Inhibition of synergy between NOD2 & TLR signaling pathways underlies the profound efficacy of RIP2 kinase inhibitors in models of inflammatory bowel disease (INM6P.415)

Abstract Loss of intestinal epithelial barrier integrity in inflammatory bowel disease (IBD) leads to aberrant interaction between commensal bacteria and mucosal immune cells. This triggers inflammation via activation of pattern recognition receptor (PRR) signaling pathways. Which PRR signaling complexes are critical in mediating disease pathogenesis remains to be elucidated. Our recent studies have shown that selective and potent inhibitors of RIP2 kinase, the signaling partner of NOD1 and NOD2, can dramatically reduce murine TNBS-induced colitis and the spontaneous release of proinflammatory cytokines in cultured intestinal biopsies from IBD patients. The striking magnitude of the inhibition observed led us to interrogate the effect of these inhibitors on the modulation of crosstalk between NOD1/2 and other PRRs. Using human PBMCs we defined conditions for observing synergistic cytokine release (TNF-α, IL-6) in response to combinations of NOD2 and either TLR2, TLR4, or TLR5 ligands. In each instance, selective inhibition of RIP2 kinase activity robustly blocked synergistic cytokine release, but had little or no effect on TLR ligand alone induced cytokine production. These results suggest that RIP2 kinase inhibitors are likely to have profound anti-inflammatory effects in situations where multiple PRRs are being stimulated simultaneously, and illustrate the potential of RIP2 inhibitors as therapeutics for the treatment of human inflammatory diseases.