Poly(ADP-ribose) polymerase inhibitors are a large number of low molecular weight compounds (NAD+ analogues) that competitively inhibit PARP activity. Among the first to be described were nicotinamide, benzamide, and 3-aminobenzamide. However, their potency and specificity is rather low. Subsequently, more sophisticated new compounds have been developed such as 4-amino-1,8-naphthalimide, 3,4-dihydro-5-methoxyisoquinolin-1(2H)-one (PD 128763), 8-hydroxy-2-methylquinazolin-4(3H)-one (NU1025), or 2-methylbenzimidazole-4-carboxamide (NU1064), to name but a few. These are much more potent than the first-generation inhibitors and possess an improved pharmacokinetic profile.
With respect to specificity, while all inhibitors inhibit PARP-1 (by definition), at least some of the first-generation inhibitors also interfered with other ADP-ribosyl transfer reactions, such as mono-ADP-ribosylation of proteins or NAD+ glycohydrolases, albeit at different IC50 levels. Furthermore, the novel...