Genetic instability and chromosomal aberrations in colorectal cancer: a review of the current models

Aspirin and the chemoprevention of cancers: A mathematical and evolutionary dynamics perspective

Epidemiological data indicate that long-term low dose aspirin administration has a protective effect against the occurrence of colorectal cancer, both in sporadic and in hereditary forms of the disease. The mechanisms underlying this protective effect, however, are incompletely understood. The molecular events that lead to protection have been partly defined, but remain to be fully characterized. So far, however, approaches based on evolutionary dynamics have not been discussed much, but can potentially offer important insights. The aim of this review is to highlight this line of investigation and the results that have been obtained. A core observation in this respect is that aspirin has a direct negative impact on the growth dynamics of the cells, by influencing the kinetics of tumor cell division and death. We discuss the application of mathematical models to experimental data to quantify these parameter changes. We then describe further mathematical models that have been used to explore how these aspirin-mediated changes in kinetic parameters influence the probability of successful colony growth versus extinction, and how they affect the evolution of the tumor during aspirin administration. Finally, we discuss mathematical models that have been used to investigate the selective forces that can lead to the rise of mismatch-repair deficient cells in an inflammatory environment, and how this selection can be potentially altered through aspirin-mediated interventions. This article is categorized under: Models of Systems Properties and Processes > Mechanistic Models Analytical and Computational Methods > Analytical Methods Analytical and Computational Methods > Computational Methods.

MACROD2 Haploinsufficiency Impairs Catalytic Activity of PARP1 and Promotes Chromosome Instability and Growth of Intestinal Tumors

ADP-ribosylation is an important posttranslational protein modification that regulates diverse biological processes, controlled by dedicated transferases and hydrolases. Here, we show that frequent deletions (∼30%) of the MACROD2 mono-ADP-ribosylhydrolase locus in human colorectal cancer cause impaired PARP1 transferase activity in a gene dosage-dependent manner. MACROD2 haploinsufficiency alters DNA repair and sensitivity to DNA damage and results in chromosome instability. Heterozygous and homozygous depletion of Macrod2 enhances intestinal tumorigenesis in Apc^Min/+ mice and the growth of human colorectal cancer xenografts. MACROD2 deletion in sporadic colorectal cancer is associated with the extent of chromosome instability, independent of clinical parameters and other known genetic drivers. We conclude that MACROD2 acts as a haploinsufficient tumor suppressor, with loss of function promoting chromosome instability, thereby driving cancer evolution.Significance: Chromosome instability (CIN) is a hallmark of cancer. We identify MACROD2 deletion as a cause of CIN in human colorectal cancer. MACROD2 loss causes repression of PARP1 activity, impairing DNA repair. MACROD2 haploinsufficiency promotes CIN and intestinal tumor growth. Our results reveal MACROD2 as a major caretaker tumor suppressor gene. Cancer Discov; 8(8); 988-1005. ©2018 AACR.See related commentary by Jin and Burkard, p. 921This article is highlighted in the In This Issue feature, p. 899.

MLH1-rheMac hereditary nonpolyposis colorectal cancer syndrome in rhesus macaques

The discovery of MLH1-rheMac hereditary nonpolyposis colorectal cancer syndrome in rhesus macaques (MLH1-rheMac HNPCC), which is an orthologue of Lynch syndrome in humans, is highly significant in the field of oncology. The hereditary nature of this disease should allow for planned cross-breeding of rhesus macaques to assess the effects of homozygous versus heterozygous MLH1 gene mutations, as well as other comutations and environmental factors that may affect the development of colon cancers. Also, the MLH1-rheMac HNPCC syndrome in rhesus macaques can serve as an important model for development of novel approaches to diagnosis and therapy of Lynch syndrome in human patients.

Over the past two decades, 33 cases of colonic adenocarcinomas have been diagnosed in rhesus macaques (Macaca mulatta) at the nonhuman primate colony of the Keeling Center for Comparative Medicine and Research at The University of Texas MD Anderson Cancer Center. The distinctive feature in these cases, based on PET/computed tomography (CT) imaging, was the presence of two or three tumor lesions in different locations, including proximal to the ileocecal juncture, proximal to the hepatic flexure, and/or in the sigmoid colon. These colon carcinoma lesions selectively accumulated [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) and [¹⁸F]fluoroacetate ([¹⁸F]FACE) at high levels, reflecting elevated carbohydrate and fatty acid metabolism in these tumors. In contrast, the accumulation of [¹⁸F]fluorothymidine ([¹⁸F]FLT) was less significant, reflecting slow proliferative activity in these tumors. The diagnoses of colon carcinomas were confirmed by endoscopy. The expression of MLH1, MSH2, and MSH6 proteins and the degree of microsatellite instability (MSI) was assessed in colon carcinomas. The loss of MLH1 protein expression was observed in all tumors and was associated with a deletion mutation in the MLH1 promoter region and/or multiple single-nucleotide polymorphism (SNP) mutations in the MLH1 gene. All tumors exhibited various degrees of MSI. The pedigree analysis of this rhesus macaque population revealed several clusters of affected animals related to each other over several generations, suggesting an autosomal dominant transmission of susceptibility for colon cancer. The newly discovered hereditary nonpolyposis colorectal cancer syndrome in rhesus macaques, termed MLH1-rheMac, may serve as a model for development of novel approaches to diagnosis and therapy of Lynch syndrome in humans.

