Abstract 3431: Prostate-derived ETS factor expression decreases prostate tumor cell aggressiveness <i>in vitro</i> and metastasis <i>in vivo</i>
Authors: Joshua J. Steffan, Sweaty Koul, Thomas R. Johnson, Hari K. Koul, Randall B. Meacham
Journal: Cancer Research (2012)

Abstract INTRODUCTION: The metastasis of a prostate tumor is the leading cause of prostate cancer deaths. Therefore the ability to prevent or limit the malignant potential of tumor cells remains a significant and clinically relevant goal. Prostate-Derived ETS Factor (PDEF) is a transcription factor which regulates multiple gene products involved in prostate tumorigenesis. There is an inverse correlation between the levels of PDEF and tumor aggressiveness. In addition, PDEF protein expression is inversely correlated with increasing tumor aggressiveness (increasing Gleason Score), suggesting that PDEF may be a tumor metastasis suppressor. Since PC3 cells express very low levels of PDEF and metastasize well in metastasis models, they serve as a model to determine: 1) if PDEF over-expression affects the metastatic capacity of these cells in mouse models of metastasis and 2) which PDEF-regulated gene product(s) may contribute to metastatic colonization. METHODS: Standard migration (scratch), invasion (Boyden chamber), clonogenic, and RNA to cDNA RT-PCR assays were performed. Cells were stably transfected to express Luciferase. In vivo, 1 x 106 cells were injected in the subcutaneous, tail vein, and intra-cardic mouse models and at various time points there after, cells are non-invasively monitored by IVIS over a twelve week period. RESULTS: Utilizing in vitro migration, invasion, and clonogenic assays we demonstrated that PDEF over-expression resulted in decreased tumor aggressiveness. PDEF re-expression differentially regulated MMP9 and FAK compared to parental cells. Surprisingly, PDEF expression had no effect on in vivo subcutaneous xenograft tumor growth; however, using both tail-vein and intra-cardiac injection mouse metastasis models we demonstrate that PC3 cells as well as PDEF over-expressing PC3 cells disperse and home in around abdominal cavity. We observed that over time PC3 cells survived and reestablished new colonies. Conversely, PDEF over-expression significantly and dramatically decreased the ability of PC3 cells to colonize metastatic sites compared to parental cells. Twelve weeks post tumor cell injection, mice injected with PC3 cells had well established micro-metastasis, while mice injected with PDEF-over-expressing PC3 cells had no detectible metastasis. CONCLUSIONS: These studies demonstrate for the first time that the re-expression of PDEF decreases the metastatic capacity of prostate cancer cells in vivo, while having no effect on subcutaneous tumor cell growth, thus establishing PDEF as a tumor metastasis suppressor gene. Therefore, future studies to determine how PDEF is silenced in advance disease may lead to increased mechanistic insight into the metastatic process and eventually to several therapeutic options for the re-expression of PDEF or the inhibition of PDEF-regulated gene products to decrease or perhaps prevent prostate tumor metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3431. doi:1538-7445.AM2012-3431