The inhibitory effect caused by suramin on the paracrine growth of human cancer cells and fibroblasts.

The growth interactions between human cancer cells and primary cultured human fibroblasts, and the effects of suramin on them, were investigated using a double-chamber technique combined with a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MTT) assay. Human fibroblasts obtained from various organs resected surgically were cultured in a monolayer and used after the third or fourth passage. In the double-chamber assay, the growth of cancer cells in the top chamber was significantly stimulated by some types of fibroblasts in the bottom chamber in a fibroblast density-dependent manner. Interestingly, the growth of cancer cells was stimulated at 140%-147% by fibroblasts obtained from an organ where cancer cells had developed, the MCF-7 versus mammary fibroblasts, and in LS-180 versus colonic fibroblasts, but not by their fibroblast-conditioned medium. Suramin completely inhibited the growth-enhancing interaction between MCF-7 and mammary fibroblasts, and between SH-101 and lung fibroblasts at a clinical concentration of from 50 micrograms/ml to 300 micrograms/ml. It also reduced the growth of LS-180 co-cultured with colon-fibroblasts, but the inhibitory effect was incomplete. These results suggest that mutual growth reliance exists between human cancer cells and primary cultured fibroblasts by diffusible factors secreted by both cells, and that these enhancing effects are related in part to the growth and metastasis of cancer cells in vivo. Suramin was found to have an inhibitory effect on their interaction at a clinically achievable concentration in vitro.