Mismatch repair proteins in recurrent prostate cancer

Normal cell function requires strict control over the repair of DNA damage, which prevents excessive mutagenesis. An enhanced accumulation of mutations results in the multistep process generally known as carcinogenesis. Defects in repair pathways fuel such mutagenesis by allowing reiterative cycles of mutation, selection, and clonal expansion that drive cancer progression. The repair of mismatches is an important mechanism in the prevention of such genetic instability. In addition, proteins of this pathway have the unique ability to function in DNA damage response by inducing apoptosis when irreparable damage is encountered. Though originally identified primarily in association with a predisposition to hereditary colon cancer, mismatch repair defects have been identified in many other cancer types, including prostate cancer. From the first discovery of microsatellite instability in prostate cancer cell lines and tumor samples, variations in protein levels and a possible association with recurrence and aggression of disease have been described. Current results suggest that the involvement of mismatch repair proteins in prostate cancer may differ from that found in colorectal cancer, in the type of proteins and protein defects involved and the type of causative mutations. Additional work is clearly needed to investigate this involvement and the possibility that such defects may affect treatment response and androgen independence.

The role of the in situ local inflammatory response in predicting recurrence and survival in patients with primary operable colorectal cancer

Colorectal cancer progression and survival is dependent on complex interactions between the tumour and the host. The pronounced local inflammatory response in and around the tumour is thought to represent the in situ host anti-tumour immune response. Since early reports, 40 years ago, there has been a continuing interest in establishing the cellular composition of immune cell infiltrates and their relationship with survival in colorectal cancer. In this review, we comprehensively examine the evidence for the local inflammatory cell reaction/in situ immune response in predicting outcome in primary operable colorectal cancer and make recommendations as to how such information may be incorporated into routine clinical assessment. Generally, an increasing number/density of immune cells in and around the tumour is associated with improved outcome in over 100 studies. Whilst the prognostic value of a generalized lymphocytic infiltrate or non-specific peritumoural inflammatory response is strongly related to survival based on 40 different studies, it is also apparent that most individual immune cell types relate to recurrence and cancer specific survival. The evidence is particularly robust for tumour infiltrating T lymphocytes and their subsets (CD3+, CD8+, CD45RO+, FOXP3+) in addition to tumour associated macrophages, dendritic cells and neutrophils. Taken together, the evidence suggests both adaptive and innate anti-tumour immune responses play key roles in determining cancer progression. In order to establish routine clinical utility there is a need to rationalise this prognostic information, published over a 40 years period, into a standardized assessment of tumour inflammatory cell infiltrate. Such standardization may also guide development of novel therapeutic interventions.

HLA-DR expression is associated with better prognosis in sporadic Australian clinicopathological Stage C colorectal cancers

Predicting patient outcome for colorectal carcinoma (CRC) with lymph node but not distant metastases remains challenging. Various prognostic markers have been identified including microsatellite instability (MSI) and possibly expression of the MHC Class II protein, HLA-DR. About 15% of sporadic CRC exhibits MSI associated with methylation of the DNA mismatch repair gene hMLH1 promoter. In addition, a significant proportion of unselected CRC demonstrates expression of HLA-DR. We sought to examine the relationship between HLA-DR expression, MSI status and prognosis in sporadic Australian Clinicopathological (ACP) Stage C CRC. Two hundred seventy consecutive patients with sporadic ACP Stage C CRC were treated at Concord Repatriation General Hospital between 1986 and 1992. None of these patients received adjuvant chemotherapy and all were followed for a minimum of 5 years or until death. DNA was extracted from paraffin sections and MSI status determined by PCR. HLA-DR expression was determined immunohistochemically using an antibody against the HLA-DR alpha chain. MSI status could be assigned in 235 cases: 176 CRCs (74.9%) were microsatellite stable, whereas 23 (9.8%) had high levels of MSI (MSI-H) and 36 (15.3%) had low levels of MSI (MSI-L). HLA-DR expression by CRC cells was seen in 148 (60.1%) cases and correlated with the presence of tumor-infiltrating lymphocytes (p = 0.0005) and peritumoral lymphocytes (p = 0.003), but not other clinicopathological features or MSI status. HLA-DR-positive CRCs were strongly associated with better patient outcome (p < 0.0001).

