Granuloma pouch assay. III. Enhancement of the carcinogenic effect of N-methyl-N'-nitro-N-nitrosoguanidine

Proliferation of granulation tissue on the inside of a subcutaneous (s.c.) air pocket was induced in rats by administration of 0.5 ml of 0.25% croton oil (granuloma pouch). Two days after induction of the granuloma, i.e., during the period of maximal cell growth, a single dose of 0.6 mg or 0.1 mg N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was administered into the pouch. Fibrosarcomas of various histopathological types developed in 87% of the rats receiving the high dose and in 64% of the low dose animals. The mean latency period was 47.5 and 51.7 weeks respectively. Only one local sarcoma developed in rats treated with 0.6 mg MNNG by the s.c. route, and no tumors were observed in the groups treated with 0.1 mg s.c. The appearance of local sarcomas in the granuloma pouch tissue is correlated with previously reported frequency of point mutations (OUAR and HGPRT-) induced in granuloma fibroblasts with the same doses of MNNG. Possible mechanisms explaining the marked enhancement of the carcinogenic effect of MNNG in the granuloma pouch assay are discussed.

Cycle-related toxicity and transformation in 10T1/2 cells treated with N-methyl-N'-nitro-N-nitrosoguanidine

Exposure of C3H 10T1/2 Cl 8 cells, synchronized by release from confluence-induced arest of proliferation, to different concentrations of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for 30 min at various points during the cell cycle causes dose-dependent toxicity (decrease in relative colony-forming efficiency or "survival") that increases linearly during the first G1 phase, reaches a maximum in early to middle S phase, and decreases during late S. In the course of the second S phase, toxicity again becomes maximal. The transformation rate (type III foci) increases and decreases with a similar pattern, increasing during the first G1 phase to a maximum during early S phase, subsequently decreasing, and then increasing again during the second S phase. Although periods of maximal toxicity and transformation roughly coincide with some portion of the S phase, the mechanisms underlying these phenomena appear to differ for the following reasons: (a) toxicity is linearly related to dose of MNNG, whereas the latter is linearly related to the logarithm of transformation rate, and (b) the ratio between toxicity and transformation varies with the cycle phase and the dose of MNNG.

[Relationship between the presence of plasmid pKM101 and the frequency of spontaneous and induced mutations of different kinds]

Ames tester strains of Salmonella typhimurium containing plasmid pKM101 have been shown to be very sensitive to UV-induced base substitutions and frameshift mutations. Plasmid pKM101 mediates the ability for base substitutions through frameshift inducing mutagens and slightly enhances frameshift mutagenesis. For the agents mainly inducing base-pair substitutions, plasmid pKM101 is found to enhance slightly the rate of base-pair substitutions but not the rate of frameshift mutations.

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.

Comparison of toxicity and mutagenicity of methylnitrosourea, methylnitronitrosoguanidine and ICR-191 among human lymphoblast lines

The toxic and mutagenic effects of the alkylating agents methylnitrosourea (MNU) and methylnitronitrosoguanidine (MNNG) and of the frameshift mutagen, ICR-191 were compared among 3 human diploid lymphoblast lines, MIT-2, WI-L2 and GM 130. The MIT-2 and WI-L2 lines were both sensitive to the toxic and mutagenic effects of all 3 agents tested. The WI-L2 line was more sensitive to the toxic effects of MNU and MNNG than the MIT-2 line, while it was somewhat less sensitive to the mutagenic effects of these alkylating agents. The GM 130 line was strikingly resistant to both the toxic and mutagenic effects of the alkylating agents. The order of sensitivity to the toxic effect of ICR-191 was MIT-2 greater than WI-L2 greater than GM 130, while the order of sensitivity to the mutagenic effects of this frameshift mutagen was GM 130 greater than MIT-2 greater than WI-L2. These results point to the importance of accounting possible variations in mutability among individuals when extrapolating from any single mutagenicity assay for human risk assessment.

Structure and reactivity of nitrosocimetidine

The major product of reaction of cimetidine in 2 M hydrochloric acid in the prescence of excess sodium nitrite is a mono-nitroso derivative, the structure of which has been determined by the application of field desorption mass and proton magnetic resonance spectrometry. The methylating ability of nitrosocimetidine in phosphate buffer at pH 7 towards 3,4-dichlorobenzenethiol is comparable to that of the known gastric carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine.

Chemical carcinogen in vitro testing: a method for sizing cell nuclei in the nuclear enlargement assay

The observation that cells often respond to carcinogens by nuclear enlargement has suggested that this property might be useful to develop a short-term screening test for such compounds. Previous methods for detecting nuclear size increases have used an image analyzer system to detect nuclear changes in individual cells. This paper details a more rapid method for obtaining nuclei by use of a stromalyzing procedure following by analysis of nuclear volumes, using a Coulter Counter Channelyzer. This new and simplified nuclear sizing method should facilitate the use of the assay as a possible carcinogenesis screen by permitting rapid and efficient testing of large numbers of compounds.

