Prognostic and predictive significance of long interspersed nucleotide element-1 methylation in advanced-stage colorectal cancer

Chromatin factors: Ready to roll as biomarkers in metastatic colorectal cancer?

Colorectal cancer (CRC) ranks as the third most prevalent cancer globally and stands as the fourth leading cause of cancer-related fatalities in 2020. Survival rates for metastatic disease have slightly improved in recent decades, with clinical trials showing median overall survival of approximately 24-30 months. This progress can be attributed to the integration of chemotherapeutic treatments alongside targeted therapies and immunotherapy. Despite these modest improvements, the primary obstacle to successful treatment for advanced CRC lies in the development of chemoresistance, whether inherent or acquired, which remains the major cause of treatment failure. Epigenetics has emerged as a hallmark of cancer, contributing to master transcription regulation and genome stability maintenance. As a result, epigenetic factors are starting to appear as potential clinical biomarkers for diagnosis, prognosis, and prediction of treatment response in CRC.In recent years, numerous studies have investigated the influence of DNA methylation, histone modifications, and chromatin remodelers on responses to chemotherapeutic treatments. While there is accumulating evidence indicating their significant involvement in various types of cancers, the exact relationship between chromatin landscapes and treatment modulation in CRC remains elusive. This review aims to provide a comprehensive summary of the most pertinent and extensively researched epigenetic-associated mechanisms described between 2015 and 2022 and their potential usefulness as predictive biomarkers in the metastatic disease.

LINE-1 Methylation Status in Canine Splenic Hemangiosarcoma Tissue and Cell-Free DNA

Splenic hemangiosarcoma is one of the most common malignant tumors in dogs, and early diagnosis is of great importance for achieving a good prognosis. DNA methylation plays an important role in cancer development. Long interspersed nuclear element 1 (LINE-1) is the most abundant repetitive element in the genome. LINE-1 hypomethylation has been shown to be related to carcinogenesis in humans, and it has been used as a novel cancer biomarker. This study aimed to evaluate the methylation status of LINE-1 in tumor tissue and circulating cell-free DNA and assess its clinical significance in canine splenic hemangiosarcoma. Genomic DNA was isolated from splenic masses of 13 dogs with hemangiosarcoma, 11 with other malignant tumors, and 15 with benign lesions. LINE-1 methylation was quantified using methylation-sensitive and -insensitive restriction enzyme digestion followed by real-time polymerase chain reaction. Additionally, blood samples were collected from eight patients to isolate cell-free DNA to determine LINE-1 methylation status changes during the treatment course. LINE-1 methylation in tumor samples was significantly lower in patients with hemangiosarcoma than in those with other malignant tumors and benign lesions. Non-significant but similar results were observed for the cell-free DNA samples. Our results demonstrate that LINE-1 methylation status is a potential biomarker for splenic hemangiosarcoma.

The Utility of Repetitive Cell-Free DNA in Cancer Liquid Biopsies

Liquid biopsy is a broad term that refers to the testing of body fluids for biomarkers that correlate with a pathological condition. While a variety of body-fluid components (e.g., circulating tumor cells, extracellular vesicles, RNA, proteins, and metabolites) are studied as potential liquid biopsy biomarkers, cell-free DNA (cfDNA) has attracted the most attention in recent years. The total cfDNA population in a typical biospecimen represents an immensely rich source of biological and pathological information and has demonstrated significant potential as a versatile biomarker in oncology, non-invasive prenatal testing, and transplant monitoring. As a significant portion of cfDNA is composed of repeat DNA sequences and some families (e.g., pericentric satellites) were recently shown to be overrepresented in cfDNA populations vs their genomic abundance, it holds great potential for developing liquid biopsy-based biomarkers for the early detection and management of patients with cancer. By outlining research that employed cell-free repeat DNA sequences, in particular the ALU and LINE-1 elements, we highlight the clinical potential of the repeat-element content of cfDNA as an underappreciated marker in the cancer liquid biopsy repertoire.

