title: Cyclin B1 is an efficacy-predicting biomarker for Chk1 inhibitors.
abstract: Chk1 is the major mediator of cell-cycle checkpoints in response to various forms of genotoxic stress. Although it was previously speculated that checkpoint abrogation due to Chk1 inhibition may potentiate the efficacy of DNA-damaging agents through induction of mitotic catastrophe, there has not been direct evidence proving this process. Here, through both molecular marker and morphological analysis, we directly demonstrate that specific downregulation of Chk1 expression by Chk1 siRNA potentiates the cytotoxicities of topoisomerase inhibitors through the induction of premature chromosomal condensation and mitotic catastrophe. More importantly, we discovered that the cellular cyclin B1 level is the major determinant of the potentiation. We show that downregulation of cyclin B1 leads to impairment of the induction of mitotic catastrophe and correspondingly a reduction of the potentiation ability of either Chk1 siRNA or a small molecule Chk1 inhibitor. More significantly, we have extended the study by examining a panel of 10 cancer cell-lines with different tissue origins for their endogenous levels of cyclin B1 and the ability of a Chk1 inhibitor to sensitize the cells to DNA-damaging agents. The cellular levels of cyclin B1 positively correlate with the degrees of potentiation achieved. Of additional interest, we observed that the various colon cancer cell lines in general appear to express higher levels of cyclin B1 and also display higher sensitivity to Chk1 inhibitors, implying that Chk1 inhibitor may be more efficacious in treating colon cancers. In summary, we propose that cyclin B1 is a biomarker predictive of the efficacy of Chk1 inhibitors across different types of cancers. Unlike previously established efficacy-predictive biomarkers that are usually the direct targets of the therapeutic agents, cyclin B1 represents a non-drug-target biomarker that is based on the mechanism of action of the target inhibitor. This finding may be potentially very useful for the stratification of patients for Chk1 inhibitor clinical trials and hence, maximize its chance of success.
authors.affiliation: Cancer Research, Abbott Laboratories, Abbott Park, IL 60064-6101, USA.
authors.forename: Zhan
authors.initials: Z
authors.lastname: Xiao
authors.forename: John
authors.initials: J
authors.lastname: Xue
authors.forename: Wen-Zhen
authors.initials: WZ
authors.lastname: Gu
authors.forename: Mai
authors.initials: M
authors.lastname: Bui
authors.forename: Gaoquan
authors.initials: G
authors.lastname: Li
authors.forename: Zhi-Fu
authors.initials: ZF
authors.lastname: Tao
authors.forename: Nan-Horng
authors.initials: NH
authors.lastname: Lin
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Sowin
authors.forename: Haiying
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015415:Biomarkers / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D000071877:Checkpoint Kinase 1; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D026942:DNA Topoisomerases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D005260:Female; D015316:Genetic Therapy / Q000379:methods*; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D016513:Mice, SCID; D008938:Mitosis / Q000187:drug effects; D009369:Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics / Q000473:pathology / Q000628:therapy*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism*; D013997:Time Factors; D059003:Topoisomerase Inhibitors; D014162:Transfection; D023041:Xenograft Model Antitumor Assays
chemical_list: D015415:Biomarkers; C534699:CCNB1 protein, human; C534700:Ccnb1 protein, mouse; D019926:Cyclin B; D056744:Cyclin B1; D004791:Enzyme Inhibitors; D006657:Histones; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; D059003:Topoisomerase Inhibitors; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; D026942:DNA Topoisomerases