Gunn Iren Meling

Different genetic pathways to proximal and distal colorectal cancer influenced by sex-related factors

Mutations in the k‐ras and TP53 genes, as well as microsatellite instability (MIN), are frequent genetic alterations in colorectal carcinomas and represent 3 different mechanisms in the carcinogenic process. Both the incidence of colorectal cancer and the frequency of genetic alterations in such tumours have been related to different clinico‐pathological variables, including age and gender of the patient and location of the tumour. A number of studies have also reported associations between different types of genetic alterations. We therefore wanted to explore the relationship between these genetic and clinico‐pathological variables using multivariate analysis on material from 282 colorectal carcinomas. Three logistic regression models were constructed: 1) the presence of K‐ras mutations was dependent on MIN and age and gender of patient, with an especially low frequency among younger males and in tumours with MIN (overall p = 0.0003); 2) the presence of TP53 mutations was only dependent on tumour location, with a positive association to cancers occurring distally (p = 0.002); and 3) the presence of MIN was dependent on age, gender and K‐ras and TP53 mutations, as well as on tumour location. MIN was most frequent among younger male and older female patients, was rare in tumours with K‐ras or TP53 mutations and was found almost exclusively in the proximal colon (overall p < 0.0001). Our data confirm that different genetic pathways to colorectal cancer dominate in the proximal and distal segments of the bowel and suggest that the K‐ras‐ and MIN‐dependent pathways are influenced by different sex‐related factors. Int. J. Cancer 74:664–669, 1997.© 1997 Wiley‐Liss, Inc.

A CpG island hypermethylation profile of primary colorectal carcinomas and colon cancer cell lines

BackgroundTumor cell lines are commonly used as experimental tools in cancer research, but their relevance for the in vivo situation is debated. In a series of 11 microsatellite stable (MSS) and 9 microsatellite unstable (MSI) colon cancer cell lines and primary colon carcinomas (25 MSS and 28 MSI) with known ploidy stem line and APC, KRAS, and TP53 mutation status, we analyzed the promoter methylation of the following genes: hMLH1, MGMT, p16INK4a(CDKN2A α-transcript), p14ARF(CDKN2A β-transcript), APC, and E-cadherin (CDH1). We compared the DNA methylation profiles of the cell lines with those of the primary tumors. Finally, we examined if the epigenetic changes were associated with known genetic markers and/or clinicopathological variables.ResultsThe cell lines and primary tumors generally showed similar overall distribution and frequencies of gene methylation. Among the cell lines, 15%, 50%, 75%, 65%, 20% and 15% showed promoter methylation for hMLH1, MGMT, p16INK4a, p14ARF, APC, and E-cadherin, respectively, whereas 21%, 40%, 32%, 38%, 32%, and 40% of the primary tumors were methylated for the same genes. hMLH1 and p14ARFwere significantly more often methylated in MSI than in MSS primary tumors, whereas the remaining four genes showed similar methylation frequencies in the two groups. Methylation of p14ARF, which indirectly inactivates TP53, was seen more frequently in tumors with normal TP53 than in mutated samples, but the difference was not statistically significant. Methylation of p14ARFand p16INK4awas often present in the same primary tumors, but association to diploidy, MSI, right-sided location and female gender was only significant for p14ARF. E-cadherin was methylated in 14/34 tumors with altered APC further stimulating WNT signaling.ConclusionsThe present study shows that colon cancer cell lines are in general relevant in vitro models, comparable with the in vivo situation, as the cell lines display many of the same molecular alterations as do the primary carcinomas. The combined pattern of epigenetic and genetic aberrations in the primary carcinomas reveals associations between them as well as to clinicopathological variables, and may aid in the future molecular assisted classification of clinically distinct stages.

