Quantitative in vitro assay for tumor cell invasion through extracellular matrix or into protein gels

A new quantitative method for the study of tumor cell invasion in vitro is presented. It is intended to facilitate the study of the mechanisms of invasion using an isolated basement membrane without the involvement of stromal structures or using defined protein gels. Cells are allowed to migrate through the pores of a Nuclepore polycarbonate filter into a protein gel on a nitrocellulose filter, or they may have to penetrate a cell-derived extracellular matrix (ECM) to reach the gel. Experiments with a nonmetastatic mouse lymphoma (Eb) and its two metastatic variants (ESb and ESb-MP) showed that the metastatic lines penetrated a Matrigel (a gel containing the components of a basement membrane) much better than the nonmetastatic cell line, but only the most metastatic line (ESb) was able to penetrate into a native collagen I gel. The presence of an ECM on the polycarbonate filter reduced the number of cells invading a fibrin gel, demonstrating that the dense, fibrillar structure of the cell-derived ECM was a barrier to the tumor cells. The metastatic lines penetrated the ECM to a 4- to 6-fold higher extent than the nonmetastatic cell line. It is concluded that in order to metastasize efficiently, the tumor cells must be able to penetrate many different kinds of barriers.