Niraparib (MK-4827) is a selective inhibitor of PARP1/2 with IC50 of 3.8 nM/2.1 nM, with great activity in cancer cells with mutant BRCA-1 and BRCA-2. It is >330-fold selective against PARP3, V-PARP and Tank1. Niraparib can form PARP–DNA complexes resulting in DNA damage, apoptosis, and cell death. Phase 3.