(770b) The Influence of Matrix Stiffness on the Behavior of Brain Metastatic Breast Cancer Cells

Our research focuses on understanding the behavior of metastatic breast cancer cells using physiologically relevant engineered environments. Metastatic cancer cells interact with the microenvironment at a distant organ site during the process of colonization. This organ specific host microenvironment provides mechanical, chemical and biological cues that dictate whether the cancer cell will survive and outgrow into metastasis. Recapitulating the physical and chemical aspects of organ specific host microenvironment using biomimetic materials and investigating metastatic cancer cell-material interactions could further understanding of the mechanisms that govern metastatic colonization. As a model system, we are studying breast cancer brain metastasis, which is associated with poor prognosis and a median survival time of only 4-9 months. A major hurdle in developing therapeutic strategies to tackle breast cancer brain metastasis is our limited understanding of mechanisms involved in metastatic progression of breast cancer to the brain. This is, in part, due to lack of biomimetic in vitro models to study the interactions between metastatic breast cancer cells and brain microenvironment. To address this need, we employed hyaluronic acid hydrogels to recapitulate the native brain microenvironment and examined how hydrogel stiffness impacted the behavior of brain metastatic breast cancer cells. Hyaluronic acid was chosen as it is a glycosaminoglycan predominantly found in the brain and is known to interact with the CD44 receptors on metastatic breast cancer cells.

Hyaluronic acid hydrogels of varying stiffness (0.2 kPa - 4.6 kPa), including the range relevant to the brain environment (0.2 kPa - 1kPa) were prepared by functionalizing hyaluronic acid with methacrylate groups followed by crosslinking with dithiothreitol. Hydrogels were also engineered to promote cell adhesion by conjugation of the RGD peptide. MDA-MB-231 Br brain metastatic human breast cancer cells were used in our studies and were seeded on top of hydrogels. We first studied the dependence of metastatic breast cancer cell adhesion on the hydrogel stiffness and surface concentration of RGD and observed that the breast cancer cell adhesion increased with increasing hydrogel stiffness and RGD concentration. We also observed that the cell morphology was significantly affected by the hydrogel stiffness and cell spreading area increased with increasing hydrogel stiffness and RGD concentration. In addition, we noted that cell proliferation increased with increasing hydrogel stiffness. Our observations, thus far, indicate the activation of mechanotransduction pathways in brain metastatic breast cancer cells. We are currently investigating the role of focal adhesion kinase (FAK) - phosphatidylinositol 3-kinase (PI3K) signaling in stiffness dependent behavior of brain metastatic breast cancer cells. Ultimately, such systems could provide mechanistic insight into the pathways involved in breast cancer brain metastasis enabling development of new therapeutic targets for metastatic disease.