Abstract LB-145: Study of prostate cancer & endosteal niche adhesive interactions can aid understanding of metastatic behavior

Introduction: Prostate cancer (PCa) is the second leading cause of cancer related death in men in the US and remains incurable in the metastatic stage. Recent reports have shown that the adhesion molecule N-cadherin, a mesenchymal cadherin associated with epithelial-to-mesenchymal transition (EMT), is expressed in a large percentage of castration resistant prostate cancer tumors, allows the interaction between N-cadherin expressing osteoblasts (OSB) at the endosteal niche and prostate cancer cells via homophilic binding, and can promote osteoclastogenesis and osteolytic disease state. There is also evidence that direct adhesive interactions between tumor cells and the bone marrow stroma are responsible for the development of drug resistance and relapse. This phenomenon termed "cell adhesion-mediated drug resistance" (CAM-DR) is thought to be one of the major mechanisms by which PCa, as well as other tumors that reside at the endosteal niche, escape the cytotoxic effects of therapeutic agents. In this study we evaluated the adhesive interaction of patient-derived primary PCa cells (i.e., conditionally reprogrammed PCa cells (Liu, X et al., Am J Pathol, 2012)) with the bone metastatic microenvironment as a first step to: 1) identify potential differences in patient response to therapy using physical cues (i.e., adhesion to the tumor microenvironment) as “physical biomarkers” of putative response to treatment, and 2) potentially target these interactions therapeutically. Materials and Methods: The human OSB cell line hFOB 1.19 was used to model the endosteal niche. Conditionally reprogrammed patient-derived PCa cells: 1) PP8T; A Gleason Score 8 CRC line from a primary site tumor and, 2) PCA3-CRC cells, which we derived from a metastatic lymph node organoid (a kind gift from Drs Charles Sawyers and Yo Chen (Gao, D, et al., Cell, 2014)), were co-cultured in a microfluidic device, layered with OSB to monitor PCa-OSB interactions using time lapse fluorescence microscopy. In separate experiments, PCa cells were labeled with the cell proliferation dye eFluor® 670 to quantify and compare proliferation of PCa as a function of their adhesive interaction with OSB. Finally, N-cadherin (CDH2) and cadherin-11 (CDH11) protein expressions were also quantified for each of the PCa lines studied as well as the OSB line utilized. Results and Conclusions: Real-time imaging showed that PCA3 cells (i.e., metastatic line) preferentially adhered to OSB whereas PP8T cells (from primary site) presented with a more invasive, yet not adherent, behavior. In addition, PP8T cells proliferated at a significantly faster rate than PCA3 cells when co-cultured with OSB. Concomitantly with these results we also found that PCA3 cells expressed significantly higher levels of N-cadherin and cadherin-11 than PP8T cells, corroborating the presence of EMT in the metastatic line. These data suggest that examination of the PCa-OSB physical interface maybe useful in determining the mechanisms by which PCa cells interact with the bone niche. Our studies represent a potential first step to predicting and targeting these interactions, prior to the development of CAM-DR. Citation Format: Jenny Zilberberg, Leah Dziopa, Eugenia Dziopa, Maia Iyer, Qiaoling Sun, Saba Choudhary, Woo Y. Lee, Lucas Tricoli, Shain Assefnia, Christopher Albanese. Study of prostate cancer & endosteal niche adhesive interactions can aid understanding of metastatic behavior [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-145. doi:10.1158/1538-7445.AM2017-LB-145