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OP0090 The human safe NLRP3 inflammasome inhibitor OLT1177 suppresses joint inflammation in murine models of experimental arthritis

Background NLRP3 is an essential component of the inflammasome, an intracellular macromolecular complex, which activates caspase-1 for the processing and release of active IL-1β and IL-18. Activation of the NLRP3 inflammasome takes place in inflammatory joint diseases, including gout. Although inhibition of IL-1β with either the IL-1 receptor antagonist anakinra or canakinumab, a neutralizing monoclonal antibody for IL-1β is highly effective for reducing the gout flares, a clinical need remains for a safe, oral treatment of recurrent gout flares refractory to standard of care. The small orally active and safe β-sulfonyl nitrile molecule OLT1177 is a specific inhibitor of the NLRP3 inflammasome, and currently being evaluated in a Phase 2 study for the treatment of acute gout flares. Objectives To investigate the anti-inflammatory effect of NLRP3 inflammasome inhibitor OLT1177 in mouse models of acute joint inflammation. Methods Two models of experimental arthritis were used in mice: zymosan- and monosodium urate (MSU)-induced arthritis. Knee joints of male C57BL/6 mice were injected intraarticularly with 180 μg heat-killed Zymosan or 300 μg of monosodium urate (MSU) crystals mixed with 200 μM C16.0 fatty acid and bovine serum albumin. Joints were assessed 24 and 4 hours after the zymosan or MSU/C16.0 injection, respectively, for clinical, histological and cytokine analyses. Results Intraarticular Zymosan induced a severe joint swelling with neutrophil infiltration, high levels of synovial IL-1β, IL-6 and the neutrophil chemokine CXCL1. Treatment with OLT1177 induced reduction of joint swelling and neutrophil infiltration (P<0.0001 and P=0.006 respectively) and suppression of IL-1β and IL-6 by 55% and CXCL1 by 30% compared to mice treated with the vehicle. Four hours following intra-articular injection of MSU crystals, an elevated clinical score for knee joint inflammation was observed in vehicle-treated mice (Fig. 1). Oral treatment with OLT1177 showed reduction in joint inflammation as depicted in Fig. 1a when compared to the vehicle group (P<0.0001). Histological analysis of the knee revealed suppression of the influx of inflammatory cells in the articular space with OLT1177 treatment (P<0.05; Fig. 1b). Treatment with OLT1177 showed significant reduction in synovial tissue extracts for IL-1β (69%; P<0.001; Fig. 1c); IL-6 (70%; P<0.001); CXCL1 (75%; P<0.001; Fig.1d) and MPO (39%; P=0.006; Fig. 1e). Mice were also treated with a single dose of OLT1177 1 hour after of intraarticular MSU and reduced joint swelling and IL-1β levels (P<0.05) were observed. OLT1177 treatment suppressed activation of the mitogen-activated protein kinases (MAPK) family, c-jun N-terminal kinase (JNK), which is implicated in the pathophysiology of rheumatoid arthritis and gout (Fig. 1f). Conclusions The orally active molecule OLT1177 is a potent inhibitor of IL-1β-driven inflammatory arthritis, particularly in a model of acute gout. Considering the outstanding safety profile in humans, OLT1177 is a potential therapeutic strategy to target NLRP3-driven IL-1β-mediated disorders. Disclosure of Interest C. Marchetti: None declared, B. Swartzwelter: None declared, M. Koenders: None declared, C. Dinarello Grant/research support from: Charles A. Dinarello serves on the Scientific Advisory Board of Olatec and receive compensation, L. Joosten Grant/research support from: Leo A. B. Joosten serves on the Scientific Advisory Board of Olatec and receive compensation