p16 inactivation by methylation of the CDKN2A promoter occurs early during neoplastic progression in Barrett's esophagus

Frequent methylation of eyes absent 4 gene in Barrett's esophagus and esophageal adenocarcinoma

Most esophageal adenocarcinomas arise within Barrett's esophagus but the cause of this increasingly prevalent condition remains unknown. Early detection improves survival and discriminant screening markers for Barrett's esophagus and cancer are needed. This study was designed to explore the natural history of eyes absent 4 (EYA4) gene methylation in the neoplastic progression of Barrett's esophagus and to evaluate methylated EYA4 as a candidate marker. Aberrant promoter methylation of EYA4 was studied by methylation-specific PCR using bisulfite-treated DNA from esophageal adenocarcinomas, Barrett's esophagus, and normal epithelia, and then confirmed by sequencing. Eight cancer cell lines were treated with the demethylation agent 5-aza-2'-deoxycytidine, and EYA4 mRNA expression with and without treatment was quantified by real-time reverse-transcription PCR. EYA4 hypermethylation was detected in 83% (33 of 40) of esophageal adenocarcinomas and 77% (27 of 35) of Barrett's tissues, but only in 3% (2 of 58) of normal esophageal and gastric mucosa samples (P < 0.001). The unmethylated cancer cell lines had much higher EYA4 mRNA expression than the methylated cancer cell lines. Demethylation caused by 5-aza-2'-deoxycytidine increased the mRNA expression level by a median of 3.2-fold in methylated cells, but its effect on unmethylated cells was negligible. Results indicate that aberrant promoter methylation of EYA4 is very common during tumorigenesis in Barrett's esophagus, occurs in early metaplasia, seems to be an important mechanism of down-regulating EYA4 expression, and represents an intriguing candidate marker for Barrett's metaplasia and esophageal cancer.

New Molecular Concepts of Barrett’s Esophagus: Clinical Implications and Biomarkers

Barrett's esophagus (BE) represents the most serious histological consequence of gastroesophageal reflux disease (GERD) that develops in 5-10% of patients with GERD. Given that BE is the only known precursor to esophageal adenocarcinoma (EA), a systematic endoscopic biopsy protocol can detect EAs at an early stage. However, endoscopic and histopathological evaluation of BE are not adequate for effective screening of high risk patients. Therefore, molecular abnormalities associated with BE have been considered as surrogate markers and their use as such is proposed. Flow cytometry is the most useful adjunct to histology, and ploidy status of BE is an independent risk factor. Cyclin D1 overexpression is inversely correlated with survival in EA. C-erbB2 (+) patients have poorer prognosis. High plasma adenomatous polyposis coli levels correlate with reduced patient survival. p53 expression allows patient risk for EA stratification. Nuclear factor-kappaB overexpression inversely correlates with good response to adjuvant chemotherapy and radiotherapy in EA. Patients with cyclooxygenase-2 overexpression have reduced survival rates. Increased E-cadherin staining is associated with shorter survival in EA patients who received chemoradiotherapy. Finally, existing data cannot rule out a correlation between EA and colorectal tumors. Seventeen BE molecular alterations yielded noteworthy clinical implications. Apart from endoscopy and histology, these data allow for better risk stratification for patients with BE and for more efficient and timely therapeutic approaches.

Targeting epigenetic regulatory mechanisms in cancer chemoprevention

Dysregulation of the epigenome plays a fundamental role in tumour development. Epigenetic events are a major mechanism for inactivating tumour suppressor and DNA repair genes and occur ubiquitously during the early stages of tumour development. Unlike genes inactivated by mutation, genes silenced epigenetically are intact and potentially responsive to reactivation by small molecules. This review discusses the potential for restoring epigenetic balance as a means to prevent cancer.

