N-Methyl-N-Nitrosourea (MNU): A positive control chemical for p53+/- mouse carcinogenicity studies.

This study evaluated the effects of a single intraperitoneal injection of N-methyl-N-nitrosourea (MNU) in citrate buffer (pH 4.5) at a dose of 75 mg/kg in thirty male and thirty female p53+/- mice followed by a six-month observation period. Fifteen control mice per sex received a single intraperitoneal injection of citrate buffer. Fifty-six of sixty mice treated with MNU died or were sacrificed before the end of the observation period. Twenty-four males and twenty-seven females treated with MNU developed malignant lymphoma of the thymus; of these, twenty-three males and twenty-seven females had corresponding enlargement or masses in the thymus at necropsy. Lymphoblasts in thymic lymphomas stained positively for mouse CD3 antigen, indicating a T-cell lineage. One control female mouse had malignant lymphoma of the spleen that did not involve the thymus. Nine males and five females treated with MNU had adenomas or adenocarcinomas of the small intestine, whereas no intestinal neoplasms were observed in control mice. These findings support the use of a single dose of MNU as a positive control chemical in six-month p53+/- mouse carcinogenicity studies and suggest that examination of the thymus alone is sufficient to evaluate the validity of the model system.

Image analysis using the fluorochromasia assay to quantify tumor drug sensitivity.

A method of assessing chemosensitivity of tissue utilizing tissue fluorescence and image analysis was implemented to provide a rapid and quantitative means of assessing the effect of drugs on tissue metabolic activity and proliferative capacity. The fluorescent microscopic image captured by a silicon-intensified target (low-light-detecting) camera and linked to an image- processing unit was measured for fluorescent brightness and tumor image area. An established rodent model served to characterize the system's ability to measure serially the tumor's metabolic activity and growth. Further studies on fresh human tumors were conducted with a novel topoisomerase II inhibitor, NC-190. Tumor image area and fluorescent brightness were measured 24 h pretreatment, 48 h posttreatment, and 48 h post-drug removal. Fifty-five percent (28/51) of fresh human tumors showed sensitivity to 48-h exposure to 10, 30, or 100 microM NC-190. The potential benefit of this technique is the ability to predict the response of tumors to chemotherapeutic agents as a laboratory tool for preclinical drug evaluation and clinically prior to the commencement of therapy.

Pronounced inhibition by a natural anthocyanin, purple corn color, of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-associated colorectal carcinogenesis in male F344 rats pretreated with 1,2-dimethylhydrazine.

The potential of purple corn color (PCC), a natural anthocyanin, to modify colorectal carcinogenesis was investigated in male F344/DuCrj rats, initially treated with 1,2-dimethylhydrazine (DMH), receiving 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the diet. After DMH initiation, PCC was given at a dietary level of 5.0% in combination with 0.02% PhIP until week 36. No PCC-treatment-related changes in clinical signs, body weight and food consumption were found. Incidences and multiplicities of colorectal adenomas and carcinomas in rats initiated with DMH were clearly increased by PhIP. In contrast, lesion development was suppressed by PCC administration. Furthermore, in the non-DMH initiation groups, induction of aberrant crypt foci by PhIP tended to be decreased by the PCC supplementation. The results thus demonstrate that while PhIP clearly exerts promoting effects on DMH-induced colorectal carcinogenesis, these can be reduced by 5.0% PCC in the diet, under the present experimental conditions.

N-methyl-N'-nitro-N-nitrosoguanidine-induced carcinogenesis: differential pattern of upper gastrointestinal tract tumours in Wistar rats after single or chronic oral doses.

Male Wistar rats were treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) either as a single dose of 50, 125 or 250 mg/kg given by gavage or via drinking water for 28 weeks at a concentration of 40, 80 or 160 micrograms/ml, in the case of the higher concentration reverting to 80 micrograms/ml after the first 8 weeks. The single dose regimen had no effect on water intake or body weight, but the chronic exposure led to a dose-dependent reduction in water intake that was paralleled by a slower weight gain, with the final body weights at approximately 90, 84 and 79% of the control weight values. The combined yield of benign and malignant tumours (79-100% of the animals treated) occurred in the forestomach in the case of the single doses, whereas the chronic exposure resulted in a maximum yield of tumours located in the pyloric region of the glandular stomach (64-100% of animals treated). The principal histological types of tumours induced were squamous cell papilloma and carcinoma in the forestomach and adenocarcinoma in the pylorus. There was a persistent, but low yield (25-30% of animals treated) of tumours in the jejunum, mainly adenocarcinoma, after administration via drinking water, whereas after single doses, multiple solitary cysts and cholangioma (30% and 25-70% respectively of the animals treated) were found in the liver. This report differs from earlier reports in that marked effects were noted on water consumption and body weight gain and that tumour induction can be achieved after much shorter periods of exposure than previously reported in the literature. These data confirm the tissue specificity of MNNG when given either as a single or chronic dose regimen and provide a suitable model for the investigation of the target cell specificity of tumour induction.

