gsk1210151a and Leukemia--Myeloid--Acute

Super-enhancers (SEs), which are composed of large clusters of enhancers densely loaded with the Mediator complex, transcription factors and chromatin regulators, drive high expression of genes implicated in cell identity and disease, such as lineage-controlling transcription factors and oncogenes. BRD4 and CDK7 are positive regulators of SE-mediated transcription. By contrast, negative regulators of SE-associated genes have not been well described. Here we show that the Mediator-associated kinases cyclin-dependent kinase 8 (CDK8) and CDK19 restrain increased activation of key SE-associated genes in acute myeloid leukaemia (AML) cells. We report that the natural product cortistatin A (CA) selectively inhibits Mediator kinases, has anti-leukaemic activity in vitro and in vivo, and disproportionately induces upregulation of SE-associated genes in CA-sensitive AML cell lines but not in CA-insensitive cell lines. In AML cells, CA upregulated SE-associated genes with tumour suppressor and lineage-controlling functions, including the transcription factors CEBPA, IRF8, IRF1 and ETV6 (refs 6-8). The BRD4 inhibitor I-BET151 downregulated these SE-associated genes, yet also has anti-leukaemic activity. Individually increasing or decreasing the expression of these transcription factors suppressed AML cell growth, providing evidence that leukaemia cells are sensitive to the dosage of SE-associated genes. Our results demonstrate that Mediator kinases can negatively regulate SE-associated gene expression in specific cell types, and can be pharmacologically targeted as a therapeutic approach to AML.

Topics: Animals; Cell Cycle Proteins; Cell Division; Cell Line, Tumor; Cell Lineage; Cyclin-Dependent Kinase 8; Cyclin-Dependent Kinases; Disease Progression; Down-Regulation; Enhancer Elements, Genetic; Female; Gene Expression Regulation, Neoplastic; Genes, Neoplasm; Genes, Tumor Suppressor; Heterocyclic Compounds, 4 or More Rings; Humans; Leukemia, Myeloid, Acute; Male; Mice; Mice, Inbred Strains; Mice, SCID; Nuclear Proteins; Polycyclic Compounds; Transcription Factors; Up-Regulation

Recurrent chromosomal translocations involving the mixed lineage leukaemia (MLL) gene initiate aggressive forms of leukaemia, which are often refractory to conventional therapies. 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 induction. Here we use a global proteomic strategy to demonstrate that MLL fusions, as part of SEC and the polymerase-associated factor complex (PAFc), 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.

Topics: Animals; Cell Line, Tumor; Chromatin; Chromatin Immunoprecipitation; Disease Models, Animal; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Heterocyclic Compounds, 4 or More Rings; Humans; Leukemia, Myeloid, Acute; Mice; Models, Molecular; Multiprotein Complexes; Myeloid-Lymphoid Leukemia Protein; Oncogene Proteins, Fusion; Protein Binding; Proteomics; Transcription Factors; Transcription, Genetic