Herbal medicines are now attracting attention as potential sources of
cancer preventive agents. Using inhibition of
tumor necrosis factor-alpha (
TNF-alpha) release assay, we studied Acer nikoense, Megusurino-ki in Japanese. Inhibitory potential was found in the leaf extract, and the main active principles were identified as
geraniin and
corilagin. The IC(50) values for
TNF-alpha release inhibition were 43 microM for
geraniin and 76 microM for
corilagin, whereas that for (-)-
epigallocatechin gallate (EGCG), the
green tea polyphenol, as control was 26 microM. Furthermore, treatment with
geraniin inhibited
okadaic acid tumor promotion in a two-stage
carcinogenesis experiment on mouse skin.
Geraniin and
corilagin are present in another well-known Japanese traditional herb, Geranium thunbergii, Genno-shoko in Japanese. Considering seasonal variations of the agents and sites of cultivation of herbs, this paper reviews the significance of
geraniin as a new
cancer preventive agent. In addition, based on accumulated results of
green tea as a
cancer preventive, we review two important results with EGCG: the synergistic effects of EGCG with
sulindac or
tamoxifen on
cancer preventive activity in PC-9 cells, and
cancer prevention of intestinal
tumor development in multiple intestinal
neoplasia (Min) mice by cotreatment using EGCG with
sulindac. We report here new findings on additional gene expression resulting from cotreatment with EGCG and
sulindac in PC-9 cells compared with gene expression by EGCG alone or
sulindac alone. Overall, our results indicate that, with the continuing spread of
cancer chemoprevention as a fundamental medical strategy, both clinicians and researchers should take a closer look at herbal medicine.