A Novel 3d Osteoblastic Niche Assay Is Useful To Study The Characteristics Of Bone Metastatic Cancers

(Background) Many patients with metastatic cancer (i.e. Prostate, breast, lung, kidney, and melanoma) struggle with skeletal metastases which is frequently causing cancer-related death. Thus, there is an imminent demand for a better understanding of how bone-homing cancers communicate and physically interact with the bone microenvironment. It is known that cancer-stromal cell interaction in bone marrow is a pivotal step in determining bone metastasis and tumor behavior and is seen in the events of competition with HSC for the osteoblastic niche, entering dormant status, and enhanced tumor growth. However, the lack of biologically relevant assay platforms has hampered interrogation of the mechanism of cancer-bone interaction as well as the development of bone-targeted anti-metastatic drugs. (Methods) Here, we present a novel method that can measure the bone-homing ability of cancers by co-culturing 3D osteoblastic niche (3D-ObN) spheroids derived from human mesenchymal stem cells along with reporter cell lines carrying hypoxia response element (HRE)-regulated reporter genes (pGF-HRE4-GFP/SecNLuc). First, the migration ability of metastatic cancers into the 3D-ObN was examined by analyses of O.C.T. frozen section images using confocal microscopy. Next, the metastatic ability of highly metastatic cancers were compared to normal epithelial cells and assessed by using either fluorescent microscopy (IncuCyte) or a luminometer. (Results) The HRE-driven reporter was activated in a 3D-ObN spheroid-specific manner in response to the nature of the hypoxia gradient within the spheroid. While the 3D-ObN provided signals that suppressed cancer cell proliferation, highly metastatic cancer cells displayed higher homing ability in the 3D-ObN assay relative to the normal epithelial cells. Prostate cancer cells expressing putative cancer stem cell markers (CD44/CD133high) showed higher homing ability compared to CD44/CD133low populations. (Conclusion) This assay platform is the first of its kind through the fact that it mimics cancer-osteoblastic niche interactions and allows for quantification of the ability of cancer cells including cancer stem-like cells to invade and anchor in osteoblastic niche. Furthermore, this assay system can be readily amended to an efficient and effective high throughput screening system useful for identifying molecules potentially preventive to critical process of bone metastases. Citation Format: Seunghwan Lim, Tej Pareek, Rasmi Palassery, John Letterio. A novel 3D osteoblastic niche assay is useful to study the characteristics of bone metastatic cancers. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A31.