Hiraku Itadani

Small-molecule inhibition of Wee1 kinase by MK-1775 selectively sensitizes p53-deficient tumor cells to DNA-damaging agents.

Wee1 is a tyrosine kinase that phosphorylates and inactivates CDC2 and is involved in G2 checkpoint signaling. Because p53 is a key regulator in the G1 checkpoint, p53-deficient tumors rely only on the G2 checkpoint after DNA damage. Hence, such tumors are selectively sensitized to DNA-damaging agents by Wee1 inhibition. Here, we report the discovery of a potent and selective small-molecule inhibitor of Wee1 kinase, MK-1775. This compound inhibits phosphorylation of CDC2 at Tyr15 (CDC2Y15), a direct substrate of Wee1 kinase in cells. MK-1775 abrogates G2 DNA damage checkpoint, leading to apoptosis in combination with DNA-damaging chemotherapeutic agents such as gemcitabine, carboplatin, and cisplatin selectively in p53-deficient cells. In vivo, MK-1775 potentiates tumor growth inhibition by these agents, and cotreatment does not significantly increase toxicity. The enhancement of antitumor effect by MK-1775 was well correlated with inhibition of CDC2Y15 phosphorylation in tumor tissue and skin hair follicles. Our data indicate that Wee1 inhibition provides a new approach for treatment of multiple human malignancies. [Mol Cancer Ther 2009;8(11):2992–3000]

Discovery of gene expression-based pharmacodynamic biomarker for a p53 context-specific anti-tumor drug Wee1 inhibitor

BackgroundWee1 is a tyrosine kinase regulating S-G2 cell cycle transition through the inactivating phosphorylation of CDC2. The inhibition of Wee1 kinase by a selective small molecule inhibitor significantly enhances the anti-tumor efficacy of DNA damaging agents, specifically in p53 negative tumors by abrogating S-G2 checkpoints, while normal cells with wild-type p53 are not severely damaged due to the intact function of the G1 checkpoint mediated by p53. Since the measurement of mRNA expression requires a very small amount of biopsy tissue and is highly quantitative, the development of a pharmacodynamic (PD) biomarker leveraging mRNA expression is eagerly anticipated in order to estimate target engagement of anti-cancer agents.ResultsIn order to find the Wee1 inhibition signature, mRNA expression profiling was first performed in both p53 positive and negative cancer cell lines treated with gemcitabine and a Wee1 inhibitor, MK-1775. We next carried out mRNA expression profiling of skin samples derived from xenograft models treated with the Wee1 inhibitor to identify a Wee1 inhibitor-regulatory gene set. Then, the genes that were commonly modulated in both cancer cell lines and rat skin samples were extracted as a Wee1 inhibition signature that could potentially be used as a PD biomarker independent of p53 status. The expression of the Wee1 inhibition signature was found to be regulated in a dose-dependent manner by the Wee1 inhibitor, and was significantly correlated with the inhibition level of a direct substrate, phosphorylated-CDC2. Individual genes in this Wee1 inhibition signature are known to regulate S-G2 cell cycle progression or checkpoints, which is consistent with the mode-of-action of the Wee1 inhibitor.ConclusionWe report here the identification of an mRNA gene signature that was specifically changed by gemcitabine and Wee1 inhibitor combination treatment by molecular profiling. Given the common regulation of expression in both xenograft tumors and animal skin samples, the data suggest that the Wee1 inhibition gene signature might be utilized as a quantitative PD biomarker in both tumors and surrogate tissues, such as skin and hair follicles, in human clinical trials.

Induction and Down-regulation of Sox17 and Its Possible Roles During the Course of Gastrointestinal Tumorigenesis

BACKGROUND & AIMS The activation of Wnt/beta-catenin signaling causes the development of gastric and colon cancers. Sox17 represses Wnt/beta-catenin signaling and is down-regulated in colon cancer. This study was designed to elucidate the role of Sox17 during the course of gastrointestinal tumorigenesis. METHODS Sox17 expression was examined in gastrointestinal tumors of mouse models and humans. The roles of Sox17 in gastric tumorigenesis were examined by cell culture experiments and by construction of Sox17 transgenic mice. RESULTS Sox17 was induced in K19-Wnt1/C2mE mouse gastric tumors and K19-Wnt1 preneoplastic lesions, where Wnt/beta-catenin signaling was activated. Consistently, Wnt activation induced Sox17 expression in gastric cancer cells. In contrast, Sox17 was rarely detected by immunohistochemistry in gastric and colon cancers, whereas strong nuclear staining of Sox17 was found in >70% of benign gastric and intestinal tumors. Treatment with a demethylating agent induced Sox17 expression in gastric cancer cells, thus indicating the down-regulation of Sox17 by methylation. Moreover, transfection of Sox17 in gastric cancer cells suppressed both the Wnt activity and colony formation efficiency. Finally, transgenic expression of Sox17 suppressed dysplastic tumor development in K19-Wnt1/C2mE mouse stomach. CONCLUSIONS Sox17 plays a tumor suppressor role through suppression of Wnt signaling. However, Sox17 is induced by Wnt activation in the early stage of gastrointestinal tumorigenesis, and Sox17 is down-regulated by methylation during malignant progression. It is therefore conceivable that Sox17 protects benign tumors from malignant progression at an early stage of tumorigenesis, and down-regulation of Sox17 contributes to malignant progression through promotion of Wnt activity.

