Figure 4.

Silibinin induces G₁ arrest and decreases CDK and cyclin-associated kinase activity in LNCaP cells. Cell cycle phase distribution of LNCaP cells grown in 10% serum (A); 10% serum + 50 μg/ml of silibinin (B); 10% cFBS (C); 10% cFBS + 1 nM DHT (D); and 10% cFBS + 1 nM DHT + 50 μg/ml of silibinin (E). The data are at 5 days of cultures; silibinin was added at day 4. After desired treatments, cells were trypsinized and FACS analysis was done as described in Materials and Methods. (F) Inhibitory effect of silibinin on CDK and cyclin kinase activity. Cells were treated with 75 μg/ml of silibinin for the indicated time, and CDK and cyclin kinase activity was determined as described in Materials and Methods; C, control cells treated with ethanol for 48 hr. The cell cycle phase distribution and kinase activity data shown are representative of three independent experiments with similar findings.