Sodium succinate enhances the colorimetric reaction of the in vitro chemosensitivity test: MTT assay.

We compared the colorimetric reactions between the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl 2H-tetrazolium bromide (MTT) assay and the succinate dehydrogenase inhibition (SDI) test, in order to evaluate the usefulness of the SDI test for in vitro chemosensitivity testing. The addition of sodium succinate enhanced the colorimetric absorbance at 565 nm in the MTT assay in a dose- and a time-dependent manner, in mouse sarcoma-180 (S-180) cells. At 10 microM of sodium succinate, a dose used in the SDI test, the absorbance of the MTT assay increased by about 2.5-fold in the S-180 cells and in 10 human tumor tissues. The absorbance in the SDI test correlated well with the viable cell number of S-180 cells (r = 0.9993). These results show that the SDI test, using MTT as a tetrazolium salt, has a higher sensitivity for predicting cell viability, compared to the MTT assay.