Extensive data exist on the inhibitory effect of antioxidants on chemical and radiation carcinogenesis. The antioxidants appear to inhibit the initiation phase of chemical carcinogenesis by inducing enzymes which favor detoxification of chemcial carcinogens thus leading to a decrease in covalent binding of the carcinogens to critical macro-molecules such as DNA. We have also recently found in preliminary experiments that certain antioxidants such as butylated hydroxyanisole (BHA) are potent inhibitors of the promotional phase of two-stage carcinogenesis in mouse skin. This data plus our recent data which shows that free radical generating compounds such as benzoyl peroxide and lauroyl peroxide are effective skin tumor promoters suggest that free radicals may be important in tumor promotion. The major objectives of this proposal are (1) to determine the generality of the inhibitory effect of antioxidants on skin tumor promotion by performing dose-response studies with 3-tert-butyl-4-hydroxyanisole (3-T-BHA), sodium benzoate, vitamin E, vitamin C and selenium and (2) to investigate the mechanism or mechanisms by which the antioxidants inhibit skin tumor promotion by 12-0-tetradecanoyl-phorbol-13-acetate (TPA) and benzoyl peroxide. Since skin tumor promotion can be divided into two stages, we will determine if the effects of the antioxidants are specific for stage I or II of promotion or both. We will also determine if the antioxidants can counteract the promoter-induced hyperplasia, dark basal keratinocytes, and polyamines which are important events associated with either stage I or II of promotion. Furthermore, we will determine if the skin tumor promoters and antioxidants cause epidermal lipid peroxidation and DNA damage. Also, the effects of tumor promoters and antioxidants on epidermal superoxide dismutase, catalase, and glutathione peroxidase activities which are enzymes important in counteracting the effects of free radicals will be determined. Since antioxidants such as BHA have an inhibiting effect on both tumor initiation and promotion and are relatively nontoxic, they may become very useful in the chemoprevention of human cancer. The proposed studies should provide a better understanding of those antoxidants which are most effective and their possible mechanism(s) of action. In addition, the effect on tumor promotion of giving a combination of the most effective antioxidants with other effective tumor promotion inhibitors will be determined.
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