Inactivation of p16, RUNX3, and HPP1 occurs early in Barrett's-associated neoplastic progression and predicts progression risk

Patients with Barrett's esophagus (BE) are at increased risk of developing esophageal adenocarcinoma (EAC). Clinical neoplastic progression risk factors, such as age and the length of the esophageal BE segment, have been identified. However, improved molecular biomarkers predicting increased progression risk are needed for improved risk assessment and stratification. Using real-time quantitative methylation-specific PCR, we screened 10 genes (HPP1, RUNX3, RIZ1, CRBP1, 3-OST-2, APC, TIMP3, p16, MGMT, p14) for promoter hypermethylation in 77 EAC, 93 BE, and 64 normal esophagus (NE) specimens. A subset of genes manifesting significant differences in methylation frequencies between BE and EAC was then analysed in 20 dysplastic specimens. All 10 genes except p14 were frequently methylated in EACs, with RUNX3, HPP1, CRBP1, RIZ1, and OST-2 representing novel methylation targets in EAC and/or BE. p16, RUNX3, and HPP1 displayed increasing methylation frequencies in BE vs EAC. Furthermore, these increases in methylation occurred early, at the interface between BE and low-grade dysplasia (LGD). To demonstrate the silencing effect of hypermethylation, we selected the EAC cells BIC1, in which the HPP1 promoter is natively methylated, and subjected them to 5-aza-2'-deoxycytidine (Aza-C) treatment. Real-time RT-PCR indicated increased HPP1 mRNA levels after 3 days of Aza-C treatment, as well as decreased levels of methylated HPP1 DNA. Hypermethylation of a subset of six genes (APC, TIMP3, CRBP1, p16, RUNX3, and HPP1) was then tested in a retrospective longitudinal study of 99 BE and nine LGD specimens obtained from 53 BE patients undergoing surveillance endoscopy. Only high-grade dysplasia (HGD) or EAC were defined as progression end points. Two patient groups were compared: eight progressors (P) and 45 nonprogressors (NP), using Cox proportional hazards models to determine the relative progression risks of age, BE segment length, and methylation events. Multivariate analyses revealed that only hypermethylation of p16 (odds ratio (OR) 1.74, 95% confidence interval (CI) 1.33-2.20), RUNX3 (OR 1.80, 95% CI 1.08-2.81), and HPP1 (OR 1.77, 95% CI 1.06-2.81) were independently associated with an increased risk of progression, whereas age, BE segment length, and hypermethylation of TIMP3, APC, or CRBP1 were not independent risk factors. In combined analyses, risk was detectable up to, but not earlier than, 2 years preceding neoplastic progression. Hypermethylation of p16, RUNX3, and HPP1 in BE or LGD may represent independent risk factors for the progression of BE to HGD or EAC. These findings have implications regarding risk stratification, early EAC detection, and the appropriate endoscopic surveillance interval for patients with BE.

Epigenetics and cancer

Both genetics and epigenetics regulate gene expression in cancer. Regulation by genetics involves a change in the DNA sequence, whereas epigenetic regulation involves alteration in chromatin structure and methylation of the promoter region. During the initiation, development, and progression of cancer, a number of genes undergo epigenetic changes. Some of these changes can be used as biomarkers for early detection of cancer as well as to follow treatment. A panel of epigenetic biomarkers is preferred to a single biomarker in clinical assays. Changes in gene expression due to epigenetic regulation can be reversed by chemicals, and this approach opens up a novel approach in cancer prevention and treatment.

p16 expression in Barrett's esophagus and esophageal adenocarcinoma: association with genetic and epigenetic alterations

Alteration of the p16 tumor suppressor gene has been implicated as a critical lesion in the molecular pathogenesis of esophageal adenocarcinoma. The aim of this study was to characterize the spectrum of p16 alterations in surgically resected esophageal tissues, comprising histologically normal esophageal squamous and gastric epithelia, premalignant Barrett's epithelia, and associated esophageal adenocarcinomas, and to explore associations between p16 mRNA expression and p16 mutations, deletions, promoter hypermethylation, p16 protein expression, and clinico-pathologic features for the same tissues. We have shown that while p16 mutations are uncommon (2%; 1/54), hypermethylation of the p16 promoter is detected in 43% (9/21) of histologically normal epithelia, in 77% (14/18) of associated Barrett's epithelia, and in 85% (18/21) of esophageal adenocarcinomas. However, p16 mRNA levels (relative to matched normal epithelia) were variable in Barrett's epithelia and adenocarcinomas, having no clear correlation with methylation status or other molecular and clinico-pathological parameters. These findings are consistent with a role for the p16 tumor suppressor gene early in the molecular progression of Barrett's epithelium to invasive esophageal adenocarcinoma, but do not support the notion that the detection of hypermethylation is systematically associated with low levels of expression.

