Abstract 344: Downregulation of osteoblastic N-cadherin decreases primary multiple myeloma cell - osteoblast interactions

Introduction: Recent reports have shown that the adhesion molecule N-cadherin, a mesenchymal cadherin associated with epithelial-to-mesenchymal transition, is expressed in a large percentage of castration resistant prostate cancer tumors, allowing the interaction between N-cadherin expressing osteoblasts (OSB) and prostate cancer cells via homophilic binding, and can promote osteoclastogenesis and osteolytic disease. There is also evidence that in multiple myeloma (MM), direct adhesive interactions between MM cells and the bone marrow stroma are responsible for the development of drug resistance and relapse. This phenomenon termed “cell adhesion-mediated drug resistance” (CAMDR) is thought to be one of the major mechanisms by which multiple myeloma cells (MMC) escape the cytotoxic effects of therapeutic agents. We recently demonstrated the technical feasibility of culturing difficult to preserve primary human MMC by reconstructing a physiological relevant 3D microfluidic bone-like tissue microenvironment. Using this platform, we found that OSB played a key role in the ex vivo maintenance and expansion of MMC. In this study, we evaluated the role of osteoblastic N-cadherin in regulating MMC-OSB interactions as a first step to elucidate the role of this molecule in the development of CAMDR in MM. Materials and Methods: Knockdown of N-cadherin protein expression in the human OSB cell line hFOB 1.19 was achieved using shRNA lentiviral technology. Patient-derived bone marrow mononuclear cells (BMMC) containing malignant MMC were cocultured in the microfluidic device with either N-cadherin+OSB or with a mixture composed of N-cadherin-OSB and N-cadherin+OSB. Monitoring and quantification of MMC-OSB interactions was performed using time lapsed images and fluorescence microscopy. Results and Conclusions: Real-time images showed that CD138+ MMC were preferentially adhered to N-cadherin+ OSB. The retention of CD138+ MMC, based on the scaffold constitution, was determined by flow cytometric analyses as the CD138+ MMC/OSB ratio. Notably, after a 2 day coculture period, only 32.78% ± 4.15% CD138+ MMC was retained in the tissue scaffold containing N-cadherin-OSB compared to 70.21% ± 4.64% retention in the mock transfected OSB group. For the first time, we demonstrated here that osteoblastic N-cadherin is responsible, at least in part, for the development of strong interactions between MMC with stromal elements from the tumor microenvironment. Our data suggest a new therapeutic intervention area in the modulation of N-cadherin expression by OSB as a way to render MMC more susceptible to drug treatments and potentially decrease CAMDR. Citation Format: Wenting Zhang, Yexin Gu, Qiaoling Sun, David S. Siegel, Peter Tolias, Zheng Yang, Woo Lee, Jenny Zilberberg. Downregulation of osteoblastic N-cadherin decreases primary multiple myeloma cell - osteoblast interactions. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 344. doi:10.1158/1538-7445.AM2015-344