Malignant cells must traverse basement membranes during their migration to sites distant from the primary tumor. Since basement membranes are thought to be a critical barrier to the passage of tumor cells, we have constructed a model basement membrane-stromal matrix consisting of laminin and type IV collagen reconstituted onto a disk of type I collagen for use in an in vitro assay of invasiveness. Metastatic tumor cells and leukocytes are able to cross this barrier, whereas nonmetastatic tumor cells, fibroblasts, and epidermal cells cannot penetrate it. Those tumor cells that penetrate the barriers were found, when isolated and subcultured, to be more invasive and to produce more metastases than the parental population. This assay system should be useful for studying the invasiveness of tumor cells and for isolating highly invasive variants.

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An animal model for human colon cancer metastasis is described in which spontaneously metastasizing colonic tumors are formed after injection of human colon cancer cells into the cecal wall of young athymic nude mice. Lymphatic and vascular invasion were demonstrated histologically after injection of both well- and poorly-differentiated cell lines, and metastases were found in a pattern similar to that of naturally occurring human colonic cancer. In contrast, little or no visceral organ involvement could be demonstrated after s.c. injection. Cells with increased liver-metastasizing potential were obtained by serial selection in this system. These cells had an enhanced ability to penetrate a reconstituted basement membrane in the presence of partially purified liver extract when compared to lung or brain extracts in a modified Boyden chamber assay. These results demonstrate the ability of human epithelial tumor cells to metastasize reproducibly in an animal model system, which may be useful for studying many aspects of the pathogenesis of cancer metastasis. In addition, it is suggested that local invasion by colon cancer cells may be influenced in part by tissue-specific factors.

The purpose of this study was to determine how interferons alpha and gamma influence the expression of M(r) 72,000 type-IV collagenase (gelatinase A) and M(r) 92,000 type-VI collagenase (gelatinase B) genes and whether there are differences in their gene expression. Special emphasis was focused on the treatment time. Total cellular RNA from A2058 human melanoma cells treated for various time periods with IFN-alpha or gamma was analyzed by Northern- and slot-blot hybridization. Both M(r) 72,000 and M(r) 92,000 type-IV collagenase mRNAs were detectable in A2058 cells and mRNA levels for both gelatinases were significantly up-regulated in the cells treated for a short time period with either IFN-alpha or gamma. In contrast, a long-term treatment (7 days) with these drugs markedly down-regulated the genes for both gelatinase A and B. Zymographic analysis showed that human melanoma primarily secretes the gelatinase-A activity, which showed changes similar to those seen in the corresponding mRNA after the treatments with interferons. The expression of gelatinase-B activity was, however, detectable only transiently during the stimulating phase with IFN-alpha. Western immunoblot analysis showed that alterations in the levels of immunoreactive protein of gelatinase A in the cells correlated with the mRNA levels after the treatments. These findings suggest that IFN-alpha and IFN-gamma are potent regulators of both M(r) 72,000 and M(r) 92,000 type-IV collagenase/gelatinase A and B genes in human melanoma showing biphasic and parallel effects on mRNA levels of both enzymes, depending on the treatment time, and that the M(r) 72,000 metalloproteinase/gelatinase A is the predominant basement-membrane-degrading type-IV collagenase in human melanoma.