstract: Fusion oncogenes in acute myeloid leukemia (AML) promote self-renewal from committed progenitors, thereby linking transformation and self-renewal pathways. Like most cancers, AML is a genetically and biologically heterogeneous disease, but it is unclear whether transformation results from common or overlapping genetic programs acting downstream of multiple mutations or by the engagement of unique genetic programs acting cooperatively downstream of individual mutations. This distinction is important, because the involvement of common programs would imply the existence of common molecular targets to treat AML, no matter which oncogenes are involved. Here we show that the ability to promote self-renewal is a generalized property of leukemia-associated oncogenes. Disparate oncogenes initiated overlapping transformation and self-renewal gene expression programs, the common elements of which were defined in established leukemic stem cells from an animal model as well as from a large cohort of patients with differing AML subtypes, where they strongly predicted pathobiological character. Notably, individual genes commonly activated in these programs could partially phenocopy the self-renewal function of leukemia-associated oncogenes in committed murine progenitors. Furthermore, they could generate AML following expression in murine bone marrow. In summary, our findings reveal the operation of common programs of self-renewal and transformation downstream of leukemia-associated oncogenes, suggesting that mechanistically common therapeutic approaches to AML are likely to be possible, regardless of the identity of the driver oncogene involved.

The Transcriptional Coactivator Cbp Regulates Self-Renewal and Differentiation in Adult Hematopoietic Stem Cells

Abstract: The transcriptional coactivator Cbp plays an important role in a wide range of cellular processes, including proliferation, differentiation, and apoptosis. Although studies have shown its requirement for hematopoietic stem cell (HSC) development, its role in adult HSC maintenance, as well as the cellular and molecular mechanisms underlying Cbp function, is not clear. Here, we demonstrate a gradual loss of phenotypic HSCs and differentiation defects following conditional ablation of Cbp during adult homeostasis. In addition, Cbp-deficient HSCs reconstituted hematopoiesis with lower efficiency than their wild-type counterparts, and this response was readily exhausted under replicative stress. This phenotype relates to an alteration in cellular fate decisions for HSCs, with Cbp loss leading to an increase in differentiation, quiescence, and apoptosis. Genome-wide analyses of Cbp occupancy and differential gene expression upon Cbp deletion identified HSC-specific genes regulated by Cbp, providing a molecular basis for the phenotype. Finally, Cbp binding significantly overlapped at genes combinatorially bound by 7 major hematopoietic transcriptional regulators, linking Cbp to a critical HSC transcriptional regulatory network. Our data demonstrate that Cbp plays a role in adult HSC homeostasis by maintaining the balance between different HSC fate decisions, and our findings identify a putative HSC-specific transcriptional network coordinated by Cbp.

Genome-wide analysis of transcriptional reprogramming in mouse models of acute myeloid leukaemia

Abstract: Acute leukaemias are commonly caused by mutations that corrupt the transcriptional circuitry of haematopoietic stem/progenitor cells. However, the mechanisms underlying large-scale transcriptional reprogramming remain largely unknown. Here we investigated transcriptional reprogramming at genome-scale in mouse retroviral transplant models of acute myeloid leukaemia (AML) using both gene-expression profiling and ChIP-sequencing. We identified several thousand candidate regulatory regions with altered levels of histone acetylation that were characterised by differential distribution of consensus motifs for key haematopoietic transcription factors including Gata2, Gfi1 and Sfpi1/Pu.1. In particular, downregulation of Gata2 expression was mirrored by abundant GATA motifs in regions of reduced histone acetylation suggesting an important role in leukaemogenic transcriptional reprogramming. Forced re-expression of Gata2 was not compatible with sustained growth of leukaemic cells thus suggesting a previously unrecognised role for Gata2 in downregulation during the development of AML. Additionally, large scale human AML datasets revealed significantly higher expression of GATA2 in CD34+ cells from healthy controls compared with AML blast cells. The integrated genome-scale analysis applied in this study represents a valuable and widely applicable approach to study the transcriptional control of both normal and aberrant haematopoiesis and to identify critical factors responsible for transcriptional reprogramming in human cancer.

Acute myeloid leukemia: leukemia stem cells write a prognostic signature

Abstract: In a recent interesting article, analysis of gene expression between phenotypically defined acute myeloid leukemia (AML) leukemia stem cells (LSCs) and more mature leukemia progenitor cells is used to generate a differentially expressed gene signature for LSCs. Through clever bioinformatic weighting analysis, the authors describe a method to convert this signature into a single score for any given sample and then test the prognostic utility of this 'LSC score' in publicly available gene expression profiles from bulk AML samples. They demonstrate that a high LSC score is associated with poor prognosis in AML patients and further demonstrate that the score is independent of known prognostic factors, including age, karyotype and mutation of the FLT3 or NPM1 genes. These findings are important and directly relate transcriptional dysregulation in AML LSCs with the outcome in patient samples, thus reinforcing the belief that these cellular populations are crucial for the initial propagation and subsequent relapse and resistance of leukemia.

Targeting Leukemia Stem Cells and Stem Cell Pathways in ALL

Abstract: Growing evidence suggests that haematological malignancies are ­sustained by a critical population of leukemia-initiating cells or leukemia stem cells. These cellular populations are likely to be the critical target for eradication of leukemia and most likely form the reservoir for relapse and disease resistance. Leukemia stem cells (LSC) have been demonstrated in Acute Lymphoblastic Leukemia (ALL), although their origins, identity and biology remain enigmatic. This chapter summarises the available evidence for the existence and identity of the LSC in ALL and identifies potential surface markers on LSC that might be used to direct immunotherapy. It then focuses on the biology of this cellular compartment and how oncogenic lesions alter normal stem cell processes such as self-renewal, quiescence, apoptosis and differentiation. This allows identification of potential therapeutics that target these aberrant processes, which also are discussed. Finally, any available clinical or preclinical results with these agents are provided and ­further suggestions are made as to how to target other critical LSC pathways.