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.”
Clinical Trial
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 Future
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.
He Almost Died from a Deadly Superbug. A Virus Saved Him.
An attacking rogue hippo, giant jumping spiders, even a coup in Timbuktu couldn't knock out Tom Patterson, but now he was losing the fight against a microscopic bacteria.
Death seemed inevitable, perhaps hours away, despite heroic efforts to keep him alive.
It was the deadly drug-resistant superbug Acinetobacter baumannii. The infection struck during a holiday trip with his wife to the pyramids in Egypt and had sent his body into toxic shock. His health was deteriorating so rapidly that his insurance company paid to medevac him first to Germany, then home to San Diego.
Weeks passed as he lay in a coma, shedding more than a hundred pounds. Several major organs were on the precipice of collapse, and death seemed inevitable, perhaps hours away despite heroic efforts by a major research university hospital to keep Tom alive.
Tom Patterson in a deep coma on March 14, 2016, the day before phage therapy was initiated.
(Courtesy Steffanie Strathdee)
Then doctors tried something boldly experimental -- injecting him with a cocktail of bacteriophages, tiny viruses that might infect and kill the bacteria ravaging his body.
It worked. Days later Tom's eyes fluttered open for a few brief seconds, signaling that the corner had been turned. Recovery would take more weeks in the hospital and about a year of rehabilitation before life began to resemble anything near normal.
In her new book The Perfect Predator, Tom's wife, Steffanie Strathdee, recounts the personal and scientific ordeal from twin perspectives as not only his spouse but also as a research epidemiologist who has traveled the world to track down diseases.
Part of the reason why Steff wrote the book is that both she and Tom suffered severe PTSD after his illness. She says they also felt it was "part of our mission, to ensure that phage therapy wasn't going to be forgotten for another hundred years."
Tom Patterson and Steffanie Strathdee taking a first breath of fresh air during recovery outside the UCSD hospital.
(Courtesy Steffanie Strathdee)
From Prehistoric Arms Race to Medical Marvel
Bacteriophages, or phages for short, evolved as part of the natural ecosystem. They are viruses that infect bacteria, hijacking their host's cellular mechanisms to reproduce themselves, and in the process destroying the bacteria. The entire cycle plays out in about 20-60 minutes, explains Ben Chan, a phage research scientist at Yale University.
They were first used to treat bacterial infections a century ago. But the development of antibiotics soon eclipsed their use as medicine and a combination of scientific, economic, and political factors relegated them to a dusty corner of science. The emergence of multidrug-resistant bacteria has highlighted the limitations of antibiotics and prompted a search for new approaches, including a revived interest in phages.
Most phages are very picky, seeking out not just a specific type of bacteria, but often a specific strain within a family of bacteria. They also prefer to infect healthy replicating bacteria, not those that are at rest. That's what makes them so intriguing to tap as potential therapy.
Tom's case was one of the first times that phages were successfully infused into the bloodstream of a human.
Phages and bacteria evolved measures and countermeasures to each other in an "arms race" that began near the dawn of life on the planet. It is not that one consciously tries to thwart the other, says Chan, it's that countless variations of each exists in the world and when a phage gains the upper hand and kills off susceptible bacteria, it opens up a space in the ecosystem for similar bacteria that are not vulnerable to the phage to increase in numbers. Then a new phage variant comes along and the cycle repeats.
Robert "Chip" Schooley is head of infectious diseases at the University of California San Diego (UCSD) School of Medicine and a leading expert on treating HIV. He had no background with phages but when Steff, a friend and colleague, approached him in desperation about using them with Tom, he sprang into action to learn all he could, and to create a network of experts who might provide phages capable of killing Acinetobacter.
"There is very little evidence that phage[s] are dangerous," Chip concluded after first reviewing the literature and now after a few years of experience using them. He compares broad-spectrum antibiotics to using a bazooka, where every time you use them, less and less of the "good" bacteria in the body are left. "With a phage cocktail what you're really doing is more of a laser."