Changes in the activities of jejunal glucosidases in experimental intestinal tumorigenesis induced by 1,2 dimethylhydrazine in rats fed different diets.

The purpose of the present study was to establish the effect of the carcinogen 1,2 dimethylhydrazine on the activities of the jejunal glucosidases and to assess the possible modifying effect of different diets. Two control groups of Wistar albino rats were used - fed standard pellet diet and fed the same diet + 1,2 dimethylhydrazine treatment. Six experimental groups treated with 1,2 dimethylhydrazine were provided. One of them was fed standard diet, containing 30% of wheaten bran and the other 5 groups received high-lipid diets, containing 30% of different fats. The rats were injected subcutaneously once a week for 12 weeks with 20 mg 1,2 dimethylhydrazine/kg b.m. and left for 12 weeks in order to develop a tumor growth. The activities of 5 glucosidases (lactase, maltase, sucrase, palatinase and cellobiase) were determined in homogenates from jejunal mucosa taken near by the tumors and in homogenates from the tumors themselves. An expressed decrease of the jejunal glucosidase activities near the tumors and in the tumors was established. The animals fed 30% wheaten bran diet did not develop tumorigenesis and showed comparatively slight decrease of the enzyme activities. In general, the high-fat regimens did not exert such a preventive effect.

Isolated malignant lymphoma of the jejunum and long-term diphenylhydantoin therapy.

We report a case of isolated malignant lymphoma of the jejunum occurring 18 18 months after continuous diphenylhydantoin therapy for epilepsy. Although this association may be purely coincidental, we suggest a possible causal relationship between the two in light of current knowledge about the immunological aberrations that may be caused by prolonged administration of diphenylhydantoin in man.

Location of N-methyl-N'-nitro-N-nitrosoguanidine-induced gastrointestinal tumors correlates with thiol distribution.

Chronic administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in the drinking water causes a high incidence of carcinomas of the glandular stomach in rats. Following a single oral dose of [14C-methyl]MNNG (80 p.p.m.; 2.5 mg/kg), the extent of DNA methylation in the glandular stomach was 9 and 20 times higher than that in the forestomach and oesophagus, respectively. The autoradiographic distribution of tissue-bound radioactivity within the glandular stomach of BONN/WIST rats coincides with strain-specific tumor location at the small curvature. Following intragastric administration of [14C-methyl]MNNG, alkylation levels in forestomach and glandular stomach were twice as high as those observed after oral exposure via the drinking water, whereas duodenal DNA showed a much lower extent of methylation. The regional differences in DNA alkylation correlated with tissue-specific variations in the concentration of cellular thiols which are known to accelerate the heterolytic decomposition of MNNG. When [14C-methyl]MNNG was given intragastrically together with the thiol-blocking agent, N-ethylmaleimide, covalent binding of the 14C-radioactivity to forestomach, glandular stomach and duodenum was almost completely abolished. This indicates that the preferential induction of glandular stomach tumors by MNNG relies on high concentrations of cellular thiols in the target tissue.

Effects of 1,2-symmetrical dimethylhydrazine on jejunocolic transposition in Sprague-Dawley rats.

In this experiment, a segment of the left colon including the upper part of the rectum was transposed to the upper jejunum, and a segment of upper jejunum was transposed to the left colon of the same animal. In another group, the same colon and jejunum segments were transsected and reanastomosed in place. A third group served as a normal control. After a recovery period, weekly s.c. 1,2-symmetrical dimethylhydrazine injections were begun. Each animal received a total of 20 injections at a dose of 20 mg/kg. Five weeks after the last 1,2-symmetrical dimethylhydrazine injection, 15 of 19 (79%) of the animals had one or more tumor(s) in the transposed colon segment, while none had tumor in the transposed jejunal segment. Transsected and reanastomosed animals showed the same distribution of tumors as did the normal control animals. All three groups had tumors at other sites in the colon and rectum. In addition, about 20% had tumors of the duodenojejunal area. These data indicate that the colonic mucosa is the primary target for the carcinogenic effect of 1,2-symmetrical dimethylhydrazine, independent of other variables such as the fecal stream.

Experimental gastric carcinoma induced by N-methyl-N'-nitro-N-nitrosoguanidine.

Serial studies by endoscopy and biopsy were made in a Beagle dog during and after oral administration of N-methyl-N'-nitro-N-nitroguanidine (MNNG). Between the 23rd and the 45th week of observation erosions and ulcers appeared at the angulus of the stomach and turned into ulcer scar. A depression with atypical glands was seen in the ulcer scar of the posterior wall of the angulus at the 94th week. It developed elevated margins at the 102nd week, when a well differentiated adenocarcinoma was found histopathologically. Ulceration and reepithelialization were observed in the early carcinoma. The carcinoma progressed into a larger one of Borrmann's type 2 at the 115th week and further into its type 3 at the 181st week. A second carcinoma with signet ring cell carcinoma developed in the anterior wall of the angulus. The two carcinomas fused and formed a single lesion. At autopsy in the 216th week the carcinoma invaded the serosa, and metastasis to regional lymph nodes was observed.