UMLS:C0699790 - FACTA Search

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Query: UMLS:C0699790 (colon cancer)
28,837 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ability of O(6)-benzylguanine (BG) to inactivate alkyltransferase (AGT) to potentiate the antitumor efficacy of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) is being tested in clinical trials. As of now, there are no examples of acquired resistance to BG+BCNU in the clinical setting. However, we hypothesized that genetically unstable tumors might develop resistance to the combination after repeated drug-exposures to achieve therapeutic efficacy. To evaluate this possibility, we treated three colon cancer cell lines that are either proficient in mismatch repair (MMR) [SW480 (MMR wild type)] or deficient in MMR [HCT116 (hMLH1 mutant) and HCT15 (hMSH6 mutant)] with three cycles of BG+BCNU. After drug-treatments, HCT116 and HCT15 were completely resistant to BG-potentiated cytotoxicity of BCNU. In these two cell lines, the acquired BG resistance resulted from two de novo and different mutations at amino acid 165 in AGT: 165-lysine (K) to glutamic acid (E) (K165E in HCT116), and 165-lysine to asparagine (N) (K165N in HCT15). Both K165-mutated AGTs had markedly decreased enzymatic activity because of unstable AGT protein but were remarkably resistant to BG inactivation. FISH analysis showed that only one copy of MGMT gene exists in HCT116 cells, and the status of promoter methylation of MGMT in HCT15 showed that one allele of the MGMT promoter has an aberrant methylation. Thus, the MGMT gene expressing AGT either from one copy (HCT116) or from unmethylated allele (HCT15) was mutated because of the exposure to BG+BCNU in these two MMR-deficient cell lines. Conversely, MMR-proficient SW480 cells, treated with three cycles of BG+BCNU, maintained wt AGT and the sensitivity to BG-potentiated BCNU-cytotoxicity. To confirm that K165-mutated AGT proteins were responsible for resistance to BG+BCNU, we transfected K165E and K165N MGMT cDNAs into Chinese hampster ovary (CHO) cells. Transfected CHO cells had low AGT activity but increased IC(50) for either BCNU or temozolomide (TMZ), compared with parental CHO cells. BG did not potentiate the cytotoxicity of these two alkylating agents at concentrations up to 200 microM; in contrast, BG, at 25 microM, sensitized CHO-AGT (transfected with wt MGMT cDNA) cells to BCNU or TMZ-cytotoxicity by 3-4 fold. These results suggest that K165 AGT mutants arising in MMR-deficient tumor cells after treatment with chemotherapeutic agents are both resistant to BG-inactivation and are active in the repair of alkylated DNA adducts.
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PMID:Chemotherapy-induced O(6)-benzylguanine-resistant alkyltransferase mutations in mismatch-deficient colon cancer. 1203 16

DNA mismatch repair genes, hMLH1 and hMSH2, assigned on chromosome 3p21-23 and 2p21-22 are involved in hereditary non-polyposis colorectal cancer (HNPCC). The heterozygous carrier of the mutated allele results in a mutator phenotype and accelerating tumorigenesis, which especially causes carcinomas in the gastrointestinal and genitourinary tracts. We screened germline mutations of mismatch repair genes hMLH1 and hMSH2 in a patient with multiple primary neoplasms (multiple stomach cancers, colon cancer and brain tumor) in a cancer clustered HNPCC family. Screening by long RT-PCR from the RNA extracted from puromycin-treated heparinized blood showed skipping of the exon 2 in hMLH1. The analysis of the genomic DNA showed a GT deletion in the splice-donor site of the exon 2, which is compatible with the splicing variant detected by long RT-PCR analysis. This is a novel germline mutation that has not been reported previously.
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PMID:A novel germline mutation of hMLH1 in a patient with hereditary non-polyposis colorectal cancer. 1211 Jun 39

