In this study, we develop a new breast cancer cell-based enzymatic assay as the output to identify small-molecule drugs that increase the activity of FOXO3 by screening a druggable library of known compounds that have been approved by the Food and Drug Administration (FDA) because it has been suggested that the most fruitful basis for the discovery of a new drug is to seek new uses for old drugs [29]. Here, FOXO3 is linked to breast cancer.