Methylation status of p14ARF and p16INK4a as detected in pancreatic secretions

Association of a Genetic Variant in the Cyclin-Dependent Kinase Inhibitor 2B with Risk of Pancreatic Cancer

BACKGROUND

Pancreatic cancer (PC) is among the most aggressive tumors with a poor prognosis, indicating the need for the identification of a novel prognostic biomarker for risk stratifications. Recent genome-wide association studies have demonstrated common genetic variants in a region on chromosome 9p21 associated with an increased risk of different malignancies.

METHODS

In the present study, we explore the possible relationship between genetic variant, rs10811661, and gene expression of CDKN2B in 75 pancreatic cancer patients, and 188 healthy individuals. DNAs were extracted and genotyping and gene expression were performed by TaqMan real-time PCR and RT-PCR, respectively. Logistic regression was used to assess the association between risk and genotypes, while the significant prognostic variables in the univariate analysis were included in multivariate analyses.

RESULTS

The patients with PDAC had a higher frequency of a TT genotype for rs10811661 than the control group. Also, PDAC patients with dominant genetic model, (TT + TC), was associated with increased risk of developing PDAC (OR= 14.71, 95% CI [1.96-110.35], p= 0.009). Moreover, patients with CC genotype had a higher expression of CDKN2B, in comparison with TT genotype.

CONCLUSION

Our findings demonstrated that CDKN2A/B was associated with the risk of developing PDAC, supporting further investigations in the larger and multicenter setting to validate the potential value of this gene as an emerging marker for PDAC.

Oncogenomic Changes in Pancreatic Cancer and Their Detection in Stool

Pancreatic cancer (PC) is an aggressive malignancy with a dismal prognosis. To improve patient survival, the development of screening methods for early diagnosis is pivotal. Oncogenomic alterations present in tumor tissue are a suitable target for non-invasive screening efforts, as they can be detected in tumor-derived cells, cell-free nucleic acids, and extracellular vesicles, which are present in several body fluids. Since stool is an easily accessible source, which enables convenient and cost-effective sampling, it could be utilized for the screening of these traces. Herein, we explore the various oncogenomic changes that have been detected in PC tissue, such as chromosomal aberrations, mutations in driver genes, epigenetic alterations, and differentially expressed non-coding RNA. In addition, we briefly look into the role of altered gut microbiota in PC and their possible associations with oncogenomic changes. We also review the findings of genomic alterations in stool of PC patients, and the potentials and challenges of their future use for the development of stool screening tools, including the possible combination of genomic and microbiota markers.

An overview of genetic mutations and epigenetic signatures in the course of pancreatic cancer progression

Pancreatic cancer (PC) is assumed to be an intimidating and deadly malignancy due to being the leading cause of cancer-led mortality, predominantly affecting males of older age. The overall (5 years) survival rate of PC is less than 9% and is anticipated to be aggravated in the future due to the lack of molecular acquaintance and diagnostic tools for its early detection. Multiple factors are involved in the course of PC development, including genetics, cigarette smoking, alcohol, family history, and aberrant epigenetic signatures of the epigenome. In this review, we will mainly focus on the genetic mutations and epigenetic signature of PC. Multiple tumor suppressor and oncogene mutations are involved in PC initiation, including K-RAS, p53, CDKN2A, and SMAD4. The mutational frequency of these genes ranges from 50 to 98% in PC. The nature of mutation diagnosis is mostly homozygous deletion, point mutation, and aberrant methylation. In addition to genetic modification, epigenetic alterations particularly aberrant hypermethylation and hypomethylation also predispose patients to PC. Hypermethylation is mostly involved in the downregulation of tumor suppressor genes and leads to PC, while multiple genes also represent a hypomethylation status in PC. Several renewable drugs and detection tools have been developed to cope with this aggressive malady, but all are futile, and surgical resection remains the only choice for prolonged survival if diagnosed before metastasis. However, the available therapeutic development is insufficient to cure PC. Therefore, novel approaches are a prerequisite to elucidating the genetic and epigenetic mechanisms underlying PC progression for healthier lifelong survival.

Regulatory Network of ARF in Cancer Development

ARF is a tumor suppressor protein that has a pivotal role in the prevention of cancer development through regulating cell proliferation, senescence, and apoptosis. As a factor that induces senescence, the role of ARF as a tumor suppressor is closely linked to the p53-MDM2 axis, which is a key process that restrains tumor formation. Thus, many cancer cells either lack a functional ARF or p53, which enables them to evade cell oncogenic stress-mediated cycle arrest, senescence, or apoptosis. In particular, the ARF gene is a frequent target of genetic and epigenetic alterations including promoter hyper-methylation or gene deletion. However, as many cancer cells still express ARF, pathways that negatively modulate transcriptional or post-translational regulation of ARF could be potentially important means for cancer cells to induce cellular proliferation. These recent findings of regulators affecting ARF protein stability along with its low levels in numerous human cancers indicate the significance of an ARF post-translational mechanism in cancers. Novel findings of regulators stimulating or suppressing ARF function would provide new therapeutic targets to manage cancer- and senescence-related diseases. In this review, we present the current knowledge on the regulation and alterations of ARF expression in human cancers, and indicate the importance of regulators of ARF as a prognostic marker and in potential therapeutic strategies.

