M.Sc Thesis

M.Sc StudentMassalha Sonbula
SubjectMophology and Force Depend on Metastatic Potential
and Microenvironment Stiffness in Breast Cancer
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Daphne Weihs


            Cancer metastasis is the leading cause for death in cancer patients. Over 90% of cancer-related mortalities occur due to spread of the primary tumor to distant metastatic sites and generation of secondary tumors, or metastases. Nowadays there are no definite procedures for determining the invasiveness, metastatic potential (MP) and especially the target site of a specific tumor. Typically, clinical oncologists rely on pathological reports and statistics known for specific cancer types to determine the metastatic phenotype of a tumor. However, the mechanical interactions between cancer cells and their microenvironment have also been shown to affect the cell’s ability to invade. Therefore, understanding the mechanical interactions of metastatic cancer cells with their substrate is critical and can reveal novel approaches for identifying and determining the invasiveness of a tumor. The initial stages of invasion include cell adhesion which regulates the migration of a tumor cell. Thus, we hypothesize that differences between the mechanical interactions of cancer cells or benign cells with their substrate, during the early stages of cell adhesion, can reveal new approaches towards predicting the metastatic potential and invasiveness of cancer cells.

We show that during adhesion, the dynamic cell morphology and the forces applied by single cells vary significantly between benign and metastatic breast cancer cells. Furthermore, we are able to distinguish between cells with different MP by measuring the forces applied by the cells on gel-substrates with varying stiffness; we used polyacrylamide gels with Young's moduli of 2-11 kPa. We have evaluated the time-dependent morphology of cells as they adhere onto a 2-dimensional collagen-coated polyacrylamide gel, and concurrently monitored the forces applied by high and low MP breast cancer cells with benign cells as a control; the forces indicate the strength of cell adherence. Cell applied forces were measured through displacement of particles embedded at the gel surface, using traction force microscopy. We observe that both high and low MP cancer cells apply significantly larger lateral traction forces than benign cells, when seeded on stiffer gels (4.3±0.3 kPa and above), while no difference in lateral forces is observed on softer gels (2.4±0.2 kPa). In addition, the cell morphology also varies with gel stiffness, as benign cells spread and become elongated on stiffer gels (7.2±0.1 kPa and above), while cancer cells remain mostly rounded on all evaluated gels. This specific morphology likely enables the breast cancer cells to remain loosely adhered and readily detach and migrate. Together, these findings reveal a direct correlation between the morphology and the forces applied by breast cancer cells with their metastatic potential, which may be used for diagnostic and prognostic applications.