PARP

PARP inhibitors block poly(ADP-ribose) polymerases (PARPs), enzymes that mark DNA damage and recruit repair proteins. PARP1 and PARP2 bind DNA single-strand breaks and attach poly(ADP-ribose) chains to themselves and to nearby chromatin proteins. Cells lacking breast cancer susceptibility proteins 1 or 2 (BRCA1, BRCA2), and therefore defective in homologous recombination, are highly sensitive to PARP inhibition. This synthetic lethal relationship, reported in 2005, has shaped much of the research on DNA repair inhibitors. Olaparib, niraparib, veliparib and talazoparib target the catalytic domains of PARP1 and PARP2, and 3-aminobenzamide is an early benzamide inhibitor. XAV 939 instead inhibits tankyrases 1 and 2 (TNKS1, TNKS2), which stabilizes axin in Wnt signaling studies.