Biomedical subjects

R F Jacoby

Publications and source records attributed to R F Jacoby.

10 recordsLinked to original sources

PubMed1995

Genetic instability associated with adenoma to carcinoma progression in hereditary nonpolyposis colon cancer.

BACKGROUND & AIMS: Genetic instability related to defective DNA mismatch repair genes may be involved in the pathogenesis of carcinoma in hereditary nonpolyposis colon cancer (HNPCC). However, nonneoplastic tissues from patients inheriting defects in human MSH2 or human MLH1 do not show significant genetic instability. The aim of this study was to determine whether acquisition of genetic instability at the adenoma stage promotes malignant transformation by studying adenoma-carcinoma progression in HNPCC. METHODS: Dinucleotide repeat loci were analyzed by polymerase chain reaction from microdissected adenoma and/or carcinoma stages from formalin-fixed paraffin-embedded HNPCC tumors. RESULTS: Although genetic instability was observed at some loci in almost all cases, the proportion of microsatellite loci altered was significantly less (P < 0.01) in completely benign adenomas (24%) than in benign areas of adenomas with malignancy (54%). Molecular fingerprints indicated intratumor heterogeneity, with evolution of related subclones of neoplastic cells. However, in all cases of tumor progression, at least one subclone from the adenoma stage was closely related to the carcinoma. CONCLUSIONS: Some genetic instability develops at the benign adenoma stage in most HNPCC tumors. Adenomas with a greater rate of genetic instability are more likely to progress to carcinoma. Topographic genotyping data provides evidence supporting the hypothesis of adenoma-carcinoma progression in HNPCC.

Adenoma↗

PubMed1995

Delayed postpolypectomy bleeding.

Complications of colonoscopic polypectomy include perforation, infection, and bleeding. The incidence of bleeding after polypectomy is reported to range from one to seven per 1000 polypectomies. This complication usually occurs within a few days after the standard procedure using bipolar electrocautery. The longest time interval between polypectomy and significant bleeding thus far reported is 14 days. Most cases of postpolypectomy bleeding are easily recognizable and can be effectively treated by colonoscopic electrocauterization. We report here a patient who underwent colonoscopic removal of a flat adenomatous polyp at the cecum and presented 29 days postprocedure with acute onset of severe bleeding from the polypectomy site. A repeat colonoscopy identified this lesion, and cauterization successfully stopped this bleeding.

Adenomatous Polyposis Coli↗

PubMed1994

Genetic analysis of colon cancer susceptibility in mice.

Mouse models may aid in the identification of genes involved in colon cancer. Our mating scheme involved mouse strains selected for maximum differences in susceptibility to DMH-induced colon tumors. Tumors were found in 40 of 122 progeny from a backcross to the resistant strain. We examined progeny animals for segregation of 177 genetic markers distributed at intervals of 5-30 cM on all mouse chromosomes. Multiple loci contribute to the phenotype, with significant linkage to a novel locus, Ccs1, between D12Mit5 and D12Mit6 on mouse Chr 12. Comparative maps suggest that the human homologue of Ccs1 is near FOS on human chromosome 14q.

1,2-Dimethylhydrazine↗

PubMed1992

K-ras oncogene mutations in rat colon tumors induced by N-methyl-N-nitrosourea.

We have been studying a rat model of colon cancer in which tumors are induced by direct application of N-methyl-N-nitrosourea (MNU) to discrete areas of the colonic mucosa for a limited period of time. Activation of the ras genes by point mutation has been observed in many experimental tumors, including tumors induced by MNU. To detect potential activating point mutations in the H-ras and K-ras oncogenes in MNU-induced rat colon tumors, DNA samples from 40 adenomas, nine carcinomas, and 14 histologically normal tissue samples from 14 rats--as well as from 16 foci induced on NIH3T3 cells by tumor DNAs--were amplified by the polymerase chain reaction and hybridized with allele-specific oligonucleotide probes. No H-ras point mutations were observed in any of these samples. We did detect K-ras point mutations, however, in four primary tumours--one adenoma (2.5%) and three carcinomas (33%); these mutations were all G----A transitions at the second nucleotide of codons 12 and 13. The absence of detectable ras mutations from the majority of tumors suggests that, in contrast to other animal models utilizing MNU, tumorigenesis in MNU-induced rat colon tumors may predominantly involve activation of genes other than ras.

