Abstract A65: Contribution of stromal-derived IL-8 on prostate cancer progression

Abstract Background: Prostate cancer (PCa) is the second leading cause of cancer deaths. Deaths invariably result from metastasis, most commonly to the bone. Tumor-microenvironment interactions of metastatic PCa in the bone are critical for growth at the metastatic site. These interactions suggest that therapies will need to target both tumor cells and the microenvironment to be successful. One target in both tumor and microenvironment is Src family kinases (SFKs), for which a phase three trial in combination with docetaxel is completed. Better targeting of SFKs will depend on understanding the tumor-stromal interactions that lead to its activation in both compartments. Aberrant Src activation de-represses cytokines including IL-8, contributing to the “vicious cycle” of metastatic growth in the bone. Stromal cells are a rich source of IL-8, but there is little information on how they affect tumor cells and viceversa. Here, we describe a feed-forward loop and paracrine mechanism of IL-8-mediated Src activation in PCa, both of which lead to increased tumor cell migration and invasion. Methods/Results: We demonstrate IL-8 and Src are overexpressed in more metastatic PC3-MM2 cells versus less metastatic PC3 cells. Previous work in the laboratory has demonstrated activated Src increases IL-8 expression. Through lentiviral knockdown of IL-8 in PC3-MM2 (PC3-MM2shIL-8) cells, we demonstrate that decreased IL-8 expression decreases Src activity in tumor cells. We also demonstrate that decreased IL-8 expression decreases migration and invasion while exogenous IL-8 rescues this phenotype. We next asked the effect of immortalized bone marrow-derived human stromal cells (HS5) on tumor cells. HS5 cells secrete high levels of IL-8. To determine if stromal-produced IL-8 affects Src activity in PCa, conditioned media from HS5 cells was added to PC3, PC3- MM2 and PC3-MM2shIL-8 cells. Src activity was increased in all cell lines. Conditioned media also increased migration and invasion of these cell lines. To determine if these increases were due, in part to IL-8, HS5 cells were infected with a lentivirus driving the expression of shIL-8 (HS5shIL-8) and conditioned media was collected. Addition of conditioned media from HS5shIL-8 cells to PC3 or PC3-MM2shIL-8 cell lines resulted in reduced Src activation, migration and invasion relative to HS-5 cells infected with a control vector. Conclusions/Future Directions: These results demonstrate stromal production of IL-8 increases Src activity and that stromal cells play a major role in metastatic properties of PCa cells. To confirm these in vitro studies, in vivo studies are being performed using co-injections of stromal cells and PCa cells. We will determine if: (1) stromal cells co-inoculated with tumor cells increase tumor growth and/or metastatic potential of PC3; (2) if knockdown of Src and/or IL-8 in stromal cells inhibits the ability to increase metastatic potential induced by stromal cells. Recent data from the Phase I/II dasatinib + docetaxel trial suggest that decreases in IL-8 levels after 21 days of treatment are associated with patient response (Araujo et al., unpublished). These results suggest that IL-8 from both tumor and stromal cells may be important inmetastatic potential and growth of prostate tumor cells in the bone. Understanding the roles of IL-8 and Src in PCa and the stromal microenvironment are important in better understanding PCa metastasis. Citation Format: Lynnelle Thorpe, John C. Araujo, Nila U. Parikh, Menashe Bar Eli, Gary E. Gallick. Contribution of stromal-derived IL-8 on prostate cancer progression [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A65.