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M G Dunlop

Publications and source records attributed to M G Dunlop.

At least 19 recordsLinked to original sources
PubMed2005

Aspirin-induced nuclear translocation of NFkappaB and apoptosis in colorectal cancer is independent of p53 status and DNA mismatch repair proficiency.

Substantial evidence indicates nonsteroidal anti-inflammatory drugs (NSAIDs) protect against colorectal cancer (CRC). However, the molecular basis for this anti-tumour activity has not been fully elucidated. We previously reported that aspirin induces signal-specific IkappaBalpha degradation followed by NFkappaB nuclear translocation in CRC cells, and that this mechanism contributes substantially to aspirin-induced apoptosis. We have also reported the relative specificity of this aspirin-induced NFkappaB-dependent apoptotic effect for CRC cells, in comparison to other cancer cell types. It is now important to establish whether there is heterogeneity within CRC, with respect to the effects of aspirin on the NFkappaB pathway and apoptosis. p53 signalling and DNA mismatch repair (MMR) are known to be deranged in CRC and have been reported as potential molecular targets for the anti-tumour activity of NSAIDs. Furthermore, both p53 and MMR dysfunction have been shown to confer resistance to chemotherapeutic agents. Here, we set out to determine the p53 and hMLH1 dependency of the effects of aspirin on NFkappaB signalling and apoptosis in CRC. We specifically compared the effects of aspirin treatment on cell viability, apoptosis and NFkappaB signalling in an HCT-116 CRC cell line with the p53 gene homozygously disrupted (HCT-116(p53-/-)) and an HCT-116 cell line rendered MMR proficient by chromosomal transfer (HCT-116(+ch3)), to the parental HCT-116 CRC cell line. We found that aspirin treatment induced apoptosis following IkappaBalpha degradation, NFkappaB nuclear translocation and repression of NFkappaB-driven transcription, irrespective of p53 and DNA MMR status. These findings are relevant for design of both novel chemopreventative agents and chemoprevention trials in CRC.

Active Transport, Cell Nucleus↗
PubMed2005

Prevalence of family history of colorectal cancer in the general population.

BACKGROUND: Robust estimates of the prevalence of a family history of colorectal cancer in the general population are essential to inform planning of provision for colonoscopic surveillance and for clinical genetics services. However, there is a paucity of high-quality data. METHODS: Computerized record linkage was used to assess systematically the family history of 160 cancer-free community subjects and thereby provide prevalence data that are independent of participant recall. The data set comprised 2664 first- and second-degree relatives of study subjects, with 148 068 years at risk. RESULTS: Of people in the 30-70 years age range, 9.4 (95 per cent confidence interval (c.i.) 5.8 to 14.9) per cent had a first-degree relative affected by colorectal cancer, and 28.8 (95 per cent c.i. 22.3 to 36.2) per cent had an affected first- or second-degree relative. Between 0 and 3.1 per cent of study subjects merited colonic surveillance, depending on the stringency of the guidelines used. CONCLUSION: An appreciable proportion of the general population has a relative affected by colorectal cancer, sufficient to merit screening under certain criteria. In the absence of good-quality evidence supporting colonoscopic surveillance in groups at moderate risk, these data directly inform the planning of services for people with a family history of colorectal cancer. However, the clinical risk and financial implications of screening should be taken into account.

Adult↗
PubMed2004

Evidence for colorectal cancer cell specificity of aspirin effects on NF kappa B signalling and apoptosis.

Epidemiological evidence indicates that non-steroidal anti-inflammatory drugs (NSAIDs) protect against colorectal cancer (CRC) to a greater degree than other non-gastrointestinal cancers, but the molecular basis for this difference is unknown. We previously reported that aspirin induces signal-specific I kappa B alpha degradation followed by NF kappa B nuclear translocation in CRC cells, and that this mechanism contributes substantially to aspirin-induced apoptosis. Here, we explored the hypothesis that cell-type specific effects on NF kappa B signalling are responsible for the observed differences in protection by aspirin against CRC compared to breast and gynaecological cancers. We also assessed whether COX-2 expression, mutation status of adenomatous polyposis coli (APC), beta-catenin, p53, or DNA mismatch repair (MMR) genes in CRC lines influenced aspirin-induced effects. We found that aspirin induced concentration-dependent I kappa B alpha degradation, NF kappa B nuclear translocation and apoptosis in all CRC lines studied. However, there was no such effect on the other cancer cell types, indicating a considerable degree of cell-type specificity. The lack of effect on NF kappa B signalling, paralleled by absence of an apoptotic response to aspirin in non-CRC lines, strongly suggests a molecular rationale for the particular protective effect of NSAIDs against CRC. Effects on NF kappa B and apoptosis were observed irrespective of COX-2 expression, or mutation status in APC, beta-catenin, p53 and DNA MMR genes, underscoring the generality of the aspirin effect on NF kappa B in CRC cells. These findings raise the possibility of cell-type specific targets for the development of novel chemopreventive agents.

