Genome-wide identification of possible methylation markers chemosensitive to targeted regimens in colorectal cancers

The Galaninergic System: A Target for Cancer Treatment

Simple Summary

Peptidergic systems play an important role in cancer progression. The galaninergic system (the peptide galanin and its receptors: galanin 1, 2 and 3) is involved in tumorigenesis, the invasion and migration of tumor cells and angiogenesis and it has been correlated with tumor stage/subtypes, metastasis and recurrence rate in many types of cancer. Galanin exerts a dual action in tumor cells: a proliferative or an antiproliferative effect depending on the galanin receptor involved in these mechanisms. Galanin receptors could be used in certain tumors as therapeutic targets and diagnostic markers for treatment, prognosis and surgical outcome. This review shows the importance of the galaninergic system in the development of tumors and suggests future promising clinical antitumor applications using galanin agonists or antagonists.

Abstract

The aim of this review is to show the involvement of the galaninergic system in neuroendocrine (phaeochromocytomas, insulinomas, neuroblastic tumors, pituitary tumors, small-cell lung cancer) and non-neuroendocrine (gastric cancer, colorectal cancer, head and neck squamous cell carcinoma, glioma) tumors. The galaninergic system is involved in tumorigenesis, invasion/migration of tumor cells and angiogenesis, and this system has been correlated with tumor size/stage/subtypes, metastasis and recurrence rate. In the galaninergic system, epigenetic mechanisms have been related with carcinogenesis and recurrence rate. Galanin (GAL) exerts both proliferative and antiproliferative actions in tumor cells. GAL receptors (GALRs) mediate different signal transduction pathways and actions, depending on the particular G protein involved and the tumor cell type. In general, the activation of GAL₁R promoted an antiproliferative effect, whereas the activation of GAL₂R induced antiproliferative or proliferative actions. GALRs could be used in certain tumors as therapeutic targets and diagnostic markers for treatment, prognosis and surgical outcome. The current data show the importance of the galaninergic system in the development of certain tumors and suggest future potential clinical antitumor applications using GAL agonists or antagonists.

Promoter methylation of galanin receptors as epigenetic biomarkers for head and neck squamous cell carcinomas

INTRODUCTION

While remarkable progress has been made in standard treatments for head and neck squamous cell carcinomas (HNSCCs), the long-term survival remains at an unsatisfactory 40-50%. To improve the survival rate, biomarkers for optimal treatment selection and prognostic prediction, as well as novel, low-toxicity treatment strategies, are required. Galanin receptor (GALR) 1 and GALR2 are well-studied tumor suppressors in HNSCCs. Compared with other clinicopathological factors, the epigenetic variants of GALRs have been found to be the most powerful markers to predict the prognosis of HNSCC patients. Areas covered: This review outlines the functions and signaling pathways of GALRs and explains the potential of GALR promoter methylation as a biomarker for HNSCC prognosis. We also summarize recent developments in promoter methylation studies in HNSCC and indicate future directions for GALR promoter methylation studies. Expert commentary: GALR studies have highlighted two major aspects with implications in HNSCC - that G-protein coupled receptors (GPCRs) act as tumor suppressor genes and that GALR promoter methylation is significantly related to the carcinogenesis of HNSCC. The findings of GALR studies can be applied to studies on other GPCRs and further in-depth DNA methylation studies. Deeper insights into GPCR epigenetics are expected to markedly improve HNSCC treatment.

Epigenetic inactivation of galanin and GALR1/2 is associated with early recurrence in head and neck cancer

