p16 Methylation is associated with chemosensitivity to fluorouracil in patients with advanced gastric cancer. Med Oncol. 2014;31:988. [PMID: 24816738 DOI: 10.1007/s12032-014-0988-2]

Gastric cancer: An epigenetic view

Gastric cancer (GC) poses a serious threat worldwide with unfavorable prognosis mainly due to late diagnosis and limited therapies. Therefore, precise molecular classification and search for potential targets are required for diagnosis and treatment, as GC is complicated and heterogeneous in nature. Accumulating evidence indicates that epigenetics plays a vital role in gastric carcinogenesis and progression, including histone modifications, DNA methylation and non-coding RNAs. Epigenetic biomarkers and drugs are currently under intensive evaluations to ensure efficient clinical utility in GC. In this review, key epigenetic alterations and related functions and mechanisms are summarized in GC. We focus on integration of existing epigenetic findings in GC for the bench-to-bedside translation of some pivotal epigenetic alterations into clinical practice and also describe the vacant field waiting for investigation.

Targeting epigenetic regulatory machinery to overcome cancer therapy resistance

Drug resistance, either intrinsic or acquired, represents a major hurdle to achieving optimal therapeutic outcomes during cancer treatment. In addition to acquisition of resistance-conferring genetic mutations, accumulating evidence suggests an intimate involvement of the epigenetic machinery in this process as well. Recent studies have revealed that epigenetic reprogramming, such as altered expression or relocation of DNA/histone modulators accompanied with chromatin structure remodeling, can lead to transcriptional plasticity in tumor cells, thereby driving their transformation towards a persistent state. These "persisters" represent a pool of slow-growing cells that can either re-expand when treatment is discontinued or acquire permanent resistance. Targeting epigenetic reprogramming or plasticity represents a new strategy to prevent the emergence of drug-refractory populations and to enable more consistent clinical responses. With the growing numbers of drugs or drug candidates developed to target epigenetic regulators, more and more epigenetic therapies are under preclinical evaluation, early clinical trials or approved by FDA as single agent or in combination with existing antitumor drugs. In this review, we highlight latest discoveries in the mechanistic understanding of epigenetically-induced drug resistance. In parallel, we discuss the potential of combining epigenetic drugs with existing anticancer regimens as a promising strategy for overcoming cancer drug resistance.

Molecular Bases of Mechanisms Accounting for Drug Resistance in Gastric Adenocarcinoma

Gastric adenocarcinoma (GAC) is the most common histological type of gastric cancer, the fifth according to the frequency and the third among the deadliest cancers. GAC high mortality is due to a combination of factors, such as silent evolution, late clinical presentation, underlying genetic heterogeneity, and effective mechanisms of chemoresistance (MOCs) that make the available antitumor drugs scarcely useful. MOCs include reduced drug uptake (MOC-1a), enhanced drug efflux (MOC-1b), low proportion of active agents in tumor cells due to impaired pro-drug activation or active drug inactivation (MOC-2), changes in molecular targets sensitive to anticancer drugs (MOC-3), enhanced ability of cancer cells to repair drug-induced DNA damage (MOC-4), decreased function of pro-apoptotic factors versus up-regulation of anti-apoptotic genes (MOC-5), changes in tumor cell microenvironment altering the response to anticancer agents (MOC-6), and phenotypic transformations, including epithelial-mesenchymal transition (EMT) and the appearance of stemness characteristics (MOC-7). This review summarizes updated information regarding the molecular bases accounting for these mechanisms and their impact on the lack of clinical response to the pharmacological treatment currently used in GAC. This knowledge is required to identify novel biomarkers to predict treatment failure and druggable targets, and to develop sensitizing strategies to overcome drug refractoriness in GAC.

Helicobacter pylori severely reduces expression of DNA repair proteins PMS2 and ERCC1 in gastritis and gastric cancer