K-ras mutation in colorectal cancer: Relations to patient age, sex and tumour location

DNA from 251 primary tumours obtained from 123 male and 125 female Norwegian patients with colorectal carcinoma was analysed for the presence of K-ras point mutations at codons 12 and 13. Mutations were found in 99 (39%) of the samples. The frequency of K-ras mutations was significantly related to age and sex of the patients, and to the location of the tumours (overall: P = 0.008). K-ras mutations were much less frequent in colonic tumours from male than female patients at younger ages (< 40 years, odds ratio < 0.014). The low frequency might indicate that a different, ras-independent, pathway to neoplasia is dominating in the colon of younger males. In contrast, older men had more mutations than older women (e.g. 90 years, odds ratio = 5.8). An inverse but less pronounced relationship was seen for rectal tumours. The type of mutation was found to be associated to sex of patient and location of tumour. G-->C transversions accounted for 35% of the mutations in rectal tumours from females, in contrast to only 2.5% in the rest of the material (P = 0.0005). This may indicate that there are specific carcinogens acting in this location.

ADAMTS1, CRABP1, and NR3C1 identified as epigenetically deregulated genes in colorectal tumorigenesis

Background: Gene silencing through CpG island hypermethylation is a major mechanism in cancer development. In the present study, we aimed to identify and validate novel target genes inactivated through promoter hypermethylation in colorectal tumor development. Methods: With the use of microarrays, the gene expression profiles of colon cancer cell lines before and after treatment with the demethylating agent 5-aza-2′-deoxycytidine were identified and compared. The expression of the responding genes was compared with microarray expression data of primary colorectal carcinomas. Four of these down-regulated genes were subjected to methylation-specific PCR, bisulphite sequencing, and quantitative gene expression analysis using tumors (n=198), normal tissues (n=44), and cell lines (n=30). Results: Twenty-one genes with a CpG island in their promoter responded to treatment in cell lines, and were simultaneously down-regulated in primary colorectal carcinomas. Among 20 colon cancer cell lines, hypermethylation was subsequently identified for three of four analyzed genes, ADAMTS1 (85%), CRABP1 (90%), and NR3C1 (35%). For the latter two genes, hypermethylation was significantly associated with absence or reduced gene expression. The methylation status of ADAMTS1, CRABP1, and NR3C1 was further investigated in 116 colorectal carcinomas and adenomas. Twenty-three of 63 (37%), 7/60 (12%), and 2/63 (3%) adenomas, as well as 37/52 (71%), 25/51 (49%), and 13/51 (25%) carcinomas were hypermethylated for the respective genes. These genes were unmethylated in tumors (n=82) from three other organs, prostate, testis, and kidney. Finally, analysis of normal colorectal mucosa demonstrated that the observed promoter hypermethylation was cancer-specific. Conclusion: By using a refined microarray screening approach we present three genes with cancer-specific hypermethylation in colorectal tumors, ADAMTS1, CRABP1, and NR3C1.

Gene methylation profiles of normal mucosa, and benign and malignant colorectal tumors identify early onset markers.

BackgroundMultiple epigenetic and genetic changes have been reported in colorectal tumors, but few of these have clinical impact. This study aims to pinpoint epigenetic markers that can discriminate between non-malignant and malignant tissue from the large bowel, i.e. markers with diagnostic potential.The methylation status of eleven genes (ADAMTS1, CDKN2A, CRABP1, HOXA9, MAL, MGMT, MLH1, NR3C1, PTEN, RUNX3, and SCGB3A1) was determined in 154 tissue samples including normal mucosa, adenomas, and carcinomas of the colorectum. The gene-specific and widespread methylation status among the carcinomas was related to patient gender and age, and microsatellite instability status. Possible CIMP tumors were identified by comparing the methylation profile with microsatellite instability (MSI), BRAF-, KRAS-, and TP53 mutation status.ResultsThe mean number of methylated genes per sample was 0.4 in normal colon mucosa from tumor-free individuals, 1.2 in mucosa from cancerous bowels, 2.2 in adenomas, and 3.9 in carcinomas. Widespread methylation was found in both adenomas and carcinomas. The promoters of ADAMTS1, MAL, and MGMT were frequently methylated in benign samples as well as in malignant tumors, independent of microsatellite instability. In contrast, normal mucosa samples taken from bowels without tumor were rarely methylated for the same genes. Hypermethylated CRABP1, MLH1, NR3C1, RUNX3, and SCGB3A1 were shown to be identifiers of carcinomas with microsatellite instability. In agreement with the CIMP concept, MSI and mutated BRAF were associated with samples harboring hypermethylation of several target genes.ConclusionMethylated ADAMTS1, MGMT, and MAL are suitable as markers for early tumor detection.