Statistical strategies to improve the efficiency of molecular studies of colorectal cancer prognosis

The evaluation of tumour molecular markers may be beneficial in prognosis and predictive in therapy. We develop a stopping rule approach to assist in the efficient utilisation of resources and samples involved in such evaluations. This approach has application in determining whether a specific molecular marker has sufficient variability to yield meaningful results after the evaluation of molecular markers in the first n patients in a study of sample size N (n⩽N). We evaluated colorectal tumours for mutations (microsatellite instability, K-ras, B-raf, PI3 kinase, and TGFβR-II) by PCR and protein markers (Bcl2, cyclin D1, E-cadherin, hMLH1, ki67, MDM2, and P53) by immunohistochemistry. Using this method, we identified and abandoned potentially uninformative molecular markers in favour of more promising candidates. This approach conserves tissue resources, time, and money, and may be applicable to other studies.

A single nucleotide substitution (-107C-->G) in the hMLH1 promoter found in colorectal cancer population reduces transcriptional activity

Inactivation of the DNA mismatch repair gene hMLH1 predisposes one to colorectal cancer. We have identified a C to G nucleotide substitution at position -107 relative to the hMLH1 gene translation initiation site in three of 163 colorectal cancer patients with an allele frequency of 0.0092 (3/326). One of the three -107G alleles occurred in one patient out of five with reduced hMLH1 expression in the tumor tissue. The -107G was not found in 63 healthy individuals. This substitution reduced transcriptional activity by 51% compared with -107C (P<0.01) and impeded the promoter-binding capacity of nuclear proteins. Although the small number of identified -107G alleles is insufficient to evaluate the contribution to the carcinogenesis and clinicopathological properties of the tumors, the effects of -107G on hMLH1 gene transcription and nuclear protein binding to the promoter sequence implicate the site, including -107C, as a crucial element interacting with the activator that maintains hMLH1 gene expression.

Screening tests for colorectal cancer: A menu of options remains relevant

Until the early 1990s, no evidence was available to show that screening for colorectal cancer (CRC) by any means actually saved lives. Subsequently, sufficient evidence for the efficacy of fecal occult blood testing (FOBT) and flexible sigmoidoscopy allowed the US Preventive Services Task Force to publish guidelines for CRC screening. Since that time the major organizations in the United States concerned with screening guidelines have recommended a menu of screening test options including FOBT, flexible sigmoidoscopy, flexible sigmoidoscopy plus FOBT, barium enema, and colonoscopy. No organization, except for the American College of Gastroenterology, has designated any one of these options as "preferred." Nevertheless, the lay press and many gastroenterology opinion leaders have encouraged Americans to have only one test--colonoscopy. In this review we discuss the rationale for caution in designating one screening test as "the best" and present information on how new stool and serum tests can be used effectively to screen for CRC.

Effective screening for bowel cancer: a United kingdom perspective

Bowel cancer is a major cause of morbidity and death and is a high cost to health care systems. Screening currently offers the best chance of improving outcomes from bowel cancer. When introducing screening, the problems encountered in other cancers need to be avoided to maximize benefits and minimize harms.

Challenges and pitfalls in HNPCC screening by microsatellite analysis and immunohistochemistry

Hereditary non-polyposis colorectal cancer (HNPCC) accounts for approximately 2 to 4% of the total colorectal cancer burden. For economic reasons a diagnostic "stepladder" is recommended. After evaluation of the family history, diagnostic microsatellite instability (MSI) analysis has found its place as a valuable screening tool for HNPCC. Immunohistochemical analysis can help to pinpoint the affected gene. The detection of a mutation in one of the responsible mismatch repair gene confirmed the diagnosis HNPCC. Here we demonstrate our experience of some important pitfalls that will be discussed in this study. In MSI testing, one potential source for false-negative results is intralesional heterogeneity. We demonstrate examples of a flat adenoma and a carcinoma, which required laser microdissection to correctly determine the microsatellite status. In these lesions manual microdissection, the most frequently applied method, was not sufficient. However, the number of cells obtained by using laser microdisssection can fall below a necessary minimum, which can also cause false-negative results of MSI analysis, as shown here in a mucinous carcinoma. In addition, evaluation of immunohistochemically stained tissue slides requires experience to avoid false-positive or false-negative interpretation. A case with two synchronous colorectal cancers revealed loss of MSH2 expression in one carcinoma, whereas the second carcinoma stained positively leading to a false-negative interpretation. In some cases, false-positive results can be obtained, if a perinuclear-staining pattern is interpreted as positive. In summary, there are several potential pitfalls in the molecular screening for HNPCC. Therefore the importance of correct interpretation of clinical data, immunohistochemistry, and microsatellite analysis in combination, performed by a pathologist with experience in molecular genetics is essential. In addition, laser microdissection of tumor areas that have been chosen by a pathologist is highly recommended in cases that cannot be resolved with manual microdissection.

