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Biomedical subjects

James G Herman

Publications and source records attributed to James G Herman.

80 records · Page 5Linked to original sources
PubMed2002

Low-level microsatellite instability in most colorectal carcinomas.

Twelve to 16% of colorectal cancers (CRCs) display a high degree of microsatellite instability (MSI-H), whereas most are believed to be microsatellite stable (MSS). The existence of a low degree of instability (MSI-L) group has also been proposed. By using the Bethesda panel of microsatellite markers, the microsatellite instability (MSI) status of CRCs can be determined. This set is recommended to distinguish between MSI-H and MSI-L/MSS. No definition for MSI-L has emerged. Most reports on MSI-L rely on the Bethesda panel, using 5-15markers. Tumors with more than 30% MSI are designated as MSI-H, but the lower limit for MSI-L is ambiguous. We hypothesized that if many markers are studied, almost all CRCs would show some MSI. It would be necessary to establish a cutoff level for MSI-L by showing that, above this cutoff level, tumors display molecular and/or clinical features different from those under the cutoff level. To perform this task, we analyzed 90 BAT26 stable CRC samples with 377 markers. MSI at 1-11 loci was observed in 71 (79%) of the 90 cases. K-RAS mutation, loss of heterozygosity, and MLH1 and MGMT hypermethylation analyses were performed, as well as clinical features being scrutinized, to examine possible differences between MSI-L and MSS tumors using all of the possible cutoff levels for MSI-L. Convincing differences between putative MSI-L and MSS groups were not observed. Our results show that the sensitivity of a typically used marker number to detect MSI-L is very low, and they suggest that MSS and MSI-L tumors have a common molecular background.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Hypermethylation of the DNA repair gene O(6)-methylguanine DNA methyltransferase and survival of patients with diffuse large B-cell lymphoma.

BACKGROUND: The gene encoding the DNA repair enzyme O(6)-methylguanine DNA methyltransferase (MGMT) is transcriptionally silenced by promoter hypermethylation in several human cancers, including diffuse large B-cell lymphoma (B-DLCL). MGMT promoter hypermethylation is a favorable prognostic marker in patients with brain tumors treated with alkylating agents. METHODS: In a retrospective cohort study, we used methylation-specific polymerase chain reaction to analyze the MGMT promoter methylation status in tumor DNA of B-DLCL patients receiving cyclophosphamide as part of multidrug regimens. Molecular data were compared with patient response with the use of Student's t test. Disease-free survival and overall survival were estimated by the Kaplan-Meier method and compared with the use of the log-rank test. Multivariable survival analyses were performed with the Cox proportional hazards model. All statistical tests were two-sided. RESULTS: Thirty (36%) of 84 B-DLCL patients showed MGMT promoter hypermethylation in their lymphomas. The presence of MGMT methylation was associated with a statistically significant increase in overall survival (hazard ratio for time to death for nonmethylation versus methylation = 2.8; 95% confidence interval (CI) = 1.2 to 7.5; P =.01) and progression-free survival (hazard ratio for time to progression for nonmethylation versus methylation = 2.6; 95% CI = 1.3 to 5.8; P =.02). MGMT promoter hypermethylation was both independent of and stronger than established prognostic factors, such as age, disease stage, serum lactic dehydrogenase level, and performance status. CONCLUSION: MGMT promoter hypermethylation appears to be a useful marker for predicting survival in patients with B-DLCL treated with multidrug regimens including cyclophosphamide.

Antineoplastic Agents, Alkylating↗
PubMed2002

Cancer as an epigenetic disease: DNA methylation and chromatin alterations in human tumours.

Cancer is an epigenetic disease at the same level that it can be considered a genetic disease. In fact, epigenetic changes, particularly DNA methylation, are susceptible to change and are excellent candidates to explain how certain environmental factors may increase the risk of cancer. The delicate organization of methylation and chromatin states that regulates the normal cellular homeostasis of gene expression patterns becomes unrecognizable in the cancer cell. The genome of the transformed cell undergoes simultaneously a global genomic hypomethylation and a dense hypermethylation of the CpG islands associated with gene regulatory regions. These dramatic changes may lead to chromosomal instability, activation of endogenous parasitic sequences, loss of imprinting, illegitimate expression, aneuploidy, and mutations, and may contribute to the transcriptional silencing of tumour suppressor genes. The hypermethylation-associated inactivation affects virtually all of the pathways in the cellular network, such as DNA repair (hMLH1, BRCA1, MGMT, em leader), the cell cycle (p16(INK4a), p14(ARF), p15(INK4b), ...), and apoptosis (DAPK, APAF-1, ...). The aberrant CpG island methylation can also be used as a biomarker of malignant cells and as a predictor of their behaviour, and may constitute a good target for future therapies.