Clinicopathological Significance of CDKN2A Promoter Hypermethylation Frequency with Pancreatic Cancer

The prognosis of pancreatic cancer patients is very poor, with a 5-year survival of less than 6%. Previous studies demonstrated that the loss of function of CDKN2A is mainly caused by the hypermethylation of CDKN2A gene promoter; however, whether or not it is associated with the incidence of pancreatic cancer still remains unclear. In this study, we systematically reviewed the association between CDKN2A promoter methylation and pancreatic cancer using meta-analysis methods. The pooled data were analyzed by Review Manager 5.2. Fourteen studies eligible studies, including 418 pancreatic cancer, 155 pancreatic intraepithelial neoplasia (PanINs) and 45 chronic pancreatitis (CP) patients were analyzed. We observed that the frequency of CDKN2A methylation was significantly higher in pancreatic cancer patients than in normal healthy controls, the pooled OR = 17.19, 95% CI = 8.72–33.86, P < 0.00001. The frequency of CDKN2A methylation was also significantly higher in PanINs patients than that in normal individual controls, OR = 12.35, 95% CI = 1.70–89.89, P = 0.01. In addition, CDKN2A methylation was associated with worse survival in pancreatic cancer, HR = 4.46, 95% CI = 1.37–14.53, P = 0.01. The results strongly suggest that CDKN2A methylation is correlated with an increased risk of pancreatic cancer. CDKN2A methylation plays a critical role in pancreatic carcinogenesis and may serve as a prognostic marker.

High-frequency aberrantly methylated targets in pancreatic adenocarcinoma identified via global DNA methylation analysis using methylCap-seq

BACKGROUND

Extensive reprogramming and dysregulation of DNA methylation is an important characteristic of pancreatic cancer (PC). Our study aimed to characterize the genomic methylation patterns in various genomic contexts of PC. The methyl capture sequencing (methylCap-seq) method was used to map differently methylated regions (DMRs) in pooled samples from ten PC tissues and ten adjacent non-tumor (PN) tissues. A selection of DMRs was validated in an independent set of PC and PN samples using methylation-specific PCR (MSP), bisulfite sequencing PCR (BSP), and methylation sensitive restriction enzyme-based qPCR (MSRE-qPCR). The mRNA and expressed sequence tag (EST) expression of the corresponding genes was investigated using RT-qPCR.

RESULTS

A total of 1,131 PC-specific and 727 PN-specific hypermethylated DMRs were identified in association with CpG islands (CGIs), including gene-associated CGIs and orphan CGIs; 2,955 PC-specific and 2,386 PN-specific hypermethylated DMRs were associated with gene promoters, including promoters containing or lacking CGIs. Moreover, 1,744 PC-specific and 1,488 PN-specific hypermethylated DMRs were found to be associated with CGIs or CGI shores. These results suggested that aberrant hypermethylation in PC typically occurs in regions surrounding the transcription start site (TSS). The BSP, MSP, MSRE-qPCR, and RT-qPCR data indicated that the aberrant DNA methylation in PC tissue and in PC cell lines was associated with gene (or corresponding EST) expression.

CONCLUSIONS

Our study characterized the genome-wide DNA methylation patterns in PC and identified DMRs that were distributed among various genomic contexts that might influence the expression of corresponding genes or transcripts to promote PC. These DMRs might serve as diagnostic biomarkers or therapeutic targets for PC.

Molecular markers in pancreatic cancer diagnosis

Pancreatic ductal adenocarcinoma (PDAC) represents a fatal neoplasia with a high mortality rate. Effective early detection methods are needed since this is the best way to cure this disease. During the last several years, many investigations focused on determining relevant biomarkers that may be present during early stages of pancreatic tumor development. Although several biomarkers have been proposed for pancreatic cancer detection, the clinical applicability has been confusing. Currently, although CA19-9 is one test used, the sensitivity and specificity for the disease are less than optimal. Here, we review several new potential serum, plasma and stool markers that are currently under evaluation. Although these have not been sufficiently validated for routine clinical use, these markers could prove valuable with further investigations. We keep the hope that a combination of some of these novel biomarkers can be a useful tool for early PDAC diagnosis before image techniques and/or patient's symptoms reveal disease in an incurable state.

