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

Although chronic myelogenous leukemia (CML) is effectively controlled by Bcr-Abl kinase inhibitors, resistance to inhibitors, progressive disease, and incomplete eradication of Bcr-Abl-expressing cells are concerns for the long-term control and suppression of this disease. We describe a novel approach to targeting key proteins in CML cells with a ubiquitin-cycle inhibitor, WP1130. Bcr-Abl is rapidly modified with K63-linked ubiquitin polymers in WP1130-treated CML cells, resulting in its accumulation in aggresomes, where is it unable to conduct signal transduction. Induction of apoptosis because of aggresomal compartmentalization of Bcr-Abl was observed in both imatinib-sensitive and -resistant cells. WP1130, but not Bcr-Abl kinase inhibitors, directly inhibits Usp9x deubiquitinase activity, resulting in the down-regulation of the prosurvival protein Mcl-1 and facilitating apoptosis. These results demonstrate that ubiquitin-cycle inhibition represents a novel and effective approach to blocking Bcr-Abl kinase signaling and reducing Mcl-1 levels to engage CML cell apoptosis. This approach may be a therapeutic option for kinase inhibitor-resistant CML patients.

Topics: Apoptosis; Benzamides; Cell Line, Tumor; Cyanoacrylates; Drug Resistance, Neoplasm; Endopeptidases; Fusion Proteins, bcr-abl; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Models, Biological; Nitriles; Phosphorylation; Piperazines; Protein Transport; Pyridines; Pyrimidines; Reactive Oxygen Species; Signal Transduction; Substrate Specificity; Ubiquitin Thiolesterase; Ubiquitination

Imatinib mesylate (Gleevec) is effective therapy against Philadelphia chromosome-positive leukemia, but resistance develops in all phases of the disease. Bcr/Abl point mutations and other alterations reduce the kinase inhibitory activity of imatinib mesylate; thus, agents that target Bcr/Abl through unique mechanisms may be needed. Here we describe the activity of WP1130, a small molecule that specifically and rapidly down-regulates both wild-type and mutant Bcr/Abl protein without affecting bcr/abl gene expression in chronic myelogenous leukemia (CML) cells. Loss of Bcr/Abl protein correlated with the onset of apoptosis and reduced phosphorylation of Bcr/Abl substrates. WP1130 did not affect Hsp90/Hsp70 ratios within the cells and did not require the participation of the proteasomal pathway for loss of Bcr/Abl protein. WP1130 was more effective in reducing leukemic versus normal hematopoietic colony formation and strongly inhibited colony formation of cells derived from patients with T315I mutant Bcr/Abl-expressing CML in blast crisis. WP1130 suppressed the growth of K562 heterotransplanted tumors as well as both wild-type Bcr/Abl and T315I mutant Bcr/Abl-expressing BaF/3 cells transplanted into nude mice. Collectively, our results demonstrate that WP1130 reduces wild-type and T315I mutant Bcr/Abl protein levels in CML cells through a unique mechanism and may be useful in treating CML.

Topics: Animals; Apoptosis; Benzamides; Blast Crisis; Cell Line, Tumor; Cyanoacrylates; Drug Screening Assays, Antitumor; Fusion Proteins, bcr-abl; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Leukemic; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; Mice, Nude; Neoplasms, Experimental; Nitriles; Piperazines; Point Mutation; Protein Kinase Inhibitors; Pyridines; Pyrimidines; Tumor Stem Cell Assay