Niraparib hydrochloride (MK-4827 hydrochloride) is a highly potent and orally bioavailable PARP1 and PARP2 inhibitor with IC 50 s of 3.8 and 2.1 nM, respectively. Niraparib hydrochloride leads to inhibition of repair of DNA damage, activates apoptosis and shows anti-tumor activity.