New perspective on the metabolism of AD-1 in vivo: Characterization of a series of dammarane-type derivatives with novel metabolic sites and anticancer mechanisms of active oleanane-type metabolites

20(R)-25-methoxyl-dammarane-3β,12β,20-triol (AD-1, CN Patent: 201010107476.7) is a novel derivative of dammarane-type ginsenoside. AD-1 has been shown to inhibit cancer cell proliferation without significant host toxicity in vivo, and has excellent development potential as a new anti-cancer agent. This study was designed systematically to explore the metabolic pathway of ginseng sapogenins. The metabolism of drugs in the body is a complex biotransformation process where drugs are structurally modified to different molecules (metabolites) through various metabolizing enzymes. The compounds responsible for the effects of orally administered ginseng are believed to be metabolites produced in the gastrointestinal tract, so understanding the metabolism of the drug candidate can help to optimize its pharmacokinetics. In this study, faeces samples were collected and extracted after oral administration of AD-1. The 16 metabolites of AD-1 were isolated and identified for the first time with various chromatographic techniques, including semi-preparative high performance liquid chromatography, nuclear magnetic resonance spectroscopy, and mass spectrometry; of these 16 metabolites, 10 were novel compounds. We first discovered the biotransformation of dammarane-type sapogenins into oleanane-type sapogenins in rats and found a series of metabolites that changed, mainly at C-25 and C-29. This study provides new ideas for the metabolic pathway of ginseng sapogenins. The isolated compounds were screened for their effect on the viability and proliferation against cancer cell lines (Human A549, MCF-7, HELA, HO-8901 and U87). The discovery of novel active metabolites 3β,12β,21α,22β-Hydroxy-24-norolean-12-ene (M6) may lead to a new or improved drug candidate. For one, M6 could inhibit the growth of all the tested cancer cells. Among the tested cell lines, M6 exhibited the most remarkable inhibitory effect on ovarian cancer HO-8901 cells, with IC₅₀ value of 2.086 μM. On this basis, we studied the anticancer mechanisms of M6. The results indicated that the pro-apoptotic feature of M6 acts via a mitochondrial pathway. Our results indicated that M6 exhibited a higher inhibitory effect on cancer-cell proliferation than AD-1 by inducing cell apoptosis. Our work provides data for future investigations on the metabolic mechanism of AD-1 in vivo and the potential for future research on developing a new drug.