The synergistic apoptotic interaction of panaxadiol and epigallocatechin gallate in human colorectal cancer cells.

Panaxadiol (PD) is a purified sapogenin of ginseng saponins, which exhibits anticancer activity. Epigallocatechin gallate (EGCG), a major catechin in green tea, is a strong botanical antioxidant. In this study, we investigated the possible synergistic anticancer effects of PD and EGCG on human colorectal cancer cells and explored the potential role of apoptosis in the synergistic activities. Effects of selected compounds on HCT-116 and SW-480 human colorectal cancer cells were evaluated by a modified trichrome stain cell proliferation analysis. Cell cycle distribution and apoptotic effects were analyzed by flow cytometry after staining with PI/RNase or annexin V/PI. Cell growth was suppressed after treatment with PD (10 and 20 µm) for 48 h. When PD (10 and 20 µm) was combined with EGCG (10, 20, and 30 µm), significantly enhanced antiproliferative effects were observed in both cell lines. Combining 20 µm of PD with 20 and 30 µm of EGCG significantly decreased S-phase fractions of cells. In the apoptotic assay, the combination of PD and EGCG significantly increased the percentage of apoptotic cells compared with PD alone (p < 0.01). The synergistic apoptotic effects were also supported by docking analysis, which demonstrated that PD and EGCG bound in two different sites of the annexin V protein. Data from this study suggested that apoptosis might play an important role in the EGCG-enhanced antiproliferative effects of PD on human colorectal cancer cells.