Hereditary nonpolyposis colorectal cancer (Lynch syndrome): criteria for identification and management

Hereditary nonpolyposis colorectal carcinoma (HNPCC), or Lynch syndrome, is an autosomal dominant syndrome accounting for 5 to 10% of the total colorectal cancer population. Patients with this syndrome develop colorectal carcinoma at an early age, but disease onset can happen in all age groups. Usually the carcinomas are synchronous or metachronous, and most of them arise proximal to the splenic flexure. The prognosis is better than for the sporadic form of cancer, and there is increased risk for cancer development in certain extracolonic sites, such as the endometrium, ovary, stomach, small bowel, hepatobiliary tract, ureter, and renal pelvis. Most patients with HNPCC have a mutation in one of two DNA mismatch repair genes, hMSH2 or hMLH 1. More than 90% of colorectal carcinoma patients with hMSH2 or hMLH1 demonstrate high-frequency microsatellite instability (MSI-H). If a patient is suspected to belong to an HNPCC family, the first screening test should be immunohistochemistry for the detection of hMLH1 and hMSH2 proteins, and if it is indicative, it should be followed by genomic sequencing for the identification of mutations in the mismatch repair genes. Genetic counseling and surveillance for high risk HNPCC family members should begin at age 25. Surveillance includes annual colonoscopy of the entire large bowel, with fecal occult blood testing performed twice a year. Systematic surveillance and individually designed treatment of affected patients may help to detect cancers at an earlier stage and subsequently improve the prognosis of the disease further.

Stool screening for colorectal cancer: molecular approaches

Assay of molecular markers in stool represents a promising noninvasive approach to screen colorectal cancer. Given that neoplasms exfoliate abundantly into the lumen and that DNA recovered from stool can be assayed with sensitive techniques, there is a strong biologic rationale to pursue this emerging technology. A challenge with DNA-based testing relates to the selection of markers. Because of the molecular heterogeneity of cancer, no single marker has yielded perfect sensitivity. Several combinations of markers in early stool assays have produced high detection rates of both colorectal cancer and advanced adenomas in selected patient groups, but observations from large representative populations are lacking at present. Potential expanded applications of stool DNA testing include detection of supracolonic aerodigestive cancers and of dysplasia in inflammatory bowel disease. Further marker discovery and technologic refinements should translate into improved test performance and fuel a continued evolution with this screening approach.

Overexpression and amplification of Aurora-A in hepatocellular carcinoma

PURPOSE

Aurora-A/STK15/BTAK, a centrosome-associated serine/threonine kinase, has been shown to induce chromosomal instability, leading to aneuploidy and cell transformation. The purpose of this study was to investigate the expression and amplification of Aurora-A in hepatocellular carcinoma (HCC).

EXPERIMENTAL DESIGN

Aurora-A mRNA levels were measured in 224 HCCs and 199 paired nontumorous liver tissues by reverse transcription-PCR. Aurora-A mRNA and protein levels of 8 were also measured by reverse transcription-PCR and Western blot hybridization in 8 liver cancer cell lines. Amplification of Aurora-A was determined by Southern blot hybridization in 99 cases.

RESULTS

Aurora-A was overexpressed in 137 of 224 (61%) HCCs and all 8 of the cell lines. Overexpression of Aurora-A was associated with high-grade (grade II-IV), and high-stage (stage IIIB-IV) tumors, p53 mutation, infrequent beta-catenin mutation, and poor outcome. Aurora-A overexpression and p53 mutation acted synergistically toward poor prognosis. Amplification of Aurora-A was detected only in 3 HCCs.

CONCLUSION

The results show that Aurora-A is overexpressed frequently in HCC, and correlated with high grade and high stage, indicating that overexpression of Aurora-A plays a role in the development and progression of HCC.

Cis-acting transmission of genomic instability

Genomic instability is a highly pleiotropic phenotype, which may reflect a variety of underlying mechanisms. Destabilization has been shown in some cases to involve mutational alteration or inactivation of trans-acting cellular factors, for example, p53 or mismatch repair functions. However, aspects of instability are not well explained by mutational inactivation of trans-acting factors, and other epigenetic and cis-acting mechanisms have recently been proposed. The trans and cis models result in divergent predictions for the distribution of instability-associated genetic alterations within the genome, and for the inheritance of genomic instability among sibling sub-clones of unstable parents. These predictions have been tested in this study primarily by tracking the karyotypic distribution of chromosomal rearrangements in clones and sub-clones exhibiting radiation-induced genomic instability; inheritance of mutator phenotypes was also analyzed. The results indicate that genomic instability is unevenly transmitted to sibling sub-clones, that chromosomal rearrangements within unstable clones are non-randomly distributed throughout the karyotype, and that the majority of chromosomal rearrangements associated with instability affect trisomic chromosomal segments. Observations of instability in trisomic regions suggests that in addition to promoting further alterations in chromosomal number, aneuploidy can affect the recovery of structural rearrangements. In summary, these findings cannot be fully explained by invoking a homogeneously distributed factor acting in trans, but do provide support for previous suggestions that genomic instability may in part be driven by a cis-acting mechanism.