Gastric cancers are the third leading cause of cancer mortality in the world. Helicobacter pylori causes over 60 % of all stomach cancers. Colonization of the gastric mucosa by H. pylori results in increased DNA damage. Repair of DNA damage may also be reduced by H. pylori infection. Reduced DNA repair in combination with increased DNA damage can cause carcinogenic mutations. During progression to gastric cancer, gastric epithelium goes through stages of increasing pathology. Determining the levels of DNA repair enzymes during progression to gastric cancer could illuminate treatment approaches. Our aim is to determine the level of gastric expression of DNA repair proteins ERCC1 (a nucleotide excision repair enzyme) and PMS2 (a mismatch repair enzyme) in the presence of H. pylori infection at successive stages of gastric pathology and in gastric cancers. We analyzed gastric tissues of 300 individuals, including 30 without dyspepsia, 200 with dyspepsia and 70 with gastric cancers. The presence of H. pylori, gastric pathology and expression of DNA repair proteins ERCC1 and PMS2 were evaluated. Infection by H. pylori carrying the common cagA gene reduced median nuclear expression of ERCC1 and PMS2 to less than 20 % and 15 % of normal, respectively, in all pathologic stages preceding cancer. ERCC1 and PMS2 nuclear expression was 0-5 % of normal in gastric cancers. H. pylori can cause deficiency of ERCC1 and PMS2 protein expression. These deficiencies are associated with gastric pathology and cancer. This reduction in DNA repair likely causes carcinogenic mutations. Substantially reduced ERCC1 and PMS2 expression appears to be an early step in progression to H. pylori-induced gastric cancer.

P16 Methylation Leads to Paclitaxel Resistance of Advanced Non-Small Cell Lung Cancer

Paclitaxel-based chemotherapy is widely used as the first-line treatment for non-small cell lung cancer (NSCLC). However, only 20%-40% of patients have shown sensitivity to paclitaxel. This study aimed to investigate whether P16 methylation could be used to predict paclitaxel chemosensitivity of NSCLC. Advanced NSCLC (N=45) were obtained from patients who were enrolled in a phase-III randomized paclitaxel-based clinical trial. Genomic DNA samples were extracted from the biopsies prior to chemotherapy. P16 methylation was detected using MethyLight. The association between P16 methylation and the sensitivity of paclitaxel in cell lines was determined by in vitro assay using a P16-specific DNA demethylase (P16-TET) and methyltransferase (P16-Dnmt). The total response rate of the low-dose paclitaxel-based chemo-radiotherapy was significantly lower in P16 methylation-positive NSCLCs than that in the P16 methylation-negative NSCLCs (2/15 vs. 16/30: adjusted OR=0.085; 95%CI, 0.012-0.579). Results revealed that P16 demethylation significantly decreased paclitaxel resistance of lung cancer H1299 cells (IC50 values decreased from 2.15 to 1.13 µg/ml, P<0.001). In contrast, P16-specific methylation by P16-Dnmt significantly increased paclitaxel resistance of lung cancer HCC827 cells and gastric cancer BGC823 cells (IC50 values increased from 18.2 to 24.0 ng/ml and 0.18 to 0.81 µg/ml, respectively; P=0.049 and <0.001, respectively). The present results suggest that P16 methylation may lead to paclitaxel resistance and be a predictor of paclitaxel chemosensitivity of NSCLC.

Novel method for DNA methylation analysis using high-performance liquid chromatography and its clinical application

The aim of this study was to develop a new methodology that is suitable for DNA methylation diagnostics and to demonstrate its clinical applicability. We developed a new anion-exchange column for high-performance liquid chromatography (HPLC) with electrostatic and hydrophobic properties. Both cytosine and thymine, corresponding to methylated and unmethylated cytosine after bisulfite modification, respectively, are captured by electrostatic interaction and then discriminated from each other by their hydrophobic interactions. The DNA methylation levels of synthetic DNA were quantified accurately and reproducibly within 10 minutes without time-consuming pretreatment of PCR products, and the measured values were unaffected by the distribution of methylated CpG within the synthetic DNA fragments. When the DNA methylation status of the FAM150A gene, a marker of the CpG island methylator phenotype specific to clear cell renal cell carcinoma (ccRCC), was examined in 98 patients with ccRCC, bulk specimens of tumorous tissue including cancer cells showing DNA methylation of the FAM150A gene were easily identifiable by simply viewing the differentiated chromatograms, even when the cancer cell content was low. Sixteen ccRCC showing DNA methylation more frequently exhibited clinicopathological parameters reflecting tumor aggressiveness (ie, a larger diameter, higher histological grade, vascular involvement, renal vein tumor thrombi, infiltrating growth, tumor necrosis, renal pelvis invasion and higher pathological TNM stage), and had significantly lower recurrence-free and overall survival rates. These data indicate that HPLC analysis using this newly developed anion-exchange column could be a powerful tool for DNA methylation diagnostics, including prognostication of patients with cancers, in a clinical setting.

MLH1 Promoter Methylation and Prediction/Prognosis of Gastric Cancer: A Systematic Review and Meta and Bioinformatic Analysis

Background: The promoter methylation of MLH1 gene and gastric cancer (GC)has been investigated previously. To get a more credible conclusion, we performed a systematic review and meta and bioinformatic analysis to clarify the role of MLH1 methylation in the prediction and prognosis of GC.

