Inhibitory effect of human breast cancer cell proliferation via p21-mediated G1 cell cycle arrest by araliadiol isolated from Aralia cordata Thunb

A new polyacetylenic compound, araliadiol, was isolated from the leaves of Aralia cordata Thunb. (Araliaceae). The structure of araliadiol was determined to be 3( S),8( R)-pentadeca-1,9( Z)-diene-4,6-diyne-3,8-diol by MS, NMR, IR, and UV spectroscopic analysis as well as Mosher ester reaction. Araliadiol displayed a significant inhibitory effect on the growth of a human breast adenocarcinoma cell line (MCF-7), with an IC (50) value for cytotoxicity of 6.41 µg/mL. Cell cycle analysis revealed that the proportion of cells in the G (1) phase of the cell cycle increased in a dose-dependent manner (from 54.7 % to 72.0 %) after 48 h exposure to araliadiol at dosages ranging from 0 to 80 µM. The results suggest that araliadiol inhibits cell cycle progression of MCF-7 at the G (1)-S transition. After treatment with araliadiol, phosphorylation of retinoblastoma protein (Rb) in MCF-7 cells was inhibited, accompanied by a decrease in the levels of cyclin D (3) and cyclin-dependent kinase 4 (CDK4) and an increase in the expression of p21 (WAF-1/Cip1). However, the expression of phosphorylated p53 (Ser15) and Chk2 was not altered in MCF-7 cells. These findings indicate that araliadiol exhibits its growth-inhibitory effects on MCF-7 cells through downregulation of CDK4 and cyclin D (3), and upregulation of p21 (WAF-1/Cip1) by a p53-independent mechanism.