3T3 Cells↗

PubMed1991

K-ras mutations in 1,2-dimethylhydrazine-induced colonic tumors: effects of supplemental dietary calcium and vitamin D deficiency.

Recent studies from our laboratory have demonstrated that dietary supplemental calcium had no significant effect on the incidence of 1,2-dimethylhydrazine-induced colonic tumors, but did decrease the number of rats with multiple tumors and reduced tumor size. Moreover, concomitant vitamin D deficiency appeared to abolish these protective effects of calcium on colonic tumors in this experimental model. To date, however, the mechanism(s) involved in these phenomena remain unclear. In order to address these important issues, 1,2-dimethylhydrazine-induced colonic tumors from animals on control, Ca(2+)-supplemented, vitamin D-sufficient, and Ca(2+)-supplemented, vitamin D-deficient diets were examined for the presence of ras oncogene mutations. DNA was extracted from each of these tumors. Targeted areas of K-ras and H-ras genes were amplified by the polymerase chain reaction and analyzed for point mutations using allele-specific oligonucleotide hybridization and subsequent DNA sequencing. The results of these studies demonstrated that: (a) approximately one-third of 1,2-dimethylhydrazine-induced colonic carcinomas in the control group had K-ras G to A mutations; (b) no mutations, however, were detected in the cancers of the calcium-supplemented group; (c) concomitant vitamin D deficiency abolished the antimutagenic effect of dietary calcium supplementation (e.g., approximately one-third of cancers in this group again had detectable K-ras mutations); and (d) no H-ras point mutations were detected in colonic tumors from any group. These findings suggest that alterations in K-ras mutations may be one possible mechanism by which calcium and vitamin D status influence colonic carcinogenesis in this experimental model.

1,2-Dimethylhydrazine↗

PubMed1991

Incidence of Harvey ras oncogene point mutations and their expression in methylbenzylnitrosamine-induced esophageal tumorigenesis.

Activation of the ras oncogene was investigated in esophageal tumors induced by methylbenzylnitrosamine (MBN) in the Sprague-Dawley rat. DNA was extracted from grossly visible carcinogen-induced tumors. H-ras and K-ras gene sequences were then amplified by the polymerase chain reaction. Point mutations in the ras genes were then identified by selective hybridization to allele-specific oligonucleotide probes. A guanine to adenine transition at the 35th nucleotide in the H-ras coding sequence (GGA to GAA in the 12 codon) was observed in 67% (10 of 15) of the papillomas examined. This mutation codes for glutamate instead of glycine as the 12th amino acid of the ras p21 protein. No other H-ras or K-ras mutations were observed. To determine the distribution of this H-ras mutation in esophageal tissues, histological sections of MBN-treated esophagi were stained with a monoclonal antibody (E184) which selectively recognizes the mutated ras p-21 with glutamate substituted for glycine as the 12th amino acid. Expression of the mutant ras p21 protein was observed in 20% of the squamous papillomas, 13.6% of hyperplastic lesions and 10% of dysplastic lesions. Thus, activation of the H-ras oncogene as a result of guanine to adenine point mutation is a frequent event in esophageal tumors induced by MBN, occurring in 67% of squamous papillomas, but expression of the corresponding mutant ras p21 protein is observed in a much smaller proportion of the tumors in this animal model.

Adenine↗

PubMed1991

Myelodysplastic syndrome and pancytopenia in a patient with non-A, non-B chronic active hepatitis.

Non-A, non-B viral hepatitis may cause many different hematologic abnormalities, such as transient anemia, granulocytopenia, thrombocytopenia, atypical lymphcytosis, or aplastic anemia. We describe a patient who developed a myelodysplastic syndrome (refractory anemia with excess blasts) after prednisone therapy for non-A, non-B chronic active hepatitis. We discuss the effects of non-A, non-B viral infection on the bone marrow and potential explanations for the previously unreported association with myelodysplastic syndrome.

Aged↗

PubMed1991

Mutations in the K-ras oncogene induced by 1,2-dimethylhydrazine in preneoplastic and neoplastic rat colonic mucosa.

