Poly(ADP-ribose) polymerases (PARPs) are activated by DNA single- and double-strand breaks and promote repair of DNA damage through the relaxation of chromatin and recruitment of other repair proteins. Inhibition of PARP activity has been linked to synthetic lethality in cells with mutations in BRCA1 or BRCA24 and is used as a therapeutic strategy to selectively target cancers. Rucaparib is a potent, cell-permeable inhibitor of PARP-1 (Ki = <5 nM) that is used in clinical therapy to sensitize cancer cells to chemotherapy. Rucaparib inactivates PARP activity in cells with homologous recombination DNA repair pathway mutations at LC50 values ranging from 1.3-5. μM.7 At 25 mg/kg, rucaparib arrests tumor growth in mice bearing epigenetically silenced BRCA1 UACC3199 xenograft tumors. It has been shown to increase efficacy of temozolomide in medulloblastoma cells and xenografts. Rucaparib (phosphate) is the phosphate salt of rucaparib (Item No. 15643) and has improved aqueous solubility.