Niraparib tosylate (MK-4827 tosylate) is an excellent PARP1 and PARP2 inhibitor with an IC50 of 3.8 and 2.1 nM, respectively.

Niraparib (MK-4827) inhibits PARP activity with EC50=4 nM and EC90=45 nM in a whole cell assay. MK-4827 inhibits proliferation of cancer cells with mutant BRCA-1 and BRCA-2 with CC50 in the 10?100 nM range. MK-4827 displays excellent PARP 1 and 2 inhibition with IC50=3.8 and 2.1 nM, respectively, and in a whole cell assay[1]. To validate that Niraparib (MK-4827) inhibits PARP in these cell lines, A549 and H1299 cells are treated with 1 μM Niraparib (MK-4827) for various times and measured PARP enzymatic activity using a chemiluminescent assay. The results show that Niraparib (MK-4827) inhibits PARP within 15 minutes of treatment reaching about 85% inhibition in the A549 cells at 1 h and about 55% inhibition at 1 h for the H1299 cells[2].

Niraparib (MK-4827) is well tolerated and demonstrates efficacy as a single agent in a xenograft model of BRCA-1 deficient cancer. Niraparib (MK-4827) is well tolerated in vivo and demonstrates efficacy as a single agent in a xenograft model of BRCA-1 deficient cancer. Niraparib (MK-4827) is characterized by acceptable pharmacokinetics in rats with plasma clearance of 28 (mL/min)/kg, very high volume of distribution (Vdss=6.9 L/kg), long terminal half-life (t1/2=3.4 h), and excellent bioavailability, F=65%[1]. Niraparib (MK-4827) enhances radiation response of p53 mutant Calu-6 tumor in both cases, with the single daily dose of 50 mg/kg being more effective than 25 mg/kg given twice daily[3].