Polyphyllin D is a potent apoptosis inducer in drug-resistant HepG2 cells

In a search for new anticancer agents, we identified a novel compound polyphyllin D (PD) (diosgenyl alpha-L-rhamnopyranosyl-(1-->2)-(alpha-L-arabinofuranosyl)-(1-->4)]-[beta-D-glucopyranoside) that induced DNA fragmentation and phosphatidyl-serine (PS) externalization in a hepatocellular carcinoma cell line HepG2 derivative with drug resistance (R-HepG2). PD is a saponin originally found in a tradition Chinese medicinal herb Paris polyphylla. It has been used to treat liver cancer in China for many years. We evaluated the cell-killing mechanisms of this compound in R-HepG2 and its parental cells. The mitochondrial apoptotic pathway was found to be involved in the PD-induced apoptosis because PD elicited depolarization of mitochondrial transmembrane potential (DeltaPsim), generation of H2O2, as well as release of cytochrome c and apoptosis-inducing factor in a dose- and time-dependent manner. In conclusion, we show for the first time that PD is a potent anticancer agent that can overcome drug resistance in R-HepG2 cells and elicit programmed cell death via mitochondrial dysfunction.