IC50: Necrostatin-1 (Nec-1), (R)-5-([7-chloro-1H-indol-3-yl]methyl)-3-methylimidazolidine-2,4-dione (Nec-1a) (Figure 1A) (Degterev et al., 2008), exhibited an inhibitory constant (IC50) of 0.32 mM for RIP1 [1].

Necroptosis is a cellular mechanism of necrotic cell death induced by apoptotic stimuli in the form of death domain receptor engagement by their respective ligands under conditions where apoptotic execution is prevented. Necrostatin-1, identified as a small-molecule inhibitor of necroptosis, is also a selective allosteric inhibitor of the death domain receptor–associated adaptor kinase RIP1.

In vitro: Previous study indicated that necrostatin-1 was a selective allosteric inhibitor of the death domain receptor–associated adaptor kinase RIP1 in vitro. In this study, RIP1 was found to be the primary cellular target responsible for the antinecroptosis activity of necrostatin-1. In addition, two other necrostatins, necrostatin-3 and necrostatin-5, were also shown to target the RIP1 kinase step in the necroptosis pathway, but through different mechanism compared with that of necrostatin-1. The findings established necrostatins as the first-in-class inhibitors of RIP1 kinase, the key upstream kinase involved in the activation of necroptosis [2].

In vivo: A previous study was designed to investigate the protective effects and mechanisms of Nec-1 in concanavalin A-induced hepatitis in mice. It was found that in Nec-1-treated mice the amelioration in liver functions and histopathological changes and the suppression of inflammatory cytokine production were observed. Western blotting analyses showed that the expression of TNF-α, IFN-γ, IL2, IL6, and RIP1 was significantly reduced in the Nec-1-treated mice, which was further confirmed by immunofluorescence and immunohistochemistry. In addition, autophagosome formation was significantly reduced by Nec-1 treatment. These results indicated that Nec-1 could prevent concanavalin A -induced liver injury via RIP1-related and autophagy-related pathways [3].

Clinical trial: Up to now, Necroptosis is still in the preclinical development stage.