Introduction: Nanaomycin K is a natural compound found in the cultured broth of “Streptomyces rosa subsp. notoensis” OS-3966 and has been reported to have an inhibitory effect on epithelial mesenchymal transition (EMT), an important mechanism of cancer cell invasion. In this study, we investigated the antitumor effect and EMT inhibitory effect of nanaomycin K on castration-resistant prostate cancer (CRPC) cell lines in vitro and in vivo. Methods: Two human prostate cancer (PCa) cell lines, castration-dependent LNCaP and castration-independent PC-3, and one mice PCa cell line, castration-independent TRAMP-C2 were used. In vitro, TGF-ß was added to PCa cell lines followed by treatment with nanaomycin K. Then the MTS assay was performed to examine cell proliferation. Also wound healing assay was conducted to evaluate cell migration. In addition, western blotting was conducted to investigate the expression of EMT markers and the MAPK pathway. In vivo, nanaomycin K was intratumorally administered to mice bearing TRAMP-C2 tumors, and tumor size and weight were observed over time. After removal, tumor immunohistochemistry (IHC) staining was conducted. Results: Nanaomycin K significantly inhibited proliferation in all cell lines with or without TGF-ß (p < 0.001). Also, nanaomycin K also significantly inhibited the migration of TGF-ß treated TRAMP-C2 (p=0.008) by wound healing.In western blotting, nanaomycin K decreased the expression of N-cadherin and Vimentin, indicating EMT progression, in all cell lines, and decreased the expression of Slug, which induces EMT, in LNCaP and TRAMP-C2. And regarding the MAPK signaling pathway, phospho-p38, phospho-SAPK/JNK and phospho-Erk1/2 were suppressed in LNCaP, while phospho-Erk1/2 was suppressed in both LNCaP and TRAMP-C2. The effect was more pronounced in TGF-ß treated groups. Finally, in animal experience, nanaomycin K showed anti-tumor effects in vivo (0.5 or 1.0 mg/body nanaomycin K: p=0.001). Also, in IHC staining using mice tumor, phospho-Erk1/2 expression was significantly decreased by nanaomycin K (1.0 mg/body: p=0.031). And the expression of Cleaved-Caspase 3 was concentration dependently increased by nanaomycin K (0.5 mg/body: p=0.009, 1.0 mg/body: p<0.001). Conclusions: Nanaomycin K had anti-tumor effects and inhibited invasion by suppressing the expression of Slug, a protein that induces EMT and the phosphorylation of MAPK signaling pathway in prostate cancer. So nanaomycin K could be a therapeutic agent for CRPC due to EMT and MAPK inhibition. SOURCE OF Funding: None