Molecular biology of adenocarcinoma of the pancreatic duct, current state and future therapeutic avenues

Pancreatic adenocarcinoma is a lethal disease; currently surgery offers five years survival of less than 5%. Any improvement in the outcome is likely to be through novel therapeutic agents that will target the genetic machinery of the cell. Knowledge of genetic alterations in the process of carcinogenesis is expanding rapidly, the targeted therapy, however, is progressing slowly. Pancreatic adenocarcinoma displays a variety of molecular changes that evolve exponentially with time and lend the cancer cells their ability not only to survive, but also to invade the surrounding tissues and metastasise to distant sites. These changes involve genetic alteration in oncogenes, cancer suppressor genes, changes in cell cycle, pathways of apoptosis and also changes in epithelial to mesenchymal transition. Monotherapeutic targeted agents seem(s) to have limited effect on cancer cells. The near future is likely to show an improvement in the treatment outcome, which is likely to be a result of the combination of targeted agents with surgery and chemotherapy.

Reduced levels of p15INK4b, p16INK4a, p21cip1 and p27kip1 in pancreatic carcinoma

Pancreatic carcinoma is one of the leading causes of cancer mortality worldwide, although the molecular mechanisms of this disease are poorly understood. The aim of this study was to examine the expression of cyclin-dependent kinase inhibitors (CDKIs) and the epigenetic modifications in the promoters of these genes. We also evaluated the correlation between the methylation status of CDKI genes and smoking habit in clinical pancreatic carcinoma specimens. Western blotting and real-time PCR were performed to assess CDKI expression. Methylation-specific PCR was carried out to examine the methylation status of the promoters of CDKI genes. In this study, we revealed that reduced levels of the CDKI proteins, p15INK4b, p16INK4a, p21cip1 and p27kip1, are a prominent feature of pancreatic carcinoma patients. The DNA hypermethylation of the promoter was observed in 40% (2 of 5) of the p15INK4b genes, 60% (3 of 5) of the p16INK4a genes and 60% of the p21cip1 genes, which markedly correlated with their decreased mRNA expression. No hypermethylation was detected in the p27kip1 gene promoter in 5 pancreatic carcinoma patients with markedly decreased expression of p27kip1 mRNA, suggesting an alternative mechanism of p27kip in these patients. In this study, patients with a smoking habit displayed methylation of 2 CDKI genes in their pancreatic carcinoma specimens. We concluded that epigenetic modification via hypermethylation represents a critical mechanism for the inactivation of CDKI genes in pancreatic carcinoma.

Advances in biomarker research for pancreatic cancer

Pancreatic cancer (PC) is a leading cause of cancer related deaths in United States. The lack of early symptoms results in latestage detection and a high mortality rate. Currently, the only potentially curative approach for PC is surgical resection, which is often unsuccessful because the invasive and metastatic nature of the tumor masses makes their complete removal difficult. Consequently, patients suffer relapses from remaining cancer stem cells or drug resistance that eventually lead to death. To improve the survival rate, the early detection of PC is critical. Current biomarker research in PC indicates that a serum carbohydrate antigen, CA 19-9, is the only available biomarker with approximately 90% specificity to PC. However, the efficacy of CA 19-9 for assessing prognosis and monitoring patients with PC remains contentious. Thus, advances in technology and the detection of new biomarkers with high specificity to PC are needed to reduce the mortality rate of pancreatic cancer.

Molecular pathogenesis of pancreatic cancer and clinical perspectives

Pancreatic cancer remains stubbornly resistant to many key cytotoxic chemotherapeutic agents and novel targeted therapies. The molecular heterogeneity of this cancer may account for therapy failures to date, although our growing arsenal of novel targeted agents could translate into patient survival. The main objectives of this review are to elucidate histological subtypes of pancreatic neoplasms that exhibit the characteristic of a gradual process of differentiation from benign entities to malignant ones. In addition, important genes, molecular abnormalities, and significant pathways of pancreatic cancer are analyzed and a potential clinical interpretation is presented (p16/cdkn2a, k-ras mutations, smad-4/tgf-/stat3, stk-11, braf, brca-2, neurotensin, mucs proteins, palb2, mitochondrial mutations, DNA mismatch repair genes, methylation, microrna expression, epithelial-to-mesenchymal transition, egfr mutations, the pi3k-akt-mtor pathway, the vegf pathway, heat shock proteins, cxcr4, the cox pathway, the src pathway, the hedgehog pathway, pancreatic stellate cells, a progression model, and molecular events in uncommon pancreatic tumors). Finally, future therapeutic directions are elucidated.

Genetic and epigenetic alterations in pancreatic carcinogenesis

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers worldwide. Despite significant progresses in the last decades, the origin of this cancer remains unclear and no efficient therapy exists. PDAC does not arise de novo: three remarkable different types of pancreatic lesions can evolve towards pancreatic cancer. These precursor lesions include: Pancreatic intraepithelial neoplasia (PanIN) that are microscopic lesions of the pancreas, Intraductal Papillary Mucinous Neoplasms (IPMN) and Mucinous Cystic Neoplasms (MCN) that are both macroscopic lesions. However, the cellular origin of these lesions is still a matter of debate.