Identification of an epigenetic biomarker panel with high sensitivity and specificity for colorectal cancer and adenomas.

BackgroundThe presence of cancer-specific DNA methylation patterns in epithelial colorectal cells in human feces provides the prospect of a simple, non-invasive screening test for colorectal cancer and its precursor, the adenoma. This study investigates a panel of epigenetic markers for the detection of colorectal cancer and adenomas.MethodsCandidate biomarkers were subjected to quantitative methylation analysis in test sets of tissue samples from colorectal cancers, adenomas, and normal colonic mucosa. All findings were verified in independent clinical validation series. A total of 523 human samples were included in the study. Receiver operating characteristic (ROC) curve analysis was used to evaluate the performance of the biomarker panel.ResultsPromoter hypermethylation of the genes CNRIP1, FBN1, INA, MAL, SNCA, and SPG20 was frequent in both colorectal cancers (65-94%) and adenomas (35-91%), whereas normal mucosa samples were rarely (0-5%) methylated. The combined sensitivity of at least two positives among the six markers was 94% for colorectal cancers and 93% for adenoma samples, with a specificity of 98%. The resulting areas under the ROC curve were 0.984 for cancers and 0.968 for adenomas versus normal mucosa.ConclusionsThe novel epigenetic marker panel shows very high sensitivity and specificity for both colorectal cancers and adenomas. Our findings suggest this biomarker panel to be highly suitable for early tumor detection.

Genetic alterations within the retinoblastoma locus in colorectal carcinomas. Relation to DNA ploidy pattern studied by flow cytometric analysis

Alterations within the retinoblastoma (Rb) gene, as detected by the VNTR probe p68RS2.0, and flow cytometric DNA pattern have been analysed in 255 colorectal carcinomas. A total of 35.3% of the tumours had alterations within the Rb gene. Amplification of one allele was demonstrated in 29.5% of the tumours, and loss of heterozygosity was found in 11.5%. No association was found between amplification within the Rb gene and clinicopathological characteristics of the patients. The high frequency of alterations demonstrated within the Rb gene, suggests that this gene is involved in colorectal carcinogenesis with amplification as by far the most abundant genetic alteration. This may imply that the Rb gene has an oncogene-like function in colorectal carcinomas, rather than acting as a tumour suppressor gene. Sixty-three per cent of the carcinomas were DNA aneuploid, and a significant association was demonstrated between amplification within the Rb gene and DNA aneuploidy (P less than 0.01). Two other chromosome loci were analysed, on chromosome 1p (probe pYNZ2) and on chromosome 2p (probe pYNH24), respectively. On chromosome 1p, heterozygous loss was found in 22.2% of the tumours, indicating an involvement of this chromosome in a subset of colorectal carcinomas.

Immunofluorometric assay for the metastasis-related protein S100A4: release of S100A4 from normal blood cells prohibits the use of S100A4 as a tumor marker in plasma and serum.

