Discovery and validation of a novel class of necroptosis inhibitors targeting RIPK1.

Necroptosis is a form of programmed cell death that, when dysregulated, is associated with cancer and inflammatory and neurodegenerative diseases. Here, starting from hits identified from a phenotypic high-throughput screen for inhibitors of necroptosis, we synthesized a library of compounds containing a 7-phenylquinoline motif and validated their anti-necroptotic activity in a novel live-cell assay. Based on these data, we designed an optimized photoaffinity probe for target engagement studies and through biochemical and cell-based assays established receptor-interacting kinase 1 (RIPK1) as the cellular target, with inhibition of necroptosis arising from the prevention of RIPK1 autophosphorylation and activation. X-ray crystallography and mass spectrometry revealed that these compounds bind at the hinge region of the active conformation of RIPK1, establishing them as type I kinase inhibitors. In addition, we demonstrated in vitro synergy with type III kinase inhibitors, such as necrostatin-1 and found that lead compounds protected mice against acute inflammation in necroptosis models in vivo. Overall, we present a novel pharmacophore for inhibition of human RIPK1, a key protein involved in necroptosis, and provide a photoaffinity probe to explore RIPK1 target engagement in cells.