Classically, neoplasm initiation or progression is driven by several genetic and epigenetic alterations. The aim of this review is to assemble the current information on genetic mutations and epigenetic disorders that affect genes during pancreatic carcinogenesis. We will further discuss the interest of the genetic and epigenetic alterations for the diagnosis and prognosis of PDAC. Large genetic alterations (chromosomal deletion/amplification) and single point mutations are well described for carcinogenesis inducers. Mutations classically occur within key regions of the genome. Consequences are various and include activation of mitogenic pathways or silencing of apoptotic processes. Alterations of K-RAS, P16 and DPC4 genes are frequently observed in PDAC samples and have been described to arise gradually during carcinogenesis. DNA methylation is an epigenetic process involved in imprinting and X chromosome inactivation. Alteration of DNA methylation patterns leads to deregulation of gene expression, in the absence of mutation. Both genetic and epigenetic events influence genes and non-coding RNA expression, with dramatic effects on proliferation, survival and invasion. Besides improvement in our fundamental understanding of PDAC development, highlighting the molecular alterations that occur in pancreatic carcinogenesis could provide new clinical tools for early diagnosis of PDAC and the molecular basis for the development of new effective therapies.

Correlation between T-cadherin gene expression and aberrant methylation of T-cadherin promoter in human colon carcinoma cells

Previous researches showed T-cadherin (CDH13) expression was downregulated in colon cancer tissues and was associated with increase of invasive and metastatic potential. This research was to observe the mechanisms responsible for inactivation of T-cadherin gene in colon carcinoma; we investigated the methylation status around the 5' promoter region of T-cadherin gene of Hct116 colon cancer cell line by methylation-specific polymerase chain reaction (MSP), also detected the expression change of T-cadherin mRNA and protein in Hct116 cell line after 5-Aza-CdR treatment by reverse transcriptase polymerase chain reaction and Western blotting, and compared the T-cadherin methylation status with T-cadherin mRNA and protein expression. We found that hypermethylation of T-cadherin was involved in Hct116 cell line, while T-cadherin mRNA and protein expression was almost lost or downregulated in Hct116 cell line. Therefore, methylation of the T-cadherin promoter region was correlated with the loss or downregulation of T-cadherin mRNA and protein expression in Hct116 colon cancer cell line. Treatment of T-cadherin-negative carcinoma cells with the demethylating agent, 5-aza-2'-deoxycytidine, induced re-expression of this gene. Our findings demonstrate that 5' CpG island methylation is common in colon carcinoma and may play an important role in the inaction of T-cadherin. Our results also suggest that demethylation of the T-cadherin gene may be a potential therapeutic strategy for colon carcinoma.

Methylation profile of circulating plasma DNA in patients with pancreatic cancer

BACKGROUND AND OBJECTIVES

Detection of pancreatic cancer by blood-based test may improve outcomes. We sought to establish the feasibility of a blood-based detection of pancreatic cancer through multiplexed array-mediated analysis of DNA methylation.

METHODS

Methylation was assessed in each plasma sample using a panel of 56 frequently methylated genes. Methylation profiles in patients with ductal cell adenocarcinoma of the pancreas (n = 30) and healthy gender and age-matched controls (n = 30) were compared. Methylation was determined as described previously; a composite biomarker was developed for classification of cancer and normal samples. Sensitivity and specificity of the biomarker were estimated using 25 rounds of fivefold cross-validation.

RESULTS

Five promoters were consistently selected for the classifier during cross-validation and comprised the final composite biomarker Five-fold cross-validation results indicate 76% sensitivity and 59% specificity of the biomarker, which included promoters of CCND2, SOCS1, THBS1, PLAU, and VHL.

CONCLUSION

Differential methylation profiling of plasma DNA can detect ductal adenocarcinoma of the pancreas with significant accuracy and should be explored further. While additional improvement of biomarkers is necessary, the blood-based biomarker may be already useful as a first-line detection tool.

Epigenetics and epigenetic alterations in pancreatic cancer

Pancreatic cancer remains a major therapeutic challenge. In 2008, there will be approximately 37,680 new cases and 34,290 deaths attributable to pancreatic cancer in the United States (U.S.), making it the fourth leading cause of cancer-related death. Recent comprehensive pancreatic cancer genome project found that pancreatic adenocarcinomas harbored 63 intragenic mutations or amplifications/homozygous deletions and these alterations clustered in 12 signaling pathways. In addition to widespread genetic alterations, it is now apparent that epigenetic mechanisms are also central to the evolution and progression of human cancers. Since epigenetic silencing processes are mitotically heritable, they can drive neoplastic progression and undergo the same selective pressure as genetic alterations. This review will describe recent developments in cancer epigenetics and their importance in our understanding of pancreatic adenocarcinomas.

Genetics and prevention of pancreatic cancer

BACKGROUND

Pancreatic cancer is an aggressive disease with a poor prognosis. Hereditary factors have been reported in up to 10% of cases of pancreatic cancer. The clinical characteristics and genetic abnormalities have been identified for a proportion of this high-risk group, and the development of preventive strategies for these individuals is now a primary goal of cancer clinicians.

