Every morning of his life, no matter what he did, a young British man woke up with a fever, a headache, a rash on his trunk and limbs, joint pain, and ever-worsening deafness. His doctors had diagnosed him with a rare illness called Muckle-Wells syndrome, in which chronic inflammation rages out of control; no treatment had been able to cure his symptoms.

Then, in 2001, researchers in California discovered the genetic explanation for his disease: a mutation in a gene called CIAS1 (since renamed NALP3 and then NLRP3), which was later found to cause the resulting protein to be constantly activated. Around the same time, a group of scientists at the University of Lausanne in Switzerland found that NALP1/NLRP1, a protein from the same family, forms a large intracellular complex called an inflammasome, which helps generate the IL-1β cytokine, triggering a cascade of inflammation. Taken together, the findings suggested that in Muckle-Wells, inflammasomes made with NLRP3 instead of NLRP1 were constantly forming and could be producing huge amounts of IL-1β, causing the man’s illness. So researchers Philip Hawkins of the Royal Free Hospital and University College Medical School (now UCL Medical School) and Michael McDermott of St. Bartholomew’s and the Royal London School of Medicine (he’s now at the University of Leeds) gave the man an existing arthritis drug called anakinra (Kineret), which blocks the IL-1 receptor. 

There’s obviously a whole portfolio of indications where inhib­iting the inflammasome could make a lot of sense.

—Guido Junge, Novar­tis Institutes for BioMedical Research

By the time the man received treatment in 2002, at 22 years old, “he had experienced fever, flu-like symptoms for his entire life, that was his normalcy, he didn’t know what it is to feel well,” recalls Fabio Martinon, who helped discover the NLRP1 inflammasome when he was a PhD student in the late Jürg Tschopp’s lab at Lausanne. “When they started to inject him with the anti–IL-1 drug, within [a] few hours the skin rashes on his body were gone, the fever was gone—that was kind of a game-changer and kind of spectacular.” Martinon, now faculty at the university, later helped confirm that elevated NLRP3 inflammasome activity had indeed caused the British man’s symptoms. 

Fast forward almost two decades from the man’s treatment, and the field of inflammasome research is booming. Studies in animals have suggested that the NLRP3 inflammasome’s impact can be felt far beyond rare genetic diseases such as Muckle-Wells. Microparticles that accumulate in tissue as a result of modern Western lifestyles and longer lives may activate the NLRP3 inflammasome, stoking inflammation and exacerbating or even causing dozens of diseases of aging and lifestyle, from Alzheimer’s disease and cancer to type 2 diabetes and cardiovascular disease. 

These developments have attracted the interest of biotech companies, too. Unlike the injected IL-1 receptor blockers that the British man received, which can dampen broader immune responses needed to fight infection, NLRP3 inhibitors could be taken orally and only inhibit NLRP3-mediated inflammation, offering a more practical, more effective, and safer therapy. Since 2016, several small pharmaceutical companies have developed targeted NLRP3 inhibitors, and in the past year, large companies have scooped up those smaller companies in huge deals or have started developing inhibitors of their own. Torreya Capital’s Biopharmaceutical Sector Update Market Outlook ranked “Inflammasome Science” as one of the top five biopharma events of 2020.

While no NLRP3-targeting drugs have hit the market just yet, “the science is unequivocal,” says Kate Schroder, an inflammasome researcher at the University of Queensland in Australia and one of the co-inventors on inflammasome inhibitor patents originally licensed to the Ireland-based company Inflazome (since acquired by Roche). “It’s really clear that this is an important pathway for human health, and if we can drug it, we will be able to improve a whole bunch of different diseases, some of which are diseases for which we don’t have any disease-modifying drug.”

The inflammasome’s early days

In the years since the discovery of the NLRP1 inflammasome in 2001, researchers have learned that there are up to 15 types of inflammasomes (though only eight are well established), each responding to a unique danger signal. Most of these complexes, including the NLRP1, NLRC4, and AIM2 inflammasomes, can be activated by pathogens. NLRP3, by contrast, seems to be activated primarily in the presence of accumulated intracellular debris, including cholesterol crystals (which lead to atherosclerosis), amyloid-β particles (which are associated with Alzheimer’s disease), and tobacco smoke particulates (which contribute to lung disease), among others. 

Although the precise mechanisms are still unclear, scientists have established the basics of how individual NLRP3 proteins come together to create an NLRP3 inflammasome. First, phagocytosing white blood cells such as macrophages engulf particles or crystals, which damage these cells’ plasma and lysosomal membranes. This causes potassium ions to move out of the macrophages, which in turn activates individual NLRP3 proteins in those cells. Once active, each NLRP3 associates with several others, forming a snowflake shape; then, so-called adaptor proteins assemble into long filaments that dangle from the NLRP3 wheel, resulting in a huge protein complex: the NLRP3 inflammasome can be the size of one of the cell’s organelles. 

