Microfluidic Platform for Investigation of Mechanoregulation of Breast Cancer Bone Metastasis

Mei, Xueting 1, 2 ; Middleton, Kevin 2 ; Ma, Yu-Heng 2 ; Xu, Liangcheng 2 ; Walji, Noosheen 1 ; Young, Edmond 1, 2 ; You, Lidan 1, 2;

 1.  Department of Mechanical and Industrial Engineering University of Toronto; 2.  Institute of Biomaterials and Biomedical Engineering University of Toronto Abstract;

INTRODUCTION: Approximately 70% of advanced breast cancer patients experience bone metastasis (1). Breast cancer cells (BCC) that invaded across the endothelium to the bone have devastating impacts on bone quality by interacting with osteoclasts to alter the bone remodeling process. Exercise, an often-used cancer intervention strategy, regulates bone remodeling process and could affect BCC metastasis to bone. As the major mechanosensory cell in bone, osteocytes can be a key regulator. Although recent studies showed that mechanically stimulated osteocytes increased BCC migration and modified endothelial cell (2), there lacks a physiological relevant in vitro model. Therefore, we present the design and validation of an in vitro microfluidic tri-culture model for studying mechanical regulation of breast cancer metastasis.

METHODS: Highly metastatic MDA-MB-231 human BCCs will be cultured inside an endothelialized lumen (human umbilical vein endothelial cells, HUVECs) (3) that is adjacent to a population of either static or mechanically-stimulated osteocyte-like MLO-Y4 cells. Soluble factors will diffuse through hydrogel-filled side channels to instigate inter-cellular communication between MLO-Y4 cells and BCCs over a period of 3 days. Microfluidic model validation experiments were based on BCC transendothelial invasion to the adjacent MLO-Y4 cells under static condition, with or without RAW264.7 differentiated osteoclast-conditioned media (CM). In addition, MLO-Y4 calcium signaling experiment will be used to validate the integration of on-chip mechanical loading, where MLO-Y4 cells stained with Fura 2-AM dye will be exposed to oscillatory fluid flow (OFF) (1Pa; 1Hz; 4min) produced by a customized pump (4).

PRELIMINARY RESULTS: An endothelial lumen was successfully cultured in the microfluidic device, with DAPI and VE-cadherin stained. Invasion validation results show that BCCs invaded further toward static osteocytes in the presence of osteoclast CM, with 37% increase (p<0.02) compared to without osteoclast CM, likely due to osteoclast support of cancer cell growth (5).   

DISCUSSION AND CONCLUSION: This platform allows the integration of physiological relevant OFF and real-time signaling between different cell populations. Future work with this platform will elucidate the effects of bone mechanical loading on BCC transendothelial invasion and determine the key mechanisms involved in osteocyte regulation of BCC metastasis. 

REFERENCES: (1) Hagberg. Cancer Epidemiology. 2013. (2) Ma. J. Cell Biochem. 2018. (3) Bischel. Biomaterials. 2013. (4) Middleton. ORS 2017 Annual Meeting. (5) Yaccoby. Cancer Res. 2004.