These experiments were conducted to determine whether point mutations activating K-ras or H-ras oncogenes, induced by the procarcinogen 1,2-dimethylhydrazine (DMH), were detectable in preneoplastic or neoplastic rat colonic mucosa. Rats were injected weekly with diluent or DMH at 20 mg/kg body wt for 5, 10, 15, or 25 wk, killed, and their colons dissected. DNA was extracted from diluent-injected control animals, histologically normal colonic mucosa from carcinogen-treated animals, and from carcinomas. Ras mutations were characterized by differential hybridization using allele-specific oligonucleotide probes to polymerase chain reaction--amplified DNA, and confirmed by DNA sequencing. While no H-ras mutations were detectable in any group, K-ras (G to A) mutations were found in 66% of DMH-induced colon carcinomas. These mutations were at the second nucleotide of codons 12 or 13 or the first nucleotide of codon 59 of the K-ras gene. The same type of K-ras mutations were observed in premalignant colonic mucosa from 2 out of 11 rats as early as 15 wk after beginning carcinogen injections when no dysplasia, adenomas, or carcinomas were histologically evident, suggesting that ras mutation may be an early event in colon carcinogenesis.

1,2-Dimethylhydrazine↗

PubMed1990

Effect of polyamine oxidase inhibition on the colonic malignant transformation process induced by 1,2-dimethylhydrazine.

Recent studies of colon adenocarcinomas in humans and experimentally induced colonic tumors in rodents have demonstrated selective elevations in the level of N1-acetylspermidine in these malignant tissues. The exact relationship of these alterations in acetylated polyamine levels to the malignant transformation process, however, remains unclear. In order to clarify this issue, rats were given s.c. injections of 1,2-dimethylhydrazine (DMH; 20 mg/kg body wt/week) or diluent for up to 26 weeks. After 10 weeks of carcinogen treatment, one-half of the animals in each group were also concomitantly given i.p. injections of MDL 72527 (20 mg/kg body wt/week), a specific inhibitor of polyamine oxidase, until they were killed. Animals were killed after 15 weeks of DMH treatment and polyamine levels as well as the activities of polyamine oxidase, ornithine decarboxylase and spermidine-N1-acetyltransferase were measured and compared in rat proximal and distal colonic mucosa of each group. Polyamine levels were also assessed in each of these groups after 26 weeks of treatment with this carcinogen +/- MDL 72527. In addition, in view of recent studies that have indicated that polyamines may influence certain oncogenes in human colonic carcinoma cells, tumors from DMH +/- MDL 72527 were analyzed for K-ras mutations. The results of these experiments demonstrated for the first time that: (i) MDL 72527 was a specific inhibitor of polyamine oxidase in normal and malignant colonic tissue; (ii) concomitant administration of this agent with DMH enhanced the elevation of colonic N1-acetylspermidine and significantly reduced the mean colonic tumor burden, as assessed by total tumor area per rat, produced by this carcinogen alone; (iii) analysis of K-ras mutations revealed a similar incidence (62-69%) in adenocarcinomas for both groups (+/- MDL 72527); (iv) however, analysis of the K-ras-mutated and non-mutated tumors revealed that in both carcinogen-treated groups (+/- MDL 72527), tumors with such mutations were smaller than their counterparts without such genetic alterations. Moreover, MDL 72527 reduced the average size of tumors, with and without such mutations, to a similar extent.

1,2-Dimethylhydrazine↗

PubMed1990

N-ras 61 oncogene mutations in Hürthle cell tumors.

Mutations of ras oncogenes are believed to play an important role in the initiation or progression of human tumors. In thyroid tumors the incidence of ras activation by specific point mutations has been reported to range from 33% in follicular adenomas up to 60% in anaplastic carcinomas. Because of our long-standing interest in Hürthle cell tumors, we began a study of 70 such cases to determine the incidence of ras mutations and their clinical correlates. Analysis of N-ras sequences at codon position 61, with the polymerase chain reaction method and oligonucleotide probe hybridization, showed point mutations of the normal codon CAA* in eight tumor samples. One was a mutation from CAA to AAA, one from CAA to CTA,* and six from CAA to CGA. These mutations would result in amino acid substitutions of lysine, leucine, or arginine for the normal glutamine at position 61 in the N-ras protein. Identical ras mutations in two tumors and some of their surrounding thyroid tissue may indicate that activating ras point mutations are an early event in carcinogenesis. The incidence of mutations was 1 of 24 (4%) of the histologically benign tumors, 5 of 34 (15%) of the intermediate tumors (with vascular or capsular permeation), and 2 of 12 (17%) in the malignant group. Four of these eight patients died of metastatic thyroid disease and four are alive without evidence of recurrence.

Adenoma↗