The MTT assay to evaluate chemosensitivity.

The assessment of the degree or rate of cellular proliferation and cell viability is critical to the assessment of the effects of drugs, antibodies, or cytokines on both normal and malignant cell populations. This can be accomplished by either direct or indirect counting methods. Direct counting by manual or automated methods, using a hemacytometer or particle counter, respectively, allows for serial cell counting at multiple time points, but these are low-throughput approaches. High-throughput and robust alternatives to direct counting utilize either radiotracers (e.g., 3H-thymidine) or dye compounds, which can be adapted to multiwell culture plate formats. This chapter focuses on the use of tetrazolium-type indicator dyes, of which the compound 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) has been the most widely utilized. Newer tetrazolium dyes that yield water-soluble products and offer added flexibility, increases in sensitivity, and fewer steps, which are offset by increased costs, are also covered.