Preferential growth stimulation of metastatic rat mammary adenocarcinoma cells by organ-derived syngeneic fibroblasts in vitro.

To determine whether organ-derived fibroblasts differentially affect the growth of cells from tumors that preferentially metastasize to specific organs, we investigated the effect of medium conditioned with primary cultured rat fibroblasts from various organs on the in vitro growth of metastatic cell lines and clones of the rat 13762NF mammary adenocarcinoma. The conditioned medium from fibroblasts derived from rat mammary fat pad differentially stimulated tumor cell growth in monolayer culture and clonogenic growth in soft agarose of the highly metastatic clone MTLn3 in a dose-dependent manner. Conditioned medium from fibroblasts derived from the lung and liver also stimulated the growth of clone MTLn3 cells but to a lesser extent than did mammary fat pad fibroblasts. In contrast, poorly metastatic cell clones (MTC, MTPa) did not respond to the growth stimulatory factor(s) from the fibroblast-conditioned medium. The factor(s) responsible for the growth stimulation were inactivated by heat and trypsin treatment and inhibited by low pH and cycloheximide. The result suggest that fibroblasts in different organs have different effects on tumor cell growth, and they may determine, in part, the organ specificity of tumor development and metastasis.