Abstract 3194: Platycodin D induces growth arrest and cell cycle arrest by activating MDM2 and interacting with FOXO3a in prostate cancer

Abstract

Abstract Purpose: The present study was designed to evaluate the anti-tumor activity and possible mechanism of action of Platycodin D (PD), a major saponin derived from Platycodin grandiflorum, in human prostate cancer. Experimental Design: Human prostate cancer cells with different p53 status (p53 wildtype LNCaP cells, p53 null PC3 cells and p53 mutant DU145 cells), and the normal human prostate cell line, RWPE-1, were exposed to various concentrations of PD to compare its cytotoxicity in vitro (via the MTT assay). Detailed invitro and invivo studies on the anti-tumor effects of PD were then performed. Results: PD exerted cytotoxicity against all three prostate cancer cell lines, with half-maximal inhibitory concentrations in the range of 11.16 to 26.13μmol/L. The PC3 cells were the most sensitive to PD, whereas RWPE-1 cells were not sensitive to PD.A further study in these cell lines showed that PD could potently affect the cell proliferation (indicated by the bromodeoxyuridine assay), induce cell apoptosis (by Annexin V-FITC flow cytometry) and cause cell cycle arrest (PI staining). After being treated with PD for 48 hours,the DU145 and LNCaP cells were arrested in the G0 /G1 phase, and the PC3 cells were arrested in the G2/M phase. A Western blot analysis indicated that PD decreased the expression of MDM2 and increased the expression levels of FOXO3a, p21 and p27 in the three cell lines. In PC3 cells, PD exposure decreased the levels of cell cycle-related proteins, including E2F1, cdk2, cdk4, cdk6, cyclin D1 and cdc2. PD exposure increased apoptosis-related proteins, Bax, caspase9 and caspase3, and downregulated Bcl-2, PARP, and caspase8. Real-time PCR indicated that the same changes had occurred at the transcriptional level for all of these targets. Moreover, PD dose-dependently inhibited the growth of PC3 xenograft tumors in BALB/c nude mice. A Western blot analysis of the xenograft tumors indicated that similar changes in protein expression also occurred in vivo. Conclusion: PD exhibits significant activity against prostate cancer cells in a p53-independent manner. MDM2 and the FOXO3a transcription factor appear to be involved in the mechanism of action of PD, which provides a basis for future development of this agent for human prostate cancer therapy. Citation Format: Hongxia Xu, Rui Zhou, Zongliang Lu, Kai Liu. Platycodin D induces growth arrest and cell cycle arrest by activating MDM2 and interacting with FOXO3a in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3194. doi:10.1158/1538-7445.AM2014-3194