Silibinin down-regulates survivin protein and mRNA expression and causes caspases activation and apoptosis in human bladder transitional-cell papilloma RT4 cells

Bladder cancer is the fourth and eighth most common cancer in men and women in the United States, respectively. Survivin, a member of inhibitor of apoptosis protein (IAP) gene family, is deregulated in a wide range of malignancies, including carcinoma of the bladder urothelium. Recent advances have identified survivin as a novel intervention target to induce apoptosis in cancer cells by phytochemicals or synthetic agents. Silibinin is a naturally occurring flavanone, isolated from milk thistle extract, and has been shown to possess cancer prevention/intervention potential against various cancers. In several animal and human studies, it is found to be safe and non-toxic. Human bladder transitional-cell papilloma RT4 cells were treated with silibinin and analyzed for survivin protein and mRNA levels by Western blotting and real-time RT-PCR, respectively. Silibinin treatment of cells for 24h at 100μM dose resulted in ~50% decrease in survivin protein level; however, treatment at 200μM dose for 24 and 48h showed a complete loss in survivin protein without any change in actin used as loading control. Employing RT-PCR analysis we also observed that silibinin causes a strong to complete decrease in survivin mRNA levels. In other studies, down-regulation of survivin by silibinin was associated with a very strong and prominent caspases-9 and -3 activation as well as PARP cleavage. Quantitative apoptotic assay showed that silibinin decreased survivin levels and caspases-PARP cleavages, in accord with a strong apoptotic death and growth inhibition of RT4 cells. Together, these findings suggest that more studies are needed to investigate in vivo effect of silibinin on survivin expression and associated biological effects in bladder cancer that could provide useful information for silibinin efficacy in the prevention/intervention of human bladder cancer.