Auranofin Protects against Anthrax Lethal Toxin-Induced Activation of the Nlrp1b Inflammasome

Abstract

Anthrax lethal toxin (LT) is the major virulence factor for Bacillus anthracis. The lethal factor (LF) component of this bipartite toxin is a protease which, when transported into the cellular cytoplasm, cleaves mitogen-activated protein kinase kinase (MEK) family proteins and induces rapid toxicity in mouse macrophages through activation of the Nlrp1b inflammasome. A high-throughput screen was performed to identify synergistic LT-inhibitory drug combinations from within a library of approved drugs and molecular probes. From this screen we discovered that auranofin, an organogold compound with anti-inflammatory activity, strongly inhibited LT-mediated toxicity in mouse macrophages. Auranofin did not inhibit toxin transport into cells or MEK cleavage but inhibited both LT-mediated caspase-1 activation and caspase-1 catalytic activity. Thus, auranofin inhibited LT-mediated toxicity by preventing activation of the Nlrp1b inflammasome and the downstream actions that occur in response to the toxin. Idebenone, an analog of coenzyme Q, synergized with auranofin to increase its protective effect. We found that idebenone functions as an inhibitor of voltage-gated potassium channels and thus likely mediates synergy through inhibition of the potassium fluxes which have been shown to be required for Nlrp1b inflammasome activation.

A screen of approved drugs and molecular probes identifies therapeutics with anti–Ebola virus activity

“…We and others have investigated the utility of screening with approved drugs to identify potential therapeutics that can be used against EBOV and other biological threat agents or emerging diseases (43,(48)(49)(50). Often with such diseases, conventional drug development is challenging because of both cost and ability to perform controlled clinical studies.…”

“…Each compound was initially tested at one concentration targeted between the IC 50 and IC 90 concentrations obtained from the eight-point dose-response confirmation with eGFP-EBOV. Results of these VLP entry assays indicate that 25 of the 30 active compounds tested inhibited EBOV-VLP entry by >90% ( Table 2).…”

The Therapeutic Potential of Modifying Inflammasomes and NOD-Like Receptors

“…This novel strategy targets an allosteric site at the dimer interface of caspases by using small molecules that have better drug-like properties (MacKenzie et al, 2010). More recently the organogold compound auranofin was shown to prevent anthrax LT-mediated activation of the Nlrp1 and Nlrp3 inflammasomes, probably by direct inhibition of caspase-1 (Newman et al, 2011). Two protease inhibitors, ritonavir and disulfiram, were shown to inhibit caspase-1 activation and suggested to be useful in abrogating IL-18 release (Nobel et al, 1997;Sloand et al, 2000;Kast, 2008).…”

“…), which brings us back to P2X7R pharmacology. Alternatively, scattered evidence suggests that drugs inhibiting voltage-gated K + channels, i.e., idebenone, may also prevent inflammasome activation (Newman et al, 2011).…”

The role of inflammasomes in ischemic stroke - from pathophysiology to treatments

“…Therefore, inhibiting K + efflux or increasing K + concentrations in the extracellular environment may provide a strategy to inhibit NLRP1 and NLRP3 receptor activation. An experimental study provided evidence that inhibiting voltage-gated K + channels (using Idebenone) prevented NLRP1 receptor activation following anthrax lethal toxin treatment in mouse macrophages (Newman et al, 2011). In addition, an experimental study showed that glibenclamide, an orally active sulfonylurea receptor 1 (SUR1) inhibitor towards the regulatory subunit of ATP-sensitive K + channels (K + ATP ) used to treat Type 2 diabetes have shown a remarkable ability to inhibit caspase-1 activation, and processing and secretion of IL-1β from murine and human macrophages through an unknown mechanism independent of SUR1 inhibition (Lamkanfi et al, 2009).…”