MK-4827 is a novel, selective and orally bioavailable PARP1/PARP2 inhibitor with IC50 of 3.8 nM and 2.1 nM, respevctively.MK-4827 has shown great activity against cancer cells with mutant BRCA-1 and BRCA-2; >330-fold selective against PARP3, V-PARP and Tank1 [1].

Poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 belong to a family of enzymes (PARP) that, using β-NAD+as a substrate, catalyze poly(ADP-ribosyl)ation of proteins, synthesize and transfer ADP-ribose polymers onto glutamate, aspartate or lysine residues of acceptor proteins, modifying their functional properties. PARP inhibitors compete with NAD+ at the highly conserved enzyme active site, making them new potential therapeutic strategies as chemo- and radio-potentiation and for the treatment of cancers with specific DNA repair defects as single-agent therapies [2].

In vitro: MK-4827displayed excellent PARP 1 and 2 inhibition with IC50 of 3.8 and 2.1 nM, respectively. In a whole cell assay, MK-4827 inhibited PARP activity with EC50 of 4 nM. MK-4827 also inhibited proliferation of cancer cells with mutant BRCA-1 and BRCA-2 with CC50 in the 10-100 nM range[1].

In vivo: In a variety of human tumor xenografts of differing p53 status,MK-4827 showed high potential to improve the efficacy of radiotherapy,such as Calu-6 (p53 null), A549 (p53 wild-type [wt]) and H-460 (p53 wt) lung cancers and triple negative MDA-MB-231 human breast carcinoma [3].