Inhibition of DNA synthesis by carcinogens in human colon mucosa in organ culture

The capability of carcinogens with different modes of action to affect replicative DNA synthesis in the human colon was tested with the use of organ culture of histologically normal mucosae from patients undergoing colectomy for colon cancer or diverticulosis. 1,2-Dimethylhydrazine, an organotropic carcinogen for the colon in rodents, inhibited DNA synthesis of mucosa at a concentration of 3.0 mM but not at 1.5 mM. Methylazoxymethanol acetate, a proximate carcinogen, inhibited DNA synthesis at a concentration of 1.5 mM. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG), a direct-acting carcinogen, inhibited DNA synthesis at a concentration of 0.5 mM. No tissue toxicity was observed at the doses of these carcinogens used. The procarcinogen benzo[a]pyrene, which is not organotropic for the colon, caused no inhibition of DNA synthesis in colon explants at concentrations of 0.01--0.05 mM. These data indicate that replicative DNA synthesis in the human colon is most sensitive to the inhibitory effect of the direct-acting carcinogen MNNG.

Sister chromatid exchanges induced in cultured mammalian cells by chromate

Chromate compounds induced sister chromatoid exchanges (SCEs) and chromosome aberrations in cultured mammalian cells. Similar increases in SCE frequency were observed in human fibroblasts exposed to the compounds K2Cr2O7 and K2CrO4. Marked increases in SCE frequency in cells exposed to chromate for a 48-h period were detected at concentrations between 10(-7) and 10(-6) M. Chromosome aberrations (primarily chromatid breaks) were also produced in human cells exposed to K2CrO4 at concentrations between 8 . 10(-7) and 3 . 10(-6) M. K2CrO4, but not the trivalent compound CrCl3, induced SCEs in Chinese hamster ovary (CHO) cells at low concentrations.

Teratogenic effect of N-methyl-N'-nitro-N-nitrosoguanidine in mice

The teratogenic effect on the mouse fetus of a potently mutagenic and carcinogenic agent, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), was studied. Pregnant mice were injected on one of gestation days 7-12 with an intraperitoneal dose of 40, 60 or 80 mg/kg of MNNG, and fetuses were examined on day 18 of gestation. Various malformations affecting the brain, face, vertebra, rib and limb appeared in high frequency. Brain malformations were the most predominant; hydrocephalus, hydromicrocephaly and microcephaly appeared in sequence with developmental stages of treatment, although exencephaly occurred infrequently. Cleft palate, sometimes associated with microglossia and micrognathia, and vertebral anomalies including tail defect were observed following almost every gestation-day treatment. Long-bone defects of fore- and hindlimbs were also predominant. Polydactyly, ectrodactyly and microdactyly frequently occurred together in the fore- or hindlimbs or both in sequence with treatment stages. Ectrodactyly and microdactyly appeared with greater frequency on the left than on the right in both fore- and hindlimbs, but polydactyly and long-bone defects appeared bilaterally.

Induction of intestinal metaplasia in the stomachs of rats by N-methyl-N'-nitro-N-nitrosoguanidine

N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) was administered orally to male Wistar rats at a concentration of 83 microgram/ml in the drinking water for 2, 4, 5, and 7 months; the rats were killed at about month 15. Intestinal metaplasia was found in the stomachs of 80-100% of the rats treated with MNNG for 4 or more months, of 37.5% treated with MNNG for 2 months, and of 10% of the controls. Metaplastic glands, composed of goblet cells and columnar cells with striated borders, were found in the pyloric region. Paneth's cells were found at the bottom of metaplastic glands in a rat treated with MNNG for 4 months. The incidence of well-differentiated adenocarcinomas of the stomach was 63-90% in rats treated with MNNG for 4 or more months and 25% in those treated with MNNG for 2 months.

Carcinogenic effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in European hamsters

Laboratory-bred European hamsters received intragastric administrations of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) once weekly for 20 weeks. The animals showed mainly squamous cell papillomas and carcinomas of the fore-stomach. The tumour incidence was higher in males (80%) than in females (30%). The average tumour latency was comparatively short (25 weeks).

