Chemoprevention of experimental mammary carcinogenesis by the synthetic organoselenium compound, benzylselenocyanate, in rats

The effect of the dietary organoselenium compound, benzyl-selenocyanate (BSC) along with its sulphur analogue, benzyl-thiocynanate (BTC) and sodium selenite (Na₂SeO₃), on 7, 12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis was examined in female Sprague- Dawley rats during the initiation phase of carcinogenesis. Semipurified diets containing 25 p.p.m. of BSC and 25 p.p.m. BTC, and 4 p.p.m. Selenium as Na₂SeO₃ in drinking water were given to 5-week-old rats for 3 weeks starting 2 weeks before, during and until 1 week after carcinogen treatment. At 7 weeks of age animals were given a single dose of DMBA (10 mg) in 1 ml olive oil by oral intubation. One week after DMBA treatment, the groups receiving BSC- and BTC-supplemented diets were transferred to the unsupplemented standard diets and the group of rats receiving Na₂SeO₃ in drinking water was transferred to regular tap water for the duration of the experiment. The results indicate that the rats receiving BSC in their diet showed a highly significant inhibition of tumor incidence and tumor multiplicity as well as a prolonged latency period when compared to the group fed the control diet. Neither BTC nor Na₂SeO₃ had any effect on the subsequent development of mammary tumors. These results indicate that dietary BSC inhibits mammary tumor incidence during the initiation phase of carcinogenesis and is a considerably more potent inhibitor than its sulphur analogue BTC and inorganic selenium. This is the first report that demonstrates the inhibition of mammary carcinogenesis by a synthetic organoselenium compound.