Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase-1 (COX-1) and COX-2 enzymes. The NLRP3 inflammasome is a multi-protein complex responsible for the processing of the proinflammatory cytokine interleukin-1β and is implicated in many inflammatory diseases. Here we show that several clinically approved and widely used NSAIDs of the fenamate class are effective and selective inhibitors of the NLRP3 inflammasome via inhibition of the volume-regulated anion channel in macrophages, independently of COX enzymes. Flufenamic acid and mefenamic acid are efficacious in NLRP3-dependent rodent models of inflammation in air pouch and peritoneum. We also show therapeutic effects of fenamates using a model of amyloid beta induced memory loss and a transgenic mouse model of Alzheimer's disease. These data suggest that fenamate NSAIDs could be repurposed as NLRP3 inflammasome inhibitors and Alzheimer's disease therapeutics.

Inflammasomes are high molecular weight complexes that sense and react to injury and infection. Their activation induces caspase-1 activation and release of interleukin-1β, a pro-inflammatory cytokine involved in both acute and chronic inflammatory responses. There is increasing evidence that inflammasomes, particularly the NLRP3 inflammasome, act as guardians against noninfectious material. Inappropriate activation of the NLRP3 inflammasome contributes to the progression of many noncommunicable diseases such as gout, type II diabetes, and Alzheimer's disease. Inhibiting the inflammasome may significantly reduce damaging inflammation and is therefore regarded as a therapeutic target. Currently approved inhibitors of interleukin-1β are rilonacept, canakinumab, and anakinra. However, these proteins do not possess ideal pharmacokinetic properties and are unlikely to easily cross the blood-brain barrier. Because inflammation can contribute to neurological disorders, this review focuses on the development of small-molecule inhibitors of the NLRP3 inflammasome.

SummaryNLRP3 is a receptor important for host responses to infection, yet is also known to contribute to devastating diseases such as Alzheimer's disease, diabetes, atherosclerosis, and others, making inhibitors for NLRP3 sought after. One of the inhibitors currently in use is 2-aminoethoxy diphenylborinate (2APB). Unfortunately, in addition to inhibiting NLRP3, 2APB also displays non-selective effects on cellular Ca2+ homeostasis. Here, we use 2APB as a chemical scaffold to build a series of inhibitors, the NBC series, which inhibit the NLRP3 inflammasome in vitro and in vivo without affecting Ca2+ homeostasis. The core chemical insight of this work is that the oxazaborine ring is a critical feature of the NBC series, and the main biological insight the use of NBC inhibitors led to was that NLRP3 inflammasome activation was independent of Ca2+. The NBC compounds represent useful tools to dissect NLRP3 function, and may lead to oxazaborine ring-containing therapeutics.

Inflammation is an established contributor to disease and the NLRP3 inflammasome is emerging as a potential therapeutic target. A number of small molecule inhibitors of the NLRP3 pathway have been described. Here we analysed the most promising of these inhibitor classes side by side to assess relative potency and selectivity for their respective putative targets. Assessed using ASC inflammasome-speck formation, and release of IL-1β, in both human monocyte/macrophage THP1 cells and in primary mouse microglia, we compared the relative potency and selectivity of P2X7 inhibitors, inflammasome inhibitors (diarylsulfonylurea vs. the NBC series), and caspase-1 inhibitors. In doing so we are now able to provide a well characterised small molecule tool kit for interrogating and validating inflammasome-dependent responses with a range of nanomolar potency inhibitors against established points in the inflammasome pathway.