The molecular biology of esophageal adenocarcinoma

BACKGROUND

Barrett's esophagus is an acquired metaplastic change that occurs in the distal esophagus secondary to chronic gastroesophageal reflux. This premalignant condition forms the most important risk factor for developing esophageal adenocarcinoma, which is an extremely aggressive tumor with a 5-year survival rate of less than 25%. Carcinomas that arise in the setting of Barrett's esophagus are thought to develop as part of the metaplasia-dysplasia-carcinoma sequence.

OBJECTIVE

To review the current knowledge on the genomic alterations involved in the development of Barrett's esophagus and its progression to dysplasia and/or cancer.

RESULTS

Several changes in gene structure, gene expression, and protein structure are associated with the progression of Barrett's esophagus to adenocarcinoma. Accumulation of these changes seems to be essential, rather than the exact sequence of these changes. Multiple molecular pathways are involved and interact with each other. Alterations in tumor suppressor genes, amongst which p53 and p16, are early events in the metaplasia-dysplasia-adenocarcinoma sequence, followed by loss of cell cycle checkpoints. Ongoing genomic instability leads to cumulative genetic errors and thereby the generation of multiple clones of transformed cells.

CONCLUSIONS

Within the multistep process of esophageal adenocarcinogenesis, to date no single molecular marker came forward able to predict who will and who will not develop cancer in the setting of Barrett's esophagus. Instead, panels of markers need to be developed in the future allowing to indicate disease progression. Identification of crucial molecular pathways involved in esophageal adenocarcinogenesis would ultimately improve therapy and facilitate development of new treatment strategies.

Aberrant methylation of secreted frizzled-related protein genes in esophageal adenocarcinoma and Barrett's esophagus

Hypermethylation of secreted frizzled-related proteins (SFRP) genes frequently occurs with several cancers but has not been studied in esophageal adenocarcinoma or its precursor-Barrett's esophagus. To explore the role of SFRP methylation in the neoplastic progression of Barrett's esophagus and to evaluate methylated SFRP genes as biomarkers for Barrett's esophagus and cancer, methylation of SFRP genes was determined in esophageal adenocarcinomas, Barrett's esophagus and normal epithelia using methylation-specific PCR. Protein expression of SFRP genes was then assessed in these tissues by immunohistochemistry. The mRNA expression of SFRP genes was quantified by real-time reverse-transcription PCR in esophageal adenocarcinoma cell lines with and without demethylation by 5-aza-2'deoxycytidine and inhibition of deacetylation by trichostatin A treatment. Hypermethylation of SFRP1, 2, 4 and 5 was detected in 93%, 83%, 73% and 85% of 40 cancers; 81%, 89%, 78% and 73% of 37 Barrett's epithelia; 25%, 64%, 32% and 21% of 28 adjacent normal epithelia from Barrett's patients; and 10%, 67%, 0% and 13% of 30 normal esophagogastric epithelia from healthy individuals, respectively (p < 0.001 for SFRP1, 4 and 5; p < 0.05 for SFRP2). Protein expression of SFRP1, 2 and 4 was downregulated in 87%, 67% and 90% of cancers, and expression correlated inversely with grade and stage of cancers and with grade of dysplasia. Expression of SFRP2 and SFRP4 proteins was lower in cancers with corresponding gene methylation (p < 0.05). Demethylation treatment effectively re-expressed SFRP mRNA in cancer cell lines. Thus, hypermethylation of SFRP genes is a common early event in the evolution of esophageal adenocarcinoma, and methylation of SFRP1, 4 and 5 might serve as biomarkers for Barrett's neoplasia. Aberrant promoter methylation appears to functionally silence SFRP gene expression in esophageal adenocarcinoma.

