Cytotoxic and apoptosis-inducing activity of C21 steroids from the roots of Cynanchum atratum.

Two new (1-2) and two known C21 steroids (3-4) were isolated from the roots of Cynanchum atratum. Their structures were elucidated by detailed 1D and 2D spectroscopic. The MTT assay showed that compounds 1-4 displayed obvious cytotoxic activities against HepG2 cells with IC50 values ranging from 10.19μM to 76.12μM. Compounds 1-3 also exhibited cytotoxic effects in A549 cells with IC50 values of 30.87-95.39μM. Compound 3 showed the antiproliferative activity via G0/G1 cell cycle arrest and proapoptosis in HepG2 cells by Flowcytometry analysis. Western blotting analysis revealed that compound 3 could induce HepG2 cell apoptosis via the mitochondrial pathway by downregulating Bcl-2 expression, upregulating Bax protein expression, and activating caspase-9 and caspase-3.