Clonal analysis of the ability of tumor cells to form colonies in semi-solid medium

Near-diploid mouse tumor cells CAK.25 AG(r) are characterized by low cloning efficiency in semi-solid medium:: about 10-5 per cell plated in methylcellulose. The properties of cells that have formed colonies in methylcellulose were compared with those of the parental population. Nine of 12 subclones of CAK-25 AG(r) picked from methylcellulose retained parental cloning efficiency when retested for growth, in semi-solid medium. Thus most colonies in methylcellulose were not formed by variant cells different from the parental cell population. Cloning efficiency of CAK-25 AG(r) and of its subclones on the solid substratum was high. All six sub-subclones randomly isolated from the solid substratum had the ability to form colonies in methylcellulose at a frequency no lower than that of the parental clone. Thus, most cells of the population had not lost the ability to form colonies in methylcellulose. The results suggest that the probability of a cell's initiating a colony in semi-solid medium is heritable and identical for most cells of the line under investigation.