Irinotecan (CPT-11), a recently introduced component of a standard chemotherapy for colorectal cancer, induces in colon cancer cell lines in vitro cell cycle arrest and apoptosis. Since sporadic colon carcinomas exhibit in 50-60% mutations in the p53 gene and in 10-15% an MSI phenotype due in the great majority of the cases to hMLH1 inactivation, we investigated how these lesions influence the cellular effects of CPT-11 by using colorectal carcinoma cell line HCT116 (which has the genotype p53(+/+),hMLH1(-)) and 2 derivative cell lines with the genotypes p53(+/+),hMLH1(+) and p53(-/-),hMLH1(-). CPT-11 treatment induced G2/M arrest in all 3 cell lines within 48 hr. In the p53(+/+),hMLH1(+) cell line, G2/M arrest was maintained for at least 12 days. There was little concomitant apoptosis, but this was enhanced when the hMLH1 protein was absent. This enhanced apoptosis was accompanied by a shorter duration of the G2/M arrest than in the hMLH1(+) cell line. Partial abrogation of G2/M arrest by caffeine enhanced apoptosis in both hMLH1(+) and hMLH1(-) cells. By contrast, in the p53(-/-) cell line, the G2/M arrest was terminated within 4 days. Termination of the G2/M arrest was accompanied by a high level of apoptosis detectable through poly(ADP-ribose)polymerase (PARP) cleavage, DNA fragmentation and by the appearance of cells with a DNA content <2N. The triggering of G2/M arrest was accompanied in the 3 cell lines by a transient phosphorylation of cdc-2, while the maintenance of the arrest in the p53(+/+) cell lines was accompanied by the overexpression of p53 and p21 proteins and, consequently, by the inhibition of cdc-2 kinase activity. These data indicate that: (i) CPT-11 induces long-term arrest in p53(+/+) cells and a short-term arrest followed by apoptosis in p53(-/-) cells; (ii) triggering of the arrest is p53 independent and is associated with a brief increase of phosphorylation of cdc-2, while the p53-dependent maintenance of G2/M arrest is associated with the inhibition of cdc-2 kinase activity by p21; and (iii) lack of hMLH1 protein enhances CPT-11-induced apoptosis. These results may be useful for designing rational therapies dependent on the p53 and mismatch-repair status in the tumor.
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PMID:Cellular effects of CPT-11 on colon carcinoma cells: dependence on p53 and hMLH1 status. 1220 84

Base excision repair (BER) is a fundamental cellular process used to reduce the cytotoxicity of alkylating agent chemotherapy. Heretofore, no therapeutic agents have targeted this DNA repair pathway. Methoxyamine (MX), which binds abasic sites, acting as an inhibitor of BER, was evaluated in combination with the methylating agent temozolomide (TMZ). Three human colon cancer cell lines were used, SW480 cells, which are wild-type for mismatch repair genes and have mutated p53, HCT116 cells, which are mutant in hMLH1 and wild-type for p53, and HCT15 cells, which are mutant in hMSH6 and mutant in p53 as well. Nude mice carrying these tumors received TMZ alone or in combination with MX or O(6)-benzylguanine (BG), an inhibitor of O(6)-alkylguanine DNA-alkyltransferase, daily i.p. for 5 consecutive days. At the highest tolerable dose of TMZ (120 mg/kg), a tumor growth delay of approximately 9.3 +/- 1.2 days was noted in SW480. Addition of BG resulted in a tumor growth delay of 25 +/- 2.4 days accompanied by significant weight loss (23%) and severe myelosuppression. In contrast, SW480 tumor-bearing mice treated with MX + TMZ had cessation of tumor growth for 50 +/- 13 days and very slow regrowth, yielding tumor growth delays of >70 +/- 14 days (P < 0.002) without additive systemic toxicity. HCT116 and HCT15 xenografts were completely resistant to treatment with TMZ alone or in combination with BG. However, treatment with MX + TMZ induced significant tumor growth delays (20 +/- 1.4 days in HCT116 and 14 +/- 3.1 days in HCT15 xenografts, P < 0.05). These studies demonstrate that a significant enhancement of the antitumor effect of TMZ by MX was observed in human colon cancer xenografts with mismatch repair proficiency and deficiency. DNA BER may be a useful pharmacological target through which tumor cells can be sensitized to alkylating therapeutic agents.
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PMID:Base excision repair as a therapeutic target in colon cancer. 1223 45

