269 Background: Although statin use has been associated with improved outcomes in prostate cancer, the molecular mechanism of this action is still unclear. Based on previous findings, we aimed to investigate the potential role of NFkB-Lin28B-let7 miRNA signaling pathway in human prostate cancer, particularly, castration-resistant prostate cancer (CRPC) cells, as a molecular mechanism of statin effect. Methods: Various human CRPC cell lines (PC3, DU145, 22Rv1, C42B) were used in this study. Proliferation of prostate cancer cells were measured by MTT assay and colony formation assay. Lin28B and NF-κB expression were controlled by siRNA transfection and the expression on Lin28 and let-7 miRNA were quantitated using RT-PCR and western blotting. Results: Notably, simvastatin treatment on various CRPC cell lines decreased cell viabilities in a dose dependent manner. It also significantly inhibited cell growth in clonogenic assay. In these CRPC cells, LIN28 gene was highly expressed in mRNa and protein levels. Conversely, micro RNA (miRNA) expressions of let7 family were remarkably downregulated in CRPC cells. By simvastatin treatment, mRNA and protein level of Lin28B were decreased, while let7 miRNA expressions were restored, which was the key finding of the current study. Considering NFkB is the upstream molecule of Lin28B, we found that the double treatment of statin and NF-κB inhibitor (CAPE) resulted in decreased cell viability, Lin28B and cyclin D1 expression, synergistically. Of note, let-7 miRNA levels were restored after simvastatin treatment, and further increased their expression levels by CAPE double treatment. In order to confirm this mechanistic clue, we specifically inhibited Lin28B and NF-κB genes, respectively, resulting in increased cell apoptosis signaling in the Lin28b or NF-κB knock down cells by combined treatment with simvastatin. Conclusions: In conclusion, simvastatin inhibited the cell growth of various human CRPC cell lines by controlling NFkB-LIN28B-let7 miRNA signaling pathway, and therefore; concurrent NF-κB inhibition with simvastatin treatment induce the synergistic anti-cancer effects in human CRPC cells.