METHODS

A review of the current literature regarding the genetics, screening, and prevention of pancreatic cancer and its precursor lesions was undertaken.

RESULTS

Risk factors for pancreatic cancer include smoking, chronic pancreatitis, and a genetic predisposition. The role of diabetes or a diet high in fat or meat remains unclear. The genetic mutations that accompany pancreatic cancer appear to occur in a temporal sequence, beginning in the earliest of precursor lesions. These mutations are detectable in pancreatic juice and, in conjunction with imaging, form the basis of screening programs for high-risk individuals. Not all precursor lesions will undergo malignant transformation, and testing is currently limited in its ability to determine which lesions will undergo transformation.

CONCLUSIONS

Avoiding tobacco smoking and minimizing risk factors associated with chronic pancreatitis are recommended to reduce the risk of pancreatic cancer. Individuals with a high-risk genetic background require counseling, genetic testing if appropriate (BRCA2 mutation or p16INK4A inactivity) and secondary screening for pancreatic cancer in specialist centers. Risk stratification will improve as more genetic abnormalities causing pancreatic cancer are defined.

Evaluation of clinical relevance of examining K-ras, p16 and p53 mutations along with allelic losses at 9p and 18q in EUS-guided fine needle aspiration samples of patients with chronic pancreatitis and pancreatic cancer

AIM: To establish an optimum combination of molecular markers resulting in best overall diagnostic sensitivity and specificity for evaluation of suspicious pancreatic mass.

METHODS: Endoscopic ultrasound (EUS)-guided fine needle aspiration cytology (FNA) was performed on 101 consecutive patients (63 males, 38 females, 60 ± 12 years; 81 with subsequently diagnosed pancreatic cancer, 20 with chronic pancreatitis) with focal pancreatic mass. Samples were evaluated on-site by an experienced cytopathologist. DNA was extracted from Giemsa stained cells selected by laser microdissection and the presence of K-ras, p53 and p16 somatic mutations was tested by cycling-gradient capillary electrophoresis (CGCE) and single-strand conformation polymorphism (SSCP) techniques. In addition, allelic losses of tumor suppressor genes p16 (INK4, CDKN2A) and DPC4 (MADH4, SMAD4) were detected by monitoring the loss of heterozygosity (LOH) at 9p and 18q, respectively.

RESULTS: Sensitivity and specificity of EUS-guided FNA were 75% and 85%, positive and negative predictive value reached 100%. The remaining 26% samples were assigned as inconclusive. Testing of molecular markers revealed sensitivity and specificity of 70% and 100% for K-ras mutations (P < 0.001), 24% and 90% for p53 mutations (NS), 13% and 100% for p16 mutations (NS), 85% and 64% for allelic losses at 9p (P < 0.001) and 78% and 57% for allelic losses at 18q (P < 0.05). When tests for different molecular markers were combined, the best results were obtained with K-ras + LOH at 9p (92% and 64%, P < 0.001), K-ras + LOH at 18q (92% and 57%, P < 0.001), and K-ras + LOH 9q + LOH 18q (96% and 43%, P < 0.001). When the molecular markers were used as complements to FNA cytology to evaluate inconclusive samples only, the overall sensitivity of cancer detection was 100% in all patients enrolled in the study.

CONCLUSION: EUS-guided FNA cytology combined with screening of K-ras mutations and allelic losses of tumor suppressors p16 and DPC4 represents a very sensitive approach in screening for pancreatic malignancy. Molecular markers may find its use particularly in cases where FNA cytology has been inconclusive.

Genetic and epigenetic biomarkers in cancer : improving diagnosis, risk assessment, and disease stratification

Gene expression patterns change during the initiation, progression, and development of cancer, as a result of both genetic and epigenetic mechanisms. Genetic changes arise due to irreversible changes in the nucleotide sequence, whereas epigenetic changes occur due to changes in chromatin conformation, histone acetylation, and methylation of the CpG islands located primarily in the promoter region of a gene. Both genetic and epigenetic markers can potentially be utilized to identify different stages of tumor development. Several such markers exhibit high sensitivity and specificity for different tumor types and can be assayed in biofluids and other specimens collected by noninvasive technologies. In spite of the availability of large numbers of diagnostic markers, only a few have been clinically validated so far. The current status and the challenges in the field of genetic and epigenetic markers in cancer diagnosis, risk assessment, and disease stratification are discussed.

Peutz-Jeghers syndrome and screening for pancreatic cancer

BACKGROUND

Cancer risk, including pancreatic, is high in those with Peutz-Jeghers syndrome (PJS). It has been suggested that such patients should undergo screening for pancreatic cancer.

METHODS

The risk of pancreatic cancer in PJS, pancreatic screening and potential screening strategies were reviewed. Cost-effectiveness was assessed according to American Gastroenterology Association guidelines and a risk stratification model proposed by the European Registry of Hereditary Pancreatitis and Familial Pancreatic Cancer.

