Cell aggregation assay: a rapid means of evaluating and selecting in vitro transformed cells

A cell aggregation assay for evaluating in vitro transformation has recently been reported. Transformed cells formed larger cell aggregates than counterpart normal cells when suspended in liquid media above an agar base, a property which correlates with growth in soft agar and tumorigenicity. Using a human osteosarcoma cell line transformed by viruses and chemicals, we found increased cell growth of the transformed aggregates over untransformed cells. Moreover, certain aggregation properties (size/survival of aggregates) of transformed rat, mouse, hamster, human, dog, cat, chimpanzee, and sheep cell lines were found to be correlated with tumor potential, regardless of the method of transformation (spontaneous, chemical, or virus induced). Certain lines derived from cell aggregates growing in liquid medium above an agar layer were tumorigenic in nude mice, whereas the parent transformed line was not. Therefore, this assay can be utilized not only to evaluate tumorigenic potential, but also for selection of cells, which have undergone malignant transformation.