New drug for schizophrenia could meet desperate need for better treatments
Schizophrenia is a debilitating mental health condition that affects around 24 million people worldwide. Patients experience hallucinations and delusions when they develop schizophrenia, with experts referring to these new thoughts and behaviors as positive symptoms. They also suffer from negative symptoms in which they lose important functions, suffering from dulled emotions, lack of purpose and social withdrawal.
Currently available drugs can control only a portion of these symptoms but, on August 8th, Karuna Therapeutics announced its completion of a phase 3 clinical trial that found a new drug called KarXT could treat both positive and negative symptoms of schizophrenia. It could mean substantial progress against a problem that has stymied scientists for decades.
A long-standing problem
Since the 1950s, antipsychotics have been used to treat schizophrenia. People who suffer from it are thought to have too much of a brain chemical called dopamine, and antipsychotics work by blocking dopamine receptors in the brain. They can be effective in treating positive symptoms but have little impact on the negative ones, which can be devastating for a patient’s quality of life, making it difficult to maintain employment and have successful relationships. About 30 percent of schizophrenia patients don't actually respond to antipsychotics at all. Current drugs can also have adverse side effects including elevated cholesterol, high blood pressure, diabetes and movements that patients cannot control.
The recent clinical trial heralds a new treatment approach. “We believe it marks an important advancement for patients given its new and completely different mechanism of action from current therapies,” says Andrew Miller, COO of Karuna.
Scientists have been looking to develop alternatives. However, “the field of drug treatment of schizophrenia is currently in the doldrums,” says Peter McKenna, a senior researcher at FIDMAG Research Foundation in Spain which specialises in mental health.
In the 2000s there was a major push to target a brain receptor for a chemical called glutamate. Evidence suggested that this receptor is abnormal in the brains of schizophrenia patients, but attempts to try glutamate failed in clinical trials.
After that, many pharmaceutical companies dropped out of the race for a more useful treatment. But some companies continued to search, such as Karuna Therapeutics, led by founder and Chief Operating Officer Andrew Miller and CEO Steve Paul. The recent clinical trial suggests their persistence has led to an important breakthrough with their drug, KarXT. “We believe it marks an important advancement for patients given its new and completely different mechanism of action from current therapies,” Miller says.
How it works
Neurotransmitters are chemical messengers that pass signals between neurons. To work effectively, neurotransmitters need a receptor to bind to. A neurotransmitter called acetylcholine seems to be especially important in schizophrenia. It interacts with sites called muscarinic receptors, which are involved in the network of nerves that calm your body after a stressful event. Post mortem studies in people with schizophrenia have shown that two muscarinic receptors in the brain, the M1 and M4 receptors, are activated at unusually low levels because they don’t receive enough signals from acetylcholine.
The M4 receptor appears to play a role in psychosis. The M1 receptor is also associated with psychosis but is primarily thought to be involved in cognition. KarXT, taken orally, works by activating both of these receptors to signal properly. It is this twofold action that seems to explain its effectiveness. “[The drug’s] design enables the preferential stimulation of these muscarinic receptors in the brain,” Miller says.
How it developed
It all started in the early 1990s when Paul was at pharmaceutical company Eli Lilly. He discovered that Xanomeline, the drug they were testing on Alzheimer's patients, had antipsychotic effects. It worked by stimulating M1 and M4 receptors, so he and his colleagues decided to test Xanomeline on schizophrenia patients, supported by research on the connection between muscarinic receptors and psychosis. They found that Xanomeline reduced both positive and negative symptoms.
Unfortunately, it also caused significant side effects. The problem was that stimulating the M1 and M4 receptors in the brain also stimulated muscarinic receptors in the body that led to severe vomiting, diarrhea and even the temporary loss of consciousness.
In the end, Eli Lilly discontinued the clinical trials for the drug, but Miller set up Karuna Therapeutics to develop a solution. “I was determined to find a way to harness the therapeutic benefit demonstrated in studies of Xanomeline, while eliminating side effects that limited its development,” Miller says.