RESULTS

The risk of pancreatic cancer is increased in PJS but screening would cost over US 35,000 dollars per life saved. Risk stratification reduces cost by 100,000 dollars and costs fall to 50,000 dollars per life saved if deaths from other forms of cancer are avoided.

CONCLUSION

Screening should be performed only on a research basis to evaluate the benefit and cost-effectiveness in high-risk groups.

The role of epigenetic alterations in pancreatic cancer

The past several years have witnessed an explosive increase in our knowledge about epigenetic features in human cancers. It has become apparent that pancreatic cancer is an epigenetic disease, as it is a genetic disease, characterized by widespread and profound alterations in DNA methylation. The introduction of genome-wide screening techniques has accelerated the discovery of a growing list of genes with abnormal methylation patterns in pancreatic cancer, and some of these epigenetic events play a role in the neoplastic process. The detection and quantification of DNA methylation alterations in pancreatic juice is likely a promising tool for the diagnosis of pancreatic cancer. The potential reversibility of epigenetic changes in genes involved in tumor progression makes them attractive therapeutic targets, but the efficacy of epigenetic therapies in pancreatic cancer, such as the use of DNA methylation inhibitors, remains undetermined. In this review, we briefly summarize recent research findings in the field of pancreatic cancer epigenetics and discuss their biological and clinical implications.

Preproenkephalin hypermethylation in the pure pancreatic juice compared with p53 mutation in the diagnosis of pancreatic carcinoma

BACKGROUND

Aberrant methylation of CpG islands is a common mechanism for the dysregulation of tumor suppressor genes in a variety of human malignancies. Preproenkephalin ppENK) hypermethylation is recognized in 90% of pancreatic carcinoma (PCa) tissues, but not in normal pancreas. We analyzed ppENK hypermethylation in pure pancreatic juice (PPJ) in patients with PCa, intraductal papillary mucinous neoplasms (IPMN), and chronic pancreatitis (CP), and elucidated its usefulness as a marker in the diagnosis of PCa compared with p53 mutation.

METHODS

PPJ was collected endoscopically from 28 patients with PCa, 15 patients with IPMN, and 20 patients with CP. DNA was extracted from the supernatant and the sediment of PPJ. Methylation-specific polymerase chain reaction was performed for hypermethylation analysis of ppENK. In addition, single-strand conformation polymorphism and direct sequencing were performed simultaneously to identify p53 mutations.

RESULTS

The incidence of ppENK hypermethylation in the supernatant and/or the sediment of PPJ was 50% (14 of 28) in patients with PCa. In contrast, the incidence of ppENK hypermethylation was 26.7% (4 of 15) in patients with IPMN, and 5% (1 of 20) in patients with CP (P < 0.002). The incidence of p53 mutations in the PPJ was 42.9% (12 of 28) in patients with PCa and 0% (0 of 20) in patients with CP. Furthermore, the incidence of ppENK hypermethylation and/or p53 mutations in the PPJ was enhanced to 67.9% (19 of 28) in patients with PCa in the combination assay.

CONCLUSIONS

These results suggest that ppENK hypermethylation in PPJ is specific for cancer, and the combination assay with p53 enhances the genetic diagnosis of PCa.

Hepatolithiasis and intrahepatic cholangiocarcinoma: carcinogenesis based on molecular mechanisms

Hepatolithiasis is more frequently seen in East Asian countries than in Western countries, and it is well known to represent a high-risk state for intrahepatic cholangiocarcinoma. Intrahepatic cholangiocarcinoma is an aggressive tumor that shows a dismal outcome even after resection. Cancer results from multistep carcinogenesis; however, the precise molecular mechanisms involved in the genetic alterations in cancer remain unknown. The accumulation of alterations in cancer-related genes leads to disruptions in cell-cycle regulation and also to continuous cell proliferation. The present review provides an overview of cancer-related genes in intrahepatic cholangiocarcinogenesis arising in hepatolithiasis. Further study of molecular mechanisms in hepatolithiasis-related intrahepatic cholangiocarcinoma, and the delineation of the influence of the genes involved should lead to our understanding of cholangiocarcinogenesis.

The inherited genetics of pancreatic cancer and prospects for secondary screening

It is estimated that pancreatic cancer has a familial component in approximately 5-10% of cases. Some of these cases are part of a defined cancer syndrome with a known gene mutation but in the remaining the causative gene remains unknown. In recent years, a better understanding of the molecular events that occur in the progression model of pancreatic cancer has lead to the development of secondary screening programmes with the aim of identifying early precursor lesions or pre-invasive cancer at a stage amenable to curative resection. High-risk groups who have an inherited predisposition for pancreatic cancer form the ideal group to study in developing a robust screening programme. Multimodality screening using computed tomography and endoluminal ultrasound in combination with molecular analysis of pancreatic juice are proving promising as diagnostics tools or at least serving as predictors of risk over a defined period.

