The genetics of colorectal cancer

Molecular Characterization of Cellular Proteins from Colorectal Tumors

Aims and background

Recent evidence has suggested that progressive stages of colorectal tumorigenesis can be defined by a sequence of genetic events characterized by altered expression of certain genes and the appearance of cancer-specific proteins. Although the significance of these events is still not clear, expression of cancer-specific protein components may be directly involved in the neoplastic transformation. The purpose of the present study was to compare molecular characteristics of cellular proteins from human colorectal tumors and normal colonic mucosa.

Methods

Normal mucosa and colorectal tumors from 18 patients were fractionated by a differential centrifugation scheme into four cellular fractions, i.e., nuclear, mitochondrial (10P), microsomal (100P) and cytosolic (100S). The proteins of these fractions from normal and tumorigenic mucosa were analyzed by one-dimensional polyacrylamide gel electrophoresis followed by Coomassie brilliant blue R-250 and silver nitrate staining. Nuclear proteins from normal and neoplastic tissues which had revealed the most significant diversities were further characterized by two-dimensional gel electrophoresis. Electrophoretically cancer-specific nuclear proteins in the molecular mass zone 35-40 kDa were used as immunogen to produce rabbit polyclonal antibodies.

Results

Electrophoretic analysis by one-dimensional gel electrophoresis showed clear differences in molecular characteristics of cellular proteins between normal and tumorigenic mucosa, especially among nuclear fractions. The latter were also confirmed by their two-dimensional electrophoresis results. Rabbit antibodies raised against electrophoretically specific nuclear proteins characterized by molecular mass of 35-40 kDa cross-reacted with 36 kDa polypeptide in 15 of 18 (83.3%) studied nuclear fractions of colorectal tumors but not with any normal mucosa. In some cases, nuclear cancer-associated components of 38 and 40 kDa were also recognized by these antibodies.

Conclusions

During colorectal carcinogenesis, specific expression of several nuclear proteins takes place. One of them, the polypeptide of 36 kDa not found in normal colonic epithelium, was shared by over 83% of the studied carcinomas despite variations in detailed cancer properties. This particular nuclear protein may be considered as a potential marker for the colon malignancy.

Meta-analysis: folic acid in the chemoprevention of colorectal adenomas and colorectal cancer

BACKGROUND

Folic acid has been identified as a possible agent for the chemoprevention of colorectal cancer.

AIM

To assess the effectiveness of folic acid in reducing the recurrence of adenomas (precursors of colorectal cancer) among populations with a history of adenomas and the incidence of colorectal cancer within average-risk populations.

METHODS

Systematic review of randomized controlled trials comparing folic acid alone, or with other agents, vs. placebo. Eight databases were searched for relevant trials. Meta-analysis was performed.

RESULTS

The literature search retrieved 3785 citations. Six studies met the inclusion criteria. Meta-analysis of three studies in individuals with a history of adenomas showed no statistically significant difference in the relative risk of adenoma recurrence (RR 0.93, P = 0.27). A sensitivity analysis of the two higher quality trials changed the direction of effect (RR 1.16, P = 0.11). Meta-analysis of three trials in general populations demonstrated no statistically significant effect on the relative risk of colorectal cancer (RR 1.13, P = 0.54). In all three analyses, outcome event rates were higher in individuals receiving folic acid.

CONCLUSION

There is no evidence that folic acid is effective in the chemoprevention of colorectal adenomas or colorectal cancer for any population.

Measures of familial aggregation depend on definition of family history: meta-analysis for colorectal cancer

OBJECTIVE

Familial aggregation, a primary theme in genetic epidemiology, can be estimated from family studies based on an index person. The excess risk due to the presence of affected family members can be classified according to whether disease in the relatives is considered a risk factor for the index person (type I relative risk) or whether the disease status of the index person is considered a risk factor for the relatives (type II relative risk).

STUDY DESIGN AND SETTING

A meta-analysis of published colorectal cancer studies reporting a measure of familial association was performed and application of multilevel linear regression to model age-specific relative risks presented.

