Abstract A53: Probing forces and modulation of cancer cell mechanical properties during transendothelial migration
Authors: Moeendarbary Emad , Kamm Roger , Scarcelli Giuliano 
Published: March 2017

For all types of cancer, the survival rate while the tumor is still localized is significantly higher than when cancer has metastasized. Though different therapeutic methods can be applied to successfully treat primary tumors, treatment of metastasised cancer is a great challenge due to its complex and systemic nature. A deeper understanding of how cancer initiates, grows and migrates is essential for creating successful therapies. Particularly, extravasation — a process during which streaming tumor cells (TCs) adhere to the blood vessels and traverse through the vascular endothelium into the surrounding tissue — is one of the crucial steps of cancer metastasis. While cancer research has mostly focused on the initial processes of metastasis, little is known about mechanisms of transmigration of tumor cells through the vascular wall. We found that during transendothelial migration (TEM), cancers cells undergo substantial shape changes transforming from semi-spherical (with a 2D contact with the endothelium) to a fully spread 3D morphology inside the ECM. This significant morphological change occurs due to forces generated intracellularly and distributed externally. During these morphological changes in transmigration, the cytoskeleton provides the force for shape change but the rate at which shape change occurs is dictated by the degree of deformability of the tumor cell, endothelial cells (ECs) and subendothelial tissue. Hence, the strength and distribution of forces, as well as mechanical properties of the cells and ECM, play a central role in the process of TEM. In this project, we investigate modulation of TCs and ECs rheological properties and the role of forces generated by the cytoskeleton and their transmission to adjacent cells and the ECM during extravasation. To address the role of mechanical modulation during TEM, we have developed in vitro assays and combed them with optical/confocal microscopy, Traction Force Microscopy (TFM) and Brillouin Confocal Microscopy (BCM). In particular, we recently designed a simple system in which ECs are cultured on a thin layer of collagen. Using a combination of different coating treatments on glass to produce surface hydrophobicity and maintain strong adhesion, we created a thin (~80 μm) layer of gel. Following seeding by ECs (HUVECs) to produce a tight and uniform EC monolayer we introduced TCs on top of the EC monolayer and monitored extravasation in real-time with high spatiotemporal resolution. Measurements of HUVEC monolayer permeability in this system show physiologically relevant values (8±3 10-8 cm2/s). We further tested our system by using different cancer cells with different invasiveness potentials and investigated their extravasation efficiencies. A major advantage of this platform is that it allows integration of TFM and BCM so it enabled us to characterize forces and modulation of cell mechanical properties during TEM. In particular, we demonstrated the feasibility of our system for application of BCM on cancer cells extravasating through a monolayer. BCM is an optical technique in which the mechanical information can be read out optically via spectral analysis of the scattered light; thanks to the interaction of light with intrinsic mechanical vibrations (phonons) of the material. Our BCM measurements indicate a significant decrease in elasticity of TCs at different stages; from 260±20 Pa for TCs that were in the process of transmigration to 195±17 Pa for those that were fully transmigrated. Our results shed a new light on the fundamental understanding of the extravasation mechanics. Furthermore, we anticipate that these studies will potentially enhance our ability to identify and screen for new therapies to inhibit the tendency for metastatic spread of disease.

Citation Format: Emad Moeendarbary, Roger Kamm, Giuliano Scarcelli. Probing forces and modulation of cancer cell mechanical properties during transendothelial migration. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A53.