Modulation of lung tumor development in mice with the soybean-derived Bowman-Birk protease inhibitor.

Male strain A mice were treated with a single i.p. injection of 3-methylcholanthrene (MCA). Four months later, the number of lung tumors was counted. In mice treated three times a week, for 8 weeks, with crude soybean extract containing the Bowman-Birk protease inhibitor (BBI), the number of lung tumors was significantly lower than in control animals receiving carcinogen treatment only (40-70% of controls). On the other hand, treatment initiated 8 weeks after MCA only had no effect on tumor development. A reduction in the number of lung tumors was also found in animals treated i.p. or orally with purified BBI three times a week for 8 weeks following MCA administration. It is concluded that BBI is capable of partially blocking the development of lung tumors in mice.