Adenomatous Polyposis Coli↗
PubMed2004

Assessment of outcomes after colorectal cancer resection in the elderly as a rationale for screening and early detection.

BACKGROUND: Clinical, social and survival outcomes in elderly patients undergoing bowel cancer surgery were studied to explore the justification for the current upper age limit in colorectal cancer screening programmes. METHODS: Scottish national data were analysed to determine age-specific population survival following a diagnosis of colorectal cancer. Detailed analysis of outcome variables was undertaken in a cohort of 180 patients aged over 80 years who underwent resection of colorectal cancer. RESULTS: Population analysis revealed that the absolute risk of developing colorectal cancer was highest in those aged over 80 years, but relative survival was disproportionately poor. Of 180 patients in this age group, 30.0 per cent required an emergency procedure and only 4.6 per cent had Dukes' stage A tumours. Determinants of all-cause mortality were tumour stage (P < 0.001) and degree of co-morbidity (P = 0.004). Some 88.0 per cent of elderly patients returned to the same category of accommodation as that before admission. CONCLUSION: Colorectal cancer is increasingly common in people aged over 80 years and survival is disproportionately poor compared with that in other age groups. Elective management of early-stage cancer has a better outcome than emergency surgery. The majority of patients maintain social independence. These population and hospital data provide a rationale for early, and even presymptomatic, detection of colorectal cancer in the elderly.

Aged↗
PubMed2004

Prognosis in DNA mismatch repair deficient colorectal cancer: are all MSI tumours equivalent?

Microsatellite instability (MSI) in colorectal tumours is the hallmark of defective DNA mismatch repair (MMR) and high level MSI can be detected in up to 15% of incident colorectal cancers. MSI in sporadic colorectal tumours is primarily due to epigenetic silencing of MLH1 while MSI is almost universal in tumours from HNPCC family members due to germline MMR gene mutation with loss or mutational inactivation of the second copy as a somatic event. There is evidence that tumour MSI is associated with a better outcome than the generality of large bowel malignancy. However, although MSI occurs in both sporadic colorectal cancer and in tumours arising in patients with germline MMR gene mutations, cancer survival should not be considered to be equivalent for these two groups with MSI tumours simply because both exhibit similarities in molecular phenotype. Here, we review the evidence on prognosis in patients with sporadic MSI tumours compared to those who have inherited a germline DNA MMR repair gene defect. In addition, we explore whether there are variables that afford opportunity to distinguish three groups on the basis of MSI status, namely: sporadic MSI tumours; MSI tumours in carriers of germline MMR gene defects; microsatellite stable (MSS) tumours. Differences in prognosis between these three groups is important because it underpins the rationale for surveillance and early identification of tumours in MMR gene carriers, as well as refining understanding of the influence of MSI on cancer progression. Furthermore, we discuss the effect of MSI on the effectiveness of chemotherapy regimens.

Base Pair Mismatch↗
PubMed2004

Accuracy of reporting of family history of colorectal cancer.

BACKGROUND AND AIMS: Family history is used extensively to estimate the risk of colorectal cancer but there is considerable potential for recall bias and inaccuracy. Hence we systematically assessed the accuracy of family history reported at interview compared with actual cancer experience in relatives. METHODS: Using face to face interviews, we recorded family history from 199 colorectal cancer cases and 133 community controls, totalling 5637 first and second degree relatives (FDRs/SDRs). We linked computerised cancer registry data to interview information to determine the accuracy of family history reporting. RESULTS: Cases substantially underreported colorectal cancer arising both in FDRs (sensitivity 0.566 (95% confidence interval (CI) 0.433, 0.690); specificity 0.990 (95% CI 0.983, 0.994)) and SDRs (sensitivity 0.271 (95% CI 0.166, 0.410); specificity 0.996 (95% CI 0.992, 0.998)). There was no observable difference in accuracy of reporting family history between case and control interviewees. Control subjects similarly underreported colorectal cancer in FDRs (sensitivity 0.529 (95% CI 0.310, 0.738); specificity 0.995 (95% CI 0.989, 0.998)) and SDRs (sensitivity 0.333 (95% CI 0.192, 0.512); specificity 0.995 (95% CI 0.991, 0.995)). To determine practical implications of inaccurate family history, we applied family history criteria before and after record linkage. Only two of five families reported at interview to meet surveillance criteria did so after validation, whereas only two of six families that actually merited surveillance were identified by interview. CONCLUSIONS: This study has quantified the inaccuracy of interview in identifying people at risk of colorectal cancer due to a family history. Colorectal cancer was substantially underreported and so family history information should be interpreted with caution. These findings have considerable relevance to identifying patients who merit surveillance colonoscopy and to epidemiological studies.