Generation of locus-specific probes for interphase fluorescence in situ hybridisation--application in Barrett's esophagus

Despite the wide range of probes commercially available for interphase fluorescence in situ hybridisation (FISH), the supply of locus-specific probes is limited to genes or chromosomal regions commonly altered in genetic diseases or during carcinogenesis. Generation of these probes is therefore desirable to accommodate individual research requirements. Hence, we detail the methodology required to design and produce custom locus-specific interphase FISH probes for any human genomic region of interest and their application was illustrated in cytogenetic investigations of Barrett's tumourigenesis. Previously utilising FISH, we observed that Barrett's tissues demonstrated chromosome 4 hyperploidy [Gut 52 (2003) 623], but as centromeric probes were used in this analysis, it was not known if the whole chromosome was amplified. We consequently generated single-copy sequence probes for the 4p16.3 and 4q35.1 subtelomeric loci. Multicolour FISH was subsequently performed on interphase preparations originating from patients with Barrett's esophagus at varying histological grades, thus demonstrating the whole region of chromosome 4 was amplified within the tissues. Additionally, probes for the DNA methyltransferase genes were produced to determine if gene dosage alterations were responsible for increasing methylation activity during Barrett's neoplastic progression. No significant alterations at the DNMT1 and DNMT3a loci were detected. An increased copy number of these genes is therefore not the basis for the hypermethylation commonly observed in this premalignant lesion.

Selectively advantageous mutations and hitchhikers in neoplasms: p16 lesions are selected in Barrett's esophagus

Neoplastic progression is an evolutionary process characterized by genomic instability and waves of clonal expansions carrying genetic and epigenetic lesions to fixation (100% of the cell population). However, an evolutionarily neutral lesion may also reach fixation if it spreads as a hitchhiker on a selective sweep. We sought to distinguish advantageous lesions from hitchhikers in the premalignant condition Barrett's esophagus. Patients (211) had biopsies taken at 2-cm intervals in their Barrett's segments. Purified epithelial cells were assayed for loss of heterozygosity and microsatellite shifts on chromosomes 9 and 17, sequence mutations in CDKN2A/MTS1/INK4a (p16) and TP53 (p53), and methylation of the p16 promoter. We measured the expanse of a lesion in a Barrett's segment as the proportion of proliferating cells that carried a lesion in that locus. We then selected the lesion having expanses >90% in the greatest number of patients as our first putative advantageous lesion. We filtered out hitchhikers by removing all expanses of other lesions that did not occur independent of the advantageous lesion. The entire process was repeated on the remaining expanses to identify additional advantageous lesions. p16 loss of heterozygosity, promoter methylation, and sequence mutations have strong, independent, advantageous effects on Barrett's cells early in progression. Second lesions in p16 and p53 are associated with later selective sweeps. Virtually all of the other lesion expansions, including microsatellite shifts, could be explained as hitchhikers on p16 lesion clonal expansions. These techniques can be applied to any neoplasm.

RUNX3 inhibits cell proliferation and induces apoptosis by reinstating transforming growth factor beta responsiveness in esophageal adenocarcinoma cells

BACKGROUND

SEG-1, a Barrett's-derived esophageal adenocarcinoma cell line, is not responsive to transforming growth factor beta (TGF-beta) growth effects. We hypothesize that SEG-1 cells lack the tumor-suppressor gene Runt domain transcription factor 3 (RUNX3) and that its reinstatement can restore the antiproliferative and apoptotic effects of TGF-beta.

METHODS

RUNX3 expression was assessed by immunoblotting. SEG-1 cells were transfected with RUNX3 and treated with TGF-beta. The effects of RUNX3 transfection on cell proliferation and apoptosis were determined. Smad-mediated TGF-beta transcriptional activity was evaluated with the use of dual-luciferase assay.

RESULTS

SEG-1 cells are not responsive to TGF-beta. SEG-1 cells lack RUNX3 protein expression, while RUNX3 is highly expressed in normal human gastric and esophageal epithelium. Although the Smad-2 signaling is activated by TGF-beta, SEG-1 cells lack Smad-mediated TGF-beta transcriptional activity. In cells transfected with RUNX3, TGF-beta acquired an antiproliferative effect and induced apoptosis (P = .001). RUNX3 transfection, in the absence of TGF-beta, had no effect on proliferation and apoptosis of SEG-1 cells. RUNX3 expression dramatically increases SMAD-mediated TGF-beta-induced transcriptional activity when compared with controls (P = .0001).

CONCLUSIONS

RUNX3 is not expressed in SEG-1 cells, while it is present in normal esophageal mucosa. RUNX3 is essential for the antiproliferative and apoptotic effects of TGF-beta in SEG-1 cells and for the Smad-mediated transcriptional activity of TGF-beta.

