Ph.D Thesis

Ph.D StudentGal Naama
SubjectTransport and Localization of Particles Internalized
in Living Cancer Cells
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Daphne Weihs
Full Thesis textFull thesis text - English Version


Mechanical properties of cells are of great importance due to their effect on function.  Cells regulate internal mechanics over short time scales for crawling and division, as well as for intracellular transport. Along the same lines, cell structure and stiffness have been shown to play an important role in different diseases, including cancer. Specifically, metastatic cells are expected to be very flexible and dynamic to change shape and penetrate the vascular wall and tissue. In this work, intracellular mechanics of cancer in relation to metastasis is characterized by tracking the motion of internalized probe-particles. We compare three closely related model cells from breast tissue, two malignant lines with high- and low-metastatic potential, and a benign cell line.

Natural uptake by endocytosis is used here to internalize particles to the cells. In this natural process, particles may be encapsulated by lipid membranes which potentially affect particle motion and the microenvironments they probe. Particle encapsulation by different lipid membranes is evaluated as a function of time and cell type. We find reduced encapsulation in benign cells as compared to cancerous ones, and that encapsulation in all cell types reduces with time. Our results suggest that particle encapsulation does not necessarily determine mechanics.

Statistical analysis approaches are employed to reveal particle transport mechanisms in living cells. Particle dynamics in complex fluids are typically characterized by the second moment of the displacement, or the mean square displacement (MSD). Despite being a conventional measure of transport modes and sample stiffness, it is also limited in its ability to reveal concurrent transport mechanisms. Hence, we evaluate other moments of the displacement. In the highly metastatic cells, we show a piecewise-linear dependence of scaling exponents on moment orders. Bilinearity indicates “strong anomalous diffusion” where particle motion is composed of active motion in confined regions separated by larger active yet non-ballistic flights.

Finally, we use intracellular particle transport to compare and contrast internal mechanics of the different cell lines. Particles in all cells demonstrate super-diffusive motion, indicating active transport processes. Those are related to non-thermal fluctuations of the microtubule network, as well as directed motion of microtubule associated molecular motors. Interiors of the highly metastatic cancer cells were in general softer and more active than the benign cells and low metastatic-potential cancer cells. We thus reveal intracellular structural and mechanical characteristics of highly metastatic cells that can support their unique function.