He analysed over 7,000 possible ways of mixing Xanomeline with other agents before settling on KarXT. It combines Xanomeline with a drug called Trospium Chloride, which blocks muscarinic receptors in the body – taking care of the side effects such as vomiting – but leaves them unblocked in the brain. Paul was so excited by Miller’s progress that he joined Karuna after leaving Eli Lilly and founding two previous startups.
“It's a very important approach,” says Rick Adams, Future Leaders Fellow in the Institute of Cognitive Neuroscience and Centre for Medical Image Computing at University College London. “We are in desperate need of alternative drug targets and this target is one of the best. There are other alternative targets, but not many are as close to being successful as the muscarinic receptor drug.”
Following a successful phase 2 clinical trial in 2019, the most recent trial involved 126 patients who were given KarXT, and 126 who were given a placebo. Compared to the placebo, patients taking KarXT had a significant 9.6 point reduction in the positive and negative syndrome scale (PANSS), the standard for rating schizophrenic symptoms.
KarXT also led to statistically significant declines in positive and negative symptoms compared to the placebo. “The results suggest that KarXT could be a potentially game-changing option in the management of both positive and negative symptoms of schizophrenia,” Miller says.
Robert McCutcheon, a psychiatrist and neuroscientist at Oxford University, is optimistic about the side effects but highlights the need for more safety trials.
McKenna, the researcher at FIDMAG Foundation, agrees about the drug’s potential. “The new [phase 3] study is positive,” he says. “It is reassuring that one is not dealing with a drug that works in one trial and then inexplicably fails in the next one.”
Robert McCutcheon, a psychiatrist and neuroscientist at Oxford University, said the drug is an unprecedented step forward. “KarXT is one of the first drugs with a novel mechanism of action to show promise in clinical trials.”
Even though the drug blocks muscarine receptors in the body, some patients still suffered from adverse side effects like vomiting, dizziness and diarrhea. But in general, these effects were mild to moderate, especially compared to dopamine-blocking antipsychotics or Xanomeline on its own.
McCutcheon is optimistic about the side effects but highlights the need for more safety trials. “The trial results suggest that gastrointestinal side effects appear to be manageable,” he says. “We know, however, from previous antipsychotic drugs that the full picture regarding the extent of side effects can sometimes take longer to become apparent to clinicians and patients. Careful ongoing assessment during a longer period of treatment will therefore be important.”
The team is currently conducting three other trials to evaluate the efficacy and long-term safety of KarXT. Their goal is to receive FDA approval next year.
Karuna is also conducting trials to evaluate the effectiveness of KarXT in treating psychosis in patients suffering from Alzheimer’s.
The big hope is that they will soon be able to provide a radically different drug to help many patients with schizophrenia. “We are another step closer to potentially providing the first new class of medicine in more than 50 years to the millions of people worldwide living with schizophrenia,” says Miller.
In 1962, the world was a remarkably different place: Neil Armstrong had yet to take his first steps on the lunar surface, John F. Kennedy was serving as president of the United States, and the Beatles were still a few years away from superstardom, having just recorded their first single.
The word “measles” was also a household name. Measles, which still exists in parts of the world today, is a highly contagious viral infection that typically causes fever, cough, muscle pain, fatigue, and a distinctive red rash. Measles was so pervasive around the world in 1962 that most children had gotten sick with it before the age of fifteen—but even though it was common, it was far from harmless. Measles killed around 400 to 500 people per year in the United States, and approximately 2.6 million people each year worldwide. Countless others suffered severe complications from measles, such as permanent blindness.
Tragedy hits home
Author Roald Dahl at his Buckinghamshire home with Olivia, daughter Chantal, and wife Patricia Neal in 1960.