Aged↗
PubMed2003

Colonoscopy surveillance of individuals at risk of familial colorectal cancer.

BACKGROUND: Individuals with first degree relatives affected with colorectal cancer (CRC) at a young age, or more than one relative affected but who do not fulfil the Amsterdam criteria for a diagnosis of hereditary non-polyposis colon cancer (HNPCC), are believed to be at an increased risk of CRC. However, there is a paucity of prospective data on the potential benefit of colonoscopic surveillance in such groups categorised by empiric family history criteria. We report a prospective study of 448 individuals seeking counselling about their perceived family history of CRC. PATIENTS AND METHODS: Following pedigree tracing, verification, and risk assignment by genetic counsellors, colonoscopy was undertaken for those at a moderate or high risk (HNPCC). Those classified as low risk were reassured and discharged without surveillance. Here we report our findings at the prevalence screen in the 176 patients of the 448 assessed who underwent colonoscopy. RESULTS: Fifty three individuals had a family history that met Amsterdam criteria (median age 43 years) and 123 individuals were classed as moderate risk (median age 43 years). No cancers were detected at colonoscopy in any group. Four individuals (8% (95% confidence limits (CL) 0.4-15%)) in the high risk group had an adenoma detected at a median age of 46 years and all four were less than 50 years of age. Five (4% (95% CL 0.6- 8%)) of the moderate risk individuals had an adenoma at a median age of 54 years, two of whom were less than 50 years of age. CONCLUSIONS: These findings indicate that the prevalence of significant neoplasia in groups defined by family history is low, particularly in younger age groups. These prospective data call into question the value of colonoscopy before the age of 50 years in moderate risk individuals.

Adult↗
PubMed2002

Mismatch repair genes hMLH1 and hMSH2 and colorectal cancer: a HuGE review.

Evidence to support a role for the mismatch repair genes human mutL homolog 1 (hMLH1) and human mutS homolog 2 (hMSH2) in the etiology of colorectal cancer has come from linkage analysis, segregation studies, and molecular biologic analysis. More recently, carriers of potentially pathogenic mutations in the hMLH1/hMSH2 genes have consistently been shown to be at a greatly increased risk of developing colorectal cancer compared with the general population. When considered together, the available evidence shows a strong, consistent, and biologically plausible association between mismatch repair gene mutations and colorectal cancer. The penetrance of mutations in hMLH1/hMSH2 is incomplete and is significantly higher in males (approximately 80%) than in females (approximately 40%). To date, evidence for gene-gene or gene-environment interactions is limited, although preliminary studies have revealed a number of avenues that merit exploration. Population screening for mutation carriers is not currently a feasible option, and mutation analysis remains restricted to either relatives of mutation carriers or colorectal cancer cases selected on the basis of phenotype.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Whole-gene APC deletions cause classical familial adenomatous polyposis, but not attenuated polyposis or "multiple" colorectal adenomas.

Familial adenomatous polyposis (FAP) is a dominantly inherited colorectal tumor predisposition that results from germ-line mutations in the APC gene (chromosome 5q21). FAP shows substantial phenotypic variability: classical polyposis patients develop more than 100 colorectal adenomas, whereas those with attenuated polyposis (AAPC) have fewer than 100 adenomas. A further group of individuals, so-called "multiple" adenoma patients, have a phenotype like AAPC, with 3-99 polyps throughout the colorectum, but mostly have no demonstrable germ-line APC mutation. Routine mutation detection techniques fail to detect a pathogenic APC germ-line mutation in approximately 30% of patients with classical polyposis and 90% of those with AAPC/multiple adenomas. We have developed a real-time quantitative multiplex PCR assay to detect APC exon 14 deletions. When this technique was applied to a set of 60 classical polyposis and 143 AAPC/multiple adenoma patients with no apparent APC germ-line mutation, deletions were found exclusively in individuals with classical polyposis (7 of 60, 12%). Fine-mapping of the region suggested that the majority (6 of 7) of these deletions encompassed the entire APC locus, confirming that haploinsufficiency can result in a classical polyposis phenotype. Screening for germ-line deletions in APC mutation-negative individuals with classical polyposis seems warranted.

