Inhibition Of Akt/Nf-Kappa B/Survivin Pathway By Embelin On Castration-Resistant Prostate Cancer Cells

Background: Natural product embelin has been reported to exhibit anti-tumor activities in prostate cancer in preclinical models. While embelin was known to be a natural inhibitor of X-linked inhibitor of apoptosis (XIAP), whether other IAP family members also play a role in drug effects are incompletely understood. In the current study, the cell functions and IAP-related signaling pathways after embelin treatment were investigated in castration-resistant prostate cancer (CRPC) cells. Materials and methods: Cell viability was detected by MTT assay. Cell death was determined by trypan blue exclusion. Flow cytometry was applied to analyze cell cycle (propidium iodide, PI staining) and apoptosis (Annexin V/PI double staining). Caspase 3 activity was detected by fluorescence-based assay. Proteins were examined by Western blot. siRNA transfection was conducted using Lipofectamine 2000, and gene expression was tested by qPCR assay. Results: Embelin suppressed viability and cell number in CRPC cells, with IC50 of 21.3 and 13.6 mu M in DU145 and PC-3, respectively. Embelin also increased trypan blue positive, Annexin V positive, G1 and sub-G1 cell populations. Further, embelin triggered caspase 3 activation and PARP cleavage, and inhibited XIAP, survivin, I kappa B alpha, p-p65 and p-Akt. Survivin knockdown partially reduced drug-induced apoptosis. In the presence of PI3K inhibitor wortmanin and proteasome inhibitor MG132, embelin-mediated inhibition on cell proliferation and survivin expression was mitigated. Conclusion: Embelin inhibits proliferation, induces G1 arrest and triggers apoptosis in CRPC cells. Genetic and pharmacologic approaches identify Akt/NF-kappa B/survivin signaling pathway as a possible target pathway for the drug. These new findings provide an alternative mechanism for embelin and suggest this natural medicine as a potential anti-tumor agent for CRPC.