I n t r o d u c t i o nGlioblastoma multiforme (GBM) is the most malignant and common brain tumor and it comprises ~23% of all primary brain tumors in adults. These malignancies are refractory to all the current therapeutic approaches, including surgery, radiotherapy and chemotherapy. Fas (CD95 or APO-1) is a member of the TNF/NGF receptor family, and Fas induces caspase-dependent apoptotic death in various transformed cells (1,2). Fas ligation with natural ligand or agonistic anti-Fas antibody is followed by recruitment of proapoptotic adaptor molecules such as Fas-associated death domain (FADD) to transduce the apoptotic signals through the caspase cascades (3). In some cells, Fas efficiently activates caspase-8 and it subsequently activates caspase-3 or 7, while other types of Fasinduced apoptosis are mediated by cytochrome-C release from the mitochondria and this is inhibited by the over-expression of antiapoptotic bcl-2 family members (4).Panax Ginseng is known for its biological and pharmacological activities such as its anti-cancer, anti-aging, anti-inflammatory and anti-oxidant properties in the nervous, immune and circulatory systems (5). These diverse physiological activities of ginseng are mainly mediated by saponin, which is a ginsenoside. Especially, the metabolites of ginsenosides that are formed by enteric bacteria have been focused on for their pharmacological activities. Among them, compound K (C-K) is known to be formed by enteric bacterial fermentation of Rb1, Rb2 and RC, and C-K has been reported to suppress tumor metastasis and inflammatory responses (6,7). Another ginsenoside Rh2, a metabolite of Rg3, is also known for its tumor suppression by inducing apoptosis or retarding growth signals (8).We have previously shown that human malignant astrocytoma cells are quite resistant to Fas-induced apoptosis even though these Cancer Res Treat. 2009;41(1):36-44 Purpose Malignant astrocytomas are among the commonest primary brain tumors and they have a grave prognosis, and so there is an urgent need to develop effective treatment. In this study, we investigated the molecular mechanisms that are responsible for the anti-tumor effect of ginsenosides on human astrocytoma cells.
Materials and MethodsWe tested 13 different ginsenosides for their anti-tumor effect on human malignant astrocytoma cells in conjunction with Fas stimulation. In addition, the cell signaling pathways were explored by using pharmacological inhibitors and performing immunoblot analysis. DCF-DA staining and antioxidant experiments were performed to investigate the role of reactive oxygen species as one of the apoptosis-inducing mechanisms.
ResultsAmong the 13 different ginsenoside metabolites, compound K and Rh2 induced apoptotic cell death of the astrocytoma cells in a caspase-and p38 MAPK-dependent manner, yet the same treatment had no cytotoxic effect on the primary cultured human astrocytes. Combined treatment with ginsenosides and Fas ligand showed a synergistic cytotoxic effect, which was mediated by the reduction of intracell...