In this study, a drug repurposing approach using the National Institutes of Health Chemical Genomics Center (NCGC) Pharmaceutical Collection (NPC) [39], a library containing drugs approved for clinical use or that have been in clinical trials, was used to identify drugs that amplify the ability of AG14361, a potent PARP1 inhibitor [21], to inhibit the growth of both human and mouse breast cancer cells, irrespective of their BRCA1 status. The gene discussed is BRCA1; the disease is breast cancer.