Takuo Okuda

Antitumor activities of ellagitannins on tumor cell lines.

Recent phytochemical studies on tannins and related polyphenols in medicinal plants traditionally used in China, Japan, and other countries have led to the characterization of numerous hydrolyzable tannins with diverse structures and have enabled studies on biological activities of individual tannins of defined structure.1 The pharmacological properties found include inhibitory effects on various enzymes including reverse transcriptase,2 histidine decarboxylase,3 protein kinase C,4 and lipoxygenase,5 as well as inhibition of autoxidation of ascorbic acid6,7 and lipid peroxidation via the free radical scavenging effects.8–11 Antitumor,12–18 antiviral,19–22 and anti-inflammatory activities23,24 have also been reported for some tannins. The biological activity of these compounds depends on their structure. For example, inhibition of replication of human immunodeficiency virus (HIV) was exhibited only by some oligomeric hydrolyzable tannins.25 Similarly, strong hostmediated antitumor activity against Sarcoma-180 tumors in mice was exhibited by some ellagitannin oligomers including agrimoniin, oenothein B, and woodfordin C, whereas monomeric ellagitannins and condensed tannins showed negligible activity in the same assay system.13–15 On the other hand, some tannins exhibited moderate selective cytotoxicity in in vitro assays using the PRMI-1951 melanoma cells,26 although most of the tannins that have been tested were inactive in assay systems using lung carcinoma (A0549), ileocecal adenocarcinoma (HCT-80), epidermoid carcinoma nasopharynx (KB), and medulloblastoma (TE-671) tumor cells.