Basic studies of chemosensitivity tests in oral cancer by MTT assay.

We applied the in vitro colorimetric dye reduction technique described by Mosmann to carry out chemosensitivity tests of human squamous cell carcinomas.The assay is based on the selective reduction of the tetrazolium salt, MTT, by cells which remain viable after exposure to drugs. Mitochondrial dehydrogenases at the sites of coenzyme Q as well as cytochromes b and c in viable cells convert the yellow form of the salt to an insoluble intracellular purple formazan. Solubilized formazan can then be quantitated spectorophotometrically.Squamous cell carcinoma cell lines which we established from oral cancer patients were used throughout the experiments. A linear relationship between the number of viable tumor cells, 0.625×104-1×104 cells/well, and absorbance at 590nm was established. With cell numbers over 2×104 cells/well, this relationship no longer existed, and this necessitated adjusting the number of target tumor cells to 1×104 in the assay. The formazan formation reached plateau by 2h of culture period. The assay was so sensitive that it could distinguish the fine sensitivities of various SCC sublines to an anti-cancer drug. By using a multititer plate, the assay can be used to readily test a large number of samples with much easier and less expensive technique. It also exhibits high sensitivity and reproducibility.All of these results indicate that chemosensitivity tests by MTT assay are useful for screening oral cancers.