No abstract

An animal model of stomach carcinogenesis was established using Mongolian gerbils with Nmethyl-N-nitrosourea (MNU) and N-methyl-N′ ′ ′ ′-nitro-N-nitrosoguanidine (MNNG) as the carcinogens. In addition, the sensitivity of these gerbils to Helicobacter pylori (H. pylori) was confirmed. One hundred and sixty specific pathogen-free male MGS/Sea animals, 7 weeks old, were treated with MNU in the drinking water (30 ppm for alternate weeks to give 10 weeks exposure, or 10 ppm or 3 ppm for 20 weeks continuous exposure), or given MNNG in the drinking water at 400 ppm or 200 ppm for 20 weeks, or orally inoculated with ATCC43504 H. pylori (1.7× × × ×10 8 CFUs/animal). Adenocarcinomas in the glandular stomach were found in 2 out of 12 effective animals (2/ 12) treated with 30 ppm MNU at week 20, although all were dead or moribund by week 30 due to MNU toxicity. At week 50, the incidences of gastric adenocarcinomas in groups treated with 10 ppm MNU, 3 ppm MNU, 400 ppm MNNG, and 200 ppm MNNG were 2/21 (9.5%), 1/23 (4.3%), 7/ 11 (63.6%), and 1/10 (10.0%). The lesions were generally well differentiated, although poorly differentiated adenocarcinoma was also found in a single gerbil in each of the 10 ppm MNU and 400 ppm MNNG groups. In control animals no tumors were found. In the infection study, the animals were killed at week 20, and H. pylori was detected in all cases, causing multiple erosions with marked inflammatory cell infiltration in the lamina propria and submucosa, and frequent formation of lymphoid follicles. Thus, MNU and MNNG in the drinking water induced neoplastic lesions in the glandular stomach epithelium of H. pylori-sensitive gerbils.

Epithelial dysplasia of gall bladder is an important precancerous lesion of gall bladder carcinogenesis. To investigate the frequency of K-ras gene mutation in gall bladder carcinoma and dysplasia, K-ras codon 12 mutations were investigated by the polymerase chain reaction/restriction enzyme based method foliowing direct sequencing. Mutation was detected in 59%/o (30 of 51) of gall bladder carcinomas, in 730/0 (8 of 11) of gall bladder dysplasia in gall stone cases, and in 00/0 of the normal gall bladder epithelium. There was, however, no correlation between K-ras mutation and clinicopathological factors of gall bladder carcinoma. K-ras gene mutation occurs even in gall bladder dysplasia at an incidence similar to that in carcinomas, suggesting that testing for K-ras gene mutation may prove useful as an adjunct to bile cytological or biopsy analysis. (Gut 1996; 38: 426-429)

H19 is an oncofetal RNA expressed in the developing embryo as well as in bladder, breast, gastric, pancreatic, hepatocellular, and prostate cancers. Recent studies have shown that H19 enhances cancer invasion and metastasis; however, its roles in cancer remain controversial. In the current study, H19 exhibited the second largest increase (82.4-fold) and represented the only non-protein coding gene among 11 genes identified that were elevated over 10-fold in lung-metastasis-derived pancreatic cancer cells compared with their parental cells using a mouse metastatic model. Subsequently, we further clarified the roles of H19 in pancreatic cancer growth and metastasis using in vitro and in vivo techniques. In situ hybridization showed that H19 was detected in 23 of 139 invasive ductal carcinomas (17%), and that H19 expression positively correlated with higher histological grades (P < 0.0001). Overexpression of H19 in PANC-1 pancreatic cancer cells induced higher motilities, whereas H19 inhibition using shRNA and siRNA showed opposite results; however, cell growth rates were not impacted. Intravenous injection of H19 shRNA vector-transfected PANC-1 cells yielded marked inhibition of metastasis in the liver and lungs of immunodeficient mice. These findings suggest that H19 has important roles in pancreatic cancer metastasis, and that inhibition of H19 represents a novel candidate for pancreatic cancer therapy.

Mutations of the p53 tumor suppressor gene constitute one of the most frequent molecular changes in a wide variety of human cancers. Mice deficient in p53 have recently attracted attention for their potential to identify chemical genotoxins. In this study we have investigated the susceptibility of p53 nullizygote (-/-), heterozygote (+/-) and wild-type (+/+) mice to N:-methyl-N:-nitrosourea (MNU) gastric carcinogenesis. p53 knockout mice were treated with 30 p.p.m. MNU in the drinking water 1 week on and 1 week off and killed after 5 weeks. The numbers of pepsinogen-altered pyloric glands (PAPG), putative preneoplastic lesions, were 1.8, 1.7 and 22.6 in p53 (+/+), (+/-) and (-/-) mice, respectively. In a 15 week experiment, adenomas were found in 0 of 19 (+/+) (0%), 2 of 21 (+/-) (9.5%) and 6 of 10 (-/-) (60.0%) animals. Also, one well-differentiated adenocarcinoma was observed in a p53 (-/-) mouse. After 40 weeks treatment with 120 or 30 p.p.m. MNU there was no significant difference in the incidence of gastric tumors between p53 (+/+) and (+/-) mice. However, mortality from carcinogen-induced lymphomas, leukemias and sarcomas was very much greater in the latter group. Homozygous knockout animals could not be maintained long term. PCR-single strand conformation polymorphism analysis of exons 5-8 of the p53 gene of DNA extracts from 68 gastric tumors consisting of 16 and 20 30 p.p.m. MNU-treated p53 (+/+) and (+/-) mice and 14 and 18 120 p.p.m. MNU-treated p53 (+/+) and (+/-) mice demonstrated no mutations. These results suggest that p53 may not be a direct target of MNU but rather play an important role as a gatekeeper in mouse stomach carcinogenesis induced by this direct acting agent.