Evaluation of global and intragenic hypomethylation in colorectal adenomas improves patient stratification and colorectal cancer risk prediction

Background

Aberrant DNA hypomethylation of the long interspersed nuclear elements (LINE-1 or L1) has been recognized as an early event of colorectal transformation. Simultaneous genetic and epigenetic analysis of colorectal adenomas may be an effective and rapid strategy to identify key biological features leading to accelerated colorectal tumorigenesis. In particular, global and/or intragenic LINE-1 hypomethylation of adenomas may represent a helpful tool for improving colorectal cancer (CRC) risk stratification of patients after surgical removal of polyps. To verify this hypothesis, we analyzed a cohort of 102 adenomas derived from 40 high-risk patients (who developed CRC in a post-polypectomy of at least one year) and 43 low-risk patients (who did not develop CRC in a post-polypectomy of at least 5 years) for their main pathological features, the presence of hotspot variants in driver oncogenes (KRAS, NRAS, BRAF and PIK3CA), global (LINE-1) and intragenic (L1-MET) methylation status.

Results

In addition to a significantly higher adenoma size and an older patients’ age, adenomas from high-risk patients were more hypomethylated than those from low-risk patients for both global and intragenic LINE-1 assays. DNA hypomethylation, measured by pyrosequencing, was independent from other parameters, including the presence of oncogenic hotspot variants detected by mass spectrometry. Combining LINE-1 and L1-MET analyses and profiling the samples according to the presence of at least one hypomethylated assay improved the discrimination between high and low risk lesions (p = 0.005). Remarkably, adenomas with at least one hypomethylated assay identified the patients with a significantly (p < 0.001) higher risk of developing CRC. Multivariable analysis and logistic regression evaluated by the ROC curves proved that methylation status was an independent variable improving cancer risk prediction (p = 0.02).

Conclusions

LINE-1 and L1-MET hypomethylation in colorectal adenomas are associated with a higher risk of developing CRC. DNA global and intragenic hypomethylation are independent markers that could be used in combination to successfully improve the stratification of patients who enter a colonoscopy surveillance program.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-021-01135-0.

The role of DNA methylation in syndromic and non-syndromic congenital heart disease

Congenital heart disease (CHD) is a common structural birth defect worldwide, and defects typically occur in the walls and valves of the heart or enlarged blood vessels. Chromosomal abnormalities and genetic mutations only account for a small portion of the pathogenic mechanisms of CHD, and the etiology of most cases remains unknown. The role of epigenetics in various diseases, including CHD, has attracted increased attention. The contributions of DNA methylation, one of the most important epigenetic modifications, to CHD have not been illuminated. Increasing evidence suggests that aberrant DNA methylation is related to CHD. Here, we briefly introduce DNA methylation and CHD and then review the DNA methylation profiles during cardiac development and in CHD, abnormalities in maternal genome-wide DNA methylation patterns are also described. Whole genome methylation profile and important differentially methylated genes identified in recent years are summarized and clustered according to the sample type and methodologies. Finally, we discuss the novel technology for and prospects of CHD-related DNA methylation.

Aberrant Methylation of LINE-1 Transposable Elements: A Search for Cancer Biomarkers

Cancer remains one of the main causes of human mortality despite significant progress in its diagnostics and therapy achieved in the past decade. Massive hypomethylation of retrotransposons, in particular LINE-1, is considered a hallmark of most malignant transformations as it results in the reactivation of retroelements and subsequent genomic instability. Accumulating data on LINE-1 aberrant methylation in different tumor types indicates its significant role in cancer initiation and progression. However, direct evidence that LINE-1 activation can be used as a cancer biomarker is still limited. The objective of this review was to critically evaluate the published results regarding the diagnostic/prognostic potential of the LINE-1 methylation status in cancer. Our analysis indicates that LINE-1 hypomethylation is a promising candidate biomarker of cancer development, which, however, needs validation in both clinical and laboratory studies to confirm its applicability to different cancer types and/or stages. As LINE-1 is present in multiple cell-free copies in blood, it has advantages over single-copy genes regarding perspectives of using its methylation status as an epigenetic cancer biomarker for cell-free DNA liquid biopsy.

Methylation-Based Therapies for Colorectal Cancer

Colorectal carcinogenesis (CRC) is caused by the gradual long-term accumulation of both genetic and epigenetic changes. Recently, epigenetic alterations have been included in the classification of the CRC molecular subtype, and this points out their prognostic impact. As epigenetic modifications are reversible, they may represent relevant therapeutic targets. DNA methylation, catalyzed by DNA methyltransferases (DNMTs), regulates gene expression. For many years, the deregulation of DNA methylation has been considered to play a substantial part in CRC etiology and evolution. Despite considerable advances in CRC treatment, patient therapy response persists as limited, and their profit from systemic therapies are often hampered by the introduction of chemoresistance. In addition, inter-individual changes in therapy response in CRC patients can arise from their specific (epi)genetic compositions. In this review article, we summarize the options of CRC treatment based on DNA methylation status for their predictive value. This review also includes the therapy outcomes based on the patient's methylation status in CRC patients. In addition, the current challenge of research is to develop therapeutic inhibitors of DNMT. Based on the essential role of DNA methylation in CRC development, the application of DNMT inhibitors was recently proposed for the treatment of CRC patients, especially in patients with DNA hypermethylation.