RESULTS

The pooled type I relative risk of colorectal cancer given any affected first-degree relative (based on 20 studies) was 2.26 (95% confidence interval CI = 1.86, 2.73) and decreased with the age of the consultand. The pooled type II estimate (based on seven studies) was 2.81 (95% CI = 2.05, 3.85).

CONCLUSION

Type I relative risks are useful in clinical counseling settings when a consultand wants to know his/her disease risk given his or her family history. Type II relative risks can be used to quantify the risk of disease to relatives of an affected individual and then identify subjects eligible for screening.

Tailored Therapy of Colorectal Cancer

Colorectal cancer is a leading cause of cancer mortality and morbidity. Despite the recent results of systemic chemotherapy, more than 40% of patients with advanced cancer still do not achieve substantial benefits with cytotoxic agents. Therefore, new tailored strategies are warranted to improve the probability of disease control. The rationale for this approach is based on the identification of the in vivo interactions among patient's characteristics, disease physiopathology, and drug pharmacodynamics and pharmacokinetics. Genomic and proteomic technologies may clarify the mechanisms involved in cancer growth and progression in each single patient and in the molecular basis of interindividual differences of anticancer drugs in terms of efficacy and toxicity. Despite the recent encouraging data, the clinical use of targeted therapy is hampered by several questions, such as: optimal biologic dose and schedule, lack of predictive surrogate biomarkers, and modalities of combination with chemotherapy/radiotherapy. Further efforts are needed to improve the reliability of genomic and proteomic technologies, in particular regarding their standardization and widespread availability. These unsolved issues make tailored therapy an open challenge.

Management of colorectal cancer

Colorectal cancer is the second most common cause of cancer death in the UK. Prompt investigation of suspicious symptoms is important, but there is increasing evidence that screening for the disease can produce significant reductions in mortality. High quality surgery is of paramount importance in achieving good outcomes, particularly in rectal cancer, but adjuvant radiotherapy and chemotherapy have important parts to play. The treatment of advanced disease is still essentially palliative, although surgery for limited hepatic metastases may be curative in a small proportion of patients.

Epidemiology of colorectal cancer

Colorectal cancer is a important public health problem: there are nearly one million new cases of colorectal cancer diagnosed world-wide each year and half a million deaths. Recent reports show that, in the US, it was the most frequent form of cancer among persons aged 75 years and older. Given that the majority of cancers occur in elder people and with the ageing of the population in mind, this observation gives further impetus to investigating prevention and treatment strategies among this subgroup of the population. Screening research, recommendations and implementation is an obvious priority. While there are many questions to be resolved, it is apparent that many facets of colorectal cancer are becoming increasingly understood and prospects for prevention are becoming apparent. Achieving colorectal cancer control is the immediate challenge.

K-ras Mutational Analysis of Polyclonal Colorectal Cancers Identifies Uniclonal Circulating Tumor Cells

The clonal development of colorectal carcinoma resulting from specific mutations in certain oncogenes and/or tumor suppressor genes is a well-accepted model. It is increasingly recognized that a majority of colorectal cancers are polyclonal on the basis of molecular analysis that demonstrates cells with different mutations within a given oncogene or tumor suppressor gene in the same tumor. This polyclonal pattern may occur as a result of either clonal convergence or divergence during the many steps of oncogenesis. Further complicating this picture is the fact that metastatic lesions may arise from only one of the clonal populations within a tumor and thereby present only a partial molecular make-up of the whole tumor. There are few data available that define clonal selection or specificity of circulating tumor cells in patients undergoing curative resection of colorectal carcinoma. The purpose of this paper is to describe the clonal distribution of circulating tumor cells in four patients with multiple K- ras mutations present in the primary lesion. Patients were selected who were known to have polyclonal primary colorectal cancers resected for cure. All patients had multiple mutations present in exon one, codon 12 and/or 13, of the K- ras gene. Blood samples were drawn immediately before surgery and at 2-week to 6-month intervals postoperatively. Epithelial cells were isolated from peripheral blood mononuclear cells using Dynal ImmunobeadsRT coated with antiepithelial antibodies. DNA was extracted from these cells and analyzed for all K- ras mutations present in codons 12 and 13 of the patient's primary tumor using allele-specific polymerase chain reaction followed by Microwell Array Diagonal Gel Electrophoresis. Circulating tumor cells were identified in all four patients. However, in each case of positive circulating cells the only mutation identified was an aspartic acid mutation at codon 13. Once positive the circulating tumor cells persisted in subsequent multiple blood samples. These results provide further strength for the theory of polyclonal progression in primary colorectal cancers, although there may be specific mutational patterns that confer the ability to metastasize. The significance of this persistence of the glycine-to-aspartic acid mutation at codon 13 remains to be defined given that none of these patients has clinical evidence of recurrent cancer at the time of this report.