The aim of this study was to investigate the prognostic value of galanin (GAL) and galanin receptor (GALR) promoter hypermethylation in patients with head and neck squamous cell carcinoma (HNSCC). The methylation status of three genes-GAL, GALR1, and GALR2 was examined in HNSCC patient tumors using quantitative methylation-specific PCR (Q-MSP). To determine the prognostic value of GAL, GALR1 and GALR2 methylation status, their associations with various clinical characteristics and patient survival were assessed in HNSCC patient tumors (n = 142). Aberrant methylation of at least one gene was observed in 84 of the 142 (59.2 %) primary tumors analyzed. The methylation index, defined as the ratio between the number of methylated genes and the number of genes examined, was positively correlated with larger tumor size (P = 0.034) and disease recurrence (P < 0.001). In the multivariate logistic-regression analysis, methylation of both GAL and GALR1 exhibited the highest association with poor survival (hazard ratio, 6.83, P = 0.002). Moreover, among patients without lymph node metastasis, a multivariate analysis showed a significant trend for poor survival as the number of hypermethylated genes increased (log-rank test, P = 0.003). CpG hypermethylation is a likely mechanism of GAL and GALR1/2 gene inactivation, indicating that GAL and its receptors play a role in HNSCC tumorigenesis. As such, GAL and GALR1/2 methylation status may serve as an important biomarker for clinical outcome.

DNA methylation status as a biomarker of anti-epidermal growth factor receptor treatment for metastatic colorectal cancer

Anti‐epidermal growth factor receptor (EGFR) treatment is an effective option for metastatic colorectal cancer (CRC) treatment. However, there are few reliable biomarkers to predict the clinical response to anti‐EGFR treatment. We investigated the genome‐wide DNA methylation status in metastatic colorectal cancer to identify associations between the methylation status and clinical response to anti‐EGFR antibody. We retrospectively reviewed the medical records of 97 patients (45 patients for the first cohort and 52 patients for the second cohort) who received anti‐EGFR treatment for KRAS wild‐type metastatic CRC. Then we analyzed the associations between genome‐wide DNA methylation status and clinical response to anti‐EGFR treatment, and evaluated the predictive power and value of the methylation status statistically. As a result, each cohort was classified into highly methylated CRC and low methylated CRC subgroups by unsupervised clustering analyses. In the first cohort, clinical outcomes were significantly better in the low methylated CRC subgroup than in the highly methylated CRC subgroup (response rate, 35.7% vs 6.3%, P = 0.03; disease control rate, 75% vs 31.3%, P = 0.005; hazard ratio for progression‐free survival, 0.27; 95% confidence interval, 0.13–0.57, P < 0.001; overall survival, 0.19; 95% confidence interval, 0.06–0.54, P < 0.001). These results were reproducible in the second cohort. The genome‐wide methylation status was a predictive factor of progression‐free survival and overall survival independently of RAS mutation status. In conclusion, we found that the genome‐wide DNA methylation status is a powerful epigenetic predictor of anti‐EGFR treatment in patients with KRAS wild‐type metastatic colorectal cancer (UMIN000005490).

G-Protein-Coupled Receptors: Next Generation Therapeutic Targets in Head and Neck Cancer?

Therapeutic outcome in head and neck squamous cell carcinoma (HNSCC) is poor in most advanced cases. To improve therapeutic efficiency, novel therapeutic targets and prognostic factors must be discovered. Our studies have identified several G protein-coupled receptors (GPCRs) as promising candidates. Significant epigenetic silencing of GPCR expression occurs in HNSCC compared with normal tissue, and is significantly correlated with clinical behavior. Together with the finding that GPCR activity can suppress tumor cell growth, this indicates that GPCR expression has potential utility as a prognostic factor. In this review, we discuss the roles that galanin receptor type 1 (GALR1) and type 2 (GALR2), tachykinin receptor type 1 (TACR1), and somatostatin receptor type 1 (SST1) play in HNSCC. GALR1 inhibits proliferation of HNSCC cells though ERK1/2-mediated effects on cell cycle control proteins such as p27, p57, and cyclin D1, whereas GALR2 inhibits cell proliferation and induces apoptosis in HNSCC cells. Hypermethylation of GALR1, GALR2, TACR1, and SST1 is associated with significantly reduced disease-free survival and a higher recurrence rate. Although their overall activities varies, each of these GPCRs has value as both a prognostic factor and a therapeutic target. These data indicate that further study of GPCRs is a promising strategy that will enrich pharmacogenomics and prognostic research in HNSCC.