Long interspersed nucleotide element-1 (LINE-1) methylation in colorectal cancer

Colorectal cancer (CRC) represents a group of molecularly heterogeneous diseases characterized by genetic and epigenetic alterations. Long interspersed nuclear elements (LINEs) are a form of retrotransposable element found in many eukaryotic genomes. These LINEs, when active, can mobilize in the cell and steadily cause genomic rearrangement. Active LINE reorganization is a source of endogenous mutagenesis and polymorphism in the cell that brings about individual genomic variation. In normal somatic cells, these elements are heavily methylated and thus mostly suppressed, in turn, preventing their potential for bringing about genomic instability. When LINEs are inadequately controlled, they can play a role in the pathogenesis of several genetic diseases, such as cancer. In tumor cells, LINE hypomethylation can reactivate the mobilization of these elements and is associated with both an advanced stage and a poor prognosis. In this article, we summarize the current knowledge surrounding LINE methylation, its correlation to CRC and its application as a diagnostic, prognostic and predictive biomarker in colon cancer.

Impact of Global DNA Methylation in Treatment Outcome of Colorectal Cancer Patients

Background: Global DNA methylation has an impact in cancer pathogenesis and progression. This study aimed at investigating the impact of global DNA methylation in treatment outcome of Colorectal Cancer (CRC).

Patients and Methods: Global DNA methylation was measured by LC/MS/MS in peripheral blood leucocytes of 102, 48, and 32 Egyptian CRC patients at baseline and after 3 and 6 months of Fluoropyrimidine (FP) therapy respectively, in addition to 32 normal healthy matched in age and sex. The genetic expressions of DNA methyl transferases (DNMTs) were determined and correlated with patients‘ survival using univariate and multivariate methods of analyses.

Results: Egyptian CRC patients had significant global hypomethylation of 5mC level and 5mC % with overexpression of DNMT3A and DNMT3B. Significant higher 5mC levels were shown in patients > 45 years, male gender, T2 tumors, stage II, negative lymph nodes, and absence of metastasis. FP therapy significantly reduced DNA methylation particularly in the subgroups of patients with high DNA methylation level at baseline and good prognostic features. After 3 years of follow up, patients with 5mC % > 8.02% had significant poor overall survival (OS) while, significant better event-free survival (EFS) was found in patients with 5mC level > 0.55. High initial CEA level and presence of metastasis were significantly associated with hazards of disease progression and death.

Conclusion: Global DNA methylation has a significant impact on the treatment outcome and survival of Egyptian CRC patients treated with FP- based therapy.

Long Interspersed Element-1 Methylation Level as a Prognostic Biomarker in Gastrointestinal Cancers

Epigenetic changes play a crucial role in human cancer development. DNA methylation is a central epigenetic process that regulates levels of gene expression. Changes in DNA methylation that occur in human tumors include global DNA hypomethylation and site-specific CpG island promoter hypermethylation. Long interspersed element-1 (LINE-1) is a repetitive DNA retrotransposon that duplicates via a copy-and-paste genetic mechanism. As LINE-1 constitutes approximately 17% of the human genome, the extent of LINE-1 methylation is regarded as a surrogate marker of global DNA methylation. In a variety of gastrointestinal (GI) cancers, LINE-1 hypomethylation is strongly associated with a poor prognosis, supporting its potential role as a prognostic biomarker. In this article, we summarize current knowledge regarding LINE-1 methylation and its prognostic impact in GI cancers.

The role of cell-free DNA in predicting colorectal cancer prognosis

Colorectal cancer is a cancer of the digestive system with poor prognosis. Cell-free DNA has received much attention with its unique predominance, especially in colorectal cancer. Areas covered: This study has summarized recent advancements and challenges regarding cell-free DNA in predicting CRC prognosis. Furthermore, the authors make predictions on the potential developments concerning cell-free DNA in future prognosis prediction techniques. Expert commentary: Cell-free DNA has the value of predicting CRC prognosis as an important biomarke. Further clinical trials should be performed to promote translating cell-free DNA into clinical applications.

