Aflatoxin B1 (AFB1 ), a potent liver carcinogen, requires the activation by epoxidation to bind DNA forming DNA adducts and to initiate carcinogenesis. Similarly, we found estrogens, both 17β-estradiol (E 2 ) and estrone (E 1 ) could also be activated by epoxidation to bind DNA forming DNA adducts. Based on this finding, we proposed that estrogen epoxidation is the underlying molecular mechanism for breast cancer carcinogensis [ Yu, FL. Asian Pac J Clin Nutr 2002; 11(Suppl.) : S460-6]. Tocopherols and tocotrienols, members of the vitamin E family, are powerful antioxidants. Studies suggest that tocotrienols are more potent than tocopherols in the prevention of liver and breast cancer. The reason for this is unknown. In this report, the preventive effect of tocopherols and tocotrienols on epoxidation of AFB1 and E 1 were studied and compared. We found tocotrienols are more potent than tocopherols against the formation of AFB1 and E 1 epoxide as measured by the lose of the ability of [3H]labeled AFB1 or E 1 to bind DNA. These results lend further support to our earlier conclusion when E 2 was used. As suggested previously, we believe this is because tocotrienols posses two antioxidative sites, the chromanol ring and the polyunsaturated phytol side chain, while tocopherols have only one antioxidative site, the chromanol ring [Yu, FL, et al. Cancer Detection and Prevention. 2005; 29: 383-8] [This work was partially supported by a grant from Malaysia Palm Oil Board].

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA