Increased Susceptibility to N‐Nitrosomethylurea Gastric Carcinogenesis in Transforming Growth Factor α Transgenic Mice with Gastric Hyperplasia

Glandular stomach carcinogenesis after N‐nitrosomethylurea (NMU) treatment was examined in transgenic mice bearing a human transforming growth factor alpha (TGF‐α) cDNA driven by the mouse metallothionein‐I promoter (mouse line MT100) in the inbred mouse line FVB/N. Untreated MT100 mice exhibit a severe age‐related gastric fundic hyperplasia. Both sexes of MT100 mice were given 10 weekly intragastric intubations of 0.5 mg NMU per mouse from 6 weeks of age and/or zinc chloride in drinking water to stimulate transgene expression from 5.5 weeks of age to the experiment termination. Animals were killed sequentially at 10, 19 and 29 experimental weeks. Several histochemical markers (AB‐PAS, TGF‐α, pepsinogen isozyme 1, proliferating cell nuclear antigen) were used. Abnormal histochemical patterns were found in untreated MT100 and NMU‐treated MT100 mice for all 4 markers of differentiation and carcinogenesis. Precancerous lesions including atypical and/or adenomatous hyperplasia were found in the fundic region of 16/22 male and 8/22 female MT100 mice but not in 27 male and 24 female FVB/N mice treated with NMU. One of 22 MT100 males had fundic carcinoma. FVB/N mice treated with NMU had neither precancerous lesions nor carcinomas in the fundus. Well differentiated adenocarcinomas in the pyloric region were induced at incidences of 2/22 male and 1/22 female MT100 mice treated with NMU and 4/27 male and 4/24 female FVB/N mice treated with NMU. Both strains also had a high incidence (55 to 92%) of squamous cell carcinomas of the forestomach. In conclusion, TGF‐α induced a hyperplastic lesion in the gastric fundus that appeared to predispose the MT100 mice to carcinogenesis by NMU.