Adenoma↗
PubMed2001

Nuclear thymidylate synthase expression, p53 expression and 5FU response in colorectal carcinoma.

Thymidylate synthase (TS) is a key enzyme in DNA synthesis and is inhibited by metabolites of the chemotherapeutic agent 5-fluorouracil (5FU). Nuclear expression of TS in human tissue in vivo has not been characterised and its clinicopathological correlates in malignancy are unknown. 52 cases of primary colorectal carcinoma (CRC) and 24 cases of matched metastatic carcinoma were studied immunohistochemically using the monoclonal antibody TS106. The degree of nuclear TS immunostaining correlated closely with levels of TS mRNA expression amongst 10 CRCs studied. Strong nuclear immunostaining was seen in normal basal crypt colonocytes and germinal centre cells, and in a varying proportion of adenocarcinoma cells. Amongst the primary carcinomas, higher TS nuclear expression was associated with prominent extracellular mucin production and right-sided location. Higher TS nuclear expression also showed a significant association with poorer response to protracted venous infusional 5FU therapy. There was no clear association between TS nuclear expression and Ki67 or p53 expression assessed immunohistochemically. There was a strong positive correlation between TS nuclear expression in primary and metastatic CRC but the latter generally showed higher expression than matched primary tumour tissue. These findings confirm the nuclear expression of TS protein in human cells in vivo and provide new insight into how such expression may relate to the behaviour of CRCs.

Adenocarcinoma↗
PubMed2001

Mutation frequency in coding and non-coding repeat sequences in mismatch repair deficient cells derived from normal human tissue.

Repetitive tracts within the coding regions of TGFBR2 and BAX are frequently mutated in mismatch repair deficient tumours and are implicated in tumour progression. However, there has been little study of the balance between selection pressure and inherent instability at sequences within these genes. To determine whether TGFBR2 and BAX are inherently prone to mutations in the presence of MMR defects, we studied MMR deficient cells derived from B-lymphocytes. By analysing cells derived from normal tissue we aimed to minimize the effects of selection pressures that bias the apparent frequency of mutation. We definitively show that certain sequences, usually repaired by MMR, are inherently unstable. Using a small pool PCR technique we confirmed these cells exhibit microsatellite instability. Additionally, we demonstrate that MMR deficiency results in an excess of mutations, specifically at the poly(A)(10) tract compared to other regions of the TGFBR2 gene (P<0.001). Conversely, an excess of mutations does not appear to arise at the poly(G)(8) tract of the BAX gene. These studies provide insight into the mechanism by which TGFBR2 and BAX genes become mutated during tumorigenesis. These findings invoke the notion of "unmasking" specific hypermutable sequences in particular genes adding further complexity to the concept of the mutator phenotype.

Alleles↗
PubMed2001

Hypermutability at a poly(A/T) tract in the human germline.

Poly(A/T) tracts are abundant simple sequence repeats (SSRs) within the human genome. They constitute part of the coding sequence of a variety of genes, encoding polylysine stretches that are important for protein function. Assessment of poly(A/T) tract stability is also used to identify microsatellite unstable colorectal cancers, which are characteristic of tumours defective in DNA mismatch repair. Despite their importance, little is known about the stability of poly(A/T) SSRs in the human germline. We have determined the stability of a paradigm poly(A/T) tract, BAT-40, by study of population allele frequencies, mutation frequency in families and mutation frequency in sperm DNA. We show that the locus is polymorphic, with a level of heterozygosity of 59.7%. Germline mutation was observed in 13 of 187 germline transmissions (7.0%) in 10 families suggesting BAT-40 is unstable in the germline. Further evidence for germline instability at BAT-40 was provided by small pool PCR analysis of matched blood and sperm DNA templates, revealing a significantly elevated frequency of mutation in the germline (P < 0.001). These findings provide insight into poly(A/T) tract stability in the germline. They also have relevance to the study of gene expression and to determination of microsatellite instability in tumours.

AT Rich Sequence↗
PubMed2001

Suppression of intestinal and mammary neoplasia by lifetime administration of aspirin in Apc(Min/+) and Apc(Min/+), Msh2(-/-) mice.