Ben Martin / Getty Images
That year, British author Roald Dahl was beginning to make a name for himself, having just published his best-selling book James and the Giant Peach. Dahl, who would go on to write some of the most well-loved children’s books of the century, lived in southern England with his wife and three children. One day, Dahl and his wife, actress Patricia Neal, received word that there was an outbreak of measles at his daughters’ school.
While some parents quarantined their children, many others also considered measles a harmless childhood disease. Neal later recalled in her autobiography that a family member had advised her to “let the girls get measles,” thinking it would strengthen their immune systems and be “good for them.” Reluctantly, Dahl and Neal let their two school-aged children, Olivia and Chantal, continue school. Olivia, then aged seven, fell sick with the measles not long after that.
Neither Dahl nor Neal were terribly concerned about Olivia’s infection. Dahl would write later that it seemed to be taking its “usual course,” and the two would read and spend time together while Olivia rested. After a few days of fever and fatigue, Dahl wrote, Olivia seemed like she was “well on the road to recovery.”
But one afternoon, as the two sat on Olivia’s bed making animals out of pipe cleaners, Dahl noticed that Olivia’s “fingers and her mind were not working together.” When Dahl asked how she was feeling, Olivia replied, “I feel all sleepy.”
Within an hour, Dahl wrote, Olivia was unconscious. Within 12 hours, she was dead.
Olivia died of measles encephalitis, an inflammation of the brain caused by an infection. Approximately 1 in 1,000 people infected with measles develop encephalitis, and of those who develop it, between 10 and 20 percent will die.
Dahl was overcome with grief and wracked with guilt for being unable to prevent his daughter’s death. Mourning, Dahl threw himself into his writing and, in his spare time, spent hours lovingly constructing a rock garden on Olivia’s grave in a local churchyard.
After Olivia’s death, Dahl wrote sixteen novels and several collections of short stories, including Matilda, Fantastic Mr. Fox, and Willy Wonka and the Chocolate Factory, which garnered him worldwide acclaim. His most influential piece of writing, however, wasn’t written until 1986.
A father's plea
Roald Dahl and the open letter he wrote in 1986, encouraging parents to vaccinate their children against measles.
By 1986, measles was no longer the global health threat that it had been in the 1960s, thanks to a measles vaccine that became available just one year after Olivia had died. Still, in the United Kingdom alone, approximately 80,000 people every year were infected with measles. This bothered Dahl, especially since measles rates in the United States had dropped by 98 percent compared to pre-vaccine years. “Why do we have so much measles in Britain when the Americans have virtually gotten rid of it?,” Dahl was reported to have said.
So Dahl set out to prevent a tragedy like Olivia’s from happening again. With encouragement from several prominent public health activists, Dahl wrote an open letter addressed to parents in the UK. The letter recounted his daughter’s death from encephalitis and begged parents to protect their own children from measles:
“...there is today something that parents can do to make sure that this sort of tragedy does not happen to a child of theirs. They can insist that their child is immunised [sic] against measles. I was unable to do that for Olivia in 1962 because in those days a reliable measles vaccine had not been discovered. Today a good and safe vaccine is available to every family and all you have to do is to ask your doctor to administer it.”
Dahl went on to say that although many parents still viewed measles as a harmless illness, he knew from experience that it was not. Measles was capable of causing disability and death, Dahl wrote, whereas a child had a better chance of “choking on a chocolate bar” than developing any serious complication from the vaccine. Dahl ended his letter by saying how happy he knew Olivia would be “if only she could know that her death had helped to save a good deal of illness and death among other children.”
Dahl’s letter was published in early 1986 and distributed to local healthcare workers, schools, and to parents of children who were particularly at risk. As the letter circulated, vaccination rates continued to climb year after year.
Thirty-one years after Dahl’s letter was published, and 55 years after Olivia’s death, the World Health Organization declared in 2017 that measles had officially been eradicated for the first time in the UK thanks to high rates of vaccination.
