Image analysis of Transwell assays in the assessment of invasion by malignant cell lines

This study aims to determine if layering of extracellular matrix (ECM) can achieve a physiological basement membrane thickness of 8 microm and to assess the use of paraffin wax-embedded Transwell plates coupled with digital image analysis as a means of determining invasion by malignant cell lines. Layers of Matrigel, a sarcoma-derived ECM was built to a concentration of 7.4 microg/mm2 in the upper chamber of a Transwell plate invasion assay. Two cell lines from extrahepatic bile duct adenocarcinoma were tested in serum-free growth medium. Conditioned medium was added to the lower chamber to act as a chemoattractant. Following attachment, cells were incubated for 48 h and the Matrigel-coated insert cut from its holder and fixed in 10% unbuffered formalin saline. Each insert was bisected and processed to paraffin wax. Serial levels were stained by haematoxylin and eosin. A Kontron image analysis system was used to measure the mean thickness of Matrigel for each cell line and the degree of invasion was assessed by measuring the depth to which cells had degraded the Matrigel. A mean thickness of 8 microm was achieved using 5.0 microg/mm2 for the OCUCh-LM1 cell line and 7.4 microg/mm2 for the SKChA-1 cell line. No significant difference was seen in the ability of either cell line to degrade Matrigel. Immunocytochemistry for laminin and cytokeratin helped to identify ECM components and cells, respectively. In conclusion, digital image analysis of paraffin wax-embedded inserts can be used to determine the invasive capacity of various cell lines; immunocytochemistry may help to identify ECM components and cells; and the assay used to assess different cell lines and their ability to degrade Matrigel.