Pancreatic cancer epidemiology

Carcinoma of the exocrine pancreas remains a challenging disease mainly due to advanced stage diagnosis, the early systemic dissemination, aggressive local tumor progression, and subsequent short patient survival. Thus, assessment of incidence markers instead of prevalence indicators is recommended because the time between diagnosis and death is usually very short. Investigations to date have led to the discovery of many rare genes and environmental factors that contribute to pancreatic cancer. However, common genes involved in genetic polymorphisms, and specific risk factors have not been identified. Furthermore, the role of gene-environment interactions on the tumorogenesis and progression of pancreatic cancer need to be further investigated. Given current therapeutic modalities, only early detection of cancer of the pancreas, followed by surgical resection, offers the possibility of lengthening survival time.

Pharmacologic inhibition of RAF-->MEK-->ERK signaling elicits pancreatic cancer cell cycle arrest through induced expression of p27Kip1

Expression of mutationally activated RAS is a feature common to the vast majority of human pancreatic adenocarcinomas. RAS elicits its effects through numerous signaling pathways including the RAF-->mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase [MEK]-->ERK MAP kinase pathway. To assess the role of this pathway in regulating cell proliferation, we tested the effects of pharmacologic inhibition of MEK on human pancreatic cancer cell lines. In eight cell lines tested, MEK inhibition led to a cessation of cell proliferation accompanied by G0-G1 cell cycle arrest. Concomitant with cell cycle arrest, we observed induced expression of p27Kip1, inhibition of cyclin/cyclin-dependent kinase 2 (cdk2) activity, accumulation of hypophosphorylated pRb, and inhibition of E2F activity. Using both antisense and RNA interference techniques, we assessed the role of p27Kip1 in the observed effects of MEK inhibition on pancreatic cancer cell proliferation. Inhibition of p27Kip1 expression in Mia PaCa-2 cells restored the activity of cyclin/cdk2, phosphorylation of pRb, and E2F activity and partially relieved the effects of U0126 on pancreatic cancer cell cycle arrest. Consistent with the effects of p27Kip1 on cyclin/cdk2 activity, inhibition of CDK2 expression by RNA interference also led to G0-G1 cell cycle arrest. These data suggest that the expression of p27Kip1 is downstream of the RAF-->MEK-->ERK pathway and that the regulated expression of this protein plays an important role in promoting the proliferation of pancreatic cancer cells. Moreover, these data suggest that pharmacologic inhibition of the RAF-->MEK-->ERK signaling pathway alone might tend to have a cytostatic, as opposed to a cytotoxic, effect on pancreatic cancer cells.

Alterations of tumor suppressor gene p16INK4a in pancreatic ductal carcinoma

BACKGROUND

Cell cycle inhibitor and tumor suppressor gene p16/MTS-1 has been reported to be altered in a variety of human tumors. The purpose of the study was to evaluate primary pancreatic ductal adenocarcinomas for potentially inactivating p16 alterations.

METHODS

We investigated the status of p16 gene by polymerase chain reaction (PCR), nonradioisotopic single strand conformation polymorphism (SSCP), DNA sequencing and hypermethylation analysis in 25 primary resected ductal adenocarcinomas. In addition, we investigated p16 protein expression in these cases by immunohistochemistry (IHC) using a monoclonal antibody clone (MS-887-PO).

RESULTS

Out of the 25 samples analyzed and compared to normal pancreatic control tissues, the overall frequency of p16 alterations was 80% (20/25). Aberrant promoter methylation was the most common mechanism of gene inactivation present in 52% (13/25) cases, followed by coding sequence mutations in 16% (4/25) cases and presumably homozygous deletion in 12% (3/25) cases. These genetic alterations correlated well with p16 protein expression as complete loss of p16 protein was found in 18 of 25 tumors (72%).

CONCLUSION

These findings confirm that loss of p16 function could be involved in pancreatic cancer and may explain at least in part the aggressive behaviour of this tumor type.

Molecular analysis to detect pancreatic ductal adenocarcinoma in high-risk groups

BACKGROUND & AIMS

Screening of high-risk groups for pancreatic cancer has not been adopted because of concerns regarding specificity and sensitivity. Suitability of a combination of 3 novel molecular screening techniques was investigated.

METHODS

Pancreatic juice was extracted from 146 patients with pancreatic ductal adenocarcinoma, chronic pancreatitis, or biliary tract stones. p53 mutations were analyzed by using a modified yeast functional assay, K-ras status was analyzed using mutation-specific real-time PCR and the proportion of p16(INK4a) promoter methylation was estimated using comparative methylation-specific real-time PCR.