Carcinogenic effect of N-methyl-N'-nitro-N-nitrosoguanidine and fission neutron irradiation in rats

Examinations were made on the carcinogenic effects of a chemical compound, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and a physical carcinogen, whole-body irradiation with fission neutrons, on the gastrointestinal tract of male albino Sprague-Dawley rats. The carcinogens were used singly and together in order to investigate their possible synergistic effects on the induction of adenocarcinomas of the stomach and small intestine. Of the 13 animals treated with the chemical, MNNG, and living more than 9 months, 9 showed gross tumors (5 gastric and 4 duodenal), confirming the high incidence of gastrointestinal carcinomas induced by MNNG in the rat. There were no gastrointestinal tumors found after neutron exposure. When the 2 carcinogens were combined, no additivity or synergism occurred. After neutron irradiation, a dental syndrome with loss of incisor teeth was observed. The effect of neutron irradiation on subgingival pathology of the teeth is being investigated.

Esophageal and gastric cancers with metastases induced in dogs by N-ethyl-N'-nitro-N-nitrosoguanidine

Three 6-month-old male beagle dogs were given a solution of 150 microng N-ethyl-N'-nitrosoguanidine (ENNG)/ml to drink ad libitum for 9 months. They all developed esophageal squamous cell carcinomas and gastric adenocarcinomas. The stomach adenocarcinomas were mostly in the antrum along the lesser curvature and were either well differentiated or poorly differentiated, with or without signet ring cells. The well-differentiated adenocarcinomas metastasized to the liver, and the poorly differentiated ones metastasized to the lymph nodes. The gastric mucosa in the antrum was atrophic, and the muscularis mucosae was fibrotic. Esophageal lesions were multicentric moderately differentiated squamous cell carcinomas, and they developed without diffuse hyperplastic changes of the epithelium. One dog with a large ulcerated carcinoma of the esophagus had metastases in the lung, liver, peritoneum, and abdominal lymph nodes. One dog also had a hemangiosarcoma with hepatic metastasis and spindle cell sarcoma in the stomach and duodenum, respectively.

Induction of hyperplasia and anaplasia by carcinogens in organ cultures of mouse prostate

In an effort to establish a test system to examine the carcinogenic potential of chemicals, mouse prostate explants were maintained as organ cultures and the effects of carcinogenic and noncarcinogenic compounds were examined at various intervals after treatment. The degree of hyperplasia produced by a compound was determined by the colcemid metaphase arrest technique. Extensive hyperplasia of the prostatic epithelium occurred at 8 days after treatment with 3-methylcholanthrene, the 11-12 epoxide of methylcholanthrene, benzo(a)pyrene and N-methyl-N-nitro-N-nitrosoguanidine. At 12 days most carcinogen-treated explants were anaplastic. The noncarcinogenic compounds, pyrene and phenanthrene, did not produce a mitotic stimulatory effect on the epithelium of the explants. The data suggest that the organ culture system of mouse prostate may be employed as a test system to obtain preliminary information regarding the cardinogenicity of a compound.

Guanine-specific DNA repair after treatment of mouse skin cells with N-methyl-N'-nitro-N-nitrosoguanidine

The incorporation of [3H]thymidine and [3H]deoxyguanosine into DNA was studied during DNA repair in mouse skin cells treated with the skin tumor initiator N-methyl-N'-nitro-N-nitrosoganidine. At high, toxic levels of N-methyl-N'-nitro-N-nitrosoguanidine, repair (incorporation of the precursor into DNA which had not replicated) was demonstrated with both precursors. At lower, less toxic doses of the carcinogen, repair could not be demonstrated with [3H]-thymidine, but it was clearly demonstrable with [3H]deoxyguanosine. Thus, we are apparently observing two kinds of DNA repair, one in which a single base (in this case, guanine) replaces a base lost by chemical or enzymatic depurination and the second in which more than one base is replaced, indicating synthesis of longer stretches DNA after extensive enzymatic excision. The guanine-specific repair shown at relatively nontoxic dose levels of N-methyl-N'-nitro-N-nitrosouanidine may be more relevant to the survival of cells than the repair demonstrated with [3H]thymidine at higher doses.

Protective effect of mucin on experimental gastric cancer induced by N-methyl-N'-nitro-N-nitrosoguanidine plus sodium chloride in rats

Studies were made on the effect of mucin on the induction of gastric carcinomas by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), with or without sodium chloride, in male Wistar rats. Seven groups of rats were treated as follows: Group 4 was given continuously 50 mg MNNG/liter solution to drink and 1 ml of saturated sodium chloride once a week and fed on stock diet supplemented with 4% mucin. Group 2 was given 50 mg MNNG/liter solution and fed on stock diet supplemented with 4% mucin. Group 3 received 1 ml of saturated sodium chloride once a week and 50 mg MNNG/liter solution to drink. Group 1 was treated with MNNG only. Group 5 was fed on stock diet supplemented with 4% mucin. Group 6 was given sodium chloride only. Group 7 was untreated. The incidence of gastric cancer in Group 3 was significantly higher than that in Group 4 (P less than 0.05) or in Group 1 (P less than 0.05). The difference in the incidence of gastric cancer in Groups 2 and 4, and of intestinal tumors in Groups 1 to 4 were not statistically significant. No malignant tumors were seen in Groups 5, 6, and 7. Thus mucin reduced the high incidence of gastric cancer induced by MNNG and sodium chloride to the level induced by MNNG alone, but it had no effect on the incidence of intestinal tumors. The effect of mucin in preventing destruction of the gastric mucosal barrier by sodium chloride and so reducing the induction of gastric cancer is discussed.

