Small-molecule collection and high-throughput colorimetric assay to identify PARP1 inhibitors.

During the last few years, poly(ADP-ribose)polymerase (PARP) proteins became a very popular target for anticancer treatment. Many PARP inhibitors have been generated and tested by pharmacological industry. However, most of them were designed to disrupt the DNA-dependent PARP1 protein activation pathway and were based on a competition with NAD for a binding site on PARP molecule and, therefore, on disruption of PARP-mediated enzymatic reaction. This limitation resulted in a discovery of mainly nucleotide-like PARP1 inhibitors which may target not only PARP, but also other pathways involving NAD and other nucleotides. Here, we describe a strategy for the identification of PARP inhibitors that target a different pathway, the histone H4-dependent PARP1 activation. Besides the identification of NAD competitors in a small-molecule collection, this approach allows finding novel classes of PARP inhibitors that specifically disrupt H4-based PARP activation.