selinexor and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

Nuclear-cytoplasmic shuttling is a highly regulated and complex process, which involves both proteins and nucleic acids. Changes in cellular compartmentalization of various proteins, including oncogenes and tumor suppressors, affect cellular behavior, promoting or inhibiting proliferation, apoptosis and sensitivity to therapies. In this review, we will recapitulate the role of various shuttling components in Chronic Myeloid Leukemia and we will provide insights on the potential role of shuttling proteins as therapeutic targets.

Topics: Apoptosis; Cell Nucleus; Cytoplasm; Cytosol; Exportin 1 Protein; Humans; Hydrazines; Karyopherins; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Nuclear Export Signals; Nuclear Localization Signals; Receptors, Cytoplasmic and Nuclear; Triazoles

Topics: Active Transport, Cell Nucleus; Animals; Antineoplastic Agents; Drug Resistance, Neoplasm; Fusion Proteins, bcr-abl; Hematopoietic Stem Cells; Humans; Hydrazines; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; Neoplastic Stem Cells; Triazoles; Tumor Cells, Cultured; Xenograft Model Antitumor Assays

The mechanisms underlying tyrosine kinase inhibitor (TKI) resistance in chronic myeloid leukemia (CML) patients lacking explanatory BCR-ABL1 kinase domain mutations are incompletely understood. To identify mechanisms of TKI resistance that are independent of BCR-ABL1 kinase activity, we introduced a lentiviral short hairpin RNA (shRNA) library targeting ∼5000 cell signaling genes into K562(R), a CML cell line with BCR-ABL1 kinase-independent TKI resistance expressing exclusively native BCR-ABL1. A customized algorithm identified genes whose shRNA-mediated knockdown markedly impaired growth of K562(R) cells compared with TKI-sensitive controls. Among the top candidates were 2 components of the nucleocytoplasmic transport complex, RAN and XPO1 (CRM1). shRNA-mediated RAN inhibition or treatment of cells with the XPO1 inhibitor, KPT-330 (Selinexor), increased the imatinib sensitivity of CML cell lines with kinase-independent TKI resistance. Inhibition of either RAN or XPO1 impaired colony formation of CD34(+) cells from newly diagnosed and TKI-resistant CML patients in the presence of imatinib, without effects on CD34(+) cells from normal cord blood or from a patient harboring the BCR-ABL1(T315I) mutant. These data implicate RAN in BCR-ABL1 kinase-independent imatinib resistance and show that shRNA library screens are useful to identify alternative pathways critical to drug resistance in CML.

Topics: Active Transport, Cell Nucleus; Benzamides; Cell Line, Tumor; Cell Survival; Drug Resistance, Neoplasm; Exportin 1 Protein; Fusion Proteins, bcr-abl; Gene Knockdown Techniques; Gene Library; Humans; Hydrazines; Imatinib Mesylate; K562 Cells; Karyopherins; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mutation; Piperazines; Protein Kinase Inhibitors; Pyrimidines; ran GTP-Binding Protein; Receptors, Cytoplasmic and Nuclear; RNA, Small Interfering; Signal Transduction; Triazoles; Tumor Stem Cell Assay

As tyrosine kinase inhibitors (TKIs) fail to induce long-term response in blast crisis chronic myelogenous leukemia (CML-BC) and Philadelphia chromosome-positive (Ph(+)) acute lymphoblastic leukemia (ALL), novel therapies targeting leukemia-dysregulated pathways are necessary. Exportin-1 (XPO1), also known as chromosome maintenance protein 1, regulates cell growth and differentiation by controlling the nucleocytoplasmic trafficking of proteins and RNAs, some of which are aberrantly modulated in BCR-ABL1(+) leukemias. Using CD34(+) progenitors from CML, B-ALL, and healthy individuals, we found that XPO1 expression was markedly increased, mostly in a TKI-sensitive manner, in CML-BC and Ph(+) B-ALL. Notably, XPO1 was also elevated in Ph(-) B-ALL. Moreover, the clinically relevant XPO1 inhibitor KPT-330 strongly triggered apoptosis and impaired the clonogenic potential of leukemic, but not normal, CD34(+) progenitors, and increased survival of BCR-ABL1(+) mice, 50% of which remained alive and, mostly, became BCR-ABL1 negative. Moreover, KPT-330 compassionate use in a patient with TKI-resistant CML undergoing disease progression significantly reduced white blood cell count, blast cells, splenomegaly, lactate dehydrogenase levels, and bone pain. Mechanistically, KPT-330 altered the subcellular localization of leukemia-regulated factors including RNA-binding heterogeneous nuclear ribonucleoprotein A1 and the oncogene SET, thereby inducing reactivation of protein phosphatase 2A tumor suppressor and inhibition of BCR-ABL1 in CML-BC cells. Because XPO1 is important for leukemic cell survival, KPT-330 may represent an alternative therapy for TKI-refractory Ph(+) leukemias.

Topics: Adult; Animals; Antigens, CD34; Antineoplastic Agents; Apoptosis; Cell Proliferation; Clinical Trials, Phase I as Topic; DNA-Binding Proteins; Drug Evaluation, Preclinical; Exportin 1 Protein; Fusion Proteins, bcr-abl; Gene Expression Regulation, Leukemic; Histone Chaperones; Humans; Hydrazines; Karyopherins; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Mice; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein Kinase Inhibitors; Protein Transport; Receptors, Cytoplasmic and Nuclear; Ribonucleoproteins; Transcription Factors; Triazoles

In this issue of Blood, Walker et al investigate the preclinical potential of KPT-330, an exportin-1 (XPO1, also known as chromosome maintenance protein 1 [CRM1]) inhibitor, against both accelerated phase (AP) and blast crisis chronic myeloid leukemia (CML-BC) and against Philadelphia chromosome-positive (Ph1) acute lymphoblastic leukemia (ALL), all of which are diseases of significant unmet clinical need.1 The authors provide encouraging data from both a leukemic mouse model and a single CML-AP patient, corroborating mechanistic studies suggesting that KPT-330 efficacy relies on targeting abundantly expressed XPO1, followed by the reactivation of protein phosphatase 2A (PP2A).

Topics: Animals; Antineoplastic Agents; Exportin 1 Protein; Gene Expression Regulation, Leukemic; Humans; Hydrazines; Karyopherins; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Receptors, Cytoplasmic and Nuclear; Triazoles