Tumor heterogeneity and stability of the metastatic phenotype of mouse KHT sarcoma cells

Heterogeneity in metastatic ability has been demonstrated in model systems for in vitro-cloned cell lines for a number of different tumors. We have examined the clonal diversity of mouse KHT sarcoma cells cloned either in vitro or in vivo by determining their ability to form lung colonies following i.v. injection into syngeneic mice. A wide range of metastatic ability was found in both the in vitro- and in vivo-isolated clones, suggesting that the diversity observed is not due to any selection occurring during in vitro growth. The stability of four in vitro-isolated clones, two of high metastatic and two of low metastatic ability, was then studied over a period of 3 to 4 months of growth in vitro. The phenotype of the highly metastatic cells remained relatively stable, declining only slightly over time. The clones with low metastatic ability, however, demonstrated a significant increase in ability to form lung colonies over the first 30 days in culture before becoming stable at levels approximately 10-fold higher than their original values. Even after this increase, however, there remained a difference of about a factor of 10 in the metastatic ability of the high and low pairs of clones. It was found that the number of lung colonies formed by all four cell lines was significantly increased when plastic microspheres were injected with the cell suspension. The cells with low metastatic ability were affected to a greater degree by the microspheres, resulting in the elimination of the difference between the four clones after 30 days in culture. This result suggests that the use of microspheres may provide a means to distinguish different cellular properties which affect the ability of cells to form lung metastases.