Interaction of metastatic tumor cells with bovine lens capsule basement membrane

The use of bovine lens capsule basement membrane as a model substratum for studies of invasion and extravasation by metastatic tumor cells is described. The abilities of three independently isolated pairs of metastatic variant cell lines to digest the purified substrates, laminin, type IV collagen, and type I collagen, were compared with their abilities to solubilize isotope from 125I-labeled lens capsule basement membrane matrix. The cell lines used were +SA and -SA mouse mammary adenocarcinoma cells, RT7-4bs and RT7-4b-Ls rat hepatocarcinoma cells, and B16-F1 and B16-F10 mouse melanoma cells. In general, imperfect correlations of lytic activity with metastatic ability were found for the purified substrate digestions, but, for each pair of variants, the more metastatic tumor cell line was always able to solubilize more surface-bound isotope from the lens capsule. Visual evidence of tumor cell-associated digestion of lens capsule basement membrane was obtained using transmission electron microscopy. Mouse mammary carcinoma cells attached more rapidly to lens capsule than to endothelial cell monolayers or tissue culture plastic. We next added endothelial cells to the model substrate. Aortic endothelial cells grew well on lens capsules without apparent synthesis of additional basement membrane matrix. In additional studies, the lens capsule was used in a chamber apparatus to demonstrate that cellular invasion of the full thickness of this basement membrane structure could be demonstrated and readily quantitated. Our results indicate that bovine lens capsule is a particularly versatile basement membrane structure useful for studies of tumor cell invasion and extravasation. In addition, the comparison of purified substrate digestions with lens capsule matrix digestion indicates the desirability of also using a matrix digest when correlating lytic abilities of tumor cells with their metastatic abilities.