Genome-wide search for loss of heterozygosity in Chinese patients with sporadic colorectal cancer

In an attempt to integrally investigate the loss of tumor suppressor genes and search for putative suppressor loci associated with tumor occurrence and progression, we conducted a genome-wide loss of hetero zygosity (LOH) study of 83 tumor samples obtained from Chinese patients with sporadic colorectal cancer. We employed 400 fluorescence-labeled microsatellite marker primers to amplify the corresponding loci of the genomic DNA and then electrophoresed the polymerase chain reaction products and analyzed the fluorescent signals. The LOH frequencies were high (>35%) but were not associated with the tumor stage and progression in 20 loci, including the regions where TP53, E-cadherin, deleted in colorectal carcinoma (DCC), phosphatase and tensin homolog deleted on chromosome 10 (PTEN), mothers against decapentaplegic, Drosophila, homolog of 2 (MADH2) and mothers against decapentaplegic, Drosophila, homolog of 4 (MADH4) reside. Loss of other loci, including two narrow regions on chromosome 2, was found to relate to the tumor stage, suggesting that this genomic instability may contribute to tumor progression.

Potential usefulness of detecting cyclooxygenase 2 messenger RNA in feces for colorectal cancer screening

BACKGROUND & AIMS

Cyclooxygenase 2 (COX-2) is overexpressed frequently in aerodigestive tumors, especially in colorectal tumors. Therefore, it may be a suitable biomarker for colorectal cancer (CRC) screening. We performed a pilot study of whether detecting COX-2 expression in fecal RNA enables us to discriminate between patients with and without CRC.

METHODS

The study cohort included 29 patients with CRC, and 22 control patients without neoplastic disease of the colon or rectum. RNA was isolated from routinely collected stool samples using a modified method. The expression levels of carcinoembryonic antigen (CEA) and COX-2 were determined by nested reverse-transcription polymerase chain reaction (RT-PCR).

RESULTS

The sensitivity and the specificity of fecal COX-2 assay for CRC were 90% (95% confidence interval [CI], 73%-98%) and 100% (95% CI, 85%-100%), respectively, whereas those of the fecal CEA assay for CRC were 100% (95% CI, 88%-100%) and 5% (95% CI, 2%-23%), respectively. COX-2 messenger RNA (mRNA) was detected in 3 of 4 patients with Dukes' stage A, 13 of 14 patients with Dukes' stage B, and 10 of 11 patients with Dukes' stage C or D. COX-2 mRNA was detected in 5 of 7 patients with proximal cancer and in 21 of 22 patients with distal cancer. The COX-2 assay was superior to the CEA assay for detecting CRC in terms of specificity, although both assays had high sensitivity.

CONCLUSIONS

This fecal COX-2 assay had high sensitivity and high specificity for detecting CRC. These results suggest that it would be a promising approach for detecting CRC, although a larger study is necessary to assess the sensitivity and the specificity.

The evolution to stool DNA testing for colorectal cancer

Despite a variety of screening strategies and recent trends showing death rate stabilization, colorectal cancer still remains the second leading cause of overall cancer death. Current screening tools suffer from performance limitations, low patient acceptability, and marginal reliable access within the health care system. Noninvasive strategies present the lowest risk with the highest potential for patient satisfaction. However, serious implementation barriers exist requiring consistent programmatic screening, strict patient adherence, and poor sensitivity for adenomas. Colonoscopy remains an invasive screening test with the best sensitivity and specificity, but faces large financial costs, manpower requirements, patient access and adherence. Development of advanced molecular techniques identifying altered DNA markers in exfoliated colonocytes signify early or precancerous growth. Stool-based DNA testing provides an entirely noninvasive population-based screening strategy which patients can perform easier than faecal occult blood testing (FOBT). Large-scale prospective randomized control trials currently pending should help characterize accurate test performance, screening intervals, cost-effectiveness, direct comparison to FOBT and analysis of patient adherence. As tumour development pathways and potential target genes are further elucidated, refinements in multi-assay stool-based DNA testing portend enhanced test characteristics to detect and treat this genetically heterogeneous disease.

Adenoma recurrences after resection of colorectal carcinoma: results from the Southwest Oncology Group 9041 calcium chemoprevention pilot study

BACKGROUND

Colorectal adenomas are the usual precursors to carcinoma in sporadic and hereditary colorectal cancers (CRC).

METHODS

A total of 220 CRC patients (stages 0, I, and II) were randomized prospectively in a double-blind pilot study of calcium chemoprevention by using recurrent colorectal adenomas as a surrogate end point. This trial is still in progress, and we report the preliminary findings on adenoma recurrence rates.

RESULTS

Synchronous adenomas were present in 60% of patients, and cancer confined in a polyp was present in 23% of patients. The overall cumulative adenoma recurrence rate was 31% (19% in the first year, 29% for 2 years, and 35% for 3 years). The recurrence rates were greater for patients with synchronous adenomas: 38% at 3 years (P =.01). Lower stage was associated with higher adenoma recurrence rates (P =.04). Factors including age, sex, site of primary cancer, and whether the cancer was confined to a polyp were not significantly associated with differences in adenoma recurrence rates.

