has mode of action has percent response based on normalization percent inhibition normalization cytotoxicity CC50 The effective concentration of a cytotoxic compound, which produces 50% of the maximum possible cell death for that compound. Although the cytotoxic compound induces cell death, we define CC50 as subclass of IC50, because critical cellular processes are inhibited and CC50 is often used as a more specific description of IC50 for cell toxicity assays. Compound cytotoxicity is an important parameter to measure when developing potential human therapeutics. Cytotoxicity can be determined for example as a measure of radioisotope (3H thymidine or 51Cr) release, lactate dehydrogenase release from damaged cells, tetrazolium salt and alamar blue reduction, fluorescent dyes that selectively stain live or dead cells, or decrease in ATP content. ATP levels are detected using a luminescence based assay kit such as CellTiter-Glo (Promega). ATP values higher than controls (untreated cells) indicate proliferation and cultures with ATP concentrations lower than controls indicate cytotoxicity. 50 percent cytotoxicity concentration response endpoint