The desmoplastic response

Desmoplasia, a process in which excessive connective tissue is deposited in a neoplasm, is discussed. To study the process, a human malignant melanoma cell line (UCT-Mel 7) was used, that was established in the laboratory, and when injected into athymic mice, it gave rise to tumours that showed a number of interesting features. The tumour induced a marked desmoplastic response and the desmoplasia was associated in UCT-Mel 7-derived tumours with an unusual phasic pattern of growth. Two possible mechanisms were identified by which UCT-Mel 7 cells could have induced the desmoplastic response. UCT-Mel 7 cells were shown to be chemotactic for mouse macrophages and human foreskin fibroblasts were stimulated, in a dose-dependent manner, to synthesize increased amounts of collagen when co-cultured with mouse peritoneal exudate cells. Tumour cells were also found to act directly. Co-culture of UCT-Mel 7 cells and fibroblasts resulted in increased collagen synthesis by the fibroblasts. DNA synthesis was not required. Dexamethasone, retinoic acid and the tumour promoter, phorbol myristate acetate, had significant primary effects on fibroblast collagen synthesis but did not modify the response to melanoma cells. Recombinant basic fibroblast growth factor did not seem to be involved in the desmoplastic response. A surprising finding was the production of a potent inhibitor of collagen synthesis by superinduced cells of the mouse macrophage cell line, P388D1. This inhibitor has not been fully characterised. 49 figs., 33 tabs., 362 refs