“They’re quite beautiful,” says Matt Cooper, a chemist at the University of Queensland. “It looks a bit like a Doric column with a starfish on the top.” On the surface of this complex, pairs of caspase-1 enzymes bind to each other, become active, and cleave precursor molecules for IL-1β and IL-18, transforming them into their mature inflammatory forms, which are then secreted from the cell. Caspase-1 also processes other compounds that trigger a form of inflammatory cell death known as pyroptosis.

“NLRP3’s major role is to sense things like particles and crystals that need to be digested by the body, but which one cell can’t cope with,” says Schroder. “It makes sense for that cell to ring the alarm by triggering IL-1 production, which recruits new cells to the site of the crystals or particles so you have a whole bunch of phagocytes to clean up the mess.” Disease can result, she suggests, when there are so many of these particles that they keep activating NLRP3 in new cells even after the previous cells die, relentlessly ramping up inflammation. 

INFLAMMATION ON TRIAL

Various companies, several of which have now been acquired, are investigating the effects of inhibiting NLRP3 inflammasomes.

Company

Drug(s)

Disease

Trials

Inflazome

Dublin, Ireland (acquired by Roche in 2020)

Inzomelid, Somalix

Cryopyrin-associated periodic syndrome (CAPS) and others

Both drugs have completed Phase 1 trials. Inzomelid completed Phase 1b in people with CAPS.

NodThera 

Cambridge, UK; Seattle; and Boston

NT-0167

(two additional candidates moving to clinical trials soon)

Liver and lung fibrosis, neurodegenerative diseases

Completed Phase 1

IFM Tre

Cambridge, Massachusetts (acquired by Novartis in 2019)

IFM-2427 (DFV890)

COVID-19 plus others

Completed Phase 1 and Phase 2 in COVID-19 patients with pneumonia (no results released yet)

Olatec Therapeutics

New York City

Dapansutrile (OLT1177)

Heart failure, gout, COVID-19, melanoma

Completed Phase 1 and Phase 1b in patients with heart failure and Phase 2a in patients with acute gout flares. A Phase 2 trial for people with moderate COVID-19 symptoms is ongoing, and the company is planning a Phase 2 trial in late-stage melanoma, along with an approved immunotherapy.

Drugging the inflammasome

For years after the inflammasome’s initial discovery, the search for drugs that target it yielded no promising leads, Cooper says. “Big pharma all went and screened their libraries of drugs and said, can we find an inhibitor? But no one could.” 

Several years ago, that began to change. Luke O’Neill, an immunologist at Trinity College Dublin, was one of the people searching for an NLRP3 inhibitor, with colleagues at his company Opsona. He knew that a scientist named Chris Gabel had been working at Pfizer in the late 1990s on a molecule called CRID3, which appeared to block IL-1β production. O’Neill was intrigued and in 2012 teamed up with Cooper to study the compound. They were eventually able to show that CRID3, which the team renamed MCC950, was a highly selective and potent inhibitor of NLRP3. Together with Schroder’s group and others, the researchers filed patents and published a paper on the compound in 2015 in Nature Medicine

Soon, independent teams of researchers began showing that MCC950 improved symptoms and biomarkers of disease in animal models of Alzheimer’s, atherosclerosis, asthma, inflammatory bowel disease, stroke, and many other conditions. In a rodent model of Parkinson’s disease, for example, inhibiting NLRP3 with MCC950 protected against neurodegeneration and reversed the animals’ motor deficits.

Meanwhile O’Neill and Cooper set out to raise venture capital to create the company Inflazome, based on the work their teams had done on MCC950 and derivatives. But it wasn’t easy. “Back then, people thought you were making it up. Like, it can’t possibly be true that one protein can mediate all these different diseases,” says Schroder, who met in 2015 and 2016 with potential investors to explain inflammasome biology. In the end, though, Fountain Healthcare Partners, headquartered in Ireland, and Novartis Venture Funds provided Inflazome with $17 million in series A funding, and Cooper moved to Dublin to be CEO, with O’Neill as chief scientific officer (CSO).

ARTWORK REPRODUCED WITH PERMISSION FROM PROFESSOR KATE SCHRODER, THE UNIVERSITY OF QUEENSLAND

It looks a bit like a Doric column with a starfish on the top.

—Matt Cooper, University of Queensland

Delving more into MCC950’s mechanism of action, Schroder’s lab, along with another group, recently determined that the compound inhibits NLRP3 by directly binding with a particular protein domain in a way that prevents NLRP3 from opening up into its active form. Although it worked well in animals, MCC950 raised blood levels of a liver enzyme in early human trials, so the team instead used it as a starting point to develop new compounds. 

