The present study was undertaken to determine whether the Bowman-Birk inhibitor (BBI) could prevent colon
carcinogenesis in rats treated with
dimethylhydrazine (
DMH) and whether there were adverse side effects associated with treatment with BBI for
cancer prevention. BBI was evaluated in the forms of purified BBI (PBBI) or an extract of soybeans enriched in BBI, termed BBI concentrate (BBIC). The results demonstrate that PBBI and BBIC reduced the incidence and frequency of
tumors in
DMH-treated rats compared with animals treated with
DMH alone. Autoclaved BBIC, in which the
protease inhibitor activity of BBI was destroyed, had a weak and statistically insignificant, suppressive effect on
DMH-induced colon
carcinogenesis in rats, suggesting that the
protease inhibitor activity of BBI is likely to be responsible for the anticarcinogenic activity of BBIC. Soy molasses, which contains soy
isoflavones, did not have an effect on
colon cancer carcinogenesis in
DMH-treated rats. Similar to results from previous studies (Nauss et al. JNCI 73, 915-924, 1984), the most aggressive, malignant
colon adenocarcinomas developed within or in association with gut-associated lymphoid tissue aggregates. No adverse side effects on the pancreas or animal growth were observed in rats treated with PBBI or BBIC. These results demonstrate that PBBI and BBIC may be used to prevent
colon cancer without significant adverse side effects.