Researchers advance drugs that treat pain without addiction
New therapies are using creative approaches that target the body’s sensory neurons, which send pain signals to the brain.
Opioids are one of the most common ways to treat pain. They can be effective but are also highly addictive, an issue that has fueled the ongoing opioid crisis. In 2020, an estimated 2.3 million Americans were dependent on prescription opioids.
Opioids bind to receptors at the end of nerve cells in the brain and body to prevent pain signals. In the process, they trigger endorphins, so the brain constantly craves more. There is a huge risk of addiction in patients using opioids for chronic long-term pain. Even patients using the drugs for acute short-term pain can become dependent on them.
Scientists have been looking for non-addictive drugs to target pain for over 30 years, but their attempts have been largely ineffective. “We desperately need alternatives for pain management,” says Stephen E. Nadeau, a professor of neurology at the University of Florida.
A “dimmer switch” for pain
Paul Blum is a professor of biological sciences at the University of Nebraska. He and his team at Neurocarrus have created a drug called N-001 for acute short-term pain. N-001 is made up of specially engineered bacterial proteins that target the body’s sensory neurons, which send pain signals to the brain. The proteins in N-001 turn down pain signals, but they’re too large to cross the blood-brain barrier, so they don’t trigger the release of endorphins. There is no chance of addiction.
When sensory neurons detect pain, they become overactive and send pain signals to the brain. “We wanted a way to tone down sensory neurons but not turn them off completely,” Blum reveals. The proteins in N-001 act “like a dimmer switch, and that's key because pain is sensation overstimulated.”
Blum spent six years developing the drug. He finally managed to identify two proteins that form what’s called a C2C complex that changes the structure of a subunit of axons, the parts of neurons that transmit electrical signals of pain. Changing the structure reduces pain signaling.
“It will be a long path to get to a successful clinical trial in humans," says Stephen E. Nadeau, professor of neurology at the University of Florida. "But it presents a very novel approach to pain reduction.”
Blum is currently focusing on pain after knee and ankle surgery. Typically, patients are treated with anesthetics for a short time after surgery. But anesthetics usually only last for 4 to 6 hours, and long-term use is toxic. For some, the pain subsides. Others continue to suffer after the anesthetics have worn off and start taking opioids.
N-001 numbs sensation. It lasts for up to 7 days, much longer than any anesthetic. “Our goal is to prolong the time before patients have to start opioids,” Blum says. “The hope is that they can switch from an anesthetic to our drug and thereby decrease the likelihood they're going to take the opioid in the first place.”
Their latest animal trial showed promising results. In mice, N-001 reduced pain-like behaviour by 90 percent compared to the control group. One dose became effective in two hours and lasted a week. A high dose had pain-relieving effects similar to an opioid.
Professor Stephen P. Cohen, director of pain operations at John Hopkins, believes the Neurocarrus approach has potential but highlights the need to go beyond animal testing. “While I think it's promising, it's an uphill battle,” he says. “They have shown some efficacy comparable to opioids, but animal studies don't translate well to people.”
Nadeau, the University of Florida neurologist, agrees. “It will be a long path to get to a successful clinical trial in humans. But it presents a very novel approach to pain reduction.”
Blum is now awaiting approval for phase I clinical trials for acute pain. He also hopes to start testing the drug's effect on chronic pain.
Learning from people who feel no pain
Like Blum, a pharmaceutical company called Vertex is focusing on treating acute pain after surgery. But they’re doing this in a different way, by targeting a sodium channel that plays a critical role in transmitting pain signals.
In 2004, Stephen Waxman, a neurology professor at Yale, led a search for genetic pain anomalies and found that biologically related people who felt no pain despite fractures, burns and even childbirth had mutations in the Nav1.7 sodium channel. Further studies in other families who experienced no pain showed similar mutations in the Nav1.8 sodium channel.
Scientists set out to modify these channels. Many unsuccessful efforts followed, but Vertex has now developed VX-548, a medicine to inhibit Nav1.8. Typically, sodium ions flow through sodium channels to generate rapid changes in voltage which create electrical pulses. When pain is detected, these pulses in the Nav1.8 channel transmit pain signals. VX-548 uses small molecules to inhibit the channel from opening. This blocks the flow of sodium ions and the pain signal. Because Nav1.8 operates only in peripheral nerves, located outside the brain, VX-548 can relieve pain without any risk of addiction.
"Frankly we need drugs for chronic pain more than acute pain," says Waxman.
The team just finished phase II clinical trials for patients following abdominoplasty surgery and bunionectomy surgery.
After abdominoplasty surgery, 76 patients were treated with a high dose of VX-548. Researchers then measured its effectiveness in reducing pain over 48 hours, using the SPID48 scale, in which higher scores are desirable. The score for Vertex’s drug was 110.5 compared to 72.7 in the placebo group, whereas the score for patients taking an opioid was 85.2. The study involving bunionectomy surgery showed positive results as well.
Waxman, who has been at the forefront of studies into Nav1.7 and Nav1.8, believes that Vertex's results are promising, though he highlights the need for further clinical trials.