Collaborating labs were able to identify two sets of phage cocktails that were sensitive to Tom's particular bacterial infection. And the FDA acted with lightning speed to authorize the experimental treatment.
A bag of a four-phage "cocktail" before being infused into Tom Patterson.
(Courtesy Steffanie Strathdee)
Tom's case was scientifically important because it was one of the first times that phages were successfully infused into the bloodstream of a human. Most prior use of phages involved swallowing them or placing them directly on the area of infection.
The success has since sparked a renewed interest in phages and a reexamination of their possible role in medicine.
Over the two years since Tom awoke from his coma, several other people around the world have been successfully treated with phages as part of their regimen, after antibiotics have failed.
The Future of Phage Therapy
The experience treating Tom prompted UCSD to create the Center for Innovative Phage Applications and Therapeutics (IPATH), with Chip and Steff as co-directors. Previous labs have engaged in basic research on phages, but this is the first clinical center in North America to focus on translating that knowledge into treating patients.
In January, IPATH announced the first phase 2 clinical trial approved by the FDA that will use phages intravenously. The viruses are being developed by AmpliPhi Biosciences, a San Diego-based company that supplied one of the phages used to treat Tom. The new study takes on drug resistant Staph aureus bacteria. Experimental phage therapy treatment using the company's product candidates was recently completed in 21 patients at seven hospitals who had been suffering from serious infections that did not respond to antibiotics. The reported success rate was 84 percent.
The new era of phage research is applying cutting-edge biologic and informatics tools to better understand and reshape the viruses to better attack bacteria, evade resistance, and perhaps broaden their reach a bit within a bacterial family.
Genetic engineering tools are being used to enhance the phages' ability to infect targeted bacteria.
"As we learn more and more about which biological activities are critical and in which clinical settings, there are going to be ways to optimize these activities," says Chip. Sometimes phages may be used alone, other times in combination with antibiotics.
Genetic engineering using tools are being used to enhance the phages' ability to infect targeted bacteria and better counter evolving forms of bacterial resistance in the ongoing "arms race" between the two. It isn't just theory. A patient recently was successfully treated with a genetically modified phage as part of the regimen, and the paper is in press.
In reality, given the trillions of phages in the world and the endless encounters they have had with bacteria over the millennia, it is likely that the exact phages needed to kill off certain bacteria already exist in nature. Using CRISPR to modify a phage is simply a quick way to identify the right phage useful for a given patient and produce it in the necessary quantities, rather than go search for the proverbial phage needle in a sewage haystack, says Chan.
One non-medical reason why using modified phages could be significant is that it creates an intellectual property stake, something that is patentable with a period of exclusive use. Major pharmaceutical companies and venture capitalists have been hesitant to invest in organisms found in nature; but a patentable modification may be enough to draw their interest to phage development and provide the funding for large-scale clinical trials necessary for FDA approval and broader use.
"There are 10 million trillion trillion phages on the planet, 10 to the power of 31. And the fact is that this ongoing evolutionary arms race between bacteria and phage, they've been at it for a millennia," says Steff. "We just need to exploit it."
This Mom Is On a Mission to End Sickle Cell Disease
[Editor's Note: This video is the third of a five-part series titled "The Future Is Now: The Revolutionary Power of Stem Cell Research." Produced in partnership with the Regenerative Medicine Foundation, and filmed at the annual 2019 World Stem Cell Summit, this series illustrates how stem cell research will profoundly impact human life.]
Kira Peikoff was the editor-in-chief of Leaps.org from 2017 to 2021. As a journalist, her work has appeared in The New York Times, Newsweek, Nautilus, Popular Mechanics, The New York Academy of Sciences, and other outlets. She is also the author of four suspense novels that explore controversial issues arising from scientific innovation: Living Proof, No Time to Die, Die Again Tomorrow, and Mother Knows Best. Peikoff holds a B.A. in Journalism from New York University and an M.S. in Bioethics from Columbia University. She lives in New Jersey with her husband and two young sons. Follow her on Twitter @KiraPeikoff.