Site specificity of colorectal neoplasms in families without an inherited syndrome

BACKGROUND

Relatives of patients with bowel neoplasia have an increased risk of bowel neoplasia. If there were concordance in location of neoplasia between relatives, then location-specific screening could be used. Such concordance might also assist in the understanding of the etiology of neoplasia within individual families.

METHODS

We have investigated the concordance in anatomic location of colonic neoplasia between first-degree relatives using a new statistical technique for paired data called alternating logistic regression.

RESULTS

A total of 146 families were ascertained, none of which had clinical evidence of a hereditary predisposition to edon neoplasia. Among those with neoplasia, there was an increased risk for right-sided disease with older age (40% for less than age 60 vs. 58% for at least 70 years of age, p = 0.008). As assessed by the odds ratio, we found no significant concordance within families for location of neoplasia (odds ratio = 1.2: CI [0.7, 2.2]), although there was a suggestion that location in family members of the same generation was more strongly associated (odds ratio 1.87: CI [0.82, 4.25]).

CONCLUSIONS

The lack of concordance within families for location argues against considering family-specific bowel screening protocols and indicates that the most important causes of bowel neoplasia are not sufficiently focused on one anatomic site to facilitate etiologic research.

Microsatellite instability assessment in prediction of drug resistance in childhood Burkitt's and large cell diffuse malignant non-Hodgkin lymphoma (MNHL)

BACKGROUND

Genomic instability may, especially with DNA directed treatment, be associated with increased therapeutic response; absence may be associated with drug resistance. In childhood MNHL, drug response is variable. At present the degree of presence of microsatellite variation, i.e., intrinsic DNA instability is not known.

AIMS

To determine presence and range of microsatellite variability in common childhood MNHL.

METHODS

1.3.1. Study Populations. Consecutive, unselected (1976-96) cases of childhood Large Cell diffuse, N = 16; (9T,7B), age range 1y5m-16y8m; Burkitt's Lymphoma, n = 13, age range 4y2m-14y. Non-malignant/pre-treatment tissue of 20 cases, 13 LC, 7 Burkitt's MNHL. 1.3.2. Molecular Pathology. Routine DNA extraction, amplifications at loci D3S 1304 and D3S1537 (both closely distal to VHL, tumour suppressor gene); ELN gene D7S1870; IFNA D1S243 (1p36) which show microsatellite variation. Isotopic labelling in amplification, non-denaturing gel electrophoresis, autoradiography.

RESULTS

Microsatellite variability was found 3/16 LC and 2/13 Burkitt's MNHL. LC MNHL, 4 abnormal areas: n = 1, 3 abnormal areas: n = 1, 2 abnormal areas n = 1; Burkitt's MNHL, 3 abnormal areas: n = 1, 1 abnormal area n = 1. No variability was found in the normal (constitutional) DNA of any of the 20 patients studied.

CONCLUSIONS

Microsatellite variability occurred in 5/29 patients with common types of childhood MNHL, indicating a limited contribution to reduced drug resistance through this mechanism.

