Colorimetric Assays for Cytotoxicity

A comparison of WST-1 and SRB colorimetric assays

Cytoscan™ SRB assay is based on the sulforhodamine B dye assay that is reported to be a standard assay of the National Cancer Institute and National Institute of Health. SRB is a bright-pink aminoxanthene dye that binds to basic amino acids of cellular proteins under mild acidic conditions, and dissociates under basic conditions. SRB binding is stoichiometric and the amount of dye extracted from stained cells is directly proportional to the total protein mass and therefore correlated to cell number.

Cytoscan™ WST-1 assay is based on the metabolism of the water soluble tetrazolium salt (WST) 4-[3-(4-Iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate. Several other tetrazolium salts are used in cell proliferation and toxicity assays, including, but not limited to, MTT, XTT and MTS.

Significant differences may exist in the sensitivity of Cytoscan™ SRB and Cytoscan™ WST-1 assays as they utilize different labeling systems to assay cell proliferation and toxicity.

This application note compares the two colorimetric assays in the detection of cytotoxicity in fibroblasts initiated by apoptotic inducers.