Cancer chemoprevention that involves the introduction of synthetic or natural materials, especially polyphenolic compounds, into the diet is profoundly attracting the attention of scientists and clinicians worldwide. Although multi-stage carcinogenesis has been established, the promotion stage is generally recognized as the most important step which produces reactive oxygen species (ROS), activates protein kinase C (PKC) activity, elevates mRNA and protein levels of ornithine decarboxylase (ODC), and increases transcription and translation of c-jun/AP-1, etc., by the stimulation of promoters including 12-O-tetradecanoyl-phorbol-13-acetate (TPA). All these tumor markers can be used to assess the inhibitory effects of natural polyphenolic compounds against TPA-promoting actions. The published data indicate that several phenolic compounds exhibit anti-tumor activity after parenteral application in standard initation-promotion animal models. Curcumin, the major component of Curcuma longa, exhibits multiple biochemical and chemopreventive actions. Recent studies indicate that curcumin has inhibitory effects on PKC, ODC, c-jun/AP-1 activities, and 8-hydroxydeoxyguanosine (8-OH-dG) formation induced by TPA. These findings suggest that certain polyphenolic compounds might inhibit the processes of tumor promotion through blocking cellular signal transduction.
Polyphenols, Curcumin, Protein kinase C (PKC), Anti-oxidant, Chemoprevention
