Chemical study of effective constituents of Vietnamese ginseng-structure-activity relationship of anti-tumor-promoting activity-

从越冬人参的根茎和根中分离得到37个皂苷类化合物，其中14个为新化合物。其中21个皂苷已从同属其他植物中分离得到，如原人参二醇型皂苷：人参皂苷-Rb_1，-Rd.，-Re，原人参三醇型皂苷：人参皂苷-Rg_1，三七皂苷。为了寻找可能的抗肿瘤促进剂，我们测定了其对EPA诱导的EB病毒早期抗原(EBV-EA)激活的抑制作用。由于活性主要集中在皂苷部分，因此对该植物的主要皂苷进行了检测。其中，主要皂苷大黄皂苷R2(MR2)对EBV-EA的抑制作用最强。用流式细胞仪检测MR2对TPA处理的Raji细胞周期的影响。经MR2处理后，Raji细胞的S期细胞比例增加，而G2+M期细胞比例降低，呈剂量依赖关系。MR2抑制TPA促癌作用的机制是通过影响细胞周期，在上述体外实验的基础上，进行了体内实验。以DMBA为引发剂，TPA和伏马菌素B1为促进剂，研究了MR2对小鼠皮肤肿瘤两阶段致癌实验的抑制作用。TPA和伏马菌素B1促进的乳头状瘤的产生明显减少，而MR2的预处理则延缓了它们的产生。MR2活性高于甘草次酸。此外，通过口服MR2，观察了DEN对小鼠肝肿瘤形成的抑制作用和戊巴比妥钠的促进作用。结论：MR2是一种独有的奥替罗皂苷，有望成为一种防癌先导化合物。

From the rhizomes and roots of Panax vietnamensis, 37 saponins including 14 new compounds were isolated and characterized. Among them, 21 saponins were already isolated from other species of the same genus, such as protopanaxadiol-type saponins : ginsenosides-Rb_1, -Rd., -Re, protopanaxatriol-type saponins : ginsenoside-Rg_1, and notoginsenoside. In addition, ocotillol-type saponins : majonoside R1 and remarkably high yield of majonoside R2 (MR2) were identified.To search for possible anti-tumor promoters, we measured the inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 'EPA.Methanol extract of Panax vietnamensis showed significant inhibitory activity. Since the activity was concentrated to the saponin fraction, the major saponins of this plant were tested. Among them, the major saponin, majonoside R2 (MR2) exhibited the strongest inhibitory effects on EBV-EA activation. This activity was unique to ocotillol skeleton.The effects of MR2 on the cell cycle of Raji cells treated with TPA were examined by flow cytometry. By the treatment with MR2, the ratio of S phase of Raji cells was increased, but the ratio of G_2 + M phases were decreased in dose-dependent manner. The inhibition mechanism of MR2 against cancer promotion of TPA was through influencing the cell cycle.On the basis of the above in vitro assay, in vivo assay was carried out. The inhibitory effect of MR2 on the two-stage carcinogenesis test of mouse skin tumor using DMBA as an initiator, and TPA and fumonsin B1 as the promoter. The papilloma production promoted by TPA and fumonisin B1 was significantly decreased and delayed by the pre-treatment of MR2. The activity of MR2 was higher than that of glycyrrhetic acid. In addition, the inhibitory effect on hepatic tumorigenesis initiated with DEN and promoted with pentobarbital was observed by oral administration of MR2.In conclusion, MR2, unique ocotillol saponin, promises to be cancer preventive lead compound.