Methods: Eligible studies were targeted after searching the PubMed, Web of Science, Embase, BIOSIS, CNKI and Wanfang Data to collect the information of MLH1 methylation and GC. The link strength between the two was estimated by odds ratio with its 95% confidence interval. The Newcastle-Ottawa scale was used for quantity assessment. Subgroup and sensitivity analysis were conducted to explore sources of heterogeneity. The Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) were employed for bioinformatics analysis on the correlation between MLH1 methylation and GC risk, clinicopathological behavior as well as prognosis.

Results: 2365 GC and 1563 controls were included in the meta-analysis. The pooled OR of MLH1 methylation in GC was 4.895 (95% CI: 3.149-7.611, P<0.001), which considerably associated with increased GC risk. No significant difference was found in relation to Lauren classification, tumor invasion, lymph node/distant metastasis and tumor stage in GC. Analysis based on GEO and TCGA showed that high MLH1 methylation enhanced GC risk but might not related with GC clinicopathological features and prognosis.

Conclusion:MLH1 methylation is an alive biomarker for the prediction of GC and it might not affect GC behavior. Further study could be conducted to verify the impact of MLH1 methylation on GC prognosis.

Promoter hypermethylation of MGMT gene may contribute to the pathogenesis of gastric cancer: A PRISMA-compliant meta-analysis

BECKGROUND

The association of MGMT (O-methyguanine deoxyribonucleic acid methyltransferase) promoter hypermethylation with gastric cancer (GC) risk has been studied extensively, but the results remained unclear. Here, we performed a meta-analysis to evaluate whether promoter hypermethylation of the MGMT gene contributed to gastric pathogenesis.

METHODS

Relevant studies were identified by retrieving the PubMed, Web of Science, Embase, and China National Knowledge Infrastructure (CNKI) databases. The Newcastle-Ottawa Scale was applied to assess methodological quality of the included studies. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to evaluate the association of MGMT promoter hypermethylation with gastric pathogenesis. Moreover, STATA 12.0 software was used to summarize the extracted data in this meta-analysis.

RESULTS

Seventeen studies, comprising 1736 cases and 1291 controls, were included in this meta-analysis. The frequency of MGMT promoter hypermethylation in the GC group (32.97%) was significantly higher than those in the control group (18.00%) (OR = 2.83, CI = 1.93-4.15, P < .05). When stratified by cancer subtype, the results indicated that the frequency of MGMT promoter hypermethylation was significantly higher in gastric adenocarcinoma than in control group (OR = 3.47, CI = 1.06-11.35, P < .05). In addition, MGMT promoter hypermethylation significantly promoted distant metastasis and lymph node (LN) metastasis of gastric tumor (for distant metastasis, OR = 4.22, CI = 2.42-7.37, P < .05; for LN metastasis, OR = 1.56, CI = 1.14-2.13, P < .05). A significant association between MGMT promoter hypermethylation and TNM-stage was also found in the present meta-analysis (OR = 2.70, CI = 1.79-4.08, P < .05).

CONCLUSION

The results of this meta-analysis suggested that MGMT gene-promoter hypermethylation was significantly associated with an increased risk of GC, especially in Asians. Furthermore, MGMT gene-promoter hypermethylation might be correlated with the distant metastasis and LN metastasis of GC.

The Correlation of MGMT Promoter Methylation and Clinicopathological Features in Gastric Cancer: A Systematic Review and Meta-Analysis

The silencing of the tumor suppressor gene O-6-methylguanine-DNA methyltransferase (MGMT) by promoter methylation commonly occurs in human cancers. The relationship between MGMT promoter methylation and gastric cancer (GC) remains inconsistent. This study aimed to evaluate the potential value of MGMT promoter methylation in GC patients. Electronic databases were searched to identify eligible studies. The pooled odds ratio (OR) and the corresponding 95% confidence interval (95% CI) were used to evaluate the effects of MGMT methylation on GC risk and clinicopathological characteristics. In total, 31 eligible studies including 2988 GC patients and 2189 nonmalignant controls were involved in meta-analysis. In the pooled analysis, MGMT promoter methylation was significantly associated with GC risk (OR = 3.34, P < 0.001) and substantial heterogeneity (P < 0.001). Meta-regression and subgroup analyses based on the testing method, sample material and ethnicity failed to explain the sources of heterogeneity. Interestingly, MGMT methylation showed a trend associated with gender, and methylation is lower in males compared with females (OR = 0.76, 95% CI = 0.56–1.03). We did not find a significant association in relation to tumor types, clinical stage, age status or H. pylori status in cancer (all P > 0.1). MGMT promoter methylation may be correlated with the prognosis of GCs in disease free survival (DFS) or overall survival (OS) for univariate analysis. MGMT promoter methylation may play a crucial role in the carcinogenesis and prognosis of GC. MGMT methylation was not correlated with tumor types, clinical stage, age status, H. pylori status. However, the result of the association of MGMT methylation and gender should be considered with caution.

