Poly(ADP-ribose) polymerase (PARP) enzymes, including PARP1, PARP2, and PARP3, play a role in normal cellular functions such as DNA transcription and repair of single-strand DNA breaks. Inhibition of PARPs alone is not lethal because DNA lesions can be repaired by other DNA repair pathways, specifically homologous recombination repair (HRR). Conversely, BRCA1 and BRCA2 proteins are crucial for the accurate repair of double-strand DNA breaks through the HRR pathway. Consequently, cancer cells deficient in BRCA1 and BRCA2 are hypersensitive to PARP inhibitors. Olaparib inhibits PARPs and has been shown to inhibit the growth of select cancer cell lines in vivo and in vitro. In vitro studies have demonstrated that olaparib-induced cytotoxicity may involve inhibition of PARP enzymatic activity and increases the formation of PARP-DNA complexes, resulting in DNA damage and cancer cell death. (The product is for research use only.)