Development of a bioassay for ovarian carcinoma colony-forming cells.

We have reviewed the application of our in vitro assay for human tumor stem cells to the cloning of human ovarian adenocarcinoma cells in soft agar. Tumor colonies grew from both effusions and biopsies from 85% of more than 100 ovarian cancer patients tested. Up to 2,000 colonies appeared after 10 to 14 days in culture, yielding a maximum plating efficiency of 1%. Cells from nonmalignant effusions did not form colonies under these conditions. The number of tumor colonies was proportional to the number of cells plated between concentrations of 104 to 106 cells/dish. Morphological and histochemical criteria showed that the colonies consisted of cells with the same characteristics as those of the original tumor. H3Tdr suicide colony-forming cells were actively in transient through the cell cycle. Removal of phagocytic cells with carbonyl iron markedly reduced the plating efficiency, and 2-mercaptoethanol could only partially substitute for macrophages. Spleen cell-conditioned medium from oil-primed BALB/c mice was not required. Endogenous macrophages within the tumor may provide the conditioning factor or factors required for in vitro growth. Thus, this assay is proving extremely useful for studying the biology and drug sensitivity of human ovarian cancer.