The receptor-interacting serine/threonine protein kinase 1 (RIPK1) is a key mediator of regulated cell death and inflammation. RIPK1 inhibition would fundamentally improve the therapy of RIPK1-dependent organ damage in stroke, myocardial infarction, kidney failure, and systemic inflammatory response syndrome[1]. RIPK1 comprises an N-terminal kinase domain, an intermediate domain, and a C-terminal death domain, and the kinase domain is the direct target of Nec-1s[2]. Necrostatin-34 is a RIPK1 kinase inhibitor, stabilizing RIPK1 kinase in an inactive conformation by occupying a distinct binding pocket in the kinase domain. Nec-34 showed no significant inhibition against commercially available RIPK2, RIPK3,RIPK4 and RIPK5 at 10 μM, while the RIPK1 kinase activity was effectively blocked by Nec-34 at the same concentration in both biochemical and cellular assays. Nec-34 had no effect on the recruitment and ubiquitination of RIPK1 or the recruitment of TRADD, Sharpin or IKKα/β in complex I, whereas RIPK1 kinase activation, indicated by p-S166 RIPK1, was strongly blocked by Nec-34, as by Nec1s.Necrostatin-34 (10 μM) inhibits the dimerization-induced RIPK1 activation as examined by phosphorylation of Ser166 (p-S166) of RIPK1, a biomarker for RIPK1 activation. Necrostatin-34 may block TNFα-induced complex II formation by inhibiting the activation of RIPK1 kinase. Necrostatin-34 shows IC50 values of 667 nM and 134 nM for TNFα in FADD def-Jurkat cells and L939 cells, respectively. Nec-34 was about 10-fold more potent in inhibiting necroptosis of murine cells than that of human cells[3].
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