Elucidating the molecular aspects of colorectal cancer and their clinical importance

Over the last 10 years, crucial improvements have been made in the pursuit of more effective therapies for colorectal cancer (CRC). In understanding the basis of CRC biology we have evolved from the classical ‘adenoma to carcinoma transition’ hypothesis, to the identification of two CRC clusters (microsatellite instability and chromosomal instability) and further classifications based on epigenetic events. Thanks to these advances in molecular analyses, key pathways, notably that of the EGFR, are now integrated into standard practice for therapeutic management and other pathways are being explored for blocking driving mutations and overcoming drug resistance. Genetic profiling is being developed to better predict prognosis and treatment response. The CRC subtyping consortium has combined and reanalyzed genetic signature data sets from several international groups. A definitive genetic CRC classification is currently being established and will be critical for clinical development of therapeutic strategies.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Epigenetics of colorectal cancer

Colorectal cancer (CRC) is one of most common malignancies and a leading cause of cancer related deaths worldwide. Epigenetic change is an important mechanism of colorectal carcinogenesis. Accumulation of epigenetic changes was found in colorectal cancer and other tumors. Aberrant changes in DNA methylation, histone modification, imprinting, and noncoding RNAs were frequently found in human colorectal cancer. Epigenetic changes may serve as a diagnostic, prognostic, and chemo-sensitive marker. It also becomes a cancer preventive or therapeutic target in some circumstances.

Functional diversity of the glutathione peroxidase gene family among human populations: implications for genetic predisposition to disease and drug response

Aim: To analyze the human genetic variation of glutathione peroxidases (GPX), estimating the functional differences among human populations and suggesting interethnic differences in predisposition to disease and drug response. Materials & methods: Using 1000 Genomes Project data, we analyzed 723 GPX variants in 1092 individuals belonging to 14 populations. Combining functional prediction analyses of coding and noncoding variants, we developed a method to estimate haplotype functionality. Results: GPX rare variants have a higher functional impact than common variants. The frequency among Asian patients of haplotypes associated with normal functionality is significantly higher for GPX1 and lower for GPX3 than for non-Asian patients; no adaptation signals in GPX1 and GPX3 were found in Asian patients. Conclusion: GPX1 and GPX3 differences may be associated with alterations in antioxidant capacity and redox regulation, which suggests diverse susceptibility to complex disease and diverse response to relevant drugs in Asians compared with individuals with other ethnic origins.

Original submitted 7 February 2013; Revision submitted 16 May 2013

Genome-wide screening for understanding the role of DNA methylation in colorectal cancer

DNA methylation analysis methods have undergone an impressive revolution over the past 15 years. Regarding colorectal cancer (CRC), the localization and distribution of several differently methylated genes have been determined by genome-wide DNA methylation assays. These genes do not just influence the pathogenesis of CRC, but can be used further as diagnostic or prognostic markers. Moreover, the identified four DNA methylation-based subgroups of CRC have important clinical and therapeutic merit. Since genome-wide DNA methylation analyzes result in a large amount of data, there is a need for complex bioinformatic and pathway analysis. Future challenges in epigenetic alterations of CRC include the demand for comprehensive identification and experimental validation of gene abnormalities. By introduction of genome-wide DNA methylation profiling into clinical practice not only the patients' risk stratification but development of targeted therapies will also be possible.

Epigenetic changes in colorectal cancer

Epigenetic changes frequently occur in human colorectal cancer. Genomic global hypomethylation, gene promoter region hypermethylation, histone modifications, and alteration of miRNA patterns are major epigenetic changes in colorectal cancer. Loss of imprinting (LOI) is associated with colorectal neoplasia. Folate deficiency may cause colorectal Carcinogenesis by inducing gene-specific hypermethylation and genomic global hypomethylation. HDAC inhibitors and demethylating agents have been approved by the FDA for myelodysplastic syndrome and leukemia treatment. Non-coding RNA is regarded as another kind of epigenetic marker in colorectal cancer. This review is mainly focused on DNA methylation, histone modification, and microRNA changes in colorectal cancer.