K-ras mutation and loss of heterozygosity of the adenomatous polyposis coli gene in patients with colorectal adenomas with in situ carcinoma

BACKGROUND

The majority of colorectal carcinomas, if not all, arise from a benign adenoma. The DNA of the carcinomatous cells frequently has mutations in several genes. However, it is not exactly clear when during the neoplastic process each mutation develops. An adenoma with an area of in situ carcinoma provides an opportunity to evaluate genetic changes within a single neoplasia whose separate areas are comprised of both the benign adenoma as well as the malignant carcinoma.

METHODS

Thirty-seven neoplasms with areas of both benign adenoma and in situ carcinoma were studied. Both portions were evaluated for loss of heterozygosity (LOH) of the adenomatous polyposis coli (APC) gene and for mutations in codons 12/13 of the K-ras oncogene using the polymerase chain reaction technique.

RESULTS

Twenty-eight neoplasms showed no LOH in either portion whereas both portions of 4 neoplasms revealed a loss of heterozygosity. In three lesions the APC gene was normal in the adenomatous portion but LOH was present in the carcinomatous portion. Two neoplasms were uninformative for LOH of the APC gene. Thirteen neoplasms showed the wild-type pattern for the K-ras oncogene whereas 15 contained the identical mutation in both portions. Of the remaining nine neoplasms, six had a K-ras mutation in the adenomatous portion only and three had one pattern in the adenomatous portion and a different pattern in the in situ carcinoma portion.

CONCLUSIONS

LOH of the APC gene is an early and persistent feature in the evolution of a benign colorectal adenoma into an in situ carcinoma. There is less consistency regarding K-ras mutations; one in five in situ carcinomas contains a K-ras mutation different from that observed in the adenomatous portion.

Neurotensin and a non-peptide neurotensin receptor antagonist control human colon cancer cell growth in cell culture and in cells xenografted into nude mice

The intestine is a large endocrine organ, but the dependence of colon cancer on hormones remains unknown. We show here that neurotensin, a paracrine/endocrine peptide in the gut, and the neurotensin receptor antagonist SR 48692 control colon cancer cell growth in vitro and in vivo by interacting with receptors that are ectopically expressed in colon cancers. In cell culture, neurotensin stimulates the growth of human colon cancer cell lines (SW480, SW620, HT29, HCT116 and Cl.19A) expressing the neurotensin receptor NTR1 but does not change the growth of Caco2 cells, which do not express NTR1. In SW480 cells, neurotensin is active in the 10(-10) to 10(-6) M concentration range (ED50 = 0.47 nM) while the neurotensin fragment (I-II) is inactive. Neurotensin also enhances the cellular cloning efficiency of SW480 cells in soft agar by inducing a 50% increase of colony formation. This effect is blocked by SR 48692, which alone does not alter colony formation. Subcutaneous delivery of neurotensin (0.54 micromol/kg every 24 hr) by osmotic pumps to nude mice that have been xenografted with SW480 cells results in a significant increase of tumor volume, i.e., up to 255% of control at day 20 of treatment. SR 48692 administered alone (1.7 micromol/kg every 24 hr) by daily i.p. injections reduces the development of tumors formed by xenografting SW480 cells in nude mice. A significant mean reduction of tumor volume of 38% is observed during the 22-day period of treatment. SR 48692 alone is also active at reducing tumor volume after xenografting HCT116 cells in nude mice. Our results support the notion that colon cancer growth may be dependent on blood-borne neurotensin and suggest that non-peptide neurotensin antagonists, such as SR 48692, may be useful for the development of novel therapeutic strategies of colon cancer.

Analysis of microsatellite instability in cervical cancer

Microsatellite instability was first reported in hereditary nonpolyposis colorectal cancer (HNPCC) as well as other cancers, including endometrial and ovarian cancers. Single base repeat markers of human MSH3 and MSH6 genes were found to precipitate the action of human MSH2. The marker BAT-26 was reported to be a simple, low-cost, and rapid marker for detection replication errors (RER) and the status of colorectal cancers. We analyzed di-nucleotide repeats of the microsatellite markers (D2 S123, D5 S82, D5S299, D10S197, D17S791, D18S34), single base repeat markers (DeltaP3, hMSH3, hMSH6, and TGFbeta-RII), and BAT-26 to evaluate microsatellite instability in cervical cancer. Altogether 80 paired cervical cancers were studied. Our results showed that microsatellite instability is not common in cervical cancer, and the mutation of the single base repeat of mismatch repair (MMR) genes (hMSH3 and hMSH6) is also uncommon. The BAT-26 is not a good marker to detect the RER status of cervical cancer.

