Inhibitory effect of natural carotenoids on Epstein-Barr virus activation activity of a tumor promoter in Raji cells. A screening study for anti-tumor promoters.

As a screening study for anti-tumor promoters, 51 carotenoids with diverse structures were examined for their inhibitory effects on the Epstein-Barr virus activation activity of 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. The results showed that most of the carotenoids exhibited inhibitory activity, and in general, no cytotoxicity on Raji cells was observed in the assay. Among the carotenoids, beta-cryptoxanthin, lutein, and lactucaxanthin showed the strongest inhibitory activity, superior to the well known anti-tumor promoter, beta-carotene. Heteroxanthin, peridinin, and halocynthiaxanthin showed cytotoxicity at the high concentration (1000 molar ratio per TPA), but indicated a strong inhibitory effect at the lower concentrations, which were only weakly toxic (500 and 100 molar ratios). Based on these results, the essential moiety for the activity of carotenoids was considered to be the 3-hydroxy-epsilon-end group.