Application of a tissue culture microtiter test for the detection of cytotoxic agents from natural products.

A method is described by which the growth inhibitory effects of cytotoxic compounds and fermentation broth cultures on adherent tumor cell lines can be quantitated. Cells are seeded into 96-well microtiter plates and 16 hours later the test compounds or broths are added to the wells. Cell growth is measured after three days (B16 mouse melanoma cells) or six days (HT-29, human colon carcinoma cells) by first fixing adherent cells, staining with Giemsa stain, washing away excess stain, then solubilizing stained cells with HCl. Absorbance is determined using a microELISA spectrophotometer and the data are transferred to and analyzed by a computer. The assay is rapid and reproducible and can be used to identify fermentation broths with cytotoxic components. Addition of DNA into the assay mixture (cells plus compound) inhibits the cytotoxic activities of certain DNA-reactive agents. The results of this study demonstrate the application of this assay system for primary and secondary evaluation of fermentation broths for in vitro antitumor activity.