7-methoxy-2-nitro-naphtho[2,1-b]
furan (
R 7000), known as a very potent
mutagen and a very active in vivo
carcinogen was employed here to develop
squamous cell carcinoma in the rat. Seventy male Wistar rats received
R 7000 p.o. dissolved in deionized water with 5%
ethanol for periods from 1 to 21 months, while 20 served as controls receiving either water or 5%
ethanol. All the animals were killed 21 months after the beginning of the experiment. Microscopic lesions were noticed in the forestomach after only 1 month of
R 7000 administration. Histologic features varied from slight dysplasia to invasive
carcinoma. Their sizes and invasive character increased significantly with the amount of
R 7000 administered (P less than 0.05).
R 7000 can be considered as a locally acting
carcinogen since its carcinogenic effects appear at a place where the compound collects after swallowing.
R 7000 is a weak
carcinogen at the concentration employed here, when compared to some
nitrosamines used in the development of forestomach
cancer in rodents. The exact mechanism of the carcinogenic effects remains to be explained.