Fluorescence in situ hybridization of cytologic specimens from Barrett's esophagus: a pilot feasibility study

BACKGROUND

Endoscopic brush cytology is a promising surveillance technique for Barrett's esophagus. However, there is a need for ancillary biomarkers to increase the sensitivity of cytology and to allow identification of patients at increased risk for disease progression. The aims of this study were to evaluate the feasibility of fluorescence in situ hybridization of endoscopic brush cytology specimens and to determine if there are specific chromosomal changes in cytologic specimens from patients with cancer that are not present in patients without dysplasia.

METHODS

Archival cytology slides from 16 patients with Barrett's esophagus were studied: 8 negative for dysplasia and 8 positive for adenocarcinoma. Fluorescence in situ hybridization was used to detect two alterations: HER-2 gene (17q11.2-q12) and 20q13.2 region amplification.

OBSERVATIONS

For 7 of 8 adenocarcinoma cases, there was amplification/aneusomy of at least one of the two analyzed regions by fluorescence in situ hybridization. None of the samples negative for dysplasia were abnormal for either of the two genomic regions studied.

CONCLUSIONS

Fluorescence in situ hybridization is feasible by using routine Barrett's esophagus cytologic specimens. Differences in genomic makeup can be detected in cells from patients negative for dysplasia and in those with adenocarcinoma.

INK4a-ARF alterations in Barrett's epithelium, intraepithelial neoplasia and Barrett's adenocarcinoma

INTRODUCTION

The INK4a-ARF [CDKN2A]- locus on chromosome 9p21 encodes for two tumour suppressor proteins, p16INK4a and p14ARF, which act as upstream regulators of the Rb-CDK4 and p53 pathways. To study the contribution of each pathway to the carcinogenesis of Barrett's adenocarcinoma, we analysed the alterations of p14ARF and p16INK4a in preneoplastic and neoplastic lesions of this disease.

MATERIALS AND METHODS

After microdissection, DNA of 15 Barrett's adenocarcinomas, 40 Barrett's intraepithelial neoplasms (n=20 low- and n=20 high-grade) and 15 Barrett's mucosa without neoplasia was analysed for INK4-ARF inactivation using DNA sequence and loss of heterozygosity (LOH) analysis, methylation-specific polymerase chain reaction, restriction-enzyme-related polymerase chain reaction and immunohistochemistry.

RESULTS

We detected 9p21 LOH, p16INK4a methylation and p16INK4a mutations in Barrett's adenocarcinomas in 5 of 15 (33%), 8 of 15 (53%) and 1 of 15 (7%) patients, respectively. P14ARF was methylated in 3 of 15 (20%) adenocarcinomas. In Barrett's intraepithelial neoplasia, p16INK4a was altered in 12 of 20 (60%) high-grade and in 4 of 20 (20%) low-grade intraepithelial neoplasms. In Barrett's mucosa without intraepithelial neoplasia p16(INK4a) was methylated in one case (7%). P14ARF was intact in Barrett's mucosa without intraepithelial neoplasia.

CONCLUSIONS

We conclude that most Barrett's intraepithelial neoplasms contain genetic and/or epigenetic INK4a-ARF alterations. Methylation of p16INK4a appears to be the most frequent epigenetic defect in the neoplastic progression of Barrett's tumourigenesis.

Cancer of the esophagus and gastric cardia: recent advances

Esophageal cancer and cancer of the gastric cardia, in particular adenocarcinomas, have shown a rapid and largely unexplained increase in incidence in many developed countries around the world. These diseases have a poor prognosis and current therapies have a modest impact on survival. This review presents recent advances in the epidemiology, etiology, diagnosis, staging, prevention and treatment of resectable and advanced disease. Although significant progress has been made in these areas of research and patient management over the past years, prognosis for most patients diagnosed with esophageal cancer or cancer of the gastric cardia remains poor. New diagnostic procedures, improved surgical procedures, combined treatment modalities and new treatment modalities are being evaluated and may be expected to contribute to improved patient outcomes and better palliation of symptoms in the future.

