Novel indication for cancer therapy: Chk1 inhibition sensitizes tumor cells to antimitotics

• Published in: International journal of cancer Vol. 115; no. 4; pp. 528 - 538
• Main Authors: Xiao, Zhan, Xue, John, Semizarov, Dimitri, Sowin, Thomas J., Rosenberg, Saul H., Zhang, Haiying
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.07.2005; Wiley-Liss
• Subjects: Antineoplastic agents; Antineoplastic Agents - toxicity; Apoptosis - drug effects; Biological and medical sciences; Cdc2; Cell Cycle - drug effects; Cell Division - drug effects; Cell Line, Tumor; Checkpoint Kinase 1; Chk1; Colonic Neoplasms; Enzyme Inhibitors - toxicity; General aspects; HeLa Cells; histone‐H3; Humans; Lung Neoplasms; Medical sciences; metaphase‐to‐anaphase transition; Mitosis - drug effects; mitotic checkpoint; Oligonucleotide Array Sequence Analysis; paclitaxel; Paclitaxel - toxicity; Pharmacology. Drug treatments; Protein Kinases - genetics; Protein Kinases - metabolism; RNA, Small Interfering - pharmacology; securin; Tumors; Antineoplastic agent; Human; mitotic checkpoint; securin; Mitosis; Chkl; Malignant tumor; In vitro; Biological activity; Cdc2; metaphase-to-anaphase transition; Cancerology; Taxane derivatives; Metaphase; Established cell line; Paclitaxel; Genetics; Inhibitor; Sensitization; histone-H3; Antimitotic; Histone H3; Control point
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.20770

Paclitaxel (Taxol) is the most‐prescribed anti‐mitotic agent for a variety of advanced metastatic cancers. It induces mitotic arrest leading to apoptosis through microtubule stabilization. Chk1 is the major cell‐cycle checkpoint kinase mediating S‐ and G2‐arrests in response to various DNA‐damages. Chk1 inhibitor is anticipated and has been demonstrated to potentiate the cytotoxicity of DNA‐damaging agents through abrogation of cell‐cycle checkpoints. Paclitaxel does not, however, induce Chk1 activation, and Chk1 has not been shown to function in mitotic checkpoint. Thus, Chk1 inhibitor is not expected to enhance the toxicity of paclitaxel. Here we show that downregulation of Chk1 sensitizes tumor cells to the toxicity of paclitaxel in cell proliferation assay. Fluorescence microscopy showed that Chk1 knockdown augments mitotic catastrophe and apoptosis in paclitaxel‐treated cancer cells. Further, we elucidated the mechanism of this sensitization. Chk1 inhibition facilitates paclitaxel‐induced M‐phase entry by activation of Cdc2 kinase and accumulation of cyclin B1, the required cofactor for Cdc2 kinase activity. Moreover, Chk1 downregulation inhibits M phase exit through induction of the anaphase inhibitor, securin/PDS1. Collectively, Chk1 elimination sustains a more effective mitotic arrest as demonstrated by the more efficient accumulation of M‐phase marker phospho‐histone H3. We show that Chk1 elimination attenuates the paclitaxel‐induced activation of the anti‐apoptotic p42/p44 (ERK1/2) MAP kinase pathway, additionally contributing to the sensitization. Our results suggest that in addition to its well‐established role as an enforcer of S and G2‐checkpoints in response to genotoxic stress, Chk1 also plays a protective role in mitotic checkpoint to lessen mitotic catastrophe and thereby limits cell‐death. Therefore Chk1 downregulation can not only potentiate DNA‐damaging agents, but also enhance the toxicity of anti‐microtubule agents, which significantly broadens its therapeutic applications. © 2005 Wiley‐Liss, Inc.