Regulation and Targeting of Eg5, a Mitotic Motor Protein in Blast Crisis CML: Overcoming Imatinib Resistance

Abstract

Patients with blast crisis (BC) CML frequently become resistant to Imatinib, a Bcr-Abl tyrosine kinase-targeting agent. Eg5, a microtubule-associated motor protein has been described to be highly expressed in BC CML by microarray analysis (Nowicki et al., Oncogene 2003; 22:3952-63). We investigated the regulation of Eg5 by Bcr-Abl tyrosine kinase and its potential as a therapeutic target in BC CML. Eg5 was highly expressed in all Philadelphia chromosome positive (Ph(+)) cell lines and BC CML patient samples. Inhibition of Bcr-Abl by Imatinib downregulated Eg5 expression in Imatinib-sensitive KBM5 and HL-60p185 cells, but not in Imatinib-resistant KBM5-STI571, harboring a T315I mutation, and Bcr-Abl-negative HL-60 cells. Blocking Eg5 expression with antisense oligonucleotide (Eg5-ASO) or inhibiting its activity with the small-molecule Eg5 inhibitor, S-trityl-L-cysteine induced G(2)/M cell cycle block and subsequent cell death in both Imatinib-sensitive and -resistant cells. Further, Eg5-ASO treatment of SCID mice harboring KBM5 cell xenografts significantly prolonged the median survival of the animals (p = 0.03). Our findings suggest that Eg5 is downstream of and regulated by Bcr-Abl tyrosine kinase in Philadelphia chromosome positive cells. Inhibition of Eg5 expression or its activity blocks cell cycle progression and induces cell death independent of the cellular response to Imatinib. Therefore, Eg5 could be a potential therapeutic target for the treatment of BC CML, in particular Imatinib-resistant BC CML.

p27Kip1 represses transcription by direct interaction with p130/E2F4 at the promoters of target genes

“…Kip1 two p27-TGs Aurka, encoding the protein kinase Aurora A, and Kif11, encoding a kinesin-related motor protein, are overexpressed in tumors and are considered as therapeutic targets for cancer, and a number of inhibitors are in clinical trials (Carter et al, 2006;Saijo et al, 2006;Malumbres and Barbacid, 2007;Huszar et al, 2009;Lapenna and Giordano, 2009). The finding that both proteins are overexpressed in p27 À/À cells supports a link between a decrease in p27, overexpression of these proteins and cancer.…”

Overexpression of Eg5 Causes Genomic Instability and Tumor Formation in Mice

“…Given the complexity of cancer-specific phenotypes, and the failure of Eg5 overexpression to cause neoplastic transformation or induce micronuclei formation in cultured cells (Supplementary Data), a mechanism involving aneuploidy and the alteration of large complements of regulatory and structural genes remains a logical mechanism for the initiation of tumorigenesis. With recent data detailing Eg5 overexpression in many human solid tumors and leukemias (49), in addition to recent work demonstrating a correlation between Eg5 expression and the response of non-small cell lung cancer to antimitotic agents used in chemotherapeutic treatments (50), understanding the role of Eg5 in cell division may aid in the development of Eg5 as a potential therapeutic cancer target. Further studies of Eg5 function may benefit from highresolution, real-time analysis of microtubule motors and spindle dynamics in mammalian cells as done with Drosophila embryos and Xenopus mitotic extracts to understand the molecular mechanism for Eg5 overexpression and its effect on the balance of net forces exerted on microtubules of the mitotic spindle.…”

Dimethylenastron suppresses human pancreatic cancer cell migration and invasion in vitro via allosteric inhibition of mitotic kinesin Eg5

“…Interestingly, parkin represses Eg5 gene transcription by Hsp70 monoubiquitination-dependent inactivation of the c-Jun NH 2 -terminal kinase pathway and blocking c-Jun binding to the activator protein 1 site in the Eg5 promoter, instead of triggering Eg5 protein degradation through the ubiquitinproteasome pathway [23] . In addition, the Bcr-Abl tyrosine kinase has been reported to regulate Eg5, although the molecular details remain unclear [6] . Considering that both parkin and Bcr-Abl have been implicated in tumorigenesis, it would be interesting to examine whether abnormalities in these proteins play a role in triggering Eg5 overexpression in pancreatic cancer cells.…”

“…Antisense oligonucleotides against Eg5 has been shown to reduce the growth of tumors in xenograft models [5] . In blast crisis chronic myeloid leukemia and prostate cancer cells, in which Eg5 is highly expressed, inhibition of Eg5 causes cell cycle arrest and significantly suppresses cell proliferation [5,6] . Over the last decade, the effects of various Eg5 inhibitors on the proliferation of cancer cells have been investigated, and the mechanisms of action of several Eg5 inhibitors have been studied [7][8][9][10][11] .…”