By the time they sold Inflazome to Roche last fall, the researchers had developed two drugs, Inzomelid (for diseases of the brain such as Alzheimer’s and Parkinson’s) and Somalix (for diseases in the rest of the body). Both have completed Phase 1 clinical trials for safety and tolerability, and Inzomelid also showed positive results in a small Phase 1b trial in patients with cryopyrin-associated periodic syndrome (CAPS), a group of diseases (including Muckle-Wells syndrome) in which mutations cause NLRP3 to be activated all the time. Last July, the US Food and Drug Administration (FDA) granted Inzomelid orphan drug status for the treatment of CAPS. A few months later, Roche bought the company and its portfolio of NLRP3 inhibitors for 380 million euros ($451 million), plus additional milestone payments. 

O’Neill and Cooper weren’t the only ones looking to commercialize drugs that target the NLRP3 inflammasome. New York–based Olatec Therapeutics, for example, had been working since 2011 on a compound called dapansutrile that later turned out to be a selective NLRP3 inhibitor, and in 2016, several companies used the Nature Medicine paper to launch searches for their own inhibitors based on MCC950’s structure. Like Olatec, NodThera (where Chris Gabel is now VP of Biology), IFM Tre (recently bought by Novartis), and others have now moved compounds into Phase 1 trials; some companies already have Phase 2 trials underway. (See table “Inflammation on Trial” above.) 

“This is truly the new frontier,” says Charles Dinarello, a professor at the University of Colorado School of Medicine and co-CSO and chairman of the Scientific Advisory Board at Olatec; the company’s compound dapansutrile recently advanced through early-stage trials for heart failure and acute gout flares, and will also be studied in late-stage melanoma patients. “Now the big challenge is to go further, crossing into cancer with a safe-in-humans nontoxic drug.” Olatec and, separately, Novartis are even testing their respective drugs as possible treatments for COVID-19. (See “NLRP3 and COVID-19” below.)

Too good to be true?

While inhibiting NLRP3 in humans seems promising to the researchers who spoke with The Scientist, more late-stage clinical data are needed to demonstrate that NLRP3 inhibitors can halt the progression of various diseases of aging and lifestyle. “There is a small issue here: there are very few studies in humans on NLRP3 and the inflammasome. Most come from mice,” says inflammasome discoverer Martinon, who has no stake in any company. “Clearly there are differences in the regulation and the role of these proteins in [mice] and humans. So we will see what the clinical trials will tell us in humans.” Larger trials could also provide more information about possible toxicities. 

Martinon notes too that scientists still don’t have a complete understanding of the precise molecular structure of the enormous inflammasome complex, making mechanistic studies challenging. “We still don’t really understand how it gets activated,” he says. Studies also suggest that NLRP3 inflammasomes play a role in adaptive immunity, an effect that needs to be further studied.

Still, most inflammasome researchers are extremely hopeful. “There’s obviously a whole portfolio of indications where inhibiting the inflammasome could make a lot of sense,” says Guido Junge, who oversees inflammasome clinical activities at Novartis Institutes for BioMedical Research. 

Schroder agrees. “It may not be our compounds that get to the clinic first, or it may not be our compounds that get to the clinic at all,” she says. “But there are so many different compounds out there now that are being developed by so many different companies to inhibit NLRP3. As long as some of them get out into the clinic, I’ll be delighted because it’s all about helping the patients in the end.” 

NLRP3 and COVID-19 

One of the most dangerous phases of infection with SARS-CoV-2 is thought to be when the immune system launches an inflammatory over-reaction called a cytokine storm, releasing a blast of cytokines into the bloodstream that can damage organs and may eventually kill the patient.

Damaris Skouras, founder and CEO of New York–based Olatec Therapeutics, says that early in the pandemic, one of the first things the data revealed globally was the various comorbidities that increase risk of hospitalization and death: high BMI, diabetes, cardiovascular or pulmonary disease, and older age, among others. She says that research has already established that the ill effects associated with many of these conditions are modulated by dysregulated IL-1β inflammation, which is then exacerbated by SARS-CoV-2 infection. Olatec’s co–Chief Scientific Officer Charles Dinarello, for example, showed activation of NLRP3 and associated inflammation in blood samples from patients early in the course of infection with SARS-CoV-2.  

Two companies have launched Phase 2 trials with NLRP3 inhibitors to treat COVID-19 patients. In January, Novartis completed its randomized, controlled, open-label multicenter study using its compound DFV890 on 143 patients infected with SARS-CoV-2 and suffering from pneumonia and impaired respiratory function. A Novartis spokesperson says in an emailed statement that the company is analyzing the data now.

Olatec has a Phase 2 randomized, double-blind, placebo-controlled trial on the safety and efficacy of dapansutrile for COVID-19 patients early in disease progression and not sick enough to be hospitalized. Launched last December, the trial has a target of 80 subjects and aims to test if dapansutrile will inhibit IL-1β and head off the cytokine storm. “We are addressing an unmet need for an ambulatory treatment for those most at risk to keep them out of the hospital, keep them safe, keep them at home,” says Skouras, “and most important, keep them from progression into severe COVID.”

Rachael Moeller Gorman is a science writer based outside Boston.