RESULTS

p53 mutations were detected in 20 of 48 (42%) cancer cases, none of 49 controls, and 2 of 49 (4%) patients with pancreatitis. K-ras mutations were detected in 31 of 57 (54%) cancer patients, 13 of 61 (21%) controls, and 23 of 67 (34%) patients with pancreatitis. Twenty-six of 42 (62%) cancer patients had promoter methylation levels > 12%, compared with 3 of 24 (13%) controls, and 2 of 26 (8%) with pancreatitis. Mutations in p53 or high-level p16(INK4a) promoter methylation occurred in 29 of 36 (80%) patients with cancer, 3 of 24 (13%) controls, and 3 of 22 (13%) with pancreatitis. Three patients (8%) of 36 with cancer; 14 of 24 (58%) controls, and 13 of 22 (59%) patients with pancreatitis had no marker. The gallstone disease patients had a high rate of positive K-ras mutations, possibly reflecting the fact that they were not disease free.

CONCLUSIONS

Combination molecular analysis increased the discrimination between patients with malignant and benign disease. This level of discrimination would allow patients in high-risk groups to be stratified from negligible risk to over 50% probability of an early cancer.

Frequent promoter methylation and gene silencing of CDH13 in pancreatic cancer

It has recently been reported that CDH13 expression is silenced by aberrant methylation of the promoter region in several cancers. We examined the methylation status of the CDH13 gene in pancreatic cancer using methylation-specific PCR (MSP), and detected aberrant methylation of CDH13 in all 6 pancreatic cancer cell lines examined. To confirm the status of the CDH13 gene in relation to the methylation pattern, we next examined CDH13 expression in these cell lines using reverse transcription (RT)-PCR. As expected, no CDH13 expression was detected in any of the 6 pancreatic cancer cell lines. Moreover, 5-aza-2'-deoxycytidine (5-aza-dC) treatment of CDH13-methylated cell lines led to restoration of CDH13 expression. Among primary pancreatic cancers, 19 of 33 (58%) cases exhibited CDH13 methylation, while no cases exhibited it in corresponding normal pancreatic tissues. CDH13 methylation was detected even in relatively early pancreatic cancers, such as stage II cancers and cancers less than 2 cm in diameter. Our results suggest that the aberrant methylation of CDH13 occurs frequently in pancreatic cancer, even at a relatively early stage.

Molecular analysis of pancreatic juice: a helpful tool to differentiate benign and malignant pancreatic tumors?

Chronic pancreatitis is an important predisposing condition leading to pancreatic carcinoma. As the differential diagnosis between these diseases may be difficult in 1 patient, the detection of specific tumor markers in pancreatic juice is an attractive diagnostic tool. Many studies have investigated tumor-mediated molecular alterations of the pancreatic juice, as k-ras mutations, telomerase reactivation, or promoter methylation of the tumor-suppressor genes p16INK4a and p14ARF. In this overview, we summarize these studies and conclude that molecular analysis of pancreatic juice is not useful for everyday care today. The high specificity of molecular alterations in pancreatic cancer in some pilot studies is waiting to be reproduced in large prospective trials, and has the potential to be a strong complementary marker of malignancy in patients with a pancreatic mass of uncertain dignity.

Detection of oncogenes in chronic pancreatitis

BACKGROUND

The pathogenesis of chronic pancreatitis (CP) remains poorly understood. Recently, molecular biology has identified the genetic background for many patients with hereditary CP. In addition, a number of studies have focused on the detection of proto-oncogenes and tumour suppressor gene mutations in the pathogenesis of CP. So far, the use of these mutations (with the exception of mutations causing hereditary CP), as diagnostic and prognostic markers is still controversial.

DISCUSSION

It is well known that the risk of pancreatic cancer in patients with CP, especially the hereditary form, is high. At present, there is insufficient evidence to show a clear relationship between the development of pancreatic cancer and certain mutations. New biotechnological methods, such as DNA array expression analysis, expand our knowledge of the molecular pathogenesis of this disease and may help to develop specific diagnostic, prognostic and therapeutic tools. However, until long-term studies examine the safety and efficacy of certain genetic markers, long-term follow-up of patients with CP who harbour mutations is needed.

DNA methylation markers in patients with gastrointestinal cancers. Current understanding, potential applications for disease management and development of diagnostic tools

DNA methylation, the modification of a cytosine nucleotide immediately preceding a guanine base in a stretch of DNA, is rapidly gaining strength in the diagnostic field as a powerful tool to be utilized for the discrimination of neoplastic tissue from its healthy counterpart. This epigenetic modification occurs often in the promoter region of genes and is associated with transcriptional silencing of tumor suppressors or other genes important for normal cellular function. These changes have been found to occur at very early stages in the progression of healthy to malignant phenotype in many cancer types. We are taking a targeted approach to finding methylation-based markers that can be used not only for the early detection of cancer but also for determining risk, monitoring patient response to therapy and even determining the degree of aggressiveness of a tumor. In this paper, we review the progress in our understanding of methylation in gastrointestinal tumors, the potential clinical applications of methylation-based markers and our process for the discovery and validation of highly specific and sensitive markers for the use in these applications.