Fatal influenza A virus (IAV) infections in humans, such as those resulting from spill over of virus from birds, are associated with excessive production of pro-inflammatory cytokines. Since 2013, avian H7N9 IAV have infected humans with over 1500 confirmed cases (30% mortality). Furthermore, the 2017 flu season resulted in 2.5 times more cases of influenza infection than the previous year, which has been associated with low vaccine efficacy. There are currently no effective drugs that can be used to dampen excessive immune responses observed in patients who present with severe disease.
We have previously identified using the small molecule inhibitor MCC950 that the NLRP3 inflammasome plays a role in promoting excessive inflammation during severe IAV infection (Tate et al 2016). We endeavoured to identify existing drugs that have well documented safety profiles that could target the NLRP3 inflammasome pathway. Probenecid is a drug that is FDA approved for the treatment of gout and AZ11645373 has undergone a range of clinical trials for inflammatory diseases. Both drugs have been shown to inhibit the P2X7 receptor which detects extracellular ATP leading to NLRP3 activation.
Our studies have confirmed that probenecid and AZ11645373 inhibit NLRP3 inflammasome responses in vitro, in a dose-dependent manner. Importantly, intranasal treatment of mice with probenecid or AZ11645373 every 48 hours from day 1 or 3 following infection with a high dose of HKx31 (H3N2), delayed the onset of disease. In particular, mortality was reduced from 100% to 40% when probenecid treatment was commenced on day 1 post-infection. Our findings suggest that drugs that are safe and inhibit P2X7 could be repurposed as quick, cheap and effective treatments for seasonal and pandemic influenza infections.