Abstract 2824: In vitro tumor extravasation model.
Authors: Jeon Jessie S. , Zervantonakis Ioannis K. , Chung Seok , Charest Joseph , Kamm Roger D. 
Published: August 2014

Abstract
Cancer cell metastasis is a series of biological processes that allow malignant tumor cells to invade from primary to secondary sites. Understanding the invasion of the secondary site remote tissue requires studying the individual steps in metastasis, particularly, those leading up to and immediately following extravasation of a circulating tumor cell from a blood vessel into the remote tissue. The platform presented here mimics the tumor microenvironment in a well-controlled manner, and provides high resolution imaging of tumor cell extravasation and the early stages of colonization. We investigate the extravasation step where tumor cells transmigrate across an endothelial monolayer into a hydrogel model of the extracellular space. We find tumor cells are more likely to extravasate soon after contact with the endothelium.
We have cultured and sustained an endothelial monolayer spanning the entire microchannel and hydrogel surface of the microfluidic system. Two days after seeding of endothelial cells, we introduced tumor cells into the same microchannel now covered with endothelium to observe cancer cell extravasation. The experimental protocol is optimized to ensure the formation of an intact endothelium prior to the introduction of tumor cells and also to observe tumor cell extravasation by having a suitable tumor seeding density.
Extravasation is observed for 35% of the tumor cells in contact with the endothelium within 1 day after their introduction. The region of interest (ROI) is imaged with confocal microscopy and can determine whether a cancer cell, labeled green with GFP, has transmigrated across the endothelium, denoted by VE-cadherin staining, and extravasated into the gel region. We also measured the permeability of the endothelial monolayer to monitor barrier integrity as well as the changes induced by interactions with tumor cells by measuring the diffusion of fluorescently-labeled dextran across the monolayer. Permeability increased 3.8 fold 24 hours after introducing tumor cells, suggesting the endothelial barrier integrity is compromised by the interactions. Average number of tumor cells in ROIs increased between day 1 and day 3 after tumor seeding while the percent of ROIs with extravasated cells did not change significantly. These results suggest that extravasation in our system occurs predominantly within the first 24 hours of tumor cell introduction and that proliferation can continue both prior to and after extravasation.
The experimental systems have a major advantage in studying cancer extravasation; they can mimic aspects of the 3D in vivo situation in a controlled environment while simultaneously providing in situ imaging capabilities for visualization. Thus, this model allows quantitative study of metastatic cancer interactions with the potential to identify novel metrics of cancer cell invasiveness and suggests possible use as a platform for drug screening.
Citation Format: Jessie S. Jeon, Ioannis K. Zervantonakis, Seok Chung, Joseph Charest, Roger D. Kamm. In vitro tumor extravasation model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2824. doi:10.1158/1538-7445.AM2013-2824