[Influence of intercellular interaction between cancer cells and normal cells on cancer metastasis]

Three highly metastatic and two weakly metastatic clones were obtained from a spontaneously arising mammary adenocarcinoma in an SHR rat. The difference in their capacity to metastasize in lungs was recognized only when the cancer cells were inoculated subcutaneously but not when they were inoculated intravenously. This evidence possibly indicates that the difference in the metastatic capacity of these clones is caused by different potential for detachment from the primary site and for intravasation during the various steps of metastasis. The motility of cancer cells, which is one of the most important factors in these steps of metastasis, showed no difference between the highly and weakly metastatic clones. However, the motility of cancer cells was decreased after the coculture with normal fibroblasts, and the motility of weakly metastatic clones used was more strongly decreased than that of highly metastatic clones. On the other hand, using a dye transfer method to examine the relationship between the metastatic capacity of cancer cells and the capacity of cancer cells to make junctional communications with normal fibroblasts, it was demonstrated that the frequency of communication between weakly metastatic clone cells and fibroblasts was significantly higher than that between highly metastatic clone cells and fibroblasts. These results suggest that the motility of cancer cells is inhibited by interaction with normal fibroblasts, and that one of these forms of interaction may be mediated by intercellular communication.