Combination of blocking agents and suppressing agents in cancer prevention.

The design of the present study was based on the premise that if blocking agents and suppressing agents are targeted at different phases of chemical carcinogenesis, a greater chemopreventive effect would be achieved by using the combination treatment compared to the single-agent treatment. The dimethylbenz[a]anthracene (DMBA)-induced mammary tumor model in rats was used to test this hypothesis, with the blocking agent given before DMBA only and the blocking agent given after DMBA until the end of the experiment. A total of three sets of combination treatment were carried out; diallyl sulfide/Se-methylselenocysteine, ellagic acid/selenomethionine, and diallyl sulfide/quercetin. In all three cases, the combination regimen was much more effective than the single-agent treatment in tumor suppression. It should be noted that only naturally occurring inhibitors were selected for these experiments. The impact of minor dietary anutrients in cancer chemoprevention is also discussed.