Inhibitory effect of herbal remedies on 12-O-tetradecanoylphorbol-13-acetate-promoted Epstein-Barr virus early antigen activation.

For the past several years we have been evaluating natural products as potential cancer chemopreventive agents in a short term in vitro assay involving Epstein--Barr virus early antigen (EBV-EA) activation in Raji cells promoted by phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). Because of the current interest in the use of herbal remedies, we considered examining them for their cancer chemopreventive activities, using their extracts with a view to uncovering such benefits (if any) these remedies might possess. Thirty-six extracts of 32 herbs belonging to 27 families in use as herbal remedies including those of gingko, black cohosh, echinacea, kava-kava, saw palmetto, turmeric, angelica, wild yam, cat's claw, passion flower, muira puama, feverfew, blueberry, chasteberry, licorice, nettle, golden seal, pygeum, ginger, valerian and hops were prepared and evaluated. Turmeric at a concentration of 10 microg x ml (-1)exhibited the most potent anti-EBV-EA activity, which is ten times more than passionflower, that is next in the order of activity. At the concentration level of 100 microg ml (-1), several of the herbal remedies tested inhibited the EBV-EA in Raji cells exposed to the tumor promoter TPA (32 pM) by more than 90%. We also report for the first time the activities of 16 new medicinal plants as potential cancer chemopreventive agents. Since inhibitors of EBV-EA promoted by TPA in vitro have been shown to be effective anti-tumor promoting agents in laboratory animal models, our results indicate new and potential applications of these herbal remedies as cancer chemopreventive agents since they are already in clinical use in the human population.