Chromatin↗
PubMed2002

Hypermethylation pathways to colorectal cancer. Implications for prevention and detection.

Epigenetic changes play an important role in the development and progression of colorectal cancer. The best characterized of these changes is the promoter region methylation of CpG islands of genes that play key roles in this disease. These changes compliment and lead to genetic changes that are well established as central to colorectal cancer progression. They may also prove useful in molecular detection approaches.

Colorectal Neoplasms↗
PubMed2002

Alterations of the p16/Rb/cyclin-D1 pathway in vulvar carcinoma, vulvar intraepithelial neoplasia, and lichen sclerosus.

Three different alterations in the p16/pRb/cyclin-D1 pathway (p16(INK4a)-promoter hypermethylation and expression of pRb and cyclin-D1) were investigated in a series of 38 cases of vulvar carcinoma (VC), 13 cases of vulvar intraepithelial neoplasia (VIN), and 21 cases of lichen sclerosus (LS). Paraffin blocks from 72 patients were selected for investigation of DNA methylation patterns in the CpG island of p16(INK4a) by methylation-specific polymerase chain reaction. Immunohistochemical studies for pRb and cyclin-D1 were performed using the standard avidin-biotin-peroxidase complex method. Epigenetic silencing of p16(INK4a) was detected in 68% of VC, 69.2% of VIN, and 42.8% of LS cases. Lack of pRb protein was found in 21% of VC, 0% of VIN, and 0% of LS cases. Overexpression of cyclin-D1 was found in 21% of VC, 30.8% of VIN, and 0% of LS cases. We conclude (1) that p16(INK4a) epigenetic inactivation most likely represents an early event, insufficient for malignant transformation, that may occur in clinically benign lesions such as LS; (2) that lack of pRb was only detected in fewer than one quarter of the carcinomas and could be considered a late secondary event; and (3) that cyclin-D1, which was overexpressed in VC and VIN, could contribute to the malignant transformation in association with p16 hypermethylation.

Adult↗
PubMed2002

Enzymatic regional methylation assay: a novel method to quantify regional CpG methylation density.

We have developed a novel quantitative method for rapidly assessing the CpG methylation density of a DNA region in mammalian cells. After bisulfite modification of genomic DNA, the region of interest is PCR amplified with primers containing two dam sites (GATC). The purified PCR products are then incubated with 14C-labeled S-adenosyl-L-methionine (SAM) and dam methyltransferase as an internal control to standardize DNA quantity. This is followed by an incubation with 3H-labeled SAM and SssI methyltransferase for methylation quantification. By use of standard mixtures of cell line DNA with a defined methylation status in every assay, the ratio (3H/14C signal) of each sample can be converted into percentage values to assess the methylation density of the amplified sequence. This methylation-sensitive technique, termed ERMA (Enzymatic Regional Methylation Assay) provides several advantages over existing methods used for methylation analysis as it determines an exact measurement of the methylation density of the region studied. We demonstrate a use of this technique in determining the methylation density of the promoter region of the tumor suppressor gene p15INK4B and changes that occur after treatment with demethylating agents.

Cell Cycle Proteins↗
PubMedDate not supplied

Specific inhibition of DNMT1 by antisense oligonucleotides induces re-expression of estrogen receptor-alpha (ER) in ER-negative human breast cancer cell lines.

Recent studies have shown that changes in epigenetic regulation, such as DNA methylation and histone acetylation, are associated with silencing of the estrogen receptor a (ER) gene in ER-negative human breast cancer cells. Treatment of these cells with the general DNMT inhibitor, 5-aza-2'deoxycytidine, led to reactivation of functional ER protein. This study addresses the hypothesis that specific inhibition of the maintenance DNA methyltransferase, DNMT1, by antisense oligonucleotides (DNMT1 ASO) is sufficient to re-express the ER gene in ER-negative human breast cancer cell lines. MDA-MB-231 and Hs578t cells were transfected with 100 nM and 150 nM DNMT1 ASO respectively for three consecutive days and evidence of DNMT1 downregulation and functional ER re-expression was sought. Significant growth reduction was observed within 48 hr and persisted after 96 hr. DNMT1 expression was blocked after exposure to DNMT1 ASO as detected by RT-PCR, Western blot and enzymatic assay whereas a mutant DNMT1 ASO had little effect. This was associated with enhanced ER mRNA and protein expression and restoration of estrogen responsiveness in MDA-MB-231 cells as demonstrated by the ability of the induced ER protein to elicit ERE-regulated reporter activity from a luciferase reporter construct. Methylation specific PCR showed that the ER CpG island was minimally demethylated, suggesting that other epigenetic events, introduced by specific DNMT1 inhibition, might also be involved in ER re-expression. Our results suggest that specific inhibition of DNMT1 expression alone is sufficient to re-express ERa in human breast cancer cell lines.

Azacitidine↗