Inhibition of N-nitrosomethylbenzylamine-induced esophageal neoplasms by the Bowman-Birk protease inhibitor.

Model systems in which carcinogenesis by given agents can be prevented or reduced offer a means of gaining insight into the mechanism(s) of action of carcinogens and the feasibility of chemoprevention in humans. In the current study, the ability of the soy-bean derived Bowman-Birk protease (BBI) to suppress esophageal carcinogenesis induced by N-nitrosomethylbenylamine (NMBzA) was examined. Esophageal lesions were produced in male Sprague-Dawley rats by i.p. injection of 2 mg/kg NMBzA twice weekly for 3 weeks. Groups receiving BBI were fed three tablets a week containing 180 mg BBI each in a mixture of Witepsol H15 and peanut butter for the duration of the experiment. The frequency of papillomas and carcinomas was reduced 45% in groups receiving BBI. Furthermore, the frequency of appearance of five separate characteristics of preneoplastic lesions was significantly reduced in the esophagi of BBI-treated animals. The most significant reduction was in the total number of lesions with simple hyperplasia. Groups receiving NMBzA and placebo tablets, containing only Witepsol H15 and peanut butter, did not display statistically significant differences in the frequency of esophageal lesions as compared to animals receiving NMBzA alone. These results demonstrate that BBI can effectively inhibit NMBzA-induced esophageal tumors when given in tablet form separate from the regular diet.