The metastasis-related protein S100A4 is released from tumor cells, and since it is highly expressed in colorectal cancer (CRC), it could be a potential tumor marker in plasma or serum. Monoclonal antibodies (MAbs) were raised against human recombinant S100A4 and shown to detect native and recombinant antigen with high sensitivity and specificity. Using two MAbs, an immunofluorometric assay (IFMA) was established to detect S100A4 in clinical samples with high sensitivity and precision. S100A4 in plasma and serum from patients with CRC was highly influenced by sample hemolysis. Both red blood cells and mononuclear cells were found to contain S100A4, possibly contributing to the measured levels in serum and plasma. Since even very low-level hemolysis influenced the results, a potential contribution from an S100A4-expressing tumor could not be discerned, indicating that S100A4 is not suitable as a plasma or serum tumor marker for CRC. The antibodies and the IFMA may still be useful for research purposes.

ColoGuidePro: A Prognostic 7-Gene Expression Signature for Stage III Colorectal Cancer Patients

Purpose: Improved prognostic stratification of patients with stage II and III colorectal cancer is warranted for postoperative clinical decision making. This study was conducted to develop a clinically feasible and robust prognostic classifier for these patients independent of adjuvant treatment. Experimental Design: Global gene expression profiles from altogether 387 stage II and III colorectal cancer tissue samples from three independent patient series were included in the study. ColoGuidePro, a seven-gene prognostic classifier, was developed from a selected Norwegian learning series (n = 95; no adjuvant treatment) using lasso-penalized multivariate survival modeling with cross-validation. Results: The expression signature significantly stratified patients in a consecutive Norwegian test series, in which patients were treated according to current standards [HR, 2.9 (1.1–7.5); P = 0.03; n = 77] and an external validation series [HR, 3.7 (2.0–6.8); P < 0.001; n = 215] according to survival. ColoGuidePro was also an independent predictor of prognosis in multivariate models including tumor stage in both series (HR, ≥3.1; P ≤ 0.03). In the validation series, which consisted of patients from other populations (United States and Australia), 5-year relapse-free survival was significantly predicted for stage III patients only (P < 0.001; n = 107). Here, prognostic stratification was independent of adjuvant treatment (P = 0.001). Conclusions: We present ColoGuidePro, a prognostic classifier developed for patients with stage II and III colorectal cancer. The test is suitable for transfer to clinical use and has best prognostic prediction potential for stage III patients. Clin Cancer Res; 18(21); 6001–10. ©2012 AACR.

Hypermethylated MAL gene - a silent marker of early colon tumorigenesis.

BackgroundTumor-derived aberrantly methylated DNA might serve as diagnostic biomarkers for cancer, but so far, few such markers have been identified. The aim of the present study was to investigate the potential of the MAL (T-cell differentiation protein) gene as an early epigenetic diagnostic marker for colorectal tumors.MethodsUsing methylation-specific polymerase chain reaction (MSP) the promoter methylation status of MAL was analyzed in 218 samples, including normal mucosa (n = 44), colorectal adenomas (n = 63), carcinomas (n = 65), and various cancer cell lines (n = 46). Direct bisulphite sequencing was performed to confirm the MSP results. MAL gene expression was investigated with real time quantitative analyses before and after epigenetic drug treatment. Immunohistochemical analysis of MAL was done using normal colon mucosa samples (n = 5) and a tissue microarray with 292 colorectal tumors.ResultsBisulphite sequencing revealed that the methylation was unequally distributed within the MAL promoter and by MSP analysis a region close to the transcription start point was shown to be hypermethylated in the majority of colorectal carcinomas (49/61, 80%) as well as in adenomas (45/63, 71%). In contrast, only a minority of the normal mucosa samples displayed hypermethylation (1/23, 4%). The hypermethylation of MAL was significantly associated with reduced or lost gene expression in in vitro models. Furthermore, removal of the methylation re-induced gene expression in colon cancer cell lines. Finally, MAL protein was expressed in epithelial cells of normal colon mucosa, but not in the malignant cells of the same type.ConclusionPromoter hypermethylation of MAL was present in the vast majority of benign and malignant colorectal tumors, and only rarely in normal mucosa, which makes it suitable as a diagnostic marker for early colorectal tumorigenesis.