Relationships between MGMT promoter methylation and gastric cancer: a meta-analysis

A DNA repair enzyme, O6-methylguanine-DNA methyltransferase (MGMT), plays an important role in the development of gastric cancers. However, the role of MGMT promoter methylation in the occurrence of gastric cancer and its relationships with clinicopathologic characteristics has not been fully clarified. Thus, we performed a meta-analysis to evaluate the associations between MGMT promoter methylation and gastric cancer. Electronic databases, including PubMed and Web of Science, were used to systematically search related clinical studies published in English until April 1, 2016. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to evaluate the associations between MGMT promoter methylation and gastric cancer risk or clinicopathologic characteristics. A total of 16 studies including 1,935 patients and 1,948 control persons were included in the analysis. Our study suggested that MGMT promoter methylation frequency was associated with gastric cancer (OR=3.46, 95% CI: 2.13–5.61, P<0.001). Moreover, the frequency of MGMT promoter methylation in the no lymph node metastasis group was lower than that in lymph node metastasis group, with marginal significance (OR=0.65, 95% CI: 0.42–1.01, P=0.05). Additionally, the methylation rate of the MGMT promoter was much lower in patients without distant metastases than in those with metastases (OR=0.27, 95% CI: 0.18–0.40, P<0.001). No significant association of MGMT promoter methylation with Lauren classification, tumor location, tumor invasion, or Helicobacter pylori infection was found. In conclusion, the methylation status of the MGMT promoter was related to gastric cancer risk, distant metastasis, and lymph node metastasis, which indicates that MGMT promoter methylation may play an important role in gastric cancer development.

Genetic Basis of Gastric Cancer

Gastric cancer is the result of multiple risk factors, including environmental factors, genetic factors and the interaction between them. The environmental factors mainly include dietary, Helicobacter pylori infection and family history of gastric cancer. Genetic factors mainly refer to the susceptible genes that cause epigenetic alterations in oncogenes, tumor suppress genes, cell cycle regulators, DNA repair genes and signaling molecules. This paper summarizes the susceptible genes of gastric cancer and explores the genetic basis of it.

Dynamic monitoring of circulating tumour cells to evaluate therapeutic efficacy in advanced gastric cancer

BACKGROUND

This study was intended to determine the clinical significance of circulating tumour cells (CTCs) in patients with advanced gastric cancer (AGC), particularly the potential role of CTCs for dynamic monitoring of the therapeutic response.

METHODS

A single-centre, prospective study was undertaken in 136 patients with newly diagnosed AGC. The patients' CTCs were enumerated using CellSearch at baseline and at the first response evaluation. In 15 patients whose clinical condition permitted longitudinal study, CTCs were longitudinally enumerated during treatment.

RESULTS

Following 6 weeks of chemotherapy, an unfavourable post-therapy CTC level (⩾3 CTCs per 7.5 ml) was closely correlated with the objective response rate (P=0.016) and the disease control rate (P=0.013), and it also independently predicted a shorter progression-free survival and overall survival. Particularly, conversion to a favourable CTC level following therapy improved the prognosis, but patients who changed to an unfavourable CTC level fared significantly worse. Elevated CTCs during therapy may be associated with a poor prognosis.

CONCLUSIONS

Post-therapy CTC level may help in evaluating therapeutic response in patients with AGC and predicting their prognosis. In addition, changes in CTCs following therapy may be useful in rapidly identifying ineffective treatments and poor prognosis.

Circulating tumor cells and cell tumor DNA methylation in gastric cancer: From bench to bedside

Gastric cancer is still one of malignant tumors with the highest morbidity and mortalit in China, and the 5-year survival rate is only 10%. Circulating tumor cells (CTCs) and cell tumor DNA (ctDNA) have gained increasing interests during the past decade. A wealth of information indicating the potential value of CTCs and ctDNA for cancer diagnosis, monitoring of the efficacy of anticancer therapies and prognosis has emerged. In this review, we discuss the biology and potential clinical use of CTCs and ctDNA in gastric cancer, as well as their role in the management of cancer patients.