Semiautomated colorimetric assay for in vitro screening of anticancer compounds.

An in vitro tetrazolium dye (MTT) reduction technique was modified and evaluated for use in the large-scale screening of anticancer compounds by examining the activity of ten clinically used drugs against 16 different human and murine cell populations. Cell populations included colon and mammary adenocarcinomas, melanomas, leukemias, and freshly isolated normal cells. Cell lines were grown in microtiter plates for 18-20 hours prior to a 72-hour continuous exposure to the drugs. Cultures were initiated at cell densities which maximized both the difference in dye reduction and the number of cell doublings between the beginning and end of the drug exposure period. Drug potency, expressed as the 50% inhibitory concentration (IC50), was comparable whether the effect on cell doublings or dye reduction was determined. There was good agreement between this method and the more labor-intensive, conventional method of counting trypan blue dye-excluding cells in a hemacytometer. Implemented as a large-scale, high-capacity system, our adaptation of the MTT technique is a rapid, sensitive, reproducible first-line screening device for detecting anticancer compounds with cytostatic or cytocidal activity.