Can Systems Biology Understand Pathway Activation? Gene Expression Signatures as Surrogate Markers for Understanding the Complexity of Pathway Activation

Cancer is thought to be caused by a sequence of multiple genetic and epigenetic alterations which occur in one or more of the genes controlling cell cycle progression and signaling transduction. The complexity of carcinogenic mechanisms leads to heterogeneity in molecular phenotype, pathology, and prognosis of cancers. Genome-wide mutational analysis of cancer genes in individual tumors is the most direct way to elucidate the complex process of disease progression, although such high-throughput sequencing technologies are not yet fully developed. As a surrogate marker for pathway activation analysis, expression profiling using microarrays has been successfully applied for the classification of tumor types, stages of tumor progression, or in some cases, prediction of clinical outcomes. However, the biological implication of those gene expression signatures is often unclear. Systems biological approaches leverage the signature genes as a representation of changes in signaling pathways, instead of interpreting the relevance between each gene and phenotype. This approach, which can be achieved by comparing the gene set or the expression profile with those of reference experiments in which a defined pathway is modulated, will improve our understanding of cancer classification, clinical outcome, and carcinogenesis. In this review, we will discuss recent studies on the development of expression signatures to monitor signaling pathway activities and how these signatures can be used to improve the identification of responders to anticancer drugs.

Mouse gastric tumor models with prostaglandin E2 pathway activation show similar gene expression profiles to intestinal-type human gastric cancer.

BackgroundGastric cancers are generally classified into better differentiated intestinal-type tumor and poorly differentiated diffuse-type one according to Laurens histological categorization. Although induction of prostaglandin E2 pathway promotes gastric tumors in mice in cooperation with deregulated Wnt or BMP signalings, it has remained unresolved whether the gastric tumor mouse models recapitulate either of human gastric cancer type. This study assessed the similarity in expression profiling between gastric tumors of transgenic mice and various tissues of human cancers to find best-fit human tumors for the transgenic mice models.ResultsGlobal expression profiling initially found gastric tumors from COX-2/mPGES-1 (C2mE)-related transgenic mice (K19-C2mE, K19-Wnt1/C2mE, and K19-Nog/C2mE) resembled gastric cancers among the several tissues of human cancers including colon, breast, lung and gastric tumors. Next, classification of the C2mE-related transgenic mice by a gene signature to distinguish human intestinal- and diffuse-type tumors showed C2mE-related transgenic mice were more similar to intestinal-type compared with diffuse one. We finally revealed that induction of Wnt pathway cooperating with the prostaglandin E2 pathway in mice (K19-Wnt1/C2mE mice) further reproduce features of human gastric intestinal-type tumors.ConclusionWe demonstrated that C2mE-related transgenic mice show significant similarity to intestinal-type gastric cancer when analyzed by global expression profiling. These results suggest that the C2mE-related transgenic mice, especially K19-Wnt1/C2mE mice, serve as a best-fit model to study molecular mechanism underlying the tumorigenesis of human gastric intestinal-type cancers.

Induction of Prostaglandin E2 Pathway Promotes Gastric Hamartoma Development with Suppression of Bone Morphogenetic Protein Signaling

Mutations in bone morphogenetic protein (BMP) receptor 1A (BMPR1A) are responsible for a subset of cases of juvenile polyposis (JP) syndrome that develops hamartomatous tumors in the gastrointestinal tract. Mouse genetic studies have shown that suppression of BMP signaling in the intestines causes JP-type hamartoma development. Here, we generated K19-Nog transgenic mice expressing noggin, a BMP antagonist, in gastric epithelium. However, inhibition of BMP signaling did not cause gastric phenotypes. We thus crossed K19-Nog with K19-C2mE mice that expressed Ptgs2 and Ptges in the stomach to generate compound transgenic mice. Expression of Ptgs2 and Ptges results in prostaglandin E(2) (PGE(2)) biosynthesis, and both enzymes are induced in most human gastrointestinal tumors. Importantly, K19-Nog/C2mE compound mice developed gastric hamartomas that were morphologically similar to those found in JP with mucin-containing dilated cysts and inflammatory infiltration. Notably, treatment of K19-Nog/C2mE mice with a cyclooxygenase-2 inhibitor, celecoxib, significantly reduced tumor size with suppression of angiogenesis, suggesting that induction of the PGE(2) pathway together with inhibition of BMP signaling is required for gastric hamartoma development. Moreover, microarray analyses revealed that canonical Wnt signaling target genes were not induced in K19-Nog/C2mE hamartomas, indicating that BMP inhibition and PGE(2) induction lead to gastric hamartoma development independent of the Wnt/beta-catenin pathway. These results, taken together, suggest that the PGE(2) pathway is an effective preventive target against BMP-suppressed gastric hamartomas, as well as for Wnt/beta-catenin-activated adenocarcinomas.