CONCLUSIONS

The substantial adenoma recurrence rate in patients resected of CRC justifies colonoscopic surveillance on a periodic basis. Patients with higher rates of adenoma recurrences, such as CRC with synchronous adenomas, are ideal subjects for chemoprevention trials.

The role of microsatellite instability in cervical intraepithelial neoplasia and squamous cell carcinoma of the cervix

OBJECTIVES

This study was conducted to define the role of microsatellite instability (MSI) in cervical intraepithelial neoplasia (CIN) and squamous cell carcinoma (SCC) of the cervix. We also tested the validity of using markers recommended for MSI study in colonic carcinoma by the National Cancer Institute (NCI) for cervical neoplasm.

METHODS

Twenty normal cervical, 24 low-grade CIN (CIN-L), 59 high-grade CIN (CIN-H), and 93 SCC tissues were examined for MSI after microdissection. A polymerase chain reaction based MSI detection was performed using five markers recommended by the NCI for colonic cancer (panel one) as well as five other markers (panel two) found to be informative in earlier studies. High-frequency MSI (MSI-H) was defined as instability in > or = 2 of 5 loci if one panel was used and > or = 30% of loci when more than five loci were used. Low-frequency MSI (MSI-L) was diagnosed if instability was noted but did not meet the criteria of MSI-H. Findings were correlated with clinicopathologic information.

RESULTS

The combined use of panel one and two markers showed no MSI in normal cervical or CIN-L tissue, MSI-L in 1 CIN-H (1.7%), MSI-L in 16 (17.2%), and MSI-H in 11 (11.8%) SCC, respectively. The NCI-recommended panel alone detected 19 of 27 MSI-positive SCC. MSI-positive was not related to patient age, disease stage, and tumor grade. The overall survival of MSI-positive patients was significantly worse than that of microsatellite stable patients (P = 0.02). An increasing trend of MSI-H rate with higher disease stages was noted (P = 0.035) but MSI-H was not associated with poor prognosis.

CONCLUSIONS

The NCI recommended panel of markers might not be useful in MSI study for SCC and using more than five markers improves the MSI detection. MSI is rare in cervical dysplasia but is present in a subset of SCC. The association between MSI-positivity and prognosis awaits future confirmation.

Multiple sites required for expression in 5'-flanking region of the hMLH1 gene

Expression of the hMLH1 gene, one of the DNA mismatch repair genes, is frequently repressed in various cancers such as colorectal, ovarian, gastric, and endometrial origins with a microsatellite instable phenotype. In this study, we investigated details of the relationship between the transcriptional activity and the protein-binding sites in the 5'-flanking region of the hMLH1 gene. Luciferase reporter gene analysis with a series of deletion mutants revealed that a region containing -301 to -76 relative to a translation start site is essential for maximal expression. Eight protein-binding sites in this region were identified by in vivo methylation footprinting analysis and homology search. A presence of binding proteins to CCAAT-box at -145 to -139 was confirmed by the electrophoresis mobility shift assay. Partial involvement of NF-Y was seen by the super gel shift assay. Three reporter plasmids having a single site-directed mutation at -163 to -158, -145 to -139, or -96 to -93 showed 14-30% less activities to that of having the wild-type. Dual or triple mutations were no greater effect than the single mutation on the activity. These results indicate that three cis-elements are essential for full expression of the hMLH1 gene and may work co-operatively.

Microsatellite instability and suppressed DNA repair enzyme expression in rheumatoid arthritis

Reactive oxygen and nitrogen are produced by rheumatoid arthritis (RA) synovial tissue and can potentially induce mutations in key genes. Normally, this process is prevented by a DNA mismatch repair (MMR) system that maintains sequence fidelity during DNA replication. Key members of the MMR system include MutSalpha (hMSH2 and hMSH6) and MutSbeta (hMSH2 and hMSH3). To provide evidence of DNA damage in inflamed synovium, we analyzed synovial tissues for microsatellite instability (MSI). MSI was examined by PCR on genomic DNA of paired synovial tissue and peripheral blood cells of RA patients using specific primer sequences for five key microsatellites. Surprisingly, abundant MSI was observed in RA synovium compared with osteoarthritis tissue. Western blot analysis for the expression of MMR proteins demonstrated decreased hMSH6 and increased hMSH3 in RA synovium. To evaluate potential mechanisms of MMR regulation in arthritis, fibroblast-like synoviocytes (FLS) were isolated from synovial tissues and incubated with the NO donor S-nitroso-N-acetylpenicillamine. Western blot analysis demonstrated constitutive expression of hMSH2, 3, and 6 in RA and osteoarthritis FLS. When FLS were cultured with S-nitroso-N-acetylpenicillamine, the pattern of MMR expression in RA synovium was reproduced (high hMSH3, low hMSH6). Therefore, oxidative stress can relax the DNA MMR system in RA by suppressing hMSH6. Decreased hMSH6 can subsequently interfere with repair of single base mutations, which is the type observed in RA. We propose that oxidative stress not only creates DNA adducts that are potentially mutagenic, but also suppresses the mechanisms that limit the DNA damage.

