Pseudolaric acid B induces apoptosis via proteasome-mediated Bcl-2 degradation in hormone-refractory prostate cancer DU145 cells.

Pseudolaric acid B (PAB), a natural diterpene acid present in the traditional Chinese medicinal herb Tu-Jin-Pi, exerted anticancer effects on various cancer cells. However, the effect of PAB on DU145 cells, an in vitro model of hormone-refractory prostate cancer (HRPC), has not been reported previously. In the study, PAB significantly suppressed proliferation of DU145 cells in a dose-dependent manner without obvious cytotoxicity. IC(50) values of 0.89 ± 0.18 and 0.76 ± 0.15 μM at 48h was determined by Cell counting kit (CCK-8) assay and clone formation assay, respectively. PAB also induced DU145 cells apoptosis as confirmed by typical morphological changes and Annexin V-FITC staining. Furthermore, we demonstrated that PAB caused a concentration-dependent elevation of reactive oxygen species (ROS) level in DU145 cells, and N-acetyl-l-cysteine (NAC, a well-known ROS scavenger) could block PAB-induced ROS generation and apoptosis. Western blotting and/or caspase activity data indicated that PAB downregulated anti-apoptotic Bcl-2 protein and activated caspase-9 and caspase-3, which were largely rescued by NAC or MG-132 (proteasome inhibitor). Taken together, these findings provide the first evidence that PAB may inhibit growth of HRPC DU145 cells and induce apoptosis through ROS generation and Bcl-2 degradation via the activation of the ubiquitin-proteasome pathway.