A recent study using colorectal cancer cell lines has identified methylation on a small region of hMLH1 promoter (-248 to -178 relative to the transcription start site) to be critical for gene silencing, but shown that methylation on a more upstream region is frequent in cell lines with hMLH1 expression. Because cultured cell lines have a higher degree of CpG methylation than primary tumors, we attempted to examine methylation profiles of CpG sites of hMLH1 promoter in primary gastric carcinomas with or without microsatellite instability (MSI). Seven cases with MSI and six cases without MSI were assessed for the methylation status of hMLH1 promoter by bisulfite-sequencing. All of the MSI-positive cases previously showed loss of hMLH1 expression and six cases displayed methylated alleles in methylation-specific PCR (MSP) for hMLH1. Sequencing analysis revealed that: (i) CpG sites were overall methylated in MSI-positive tumors with positive MSP results; (ii) a small region (-248-178) was almost invariably methylated in MSI-positive tumors; and (iii) the vast majority of CpG sites were unmethylated in MSI-negative tumors, including a more upstream region (proximal to -248). Our study suggests that methylation of a more upstream region observed in colon cancer cell lines may be an acquired change during cell line establishment and it was not identified in primary gastric carcinomas without MSI.
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PMID:Profile of methylated CpG sites of hMLH1 promoter in primary gastric carcinoma with microsatellite instability. 1258 45

The first-degree relatives of patients affected by colorectal cancer, who do not belong to familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer families, have a doubled risk of developing tumors of the large intestine. We have previously demonstrated that subjects with a single first-degree relative (SFDR) with colon cancer have a doubled risk for developing colorectal adenomas, and in these cases, polyps recur more frequently. The mechanism underlying this predisposition has not been clarified. In this study, we evaluated the frequency of microsatellite instability (MSI) using the five markers suggested by the National Cancer Institute workshop, target gene mutations, hMLH1 and hMSH2 expression, and hMLH1 promoter hypermethylation in the adenomas of patients with and without a SFDR affected by colon cancer. Seventy polyps were obtained from 70 patients: 27 with a single FDR with colon cancer and 43 without such a history. Of the 70 polyps, 12 were MSI-H (17.1%), 20 were MSI-L (28.6%), and 30 were microsatellite stable (42.9%). Of the 27 patients with positive family history, 8 polyps (29.6%) were MSI-H compared with those with negative history in which 4 polyps (9.3%) were MSI-H (P < 0.02). Of the 12 MSI-H polyps, all of the polyps obtained from patients with positive family history had loss of hMLH1 immunostaining versus one with negative family history (P < 0.02). Of the MSI-H polyps, 2 had a somatic frameshift mutation of the MBD4 gene, 1 of MSH6, 1 of BAX, and 2 of transforming growth factor betaRII. Furthermore, 6 of 8 polyps from patients with positive family history with MSI-H and loss of MLH1 had hypermethylation of the MLH1promoter versus none of the MSI-H with negative family history (P < 0.02). All 6 polyps of the 27 from SFDR positive subjects, with hMLH1 promoter hypermethylation loss of hMLH1 and MSI, were located in the right colon (P < 0.02). Hypermethylation of the promoter of hMLH1, consequent loss of hMLH1 expression, and MSI are at the basis of approximately 25% of adenomatous polyps developed in subjects with a SFDR affected by colorectal cancer.
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PMID:Frequent loss of hMLH1 by promoter hypermethylation leads to microsatellite instability in adenomatous polyps of patients with a single first-degree member affected by colon cancer. 1259 27

Basic studies of DNA replication and repair have provided surprising and pivotal insights into a novel pathway of tumorigenesis. Defects in the DNA mismatch repair process dramatically increase the risk for specific types of cancer because of instability in microsatellite DNA sequences. A germline mutation in either the hMSH2 or hMLH1 mismatch repair gene results in the hereditary nonpolyposis colorectal cancer (HNPCC), or Lynch, syndrome. The lifetime risk for colon cancer is 80% in affected persons, and an aggressive cancer surveillance program is essential not only for these individuals but also for at-risk family members. The diagnosis of HNPCC can be made by fulfillment of the Amsterdam clinical criteria or through genetic testing for germline mutations in hMSH2 or hMLH1. Genetic testing is particularly useful in families with atypical clinical features and also for cancer risk assessment within an established HNPCC kindred. Microsatellite instability (MSI) of DNA is a hallmark feature of HNPCC-associated tumors, and as many as 15% of cases of sporadic colorectal cancer also display MSI. The biological behavior of colorectal tumors with MSI is distinctive; the most intriguing feature is their favorable natural history. The study of HNPCC has provided an example of the powerful interplay between molecular genetics and clinical care.
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PMID:The hereditary nonpolyposis colorectal cancer syndrome: genetics and clinical implications. 1266 48