DNA methylation aberrancies delineate clinically distinct subsets of colorectal cancer and provide novel targets for epigenetic therapies

Colorectal cancer (CRC) is a worldwide health concern with respect to both incidence and mortality, and as a result, CRC tumorigenesis, progression and metastasis have been heavily studied, especially with respect to identifying genetic, epigenetic, transcriptomic and proteomic profiles of disease. DNA methylation alterations are hallmarks of CRC, and epigenetic driver genes have been identified that are thought to be involved in early stages of tumorigenesis. Moreover, distinct CRC patient subgroups are organized based on DNA methylation profiles. CRC tumors displaying CpG island methylator phenotypes (CIMPs), defined as DNA hypermethylation at specific CpG islands in subsets of tumors, show high concordance with specific genetic alterations, disease risk factors and patient outcome. This review details the DNA methylation alterations in CRC, the significance of CIMP status, the development of treatments based on specific molecular profiles and the application of epigenetic therapies for CRC patient treatment.

Non-Coding RNAs as Predictive Biomarkers to Current Treatment in Metastatic Colorectal Cancer

The onset and selection of resistant clones during cancer treatment with chemotherapy or targeted therapy is a major issue in the clinical management of metastatic colorectal cancer patients. It is possible that a more personalized treatment selection, using reliable response-to-therapy predictive biomarkers, could lead to an improvement in the success rate of the proposed therapies. Although the process of biomarker selection and validation could be a long one, requiring solid statistics, large cohorts and multicentric validations, non-coding RNAs (ncRNAs) and in particular microRNAs, proved to be extremely promising in this field. Here we summarize some of the main studies correlating specific ncRNAs with sensitivity/resistance to chemotherapy, anti-VEGF therapy, anti-EGFR therapy and immunotherapy in colorectal cancer (CRC).

The dynamic DNA methylation landscape of the mutL homolog 1 shore is altered by MLH1-93G>A polymorphism in normal tissues and colorectal cancer

BACKGROUND

Colorectal cancers (CRCs) undergo distinct genetic and epigenetic alterations. Expression of mutL homolog 1 (MLH1), a mismatch repair gene that corrects DNA replication errors, is lost in up to 15% of sporadic tumours due to mutation or, more commonly, due to DNA methylation of its promoter CpG island. A single nucleotide polymorphism (SNP) in the CpG island of MLH1 (MLH1-93G>A or rs1800734) is associated with CpG island hypermethylation and decreased MLH1 expression in CRC tumours. Further, in peripheral blood mononuclear cell (PBMC) DNA of both CRC cases and non-cancer controls, the variant allele of rs1800734 is associated with hypomethylation at the MLH1 shore, a region upstream of its CpG island that is less dense in CpG sites.

RESULTS

To determine whether this genotype-epigenotype association is present in other tissue types, including colorectal tumours, we assessed DNA methylation in matched normal colorectal tissue, tumour, and PBMC DNA from 349 population-based CRC cases recruited from the Ontario Familial Colorectal Cancer Registry. Using the semi-quantitative real-time PCR-based MethyLight assay, MLH1 shore methylation was significantly higher in tumour tissue than normal colon or PBMCs (P < 0.01). When shore methylation levels were stratified by SNP genotype, normal colorectal DNA and PBMC DNA were significantly hypomethylated in association with variant SNP genotype (P < 0.05). However, this association was lost in tumour DNA. Among distinct stages of CRC, metastatic stage IV CRC tumours incurred significant hypomethylation compared to stage I-III cases, irrespective of genotype status. Shore methylation of MLH1 was not associated with MSI status or promoter CpG island hypermethylation, regardless of genotype. To confirm these results, bisulfite sequencing was performed in matched tumour and normal colorectal specimens from six CRC cases, including two cases per genotype (wildtype, heterozygous, and homozygous variant). Bisulfite sequencing results corroborated the methylation patterns found by MethyLight, with significant hypomethylation in normal colorectal tissue of variant SNP allele carriers.

CONCLUSIONS

These results indicate that the normal tissue types tested (colorectum and PBMC) experience dynamic genotype-associated epigenetic alterations at the MLH1 shore, whereas tumour DNA incurs aberrant hypermethylation compared to normal DNA.