We have recently reported that inhibition of tumor necrosis factor-a (TNF-a) release is a useful method for screening of cancer preventive agents, 1) because TNF-a and other inflammatory cytokines stimulate tumor promotion and progression of initiated cells as well as premalignant cells. 2,3) Since TNFa and interleukin-1 (IL-1), as endogenous tumor promoters, activate nuclear factor kB (NF-kB), 4,5) inhibitors of NF-kB activation are also assumed to be cancer preventive agents. 6) However, in a practical sense, it is quantitatively easier to measure inhibition of TNF-a release from cells treated with a tumor promoter such as okadaic acid than inhibition of NFkB activation using a gel mobility shift assay. 7) Based on the study of green tea as cancer preventive agent in the United States 8) and as cancer preventive beverage in Japan, 9) we decided to take a closer look at Japanese herbal medicine for other likely cancer preventives. One classical Japanese herb, Geranium thunbergii SIEB. et ZUCC. (Gennoshoko in Japanese), is used as an antidiarrhetic 10) ; it contains geraniin, which has been intensively studied as a representative tannin. 11) And the bark of Acer nikoense MAXIM (Megusurino-ki in Japanese), which contains diarylheptanoids, is sold as a folk medicine for eye and liver diseases in Japan. 12) The Forestry Experiment Station of Saitama Prefecture succeeded in culturing young plants of A. nikoense collaborated with us on the scientific utilization of the plant. We received four water extracts-leaves, bark, small branches, and timber-from the Station and subjected them to inhibition of TNF-a release assay using BALB/3T3 cells treated with okadaic acid 13) : The leaves showed the strongest activity among the four extracts. Each extract was subjected to highperformance liquid chromatography (HPLC) with CAP-CELL PAK C18, and geraniin and corilagin were identified in the active leaf extract (Fig. 1).In The success of green tea as a cancer preventive is based on evidence that green tea contains tannins and antioxidants, does not show toxicity in humans and has long traditional use in Asia. In the light of this, herbal medicines are now also attracting attention as potential sources of cancer preventive agents. Using the inhibition of TNF-a a release assay, we studied Acer nikoense (Megusurino-ki in Japanese), one of the herbal medicines. The inhibitory activity of TNF-a a release was found in the leaf extract rather than the bark extract, and the main active constituents were identified as geraniin and corilagin, which are present in another Japanese traditional herb, Geranium thunbergii (Genno-shoko). The IC 50 values of TNF-a a release inhibition were 43 m mM for geraniin and 76 m mM for corilagin, whereas that for (؊)-epigallocatechin gallate (EGCG) was 26 m mM. Treatment with geraniin prior to application of okadaic acid, a tumor promoter on mouse skin initiated with 7,12-dimethylbenz(a)anthracene, reduced the percentage of tumor-bearing mice from 80.0 to 40.0% and the average numbers of tumor per mouse ...
