Measurement of cell viability by the MTT method is commonly used to assay cell survival during apoptosis. This method was originally described to measure cell proliferation in cytotoxic assays.
11 It has been very widely used in drug screening and drug sensitivity testing for various tumor cell lines. 27 The main advantage of this assay is that it is a rapid and quantitative (colorimetric) method to measure the number of surviving cells. This assay is based on the ability of live cells to reduce a light yellow compound, MTT, into a dark blue product, formazan MTT, that is quantitated spectrophotometrically by absorbance measurement at 570 nm. 11 The cellular reduction of MTT is now believed to occur both in the mitochondria by the enzyme succinate dehydrogenase and also extra-mitochondrially involving the pyridine nucleotide cofactors, NADH and NADPH.28