Characterisation of p53 status at the gene, chromosomal and protein levels in oesophageal adenocarcinoma

p53 mutations and loss of heterozygosity have been commonly associated with oesophageal adenocarcinoma. In this investigation, the p53 status of a Welsh population of Barrett's-associated oesophageal adenocarcinomas were fully characterised at the gene sequence, chromosomal, mRNA and protein levels. In total, 31 tumours were examined for p53 gene sequence mutations using RFLP with sequencing, allelic loss of the gene was characterised by FISH, mRNA expression by p53 pathway signalling arrays and protein levels by p53 immunohistochemistry. In all, 9.6% of adenocarcinomas harboured p53 mutations, 24% displayed p53 allelic loss and 83% exhibited p53 protein accumulation. Point mutations and deletions of the gene did not coexist within the same samples. All samples containing p53 mutations also displayed positive immunostaining; however; in the majority of cases, p53 protein accumulation developed in the absence of mutations. The gene expression analysis demonstrated no differences in p53 and mdm-2 transcription levels between the p53 immunonegative and immunopositive samples, indicating other mechanisms underlie the proteins' overexpression. In conclusion, p53 mutations and deletions do not appear to be frequent events in oesophageal adenocarcinomas; however, abnormal accumulation of the protein is present in a vast majority of cases. P53 gene mutations are not the primary cause of protein overexpression--an alternative mechanism is responsible for the positive p53 immunohistochemistry detected.

Barrett esophagus

PURPOSE

The importance of an in-depth understanding about Barrett esophagus is ultimately to decrease the mortality and morbidity from esophageal adenocarcinoma cancer by early detection of metaplasia and dysplasia and appropriate therapy. This review summarizes several publications in the past year related to the epidemiology, pathogenesis, screening and surveillance, new methods for detection of metaplasia/dysplasia, and advances in the treatment of Barrett esophagus.

RECENT FINDINGS

Patients with Barrett esophagus are characterized by the presence of risk factors usually indicative of severe types of gastroesophageal reflux disease. Recent insights into epidemiology and pathogenesis have shown that the risk of high-grade dysplasia and adenocarcinoma may be related to the increasing length of Barrett esophagus, size of hiatus hernia, and severity of acid reflux. The role of smoking and alcohol consumption remains controversial. Increasing the number of biopsies by repeat standard endoscopy can enhance the yield of intestinal metaplasia in patients with suspected short-segment Barrett esophagus. Costs of surveillance using standard endoscopy and random biopsies would be very high and using special techniques to target specific areas could ultimately help in cost reduction. Emerging data on new techniques and technology such as vital staining with methylene blue and protoporphyrin fluorescence can increase the yield of metaplasia and dysplasia. Biomarkers studies have revealed that p53 mutation by the loss of heterozygosity can help detect patients with low and high risk for cancer progression. Studies thus far have been unclear whether acid suppression alone can impact the malignant progression in Barrett esophagus patients. Inhibition of cyclooxygenase by aspirin or nonsteroidal anti-inflammatory drugs may be a promising chemoprevention strategy against dysplasia and esophageal adenocarcinoma development as shown in some recent studies. Nonsurgical treatment by photodynamic therapy or mucosal resection may be a less invasive and organ-sparing option for some patients with high-grade dysplasia and early adenocarcinoma.

SUMMARY

In the past year we have made major strides in our knowledge of this premalignant lesion. Recent studies have shed light in a better understanding of the epidemiology of Barrett esophagus, including clinical and endoscopic factors associated with high-grade dysplasia or esophageal adenocarcinoma and various biomarkers that would identify patient subsets with low and high risk for cancer progression. This will eventually have significant implications on the screening, surveillance, and treatment of the disease. Advanced endoscopic therapies including mucosectomy or photodynamic therapy may be emerging options in patients with intraepithelial neoplasia.

