Developing predictive assays: The phenotypic screening “rule of 3”

Phenotypic drug discovery approaches can positively affect the translation of preclinical findings to patients. However, not all phenotypic assays are created equal. A critical question then follows: What are the characteristics of the optimal assays? We analyze this question and propose three specific criteria related to the disease relevance of the assay—system, stimulus, and end point—to help design the most predictive phenotypic assays.