Epidemiological study of p53 tumor suppressor gene mutations in patients from Luxembourg and the German Saar region with an advanced colorectal cancer using PCR-SSCP analysis

Mutations in the p53 tumor suppressor gene are usually associated with an advanced development of colorectal cancer characterized by the transition from the adenoma to the carcinoma stage. We used the polymerase chain reaction (PCR) followed by single-strand conformation polymorphism (SSCP) analysis to screen for the presence of mutations in the p53 gene of patients from Luxembourg and the German Saar region with colorectal cancers at various developmental stages. While we detected no mutations in 16 colic polypi at an early to intermediate stage (adenoma), we revealed seven (13.7%) non-silent point mutations (transitions) in exons 5 to 9 of the p53 gene in 51 colorectal tumors at a late stage (carcinoma). In addition to confirming previous observations, these results show that PCR-SSCP analysis can provide both a sensitive and rapid method for the genetic determination of the histopathological stage of colorectal samples.

Chromosomal aberrations associated with invasion in papillary superficial bladder cancer

Non-invasive and invasive papillary transitional cell carcinomas of stages pTa and pT1 represent the first steps of tumour progression in bladder cancer. In order to analyse different chromosomal alterations of pTa and pT1 superficial bladder cancer, 46 tumour specimens were examined by comparative genomic hybridization (CGH). Losses of chromosome 9 material (11/20) and gains of chromosome 17 material (6/20) were frequently found in pTa tumours. Stage pT1 tumours were characterized by gains of chromosome 1q (14/26; including amplification at 1q21-q24 in three cases) and chromosome 17 material (15/26), as well as by losses of 11p (15/26) and 11q (13/26). Other loci frequently showing losses in pT1 tumours were 2q (9/26), 4q (10/26), 5q (9/26), 8p (10/26), 9p (9/26), 9q (12/26), 10q (8/26), 17p (7/26), and 18q (8/26). Amplifications were detected at 8q21/22, 5q21, 7q36, 10p14, 10p12, 10q25, 12q12, and 12q14. The most striking differences between grade 2 pTa and pT1 tumours were gains of 1q (P < 0.01) and losses at 2q (P < 0.025), 10q (P < 0.05), 11p (P < 0.01), 11q (P < 0.01), and 17p (P < 0.05), as well as the total number of aberrations (pTa grade 2: 4.1; pT1 grade 2: 8.6 aberrations per tumour). These data show characteristic chromosomal aberrations associated with invasion in superficial bladder cancer.

Cytogenetics and the surgeon: an invaluable tool in diagnosis, prognosis and counselling of patients with solid tumours

BACKGROUND

Cytogenetic studies have become an important part of tumour characterization. In a minority of tumours cytogenetic and/or molecular studies may be of help for diagnosis, selection of treatment protocols and predicting outcome.

METHODS

This article reviews the literature on solid tumour translocations and established family cancer syndromes. In addition, the potential importance of genetics in management of patients with breast, ovarian and pancreatic carcinoma is reviewed.

RESULTS AND CONCLUSION

Cytogenetic analysis of tumours may help confirm the diagnosis when conventional histology demonstrates no evidence of differentiation along a particular tissue pathway. For patients with well defined cancer syndromes, cytogenetic and molecular analysis offers the prospect of screening to reduce the risk of malignant disease. For many malignancies the underlying genetic anomalies are gradually being elucidated. Further studies designed to demonstrate the significance of these findings can only be undertaken if tumour material is collected and stored in optimal conditions for cytogenetic and/or molecular biological studies.