Numerous studies have indicated that exposure to nonsteroidal anti-inflammatory drugs is associated with a lowered risk of colorectal cancer. However, analyses of the effect of aspirin upon tumorigenesis in Apc(Min/+) mice have yielded contrasting results. We show that adult dietary exposure to aspirin does not suppress intestinal tumorigenesis in Apc(Min/+) mice, but that continual exposure from the point of conception does. To test whether this regime could suppress the phenotype of murine models of hereditary nonpolyposis colorectal cancer, Msh2-deficient mice were exposed to aspirin. This did not modify the mutator phenotype of Msh2(-/-) mice, but weakly extended survival. Finally, we analyzed (Apc(Min/+), Msh2(-/-)) mice and found that lifetime aspirin exposure significantly delayed the onset of both intestinal and mammary neoplasia. Thus embryonic and perinatal exposure to aspirin suppresses neoplasia specifically associated with the loss of Apc function, opening a potential window of opportunity for nonsteroidal anti-inflammatory drug intervention.

Animals↗
PubMed2001

Early-onset colorectal cancer with stable microsatellite DNA and near-diploid chromosomes.

Colorectal cancer has been described in terms of genetic instability selectively affecting either microsatellite sequences (MIN) or chromosome number and structure (CIN). A subgroup with apparently stable, near-diploid chromosomes and stable microsatellites (MACS) also exists. These distinctions are important, partly because of their value in highlighting different pathways of carcinogenesis, and partly because of their direct relevance to prognosis. Study of early-onset cancer has often proved a fruitful resource for the identification of the nature and function of cancer susceptibility genes. In a study of colorectal cancer with stable microsatellite DNA, we describe 22 early-onset tumours (mean age=33), compared with 16 late-onset tumours (mean age=68). Both groups contained carcinomas with the MACS phenotype, characterized by near diploid DNA content, as defined by flow cytometry, and minimal chromosome arm deletion or amplification (six or less events per genome), determined by comparative genomic hybridization (CGH). Minimal chromosome imbalance correlated strongly with diploid DNA content (P<0.001). The proportion of MACS cancers was significantly greater in early-onset as compared to late-onset tumours (64 vs 13%, P=0.005). Of the chromosome arm imbalances commonly observed in late-onset tumours, only 18q- was observed more than twice amongst the 14 early-onset MACS tumours. Seventy-nine per cent of these MACS tumours were located in the distal colon, and 69% were at advanced clinico-pathological stages (with lymph node or distant metastasis). A positive family history of colorectal or other cancers was elicited in seven patients in the MACS early-onset group, and one additional patient in this group had a metachronous ovarian cancer. The results suggest that MACS cancer may have a genetic basis different from either MIN or CIN, and further studies of these cancers may lead to discovery of new mechanisms of colorectal carcinogenesis and cancer susceptibility.

Aged↗
PubMed2000

Sequence interruptions confer differential stability at microsatellite alleles in mismatch repair-deficient cells.

Determinants of instability at a given microsatellite repeat merits investigation in view of relevance to understanding evolution of mutations at such sequences in human populations. The microsatellite D2S123 was studied as a paradigm CA repeat marker. Furthermore, this marker is one of a recommended panel used in molecular screening for hereditary non-polyposis colorectal cancer (HNPCC). In this investigation we show that the mutation rate at the D2S123 locus is markedly influenced by intra-allelic sequence variation within the repetitive tract itself. We employed a novel approach to characterize the nature of instability at D2S123, by utilizing cells derived from a non-tumour lineage, which harbour a dominant negative mismatch repair (MMR) mutation and a mutator phenotype. Individual alleles were typed using a semi-quantitative small pool PCR technique and this demonstrated substantial allele-these specific bias in susceptibility to mutation at the D2S123 locus. In support of these in vitro data, bias in allele mutation rate was also observed in tumours from 41 HNPCC patients, which was dependent on constitutional genotype. Sequencing of cell line and patient DNAs revealed that short alleles are significantly more susceptible to mutation due to the presence of uninterrupted CA repeats. Long D2S123 alleles are intrinsically more stable because of a TA interspersion within the repetitive tract. In addition to extending understanding of mutation at CA repeat dinucleotide tracts, these findings have considerable relevance both to screening programmes and to correlation of microsatellite instability (MSI) with colon cancer survival. The manifestation of tumour MSI may be substantially influenced by constitutional genotype.

Alleles↗