The natural plant products turmeric, beta-carotene, catechin, and betel leaf extract were evaluated for their antitumor effects on mammary tumorigenesis in murine mammary tumor expressing C3H (Jax) mice and in Wistar rats treated with the chemical carcinogen 7-12-dimethylbenz(a)anthracene (DMBA). Administration of turmeric through the diet and of beta-carotene, catechin, and betel leaf extract through the drinking water to virgin female C3H mice resulted in decreased tumor incidence and tumor burden. Administering 5% turmeric in the diet from 2 months of age showed suppression of mammary tumor virus-related reverse transcriptase activity and of preneoplastic changes in the mammary glands. Furthermore, feeding turmeric from 6 months of age resulted in a 100% inhibition of mammary tumors. In the DMBA model of rat mammary tumorigenesis, administration of turmeric, catechin, and betel leaf extract resulted in decreased tumor burden and tumor incidence, and a delay in the onset of mammary tumors.

Our earlier experiments have shown that the plant phenols-hydroxychavicol, eugenol, catechin, curcumin, and the vitamins--6-carotene and a-tocopherol-are potent inhibitors of polycyclic aromatic hydrocarbon (PAH) induced mutagenesis and carcinogenesis. In an attempt to elucidate their mode of action, we studied their effect on mouse skin DNA synthesis following 7,12 dimethylbenzanthracene (DMBA) treatment and 'H-7,12 dimethylbenzanthracene-DNA interaction in u h o (in the presence of mouse skin S9). With the exception of eugenol, all the phenols and vitamins tested inhibited 'H-DMBA-DNA interaction in uilro. In the DNA biosynthesis assay, of the chemopreventive agents tested only b-carotene effectively modulated DMBA suppressed DNA synthesis in the mouse skin. Our results indicate that the assay of DNA biosynthesis is not of predictive value with respect to the chemopreventive effect of a chemical, while assay of carcinogen-DNA interaction shows correlation between the chemopreventive property and the inhibition of the interaction of carcinogen with DNA.