In vivo antimetastatic action of ginseng protopanaxadiol saponins is based on their intestinal bacterial metabolites after oral administration.

The present study demonstrated in vivo and in vitro antimetastatic activities of a major intestinal bacterial metabolite M1 formed from protopanaxadiol saponins of ginseng (the root of Panax ginseng C. A. Meyer) in comparison with its whole standardized extract and ginsenosides Rb1, Rb2, and Rc. Although Ginseng extract (1 mg/mouse) and ginsenosides (0.5 mg/mouse) significantly inhibited lung metastasis produced by i.v. injection of B16-BL6 melanoma cells in syngeneic mice (27-61% of untreated control), they hardly inhibited the invasion and migration of B16-BL6 melanoma and HT1080 fibrosarcoma cells in vitro. However, the intestinal bacterial metabolite M1 inhibited lung metastasis of melanoma cells and in vitro tumor cell invasion and migration at nontoxic or marginally toxic concentrations. Additionally, pharmacokinetic studies of ginsenoside Rb1 and M1 after oral administration (2 mg/mouse) revealed that intact Rb1 was not detectable in serum for 24 h by HPLC analysis, whereas the level of M1 in the serum reached maximum at 8 h (8.5 +/- 0.4 micrograms/ml) after Rb1 administration and at 2 h (10.3 +/- 1.0 micrograms/ml) after M1 administration. These findings suggest that the in vivo antimetastatic effect by oral administration of ginsenosides is mediated by their metabolic component M1.