cgp-57380 and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

Chronic myeloid leukemia (CML) is a myeloproliferative disease caused by bcr-abl1, a constitutively active tyrosine kinase fusion gene responsible for an abnormal proliferation of leukemic stem cells (LSCs). Inhibition of BCR-ABL1 kinase activity offers long-term relief to CML patients. However, for a proportion of them, BCR-ABL1 inhibition will become ineffective at treating the disease, and CML will progress to blast crisis (BC) CML with poor prognosis. BC-CML is often associated with excessive phosphorylated eukaryotic translation initiation factor 4E (eIF4E), which renders LSCs capable of proliferating via self-renewal, oblivious to BCR-ABL1 inhibition. In vivo, eIF4E is exclusively phosphorylated on Ser209 by MNK1/2. Consequently, a selective inhibitor of MNK1/2 should reduce the level of phosphorylated eIF4E and re-sensitize LSCs to BCR-ABL1 inhibition, thus hindering the proliferation of BC LSCs. We report herein the structure-activity relationships and pharmacokinetic properties of a selective MNK1/2 inhibitor clinical candidate, ETC-206, which in combination with dasatinib prevents BC-CML LSC self-renewal in vitro and enhances dasatinib antitumor activity in vivo.

Topics: Animals; Blast Crisis; Cell Proliferation; Female; Humans; Intracellular Signaling Peptides and Proteins; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; Mice, SCID; Models, Molecular; Molecular Structure; Protein Conformation; Protein Kinase Inhibitors; Protein Serine-Threonine Kinases; Tumor Cells, Cultured; Xenograft Model Antitumor Assays

Chronic myeloid leukemia responds well to therapy targeting the oncogenic fusion protein BCR-ABL1 in chronic phase, but is resistant to treatment after it progresses to blast crisis (BC). BC is characterized by elevated β-catenin signaling in granulocyte macrophage progenitors (GMPs), which enables this population to function as leukemia stem cells (LSCs) and act as a reservoir for resistance. Because normal hematopoietic stem cells (HSCs) and LSCs depend on β-catenin signaling for self-renewal, strategies to specifically target BC will require identification of drugable factors capable of distinguishing between self-renewal in BC LSCs and normal HSCs. Here, we show that the MAP kinase interacting serine/threonine kinase (MNK)-eukaryotic translation initiation factor 4E (eIF4E) axis is overexpressed in BC GMPs but not normal HSCs, and that MNK kinase-dependent eIF4E phosphorylation at serine 209 activates β-catenin signaling in BC GMPs. Mechanistically, eIF4E overexpression and phosphorylation leads to increased β-catenin protein synthesis, whereas MNK-dependent eIF4E phosphorylation is required for nuclear translocation and activation of β-catenin. Accordingly, we found that a panel of small molecule MNK kinase inhibitors prevented eIF4E phosphorylation, β-catenin activation, and BC LSC function in vitro and in vivo. Our findings identify the MNK-eIF4E axis as a specific and critical regulator of BC self-renewal, and suggest that pharmacologic inhibition of the MNK kinases may be therapeutically useful in BC chronic myeloid leukemia.

Topics: Aniline Compounds; Animals; beta Catenin; Blast Crisis; Bone Marrow Cells; Eukaryotic Initiation Factor-4E; Female; Humans; Intracellular Signaling Peptides and Proteins; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; Mice, Inbred NOD; Neoplastic Stem Cells; Phosphorylation; Protein Kinase Inhibitors; Protein Serine-Threonine Kinases; Purines; RNA, Small Interfering; Xenograft Model Antitumor Assays

Dysregulated mRNA translation is implicated in the pathogenesis of many human cancers including chronic myelogenous leukemia (CML). Because our prior work has specifically implicated translation initiation in CML, we tested compounds that could modulate translation initiation and polysomal mRNA assembly. Here, we evaluated the activity of one such compound, CGP57380, against CML cells and explored its mechanisms of action. First, using polysomal mRNA profiles, we found that imatinib and CGP57380 could independently, and cooperatively, impair polysomal mRNA loading. Imatinib and CGP57380 also synergistically inhibited the growth of Ba/F3-Bcr-Abl and K562 cells via impaired cell cycle entry and increased apoptosis. Mechanistically, CGP57380 inhibited efficient polysomal assembly via two processes. First, it enhanced imatinib-mediated inhibition of eukaryotic initiation factor 4F induction, and second, it independently impaired phosphorylation of ribosomal protein S6 on the preinitiation complex. We also identified multiple substrates of the mTOR, Rsk, and Mnk kinases as targets of CGP57380. Finally, we found a novel negative-feedback loop to the mitogen-activated protein kinase/Mnk pathway that is triggered by CGP57380 and demonstrated that an interruption of the loop further increased the activity of the combination against imatinib-sensitive and -resistant CML cells. Together, this work supports the inhibition of translation initiation as a therapeutic strategy for treating cancers fueled by dysregulated translation.

Topics: Aniline Compounds; Apoptosis; Benzamides; Cell Cycle; Cell Proliferation; Cell Transformation, Neoplastic; Drug Resistance, Neoplasm; Drug Synergism; Enzyme Activation; Eukaryotic Initiation Factor-4F; Feedback, Physiological; Humans; Imatinib Mesylate; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mitogen-Activated Protein Kinases; Peptide Chain Initiation, Translational; Phosphorylation; Piperazines; Polyribosomes; Protein Kinases; Purines; Pyrimidines; Ribosomal Protein S6; RNA Caps; RNA Transport; RNA, Messenger; Signal Transduction; Substrate Specificity; TOR Serine-Threonine Kinases