Flavan enantiomers from Daphne giraldii selectively induce apoptotic cell death in p53-null hepatocarcinoma cells in vitro

Hepatocellular carcinoma (HCC) is a primary malignant tumor with very poor prognosis. To search for more effective compounds for HCC treatment, two new pairs of flavan enantiomers, daphnegiranol C-1/C-2 (1a/1b) and daphnegiranol D-1/D-2 (2a/2b), were isolated from the stem bark and roots of Daphne giraldii by using chiral chromatography. MIT assay was applied to evaluate their cytotoxicity against three hepatocarcinoma cell lines (Hep3B, MHCC97H, HepG2) as well as a normal liver cell line L02. The results showed that these compounds preferred to inhibit the growth of Hep3B cells (p53 null). Among them, 2a/2b (the IC50 value was 4.87 and 3.35 mu M, respectively) exhibited a stronger cytotoxic effect than sorafenib (IC50 = 6.59 mu M) in Hep3B cells. A further study demonstrated that 2a/2b could induce apoptotic cell death with an increase in reactive oxygen species (ROS) in Hep3B cells. In addition, the IC50 values of 2a/2b in HepG2 and MHCC97H cells (both harbored p53 gene) were more than 10-folds greater when compared with Hep3B cells, indicating that 2a/2b selectively exhibited cytotoxicity in p53-null hepatocarcinoma cells. Moreover, inhibition of p53 increased the inhibitory effect in p53-wild hepatocarcinoma cells, as well as apoptotic cells and ROS generation. Taken together, flavan enantiomers 2a/2b selectively induced apoptosis in Hep3B cells because of p53 deficiency.