Niraparib (MK-4827) is a selective inhibitor of PARP1 and PARP2 with IC50 of 3.8 nM and 2.1 nM, respectively. MK 4827 inhibited PARP activity with an EC50 of 4 nM, and inhibited proliferation of brCA-1 and BRCA-2 mutated tumor cells in a CC50 range of 10-100 nM. Inhibits cell repair of DNA damage.

Niraparib  is an orally active small molecule PARP inhibitor developed by Tesaro to treat ovarian cancer.The drug is approved by the US FDA for the maintenance treatment of adult patients with recurrent epithelial ovarian, fallopian tube, or primary peritoneal cancer who are in complete or partial response to platinum-based chemotherapy.