Barrett's esophagus and Barrett's carcinoma

The alarming rise in the incidence of esophageal adenocarcinomas in the Western world has focused interest on so-called Barrett's esophagus. Barrett's esophagus is characterized by specialized intestinal epithelium replacing the normal squamous epithelium in the distal esophagus and is considered a consequence of long-lasting and severe gastroesophageal reflux disease. A metaplasia-dysplasia-carcinoma sequence links Barrett's esophagus with adenocarcinoma of the distal esophagus (Barrett's cancer). Despite intensive research, many questions concerning the pathogenesis, diagnosis, and treatment of Barrett's esophagus and associated adenocarcinoma are still unanswered. Based on current data, the malignant progression of Barrett's esophagus cannot be substantially prevented by medical or surgical therapy for reflux. Although no firm data are available to show that surveillance strategies can reduce overall mortality from Barrett's cancer, early detection and cure are possible. Management of Barrett's esophagus and carcinoma is reviewed with reference to the sequence of disease from metaplasia to carcinoma.

Barrett's esophagus: an update

Barrett's esophagus (BE) is a complication observed in a small subset of patients with chronic gastroesophageal reflux. It is characterized by the presence of intestinal-type goblet cells in biopsies from the lower esophagus. The prevalence of BE increases with age, affecting 1% of the population older than 60 years. A genetic predisposition to reflux disease has been proposed. In a twin study of reflux disease, concordance was greater in monozygotic than dizygotic twins. An association between BE and esophageal adenocarcinoma, the incidence of which has increased remarkably in the last few decades, has been established. Esophagogastric junction cancers can arise from small areas of cardia intestinal metaplasia (CIM). Regular endoscopic and histologic follow-up of BE patients is recommended. Surveillance of patients with CIM is not advised. Chromoendoscopy may help to detect areas of high-grade dysplasia (HGD). The ablation of BE, e.g. by PDT or argon plasma coagulation, is not yet proven to reduce the cancer risk. Esophagectomy is still the standard management of HGD. Endoscopic mucosal resection may be used for visible, localized lesions with HGD, and this technique may be combined with thermal ablation for areas of HGD without visible abnormality.

The pathogenesis of Barrett's esophagus

Significant progress has been made in clinicians' understanding of the molecular pathogenesis of BE, and the laboratory findings are beginning to lead to hypothesis-driven clinical studies; however, the following questions remain unanswered: (1) how can clinicians identify the persons most at risk for the development of esophageal adenocarcinoma, (2) what are the environmental gene interactions in esophageal carcinogenesis, and (3) can clinicians prevent the development of esophageal adenocarcinoma in the population at risk? As esophageal adenocarcinoma starts to reach epidemic proportions, further research in these areas is urgently required. With the advent of the genomic era and an explosion in studies in BE, significant progress can be made.

Biomarkers in Barrett's esophagus

This article provides a framework for clinicians who are attempting the difficult task of interpreting the Barrett's biomarker literature with the goal of improving care for their patients. Although many articles. including more that 60 proposed biomarkers, have been published on this subject, only a few describe phase 3 and 4 studies that are of interest to the clinical gastroenterologist (Table 1). For year, dysplasia grade has been the sole means of risk stratification for patients with BE, and it likely will continue to be used in the foreseeable future. The current authors believe that dysplasia classification can be valuable using the team management approach and quality controls described previously. Significant problems, however, have emerged in phase 2 through 4 studies of dysplasia that make it imperative for the Barrett's field to incorporate additional biomarkers as they are validated. These problems include poor reproducibility of dysplasia interpretations, poor predictive value for negative, indefinite, and low-grade dysplasia, and inconsistent results for HGD in different centers, all of which makes it virtually impossible to develop national guidelines for surveillance. Some studies have even suggested that endoscopic biopsy surveillance using dysplasia may not be worthwhile. Currently, flow cytometric tetraploidy and aneuploidy have progressed furthest in biomarker validation (see Table 1). With proper handling, endoscopic biopsy specimens can be shipped to reference laboratories that have the instruments, computer analytic methods, and expertise to reproducibly detect tetraploidy and aneuploidy. The results of phase 4 studies indicate that flow cytometry appears to be useful in detecting a subset of patients who do not have HGD and yet have an increased risk of progression to cancer that cannot be identified by dysplasia grade. For many reasons, the authors anticipate that the number of validated biomarkers will increase substantially in the future. Biopsy repositories are now readily available for phase 3 studies that can evaluate and compare biomarkers. There are initiatives for multi-institutional Barrett's Centers of Excellence that could provide rapid progress in biomarker evaluation. In addition to new candidate biomarkers, the human genome project has provided high-throughput methodologies and methods for computer analysis of data, which can provide the volume and quality control required for clinically useful biomarkers. Currently, 17p (p53) LOH has progressed the furthest among molecular biomarkers. The authors do not recommend its routine clinical use at the present time, however. Finally, it is likely that clinicians will want to follow the results of clinical treatment-response studies and epidemiologic studies that evaluate relationship between clinical interventions or environmental risk and protective factors and surrogate endpoints, especially if the endpoints are progessing well along the phases of biomarker validation. These studies are likely to be of clinical interest because they may becoming the basis for randomized clinical trials to prevent cancer in BE.

