Targeting Novel Protein Complexes for the Treatment of Acute Myeloid Leukemia

Despite recent advances in the treatment of acute myeloid leukemia (AML), the morbidity and mortality of the disease remains very high and novel therapeutic approaches are urgently needed. This is a competing renewal application whose overall objective is to define the functional significance of novel protein complexes in AML cells and to exploit their potential therapeutic targeting. We have identified cyclin dependent kinase 9 (CDK9) as a novel binding partner of the mTOR complex scaffold protein, mLST8 and demonstrated that CDK9 is present in distinct mTOR-like (CTOR) complexes in the cytoplasm and nucleus. In the nucleus, CDK9 binds to RAPTOR and mLST8, forming CTORC1, to promote transcription of genes important for leukemogenesis. In the cytoplasm, CDK9 binds to RICTOR, SIN1 and mLST8 forming CTORC2, and controls mRNA translation through phosphorylation of LARP1 and rpS6. Targeting C-TOR complexes results in suppression of growth of primary human AML progenitors in vitro and generation strong antileukemic responses in AML xenografts in vivo, suggesting an essential role for these complexes in the survival of AML leukemic precursors. Specific aim 1 will define the mechanisms by which nuclear CTORC1 complexes control expression of genes that promote leukemogenesis. Studies will be performed to map the interactions between CDK9 and other CTORC1 elements and define mechanisms by which CTORC1 complexes control transcriptional activation of mitogenic genes and mRNA splicing. Specific Aim 2 will determine the functions of CTORC2 complexes and their roles in mRNA translation of target genes and survival of primitive leukemic precursors. Experiments will be performed to define components and effectors of CTORC2 complexes andtheir roles in mRNA translation, protein expression and leukemic cell survival. Specific aim 3 will examine the antileukemic properties of CTORC1 and CTORC2 targeting on primary leukemic precursors in vitro and in vivo. It will involve studies using primary leukemic progenitors from a large group of AML patients and xenograft AML mouse models determine the impact of the different CTOR complexes on leukemogenesis and the potential synergistic effects of CTORC targeting with other antileukemic agents. Altogether, these studies will advance our understanding of the mechanisms of leukemogenesis and will provide the basis for important future clinical-translational efforts, involving targeting of CDK9 and other elements of C-TOR complexes for the treatment of AML.