Expression levels of NF-Y target genes changed by CDKN1B correlate with clinical prognosis in multiple cancers.

CDK inhibitors CDKN1B (p27) and CDKN2A (p16) inhibit cell cycle progression. A lower expression level of only p27 has been correlated with poorer prognosis in various types of clinical cancers. The difference may be the result of distinct genes downstream of these CDK inhibitors. Here, we report that NF-Y transcription factor-targeted genes specifically down-regulated by p27 correlate with poor prognosis in multiple tumor types. We performed mRNA expression profiling in HCT116 cells over-expressing either p16 or p27 and identified their regulatory genes. In silico transcription factor prediction indicated that most of the genes specifically down-regulated by p27 are controlled by NF-Y. Under the hypothesis that NF-Y-targeted genes are responsible for poor prognosis, we predicted prognosis in four types of cancer based on genes with the NF-Y motif, and found a significant association between the expression of NF-Y-targeted genes and poor prognosis.

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

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, p18INK4C, 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]

Expression ratio of CCND1 to CDKN2A mRNA predicts RB1 status of cultured cancer cell lines and clinical tumor samples

BackgroundThe retinoblastoma product (RB1) is frequently deregulated in various types of tumors by mutation, deletion, or inactivation through association with viral oncoproteins. The functional loss of RB1 is recognized to be one of the hallmarks that differentiate cancer cells from normal cells. Many researchers are attempting to develop anti-tumor agents that are preferentially effective against RB1-negative tumors. However, to identify patients with RB1-negative cancers, it is imperative to develop predictive biomarkers to classify RB1-positive and -negative tumors.ResultsExpression profiling of 30 cancer cell lines composed of 16 RB1-positive and 14 RB1-negative cancers was performed to find genes that are differentially expressed between the two groups, resulting in the identification of an RB1 signature with 194 genes. Among them, critical RB1 pathway components CDKN2A and CCND1 were included. We found that microarray data of the expression ratio of CCND1 and CDKN2A clearly distinguished the RB1 status of 30 cells lines. Measurement of the CCND1/CDKN2A mRNA expression ratio in additional cell lines by RT-PCR accurately predicted RB1 status (12/12 cells lines). The expression of CCND1/CDKN2A also correlated with RB1 status in xenograft tumors in vivo. Lastly, a CCND1/CDKN2A assay with clinical samples showed that uterine cervical and small cell lung cancers known to have a high prevalence of RB1-decifiency were predicted to be 100% RB1-negative, while uterine endometrial or gastric cancers were predicted to be 5-22% negative. All clinically normal tissues were 100% RB1-positive.ConclusionsWe report here that the CCND1/CDKN2A mRNA expression ratio predicts the RB1 status of cell lines in vitro and xenograft tumors and clinical tumor samples in vivo. Given the high predictive accuracy and quantitative nature of the CCND1/CDKN2A expression assay, the assay could be utilized to stratify patients for anti-tumor agents with preferential effects on either RB1-positive or -negative tumors.

ARHGEF15 overexpression worsens the prognosis in patients with pancreatic ductal adenocarcinoma through enhancing the motility and proliferative activity of the cancer cells

BackgroundPancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive neoplastic diseases, associated with a remarkably poor prognosis. However, the molecular mechanisms underlying the development of PDAC remain elusive. The aim of this study was to identify genes whose expressions are correlated with a poor prognosis in PDAC patients, and to unravel the mechanisms underlying the involvement of these genes in the development of the cancer.MethodsGlobal gene expression profiling was conducted in 39 specimens obtained from Japanese patients with PDAC to identify genes whose expressions were correlated with a shorter overall survival. The effect of gene silencing or overexpression of ARHGEF15 in pancreatic cancer cell lines was examined by introducing siRNAs of ARHGEF15 or the ARHGEF15 expression vector. After assessing the effect of ARHGEF15 deregulation on the Rho-family proteins by pull-down assay, wound healing, transwell and cell viability assays were carried out to investigate the cellular phenotypes caused by the perturbation.ResultsThe global mRNA expression profiling revealed that overexpression of ARHGEF15, a Rho-specific GEF, was significantly associated with a poor prognosis in patients with PDAC. We also found that the depletion of ARHGEF15 by RNA interference in pancreatic cancer cell lines downregulated the activities of molecules of the Rho signaling pathway, including RhoA, Cdc42 and Rac1. Then, we also showed that ARHGEF15 silencing significantly reduced the motility and viability of the cells, while its overexpression resulted in the development of the opposite phenotype in multiple pancreatic cancer cell lines.ConclusionThese data suggest that upregulation of ARHGEF15 contributes to the development of aggressive PDAC by increasing the growth and motility of the pancreatic cancer cells, thereby worsening the prognosis of these patients. Therefore, ARHGEF15 could serve as a novel therapeutic target in patients with PDAC.