This paper describes a simple method for the freeze-fracturing of cells in monolayers or multi-layer tissue cultures. The method produces high quality replicas and is applicable to the study of virtually any tissue culture or organ culture system. It uses standard materials and equipment for both tissue culture and freeze-fracturing.

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Human osteosarcoma and mammary carcinoma cells were cultured separately in a medium supplemented with fetal calf serum, until they were confluent. The medium was then replaced by serum-free medium supplemented with heparin. Both cell cultures secreted collagenase, and this activity was inhibited by a cartilage-derived protein of low molecular weight. Since cartilage is rarely invaded by neoplasms, the presence of this inhibitor may play an important role in the regulation of tumor invasion.

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