Comparison of selection strategies for genetic testing of patients with hereditary nonpolyposis colorectal carcinoma: effectiveness and cost-effectiveness

BACKGROUND

Molecular testing for hereditary nonpolyposis colorectal carcinoma (HNPCC) is becoming standard care and it is cost-effective compared with no genetic testing. However, the best strategy for detection of HNPCC gene carriers is unknown.

METHODS

We use a decision analytic model to evaluate the effectiveness and incremental cost-effectiveness of four commonly used testing strategies to detect HNPCC gene carriers. The model starts with a population of colorectal carcinoma (CRC) patients and measures costs, the number of gene carriers detected, and incremental costs per gene carrier detected.

RESULTS

We found that germline testing on only those CRC probands who meet the Amsterdam criteria detects the fewest gene carriers and has the lowest cost whereas tumor microsatellite instability (MSI) testing of all CRC patients and families has the highest cost and detects the most gene carriers. When cost-effectiveness is considered, the mixed strategy (MSH2 and MLH1 testing on those who meet the Amsterdam criteria and germline testing for the remainder who meet less stringent modified criteria and are MSI-High) seems superior. The mixed strategy detects 59.6 mutation carriers per 1000 CRC cases and costs much less than the test all strategy, which has an incremental cost-effectiveness of $51,151. The mixed strategy often other strategies and when compared to the Amsterdam strategy, has a cost-effectiveness of only $6441 per gene carrier detected.

CONCLUSIONS

It is not very effective to limit genetic testing to only individuals who meet the Amsterdam criteria, as many gene carriers are missed. However, testing all CRC patients for tumor MSI-H, although effective, may be prohibitively expensive. A mixed strategy is the more cost-effective approach.

The genetics of the target tissue in rheumatoid arthritis

The genetic mechanisms that are complementary in predisposing and then establishing disease are yet to be fully elucidated. During a lifetime, the genetic composition of the host is not only hereditary but undergoes rearrangements, integrations, and more subtle single-base pair alterations. These changes can be inconsequential or lead to aberrant and deleterious pathologic changes. In a complex multifactorial disease such as RA, the relative roles of the dynamic versus germline elements of the disease have yet to be fully determined. Further studies of large populations are likely to segregate out factors affecting specific ethnic, clinical, and genetic subgroups.

Microsatellite instability, expression of hMSH2 and hMLH1 and HPV infection in cervical cancer and their clinico-pathological association

Infection with specific genotypes of human papillomavirus (HPV) has been strongly implicated in cervical carcinogenesis. However, HPV infection alone is insufficient for malignant transformation of the cervical epithelium. An alteration of microsatellite repeats is the result of slippage owing to strand misalignment during DNA replication and is referred to as microsatellite instability (MSI). These defects in DNA repair pathways have been related to human carcinogenesis; however, the role of MSI in the tumorigenesis of cervical cancer remains unclear. The clinical and pathological features of cervical cancers which are MSI-positive have also not been fully characterized. This study investigated the prevalence of MSI in cervical cancer and its relationship to clinico-pathological characteristics and HPV infection. Polymerase chain reaction-based microsatellite assay combined with tissue microdissection was used to examine for MSI in 50 cervical squamous cell carcinomas in Hong Kong women. In addition, the immunohistochemical staining was performed to determine the expression of major DNA mismatch repair genes, hMSH2 and hMLH1. Six cases (12%) displayed a low frequency of MSI (MSL-L) showing MSI at one locus only in 5 loci examined. Seven cases (14%) showed a high frequency of MSI (MSI-H) having MSI at 2 or more loci. Grouping MSI-L and MSI-H cases together as MSI-positive, statistical analysis of HPV infection, tumor grade, clinical stage and clinical status failed to disclose differences between MSI-positive and MSI-negative cases (p > 0.05). However, MSI-H correlated with advanced stage of disease (p < 0.05). Individuals with MSI-H tumors appeared to have reduced overall survival compared to individuals with MSI-L and MSI-negative tumors, but the difference was not statistically significant (p = 0.059). An absence of either MSH2 or MLH1 expression was observed in 2 MSI-L and 4 MSI-H cases, respectively. The results suggest that MSI is present in a subgroup of cervical squamous cell carcinomas, and defects resulting in MSI may be related to tumor progression and possibly poor prognosis in cervical cancer.

Stool screening for colorectal cancer: evolution from occult blood to molecular markers

BACKGROUND

Colorectal cancer is the second leading cause of malignant death, and better preventive strategies are needed. Participation rates for colorectal cancer screening remain low due, in part, to perceived discomfort, potential harm, and high costs with available tools.

