Isolation from a murine fibrosarcoma of cell lines with enhanced plating efficiency in vitro.

The technique for the isolation of mutants was applied to establish highly clonogenic cells from a fibrosarcoma (FSA) that had an extremely poor growth capacity in vitro (10(-6)--10(-7) of surviving fraction of cells). After consecutive clonings, the surviving fraction of cells increased to 1--5 X 10(-1), whereas that of the ordinarily maintained culture remained at a low level. Selected clones were analyzed in vitro and/or in vivo. The results indicated that the FSA was composed of heterogeneous cells or cells having a potential variability in cloning ability in vitro, metastatic ability in vivo [lung colony-forming efficiency (LCFE)], and DNA content. The relatively high DNA content of one of the clones, FSA 1233, continued after growth in vivo or in vitro, indicating its hereditary nature. FSA 1233 was also demonstrated to have a lower LCFE when the cell suspension was made from a tumor rather than from a culture in vitro. The difference of surviving fractions between the cells in the two conditions was not enough to explain the difference in LCFE's between them. These cells could grow under either in vitro or in vivo conditions and could be made readily into single-cell suspensions. The cells are, therefore, available as a system for analysis of the response of cells in vitro after in vivo treatment with various agents.