Epigenetics: the role of methylation in the mechanism of action of tumor suppressor genes

Epigenetics is the study of mitotically heritable changes in gene expression without any changes in the primary DNA sequence. The major step in epigenetic gene regulation is gene inactivation by hypermethylation of CpG islands located in the promoter region. Specific enzymes and methylated DNA binding proteins play a major role in causing reduced expression of tumor suppressor genes, resulting in tumor formation and its progression. Prevention approaches are needed to avoid tumor formation. One approach to inhibiting inactivation of tumor suppressor genes is to use chemical agents such as 5-azacytidine to prevent hypermethylation of DNA. Increased understanding of the mechanism of epigenetic silencing and the identification of additional molecular mechanisms (e.g., histone methylases) that may be targeted by pharmaceutical interventions may lead to more preventive strategies. The current status of the epigenetic regulation of tumor suppressor genes is discussed in this review article.

Epigenetic gene silencing in cancer initiation and progression

Hypermethylation of CpG islands, an epigenetic event that is not accompanied by changes in DNA sequence, represents an alternative mechanism to deletions or mutations to inactivate tumor suppressor genes. Recent evidence supports the notion that CpG island hypermethylation, by silencing key cancer-related genes, plays a major causal role in cancer. However, a long-standing issue in the field is the sequence of molecular events leading to epigenetic gene silencing. A new model has been proposed that chromatin remodeling, as a result of histone deacetylation and methylation, is the primary event in abrogating transcriptional initiation; subsequently, CpG island hypermethylation establishes a permanent state of gene silencing. Accumulating evidence indicates that CpG island hypermethylation is an early event in cancer development and, in some cases, may precede the neoplastic process. Because of their heritable nature, hypermethylated CpG islands leave 'molecular footprints' in evolving cancer cells and can be used as molecular markers to reconstruct epigenetic progression during tumorigenesis. Furthermore, hypermethylated CpG islands are proving to be useful for molecular classification of different cancer types.

Hypermethylation-mediated regulation of CD44 gene expression in human neuroblastoma

The CD44 adhesion receptor is silenced in highly malignant neuroblastomas (NBs) with MYCN amplification. Because its functional expression is associated with decreased tumorigenic properties, CD44 behaves as a tumor suppressor gene in NB and other cancers. Given that the precise mechanisms responsible for CD44 silencing are not elucidated, we investigated whether CD44 expression could be regulated by DNA hypermethylation. The methylation status of CD44 gene promoter and exon 1 regions was analyzed in 12 NB cell lines and 21 clinical samples after bisulfite genomic modification, followed by PCR and single-strand conformation polymorphism analysis and genomic sequencing. The results showed that almost all CD44-negative cell lines displayed hypermethylation in both regions, whereas all CD44-expressing cell lines were unmethylated. These observations correlated with the ability to restore CD44 mRNA and protein expression by treatment of CD44-negative cells with the 5-aza-2'-deoxycytidine demethylating agent. In contrast, no CD44 gene hypermethylation could be detected in 21 NB clinical samples of different stages, irrespective of CD44 expression. Although our results suggest that aberrant methylation of promoter and exon 1 regions is involved in CD44 silencing in NB cell lines, they also indicate that methylation of unidentified regulatory sequences or methylation-independent mechanisms also control the expression of CD44 in primary NB tumors and cell lines. We therefore conclude that CD44 silencing is controlled by complex and tumor cell-specific processes, including gene hypermethylation. Further investigation of other mechanisms and genes involved in CD44 regulation will be needed before demethylation-mediated reactivation of the CD44 gene can be considered as therapeutic strategy for neuroblastoma and perhaps other related cancers.