Characterization of stable spontaneous metastatic variant lines of RSV-transformed mouse fibroblasts

The correlation between metastatic potential and a series of biological properties was investigated in two mouse fibrosarcoma lines (SR-BALB and B77-3T3), transformed by different strains of Rous sarcoma virus (RSV). In the absence of selective pressure the metastatic potential was different in the two lines. The SR-BALB sarcoma did produce both spontaneous metastases from s.c. site and i.v. lung colonization with a high incidence (respectively in 60% and 80% of treated animals). Conversely, the metastatic incidence of the B77-3T3 sarcoma was much lower. Differences in lung implantation between the two lines turned out to be even greater when the number of colonies growing in the lung was evaluated. Organ distribution of cells after i.v. injection, tumorigenicity, growth rate in vivo and in vitro, plating efficiency in liquid medium and cloning efficiency in semi-solid agar medium were evaluated in the two lines. A strict correlation was found only between the metastatic potential and the capability of growth in 0.6% ("hard") agar. Such a correlation was supported by the isolation in "hard" agar of highly metastasizing subclones of the low-metastasizing B77-3T3 line.