Ki-ras oncogene and p53 tumour suppressor gene mutations in colorectal carcinomas from the European Saar-Luxembourg region are less frequent than predicted by the classic adenoma-carcinoma sequence model

Recent investigations of colorectal cancer (CRC) have suggested that the accumulation of specific alterations in cell-growth regulating genes trigger the stage-wise progression to malignancy and that at least some of them could be useful for prognosis. In this study, the frequency, location and type of mutations of the Ki-ras proto-oncogene exons 1-2 and p53 tumour-suppressor gene exons 5-9 were analysed in colorectal carcinomas of 72 patients from the European Saar-Luxembourg region using PCR-SSCP screening and direct sequencing. The incidences of Ki-ras activating and p53 inactivating point mutations in these European samples were much lower (Ki-ras: 5 (6.9%) and p53: 13 (18.1%)) than reported for both genes in American studies (40-50% at least) (P < 1 x 10(-3)). These results suggest that other genetic mechanisms than those proposed for the classic adenoma-carcinoma sequence model can frequently underlie CRC development and that Ki-ras and p53 mutations should not be considered as universal markers for CRC.

Colorectal carcinogenesis: from chromosomal evolution pathways to molecular pathogenesis

Since the mid-1980s, research in the field of colorectal carcinogenesis has seen a series of breakthroughs such, as the process of loss of heterozygosity for large chromosomal segments and the consequent characterization of a series of suppressor genes considered to be the targets of the allelic deletions. More recently, a new perspective has been opened, with the discovery of germinal mutations of genes involved in mismatch repair in certain inherited forms of the disease. Through the retrospective analysis of our data on colorectal adenomas and cancers, we have tried to critically reassess a number of theoretical considerations relating to the instability of the genome viewed at the chromosome level and its consequence on tumor progression.

Loss of heterozygosity at 5q21 in non-small cell lung cancer: a frequent event but without evidence of apc mutation

Four genetic polymorphisms in the APC and MCC genes at chromosome 5q21 were analysed for loss of heterozygosity (LOH) in 97 primary squamous carcinomas and adenocarcinomas of the lung. LOH was identified in at least two polymorphic loci in 41 percent of informative cases. There was no significant difference in the frequency of LOH between squamous carcinomas and adenocarcinomas. Within the adenocarcinoma group, however, LOH appeared to be more common in tumours having a bronchial origin (5/9; 56 per cent) than in parenchymal adenocarcinoma (6/21; 29 per cent). All 32 tumours showing LOH at one or more polymorphic sites were examined for mutations in the mutation cluster region (MCR) of APC by single-strand conformational polymorphism (SSCP) analysis. Mutations were not detected in any of these cases. We therefore propose that it is likely that a tumour suppressor gene on 5q other than APC is involved in the pathogenesis of lung cancer.

The adenomatous polyposis coli tumor suppressor protein localizes to plasma membrane sites involved in active cell migration

Mutations in the adenomatous polyposis coli (APC) gene are linked to polyp formation in familial and sporadic colon cancer, but the functions of the protein are not known. We show that APC protein localizes mainly to clusters of puncta near the ends of microtubules that extend into actively migrating regions of epithelial cell membranes. This subcellular distribution of APC protein requires microtubules, but not actin filaments. APC protein-containing membranes are actively involved in cell migration in response to wounding epithelial monolayers, addition of the motorgen hepatocyte growth factor, and during the formation of cell-cell contacts. In the intestine, APC protein levels increase at the crypt/villus boundary, where cell migration is crucial for enterocyte exit from the crypt and where cells accumulate during polyp formation that is linked to mutations in the microtubule-binding domain of APC protein. Together, these data indicate that APC protein has a role in directed cell migration.

Gene regulation and the origin of cancer: a new model

The genome is a dynamical system in which regulation is achieved by the algebraic logic of Boolean functions. A model of a webbed genetic network is presented. In this, all genes lie on interconnected loops, within which each can influence the others, forming the basis of a regulatory network. The normal proto-oncogenes and tumor suppressor genes serve as gateways or switch points in the genetic circuitry, controlling the transition between different cell states. The model explains why multiple genes must be perturbed for the formation of a cancer.