Abstract 427: Integrated PDEF and Twist1 expression distinguishes lethal prostate cancer from an indolent disease

Introduction: Prostate cancer (PCa) is the third most commonly diagnosed cancer in the world. Advanced genomic studies have characterized it as a molecularly heterogeneous disease with a multiple clinical spectrum ranging from indolent to highly aggressive. Conventional therapies produce a high rate of cure for patients with localized PCa, but there is no effective treatment for metastatic PCa. These facts underline the urgent, yet unmet, need for identification and characterization of new targets that can help distinguish metastatic PCa from an indolent disease, and pave a way for novel mechanism based anti-metastasis therapies against PCa. Our previous studies have shown that loss of PDEF, a putative tumor suppressor, could lead to more invasive phenotype in PCa cell lines through promoting Epithelial to Mesenchymal transition (EMT). In this study, we evaluate the role of PDEF and Twist1 in PCa through NCBI omnibus and The Cancer Genome Atlas. We also evaluated the mechanism by which PDEF is regulated epigenetically. Methods: PDEF expression was monitored by immunohistochemistry using tissue microarray. Western blot was employed to measure the PDEF level in PCa cell lines. PDEF and Twist1 gene expression was measured by real time PCR. The PDEF promoter was cloned and methylation specific PCR was performed. PDEF methylation in clinical samples was extracted from TCGA database and PDEF/Twist1 microarray data was extracted from GSE16560 in NCBI gene expression omnibus with R language. GraphPad prism was used to generate figure and statistical analysis. P Results: IHC staining of PDEF on PCa patient samples and in commonly used PCa cell lines suggested an inverse correlation between the level of PDEF and Twist1. Over-expression of PDEF in PC3 cells inhibits Twist1 expression. DNA Methylation status near the promoter region of PDEF was negatively associated with the expression levels of PDEF in established PCa cells. These results suggest that PDEF levels are regulated in part by promoter methylation. Using TCGA data we identified 12 methylation site and the methylation level of multiple site correlates with the increased of Gleason Score (GS). Analysis of gene expression data from GSE16560 revealed that low expression of PDEF and high expression of Twist1 were independently associated with poor survival in PCa patients. Integrated PDEF and Twist1 expression can distinguished a high-risk group of people for hormone refractory PCa along with short median survival time. Conclusions: Loss of PDEF combined with gain of Twist1 expression can serve as a potential biomarker set for distinguishing aggressive PCa from an indolent disease. PDEF expression is epigenetically regulated in part by promoter hyper-methylation. Acknowledgement: Carroll W. Feist Endowed Chair Funds. Citation Format: Fengtian Wang, Sweaty Koul, Parveen K. Jaiswal, Runhua Shi, Glenn Mills, Hari K. Koul. Integrated PDEF and Twist1 expression distinguishes lethal prostate cancer from an indolent disease. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 427.