Hereditary non-polyposis colon cancer (HNPCC) is an autosomal dominant form of inherited predisposition to colorectal and other malignancies. It is associated with mutations in DNA mismatch-repair genes, especially hMSH2 and hMLH1. Management of HNPCC families is improved if the underlying mutation in each family can be discovered. We describe a Newfoundland kindred, meeting the Amsterdam Criteria for HNPCC, in which a mutation in the promoter region of the hMLH1 gene co-segregates with the disease phenotype. The -42C > T mutation is within a putative Myb proto-oncogene binding site. Using electrophoretic mobility shift assays, we demonstrated that the mutated Myb binding sequence is less effective in binding nuclear proteins than the wild-type promoter sequence. Using in vivo transfection experiments in HeLa cells, we further demonstrated that the mutated promoter has only 37% of the activity of the wild-type promoter in driving the expression of a reporter gene. The average age of onset in six family members affected with colorectal cancer is 62 years, which is substantially later than the typical age of onset in HNPCC families. This is consistent with a substantial decrease, but not total elimination, of mismatch repair function in affected members of this family. This is the first report of a heritable hMLH1 promoter mutation in any HNPCC family.
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PMID:Germline hMLH1 promoter mutation in a Newfoundland HNPCC kindred. 1291 37

A CpG island DNA methylator phenotype has been postulated to explain silencing of the hMLH1 DNA mismatch repair gene in cancer of the microsatellite mutator phenotype. To evaluate this model, we analyzed methylation in CpG islands from six mutator and suppressor genes, and thirty random genomic sites, in a panel of colorectal cancers. Tumor-specific somatic hypermethylation was a widespread age-dependent process that followed a normal Gaussian distribution. Because there was no discontinuity in methylation rate, our results challenge the methylator phenotype hypothesis and its hypothetical pathological underlying defect. We also show that the mutator phenotype dominates over the gradual accumulation of DNA hypermethylation in determining the genotypic features that govern the phenotypic peculiarities of colon cancer of the mutator pathway.
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PMID:Genetics supersedes epigenetics in colon cancer phenotype. 1295 87

Microsatellite instability (MSI) occurs in 10-20% of the sporadic colon carcinomas and appears to be primarily due to alterations in hMLH1 and hMSH2. Little is known about the role of diet in MSI-related colon carcinogenesis. We used data from a Dutch population-based case-control study on sporadic colon carcinomas (184 cases and 259 controls) to evaluate associations between dietary factors previously reported as being associated with colon cancer risk and MSI, hMLH1 expression, and hMLH1 hypermethylation. Red meat intake was significantly differently related to microsatellite instability-high (MSI-H) tumors compared with microsatellite instability-low/microsatellite stable (MSI-L/MSS) [odds ratio (OR), 0.3; 95% confidence interval (CI), 0.1-0.9]. It was inversely associated with MSI-H tumors when compared with the population-based controls (OR, 0.5; 95% CI, 0.2-1.2) and positively associated with MSI-L/MSS tumors (OR, 1.5; 95% CI, 0.9-2.6). A positive association was observed for alcohol intake with MSI-H tumors (OR, 1.9; 95% CI, 0.8-4.7). Fruit consumption seemed to especially decrease the risk of MSI-H tumors with hypermethylated hMLH1 (Methyl(+) tumors) [Methyl(+) versus controls: OR = 0.4 and 95% CI = 0.2-0.9; MSI-H tumors without hypermethylated hMLH1 (Methyl(-) tumors) versus controls, OR = 1.2 and 95% CI = 0.8-1.7; Methyl(+) versus Methyl(-) tumors, OR = 0.2 and 95% CI = 0.1-0.9]. Most other evaluated dietary factors were not distinctively associated with a specific MSI or hMLH1 methylation status. Our data suggest that red meat consumption may enhance the development of MSI-L/MSS carcinomas in particular, whereas alcohol intake appears to increase the risk of MSI-H tumors. Fruit consumption may especially decrease the risk of MSI-H carcinomas exhibiting epigenetically silenced hMLH1.
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PMID:Dietary factors and microsatellite instability in sporadic colon carcinomas. 1465 71

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