Leiomyosarcomas of the small intestine induced in dogs by N-methul-N'-nitro-N-nitrosoguanidine

Leiomyosarcomas of the small intestine were found in dogs during experimental induction of gastric carcinoma by oral administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Leiomyosarcomas were found most frequenly in the duodenum and jejunum, and occasionally in the stomach but never in the ileum, colon, or rectum. The leiomyosarcomas developed in all the dogs given 50 mug/ml of MNNG in deionized water to drink but not in dogs fed on porridge food made from standard pellet diet mashed with MNNG at the same concentration in tap water. Intestinal sarcomas developed in 3 months to 5 years after the end of MNNG administration, and frequently metastasized to the liver and/or the peritoneum.

Comparative mutagenic effects of ethyl methane-sulfonate, n-methyl-n'-nitro-n-nitrosoguanidine, ultraviolet radiation and caffeine on Dictyostelium discoideum

A high frequency of morphogenetic mutants of Dictyostelium discoideum can be induced by treatment with MNNG under conditions which result in relatively low cell killing. Six temperature-sensitive growth mutants induced by this treatment were isolated by replica plating. Among these, five showed spontaneous reversion rates of 10(-4) to 10(-5). The mutagenic activity of ems, measured for the induction of both morphogenetic and temperature-sensitive mutants, was weaker than that of MNNG and UV radiation. High frequencies of morphogenetic mutants were obtained only with doses of UV irradiation that resulted in high killing of cells or spores. Caffeine, at concentrations that slightly decreased the growth rate of amoebae in axenic medium, induced morphogenetic defects and also enhanced the mutagenic effect of UV irradiation. However, all the aggregateless clones derived from caffeine treatment that were studied reverted to the wild-type phenotype after a variable number of clonal re-isolations.

Mammalian cell transformation and cell-mediated mutagenesis by carcinogenic polycyclic hydrocarbons

The introduction of a polycyclic hydrocarbon such as benzo(alpha)pyrene (BP) into normal golden hamster embryo cell cultures results, in addition to cytotoxicity, in malignant cell transformation. Studies on the effect of different doses of BP on the normal cells showed that the frequency of transformed colonies was directly related to the dose of the carcinogen. Analysis of this dose-response curve suggests a one-event ("one-hit") response for transformation by this carcinogen. The one-event response for transformation by carcinogenic polycyclic hydrocarbons and the fact that these carcinogens bind to DNA in susceptible cells suggests that transformation can involve a single alteration in the genetic constitution of the treated cells. Carcinogens may, therefore, produce somatic mutations, some of which may involve the genes that control malignancy. Recently, considerable progress has been made in developing models for the study of chemical mutagenesis in mammalian cells. Using resistance to 8-azaguanine as a marker, positive correlations between mutagenicity and transformation were obtained with chemically reactive carcinogens such as N-acetoxy-N-2-fluorenyl-acetamide, N-methyl-N'-nitro-N-nitrosoguanidine and K-region epoxides of polycyclic hydrocarbons. However, no such correlations were obtained with the carcinogenic polycyclic hydrocarbons themselves, since the cell lines used in chemical mutagenesis do not metabolize these carcinogens. In order to obtain better correlations, we have developed a cell-mediated mutagenic assay with carcinogenic hydrocarbons in which Chinese hamster cells, which are susceptible for mutagenesis, were co-cultivated with lethally irradiated rodent cells that can metabolize these compounds. Using this cell mediated assay, we obtained mutagenesis with the carcinogenic hydrocarbons 7,12-dimethylbenz(alpha)anthracene (DMBA), BP, 3-methylcholanthrene and 7-methylbenz(alpha)anthracene; the most potent carcinogen, DMBA, gave the highest frequency of mutations. The polycyclic hydrocarbons, pyrene and benz(alpha)anthracene, which are not carcinogenic were also not mutagenic. We have therefore demonstrated a relationship between the carcinogenecity of polycyclic hydrocarbons and their mutagenicity in mammalian cells, without having to isolate their reative metabolic intermediates. It should be possible to use in this system human cells from different organs and individuals to screen for environmental chemicals hazardous to humans which have to be metabolically activated.