Relationship between the structures and the antitumor activities of tannins

Sixty-three tannins and related polyphenols were intraperitoneally injected into mice at 4 d before intraperitoneal sarcoma-180 cell inoculation, and their antitumor activities were evaluated. The condensed tannins and related compounds all showed negligible activity. As regards the hydrolyzable tannins, active compounds were found among ellagitannins. In particular, dimeric ellagitannins such as oenothein B, rugosin E, rugosin D, gemin A and coriariin A showed significantly higher antitumor activity than agrimoniin, which we previously reported as an antitumor tannin. Coriariin A, which has four galloyl groups instead of two hexahydroxydiphenoyl groups of agrimoniin, showed the strongest activity. It seems to be essential for marked antitumor activity that ellagitannins should possess a dimeric structure with several galloyl groups on the glucose core.