A small step back
As vaccination rates decline, measles is now making a strong comeback in the United States and elsewhere.
Today, vaccination rates for the measles are in decline, and countries like the UK and the US, who had once eradicated measles completely, are now seeing a comeback. The Centers for Disease Control and Prevention (CDC) recently reported that between December 1, 2023 and January 23, 2024, 23 cases of measles had been confirmed across multiple states. The majority of these cases, they reported, were among children and adolescents who had traveled internationally and had not yet been vaccinated even though they were eligible to do so.
Roald Dahl passed away in 1990, but fortunately, his writing continues to live on. While readers can explore fantastical worlds through his novels and short stories, they can also look back to a reality when tragic deaths like Olivia’s happened far too often. The difference is that today, thanks to modern science, we now have the tools to stop them.
Sarah Watts is a health and science writer based in Chicago.
On today’s episode of Making Sense of Science, I’m honored to be joined by Dr. Paul Song, a physician, oncologist, progressive activist and biotech chief medical officer. Through his company, NKGen Biotech, Dr. Song is leveraging the power of patients’ own immune systems by supercharging the body’s natural killer cells to make new treatments for Alzheimer’s and cancer.
Whereas other treatments for Alzheimer’s focus directly on reducing the build-up of proteins in the brain such as amyloid and tau in patients will mild cognitive impairment, NKGen is seeking to help patients that much of the rest of the medical community has written off as hopeless cases, those with late stage Alzheimer’s. And in small studies, NKGen has shown remarkable results, even improvement in the symptoms of people with these very progressed forms of Alzheimer’s, above and beyond slowing down the disease.
In the realm of cancer, Dr. Song is similarly setting his sights on another group of patients for whom treatment options are few and far between: people with solid tumors. Whereas some gradual progress has been made in treating blood cancers such as certain leukemias in past few decades, solid tumors have been even more of a challenge. But Dr. Song’s approach of using natural killer cells to treat solid tumors is promising. You may have heard of CAR-T, which uses genetic engineering to introduce cells into the body that have a particular function to help treat a disease. NKGen focuses on other means to enhance the 40 plus receptors of natural killer cells, making them more receptive and sensitive to picking out cancer cells.
Paul Y. Song, MD is currently CEO and Vice Chairman of NKGen Biotech. Dr. Song’s last clinical role was Asst. Professor at the Samuel Oschin Cancer Center at Cedars Sinai Medical Center.
Dr. Song served as the very first visiting fellow on healthcare policy in the California Department of Insurance in 2013.He is currently on the advisory board of the Pritzker School of Molecular Engineering at the University of Chicago and a board member of Mercy Corps, The Center for Health and Democracy, and Gideon’s Promise.
Dr. Song graduated with honors from the University of Chicago and received his MD from George Washington University. He completed his residency in radiation oncology at the University of Chicago where he served as Chief Resident and did a brachytherapy fellowship at the Institute Gustave Roussy in Villejuif, France. He was also awarded an ASTRO research fellowship in 1995 for his research in radiation inducible gene therapy.
With Dr. Song’s leadership, NKGen Biotech’s work on natural killer cells represents cutting-edge science leading to key findings and important pieces of the puzzle for treating two of humanity’s most intractable diseases.
- Paul Song LinkedIn
- NKGen Biotech on Twitter - @NKGenBiotech
- NKGen Website: https://nkgenbiotech.com/
- NKGen appoints Paul Song
- Patient Story: https://pix11.com/news/local-news/long-island/promising-new-treatment-for-advanced-alzheimers-patients/
- FDA Clearance: https://nkgenbiotech.com/nkgen-biotech-receives-ind-clearance-from-fda-for-snk02-allogeneic-natural-killer-cell-therapy-for-solid-tumors/Q3 earnings data: https://www.nasdaq.com/press-release/nkgen-biotech-inc.-reports-third-quarter-2023-financial-results-and-business