M.Sc Thesis

M.Sc StudentMuscal Revital
SubjectMetastatic Cancer Cells Indent and Attempt to Invade
a Soft Substrate
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Daphne Weihs
Full Thesis textFull thesis text - English Version


The process of invasion is of special importance in cancer metastasis, the main cause of death in cancer patients. Cells typically penetrate a matrix by degrading it or by squeezing through pores. However, cell mechanics and forces applied by cells especially during the initial stages of metastatic penetration are still unknown. Hence, we focus on the initial stages of penetration, by studying cells as they indent a soft substrate. In this thesis, we have focused on the effect of two parameters: the metastatic potential of the cells and the substrate stiffness. Our leading hypothesis was that indentation capabilities correlate with metastatic potential of the cells and substrate stiffness affects these abilities.

We used soft, non-degradable substrates with small pores. The cell cannot penetrate the pores but can bend the substrate allowing us to focus on the initial stages of penetration. We used polyacryl amide gel substrate, with stiffness similar to live tissues. Human mammary gland epithelial cells with different levels of metastatic potential (MP) were used. Specifically, we have used high and low MP cells and non-cancerous cell line as a control. To correlate the indentation capabilities to the metastatic potential of the cells, we have also modified the highly metastatic cells by treating them with trans-retinoic acid, which is known for its ability to reduce invasive capabilities of the cells.

We show that only the cancer cells attempt to penetrate an elastic substrate by repeatedly indenting it for several hours; applied forces differ between the cancer cells. We evaluate the initial stages of cancer cell metastatic-penetration, monitoring morphology and forces applied during substrate indentation. Cells were initially seeded on a flat 2D gel and when indentation occurs, we reveal the initial stages of mechanical penetration into 3D gels. We distinguish two unique morphologies as this cancer cells indent the gels: skirt-like and blebbing.  We show that cells apply more force and attempt penetration more times on stiffer gels; forces are lower in the low MP cells. Furthermore, a model is proposed for the cell-indentation mechanism and highlights a special role for the nucleus in the indention process. The trans-retinoic acid treated high MP cells showed 60-65% reduction of the cells invasive capacity. We observe that those treated cells apply less force and indent the gel less than the high MP cells, behaving more like the low MP cells. Hence, the indention process is directly related to the invasive capabilities.