METHODS

Stool testing, unlike other conventional screening approaches, is noninvasive and requires no cathartic preparation. However, widely used fecal blood tests yield frequent false-negative and false-positive results that lower screening effectiveness and raise program costs. There is a compelling biological rationale to target DNA alterations exfoliated from neoplasms into stool, and multiple DNA markers would need to be assayed because of the genetic heterogeneity of colorectal neoplasia. Early clinical studies with this multi-target DNA-based stool assay approach suggest high sensitivity for both colorectal cancer and premalignant adenomatous polyps while maintaining high specificity.

CONCLUSIONS

This apparently accurate and user-friendly new approach holds promise to improve the effectiveness, efficiency, and appeal of colorectal cancer screening. Large-scale clinical studies are clearly warranted to corroborate the early results.

High frequency of microsatellite instability in young patients with head-and-neck squamous-cell carcinoma: lack of involvement of the mismatch repair genes hMLH1 AND hMSH2

The most prevalent risk factors in the development of head-and-neck squamous-cell carcinoma (HNSCC) are excessive tobacco and alcohol consumption. In young patients with HNSCC, these risk factors are often absent. Our purpose was to investigate the risk factors, microsatellite instability (MSI) changes and status of the mismatch repair genes hMLH1 and hMSH2 in a cohort of young patients with HNSCC. Fifty-seven HNSCC tumors were examined for the presence of MSI at 16 microsatellite sites using PCR. In the young patient group (24 cases, < or = 44 years old), 100% of tumors had MSI at 1 site at least and 88% had MSI at 2 or more loci. In older patients (33 cases, > or = 45 years), MSI at 1 or more sites was found in 61% of tumors (young vs. old, p = 0.0003) and instability at 2 or more sites was found in 36% of tumors (young vs. old, p = 0.0001). The involvement of the mismatch repair genes was investigated by examining promoter methylation, exon mutation and gene expression of hMLH1 and hMSH2. All results were negative, indicating that inactivation of these 2 genes does not play a role in the development of MSI in tumors from this patient group. Furthermore, the young patient group had a significantly lower incidence of smoking (46% young, 88% old; p = 0.001) and alcohol consumption (33% young, 67% old; p = 0.0169), emphasizing the probable importance of other environmental and/or genetic factors in the development of their disease.

Colorectal cancer screening by detection of altered human DNA in stool: feasibility of a multitarget assay panel

BACKGROUND & AIMS

Assay of altered DNA exfoliated into stool represents an intriguing approach to screen for colorectal neoplasia, but multiple markers must be targeted because of genetic heterogeneity. We explored the feasibility of a stool assay panel of selected DNA alterations in discriminating subjects with colorectal neoplasia from those without.

METHODS

Freezer-archived stools were analyzed in blinded fashion from 22 patients with colorectal cancer, 11 with adenomas > or =1 cm, and 28 with endoscopically normal colons. After isolation of human DNA from stool by sequence-specific hybrid capture, assay targets included point mutations at any of 15 sites on K-ras, p53, and APC genes; Bat-26, a microsatellite instability marker; and highly amplifiable DNA.

RESULTS

Analyzable human DNA was recovered from all stools. Sensitivity was 91% (95% confidence interval, 71%-99%) for cancer and 82% (48%-98%) for adenomas > or =1 cm with a specificity of 93% (76%-99%). Excluding K-ras from the panel, sensitivities for cancer were unchanged but decreased slightly for adenomas to 73% (39%-94%), while specificity increased to 100% (88%-100%).

CONCLUSIONS

Assay of altered DNA holds promise as a stool screening approach for colorectal neoplasia. Larger clinical investigations are indicated.

Genetic analysis of multiple synchronous lesions of the colon adenoma-carcinoma sequence

The colorectal adenoma-carcinoma sequence represents a well-known paradigm for the sequential development of cancer driven by the accumulation of genomic defects. Although the colorectal adenoma-carcinoma sequence is well investigated, studies about tumours of different dignity co-existent in the same patient are seldom. In order to address the distribution of genetic alterations in different lesions of the same patient, we coincidently investigated carcinomas, adenomas and aberrant crypt foci in patients with sporadic colon cancer. By utilizing polymerase chain reaction, single-strand conformation polymorphism, heteroduplex-analysis, restriction fragment length polymorphism, protein truncation test and sequencing techniques we looked for mutations and microsatellite instability of APC, H-ras, K-ras, p53, DCC and the DNA repair genes hMLH1/hMSH2. In accordance with the suggested adenoma-carcinoma sequence of the colon, four patients reflected the progressive accumulation of genetic defects in synchronously appearing tumours during carcinogenesis. However, two patients with non-hereditary malignomas presented different genetic instabilities in different but synchronously appearing tumours suggesting non-clonal growth under almost identical conditions of the environment. Thus, sporadically manifesting multiple lesions of the colon were not necessarily driven by similar genetic mechanisms. Premalignant lesions may transform into malignant tumours starting from different types of genetic instability, which indicates independent and simultaneous tumorigenesis within the same organ.