Expression levels of p18INK4C modify the cellular efficacy of cyclin-dependent kinase inhibitors via regulation of Mcl-1 expression in tumor cell lines

• Published in: Molecular cancer therapeutics Vol. 8; no. 6; pp. 1460 - 1472
• Main Authors: Eguchi, Tomohiro, Itadani, Hiraku, Shimomura, Toshiyasu, Kawanishi, Nobuhiko, Hirai, Hiroshi, Kotani, Hidehito
• Format: Journal Article
• Language: English
• Published: United States American Association for Cancer Research 01.06.2009
• Subjects: Animals; Apoptosis - drug effects; biomarker; Blotting, Western; CDK; CDK inhibitor; Cell Cycle - drug effects; Cell Line; Cell Line, Tumor; Cell Proliferation - drug effects; Cyclin-Dependent Kinase Inhibitor p18 - genetics; Cyclin-Dependent Kinase Inhibitor p18 - metabolism; Cyclin-Dependent Kinases - antagonists & inhibitors; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Flow Cytometry; Gene Expression Profiling; Gene Expression Regulation, Neoplastic - drug effects; HCT116 Cells; HeLa Cells; Humans; Macrocyclic Compounds - chemistry; Macrocyclic Compounds - pharmacology; microarray; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasms - genetics; Neoplasms - metabolism; Neoplasms - pathology; Oligonucleotide Array Sequence Analysis; p18INK4C; Proto-Oncogene Proteins c-bcl-2 - genetics; Proto-Oncogene Proteins c-bcl-2 - metabolism; Quinoxalines - chemistry; Quinoxalines - pharmacology; Reverse Transcriptase Polymerase Chain Reaction; RNA, Small Interfering - genetics; Spodoptera; Transfection
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-08-1159

Because cyclin-dependent kinases (CDK) play a pivotal role in cancer progression, the development of CDK inhibitors has attracted attention in antitumor therapy. However, despite significant preclinical and clinical developments, CDK inhibition biomarkers for predicting efficacy against certain cancers in individual patients have not been identified. Here, we characterized a macrocyclic quinoxalin-2-one CDK inhibitor, compound A, and identified a gene biomarker for predicting its efficacy. Compound A showed 100-fold selectivity for CDK family proteins over other kinases and inhibited both E2F transcriptional activity and RNA polymerase II phosphorylation. Compound A treatment resulted in decreased proliferation in various tumor cell lines; however, the apoptosis induction rate differed significantly among the cell lines examined, which was consistent with roscovitine. By comparing the mRNA expression profiles of sensitive and resistant cell lines, we found that expression levels of an endogenous CDK inhibitor, p18 INK4C , showed a strong negative correlation to the sensitivity. In fact, p18 status was correlated with the response to CDK inhibitor in an independent data set of multiple myeloma cell lines and silencing p18 expression increased the susceptibility of resistant cells to CDK inhibitors. The analysis of molecular mechanisms revealed that cells with lowered p18 had aberrant CDK6 and E2F activities, which resulted in a transcriptional down-regulation of Mcl-1, a key molecule associated with flavopiridol-induced apoptosis, thereby leading to susceptibility to therapeutic intervention with CDK inhibitors. These results identified a molecular basis for CDK inhibitors to exert an antitumor effect in p18-deficient cancers and support the clinical use of CDK inhibitors. [Mol Cancer Ther 2009;8(6):1460–72]