Tumor cell migration and invasion of basement membranes is a crucial step in the multistage process which leads to the formation of a metastasis. Cancer cells cross the basement membranes as they initially invade the lymphatic or vascular beds during dissemination and when they penetrate their target tissue. The process of cellular invasion is comprised of distinct events which include attachment of cells into the basement membrane, secretion of enzymes which degrade the basement membrane and the migration of cells into the target tissue in response to specific chemotactic stimuli.
A variety of in vitro systems have been developed to assess the invasiveness of tumor cells. The BD Biocoat FluoroBlok Invasion System is based on studying the movement of tumor cells through a porous filter coated with Matrigel according to the method of Albini et al. ( 1987). The original protocol for this assay is extremely tedious. Briefly, the tumor cells are seeded into the upper chamber of a porous filter (coated with matrigel) which separates upper and lower fluid-filled chambers. A chemoattractant is added to the lower chamber to stimulate cells to migrate through the pores of the filter. After incubation at 37oC, the non-migrating cells on the upper surface of the filters are wiped with cotton swabs. The cells migrating to the lower side of the pores are counted by microscopy. Obviously, this assay is extremely labor intensive and prone to several errors. The first source of error is the variability of coating the inserts with matrigel, which can make critical interpretation of results difficult. The second source of error loss of cells is during the washing, scraping and fixing of the cells on these filters. Thirdly, scoring the number of migrating cells through the filters involves arduous counting by microscopic examination, which may be unreliable. If you are thinking of screening hundreds of compounds from a drug library for their anti-metastatic activity by this protocol, it is truly a formidable task.
The BD Biocoat Fluoro Blok Invasion System makes this complicated assay much easier. Each of these inserts is precoated with matrigel which removes errors prone to occur during manual coating of the filters. No washing or scraping is required which markedly reduces intra and inter-assay variability. The filters are arranged as a 24-insert block plate which fits perfectly into a 24-well culture plate (also supplied in the kit). The kit contains a detailed protocol for fluorescent labeling of cells and protocols for actually doing the assay. The best part of the kit is the ease of quantitating invasive potential of cells using fluoresence intensities. The assay is much more reliable and sensitive than manual counting of migrating cells which allows accurate assessment of metastatic ability of cells. Also the automation-compatible format of the assay kit allows rapid screening of combinatorial drug libraries. The only disadvantage of the kit is that it is quite expensive. And when you want to screen a large number of drug candidates by the kit the cumulative expense may not be affordable for all research laboratories. However, if expense is not a consideration then the BD Biocoat Fluoro Blok Invasion System is an excellent tool for research into tumor metastasis.
Piyali Dasgupta, Ph.D.
Post-Doctoral Fellow
Moffitt Research Center
References:
Albini, A. Iwamoto, Y, Kleinman, H.K., Martin, G.R., Aaronsen, S.A., Kozolowski, J.M. and McEwan, R.N. Cancer Res., 47; 3239-3245, 1987