Abstract 2474: Microenvironments of tumor cell intravasation
Authors: Gligorijevic Bojana , Bergman Aviv , Gil-Henn Hava , Condeelis John 
Published: August 2012

Abstract
Using intravital imaging, we and others have previously reported that some tumor cells within primary breast tumors have the ability to migrate and intravasate. In order to get an understanding of the microenvironments that are associated with migration and intravasation, we have applied a machine learning classification technique called “support vector machine” (SVM) to classify microenvironments using the density of tumor cells, macrophages, collagen fibers and blood vessels as microenvironmental parameters. Results produced using SVM approach indicate that there are three microenvironments: one associated with migratory cells and two distinct microenvironments populated with non-migratory cells. Higher resolution imaging revealed the difference between the two non-migratory microenvironments- one of them was populated with tumor cells forming small, persistent protrusions while in the other microenvironment no processes were observed. Detailed characterization of persistent protrusions showed that they have a characteristic morphology, lifetime and directionality compared to migration-associated protrusions. We hypothesized that persistent protrusions are the in vivo equivalents of invadopodia, proteolytic invasive protrusions uniquely present on metastatic tumor cells in in vitro cell culture. Invadopodia are able to degrade several components of extracellular matrix abundant in the basement membrane surrounding tumor blood vessels, presumably making tumor cells able to cross the blood vessel wall and enter the circulation. In order to determine if the special persistent protrusions are invadopodia as defined in vitro, we have done a comparative study utilizing several levels of information: morphology, assembly kinetics, extension dynamics, presence of molecular components typical of invadopodia and degradative activity. Moreover, we have shown that short-term treatment by proteolytic inhibitors decreases the frequency of persistent protrusions adjacent to blood vessels, but not cell migration in the interstitial tissue. Finally, by deletion or overexpression of invadopodial protein components we were able to modulate the frequency of invadopodia in vitro, and that of the special persistent protrusions in vivo. Our findings indicate that invadopodia exist in vivo under a specific set of microenvironmental conditions and that they catalyze the intravasation step of metastasis. This means that the body of knowledge about invadopodia gained using in vitro cell culture models can now be linked to tumor cell behavior in specific microenvironments during tumor metastasis in vivo. This approach might be used to generate diagnostic markers for early metastasis of breast cancer and metastatic treatment end points.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2474. doi:1538-7445.AM2012-2474