“Blocking Nav1.8 is an attractive target,” he says. “[Vertex is] studying pain that is relatively simple and uniform, and that's key to having a drug trial that is informative. But the study needs to be replicated and frankly we need drugs for chronic pain more than acute pain. If this is borne out by additional studies, it's one important step in a journey.”
Vertex will be launching phase III trials later this year.
Finding just the right amount of Nerve Growth Factor
Whereas Neurocarrus and Vertex are targeting short-term pain, a company called Levicept is concentrating on relieving chronic osteoarthritis pain. Around 32.5 million Americans suffer from osteoarthritis. Patients commonly take NSAIDs, or non-steroidal anti-inflammatory drugs, but they cannot be taken long-term. Some take opioids but they aren't very effective.
Levicept’s drug, Levi-04, is designed to modify a signaling pathway associated with pain. Nerve Growth Factor (NGF) is a neurotrophin: it’s involved in nerve growth and function. NGF signals by attaching to receptors. In pain there are excess neurotrophins attaching to receptors and activating pain signals.
“What Levi-04 does is it returns the natural equilibrium of neurotrophins,” says Simon Westbrook, the CEO and founder of Levicept. It stabilizes excess neurotrophins so that the NGF pathway does not signal pain. Levi-04 isn't addictive since it works within joints and in nerves outside the brain.
Westbrook was initially involved in creating an anti-NGF molecule for Pfizer called Tanezumab. At first, Tanezumab seemed effective in clinical trials and other companies even started developing their own versions. However, a problem emerged. Tanezumab caused rapidly progressive osteoarthritis, or RPOA, in some patients because it completely removed NGF from the system. NGF is not just involved in pain signalling, it’s also involved in bone growth and maintenance.
Levicept has found a way to modify the NGF pathway without completely removing NGF. They have now finished a small-scale phase I trial mainly designed to test safety rather than efficacy. “We demonstrated that Levi-04 is safe and that it bound to its target, NGF,” says Westbrook. It has not caused RPOA.
Professor Philip Conaghan, director of the Leeds Institute of Rheumatic and Musculoskeletal Medicine, believes that Levi-04 has potential but urges the need for caution. “At this early stage of development, their molecule looks promising for osteoarthritis pain,” he says. “They will have to watch out for RPOA which is a potential problem.”
Westbrook starts phase II trials with 500 patients this summer to check for potential side effects and test the drug’s efficacy.
There is a real push to find an effective alternative to opioids. “We have a lot of work to do,” says Professor Waxman. “But I am confident that we will be able to develop new, much more effective pain therapies.”
Podcast: Trusting Science with Dr. Sudip Parikh, CEO of AAAS
The "Making Sense of Science" podcast features interviews with leading experts about health innovations and the big ethical and social questions they raise. The podcast is hosted by Matt Fuchs, editor of the award-winning science outlet Leaps.org.
As Pew research showed last month, many Americans have less confidence in science these days - our collective trust has declined to levels below when the pandemic began. But leaders like Dr. Sudip Parikh are taking important steps to more fully engage people in scientific progress, including breakthroughs that could benefit health and prevent disease. In January 2020, Sudip became the 19th Chief Executive Officer of the American Association for the Advancement of Science (AAAS), an international nonprofit that seeks to advance science, engineering and innovation throughout the world, with 120,000 members in 91 countries. He is the executive publisher of Science, one of the top academic journals in the world, and the Science family of journals.
Listen to the episode
Listen on Apple | Listen on Spotify | Listen on Stitcher | Listen on Amazon | Listen on Google
In this episode, Sudip and I talk about:
- Reasons to be excited about health innovations that could come to fruition in the next several years.
- Sudip's thoughts about areas of health innovation where we should be especially cautious.
- Strategies for scientists and journalists to instill greater trust in science.
- How to tap into and nurture kids' passion for STEM subjects.
- The best roles for experts to play in society and the challenges they face.
And we pack several other fascinating topics into our 35 minutes. Here are links to check out and learn more about Sudip Parikh and AAAS:
- Sudip Parikh's official bio - https://www.aaas.org/person/sudip-parikh
- Sudip Parikh, Why We Must Rebuild Trust in Science, Trend Magazine, Feb. 9, 2021 - https://www.pewtrusts.org/en/trend/archive/winter-...
- Follow Sudip on Twitter - https://twitter.com/sudipsparikh
- AAAS website - https://www.aaas.org/
- AAAS podcast - https://www.science.org/podcasts
- The latest issue of Science - https://www.science.org/
- Science Journals homepage - https://www.science.org/journals
- AAAS Mentor Resources - https://www.aaas.org/stemmentoring
- AAAS Science Journalism Awards - https://sjawards.aaas.org/enter
- Pew Research Center Report, Americans' Trust in Scientists, Other Groups Declines, Feb. 15, 2022 https://www.pewresearch.org/science/2022/02/15/ame...
An implant, combined with the glasses and tiny video camera modeled in this photo, could improve the eyesight of millions of people with degenerative eye diseases in the coming years.
For millions of people with macular degeneration, treatment options are slim. The disease causes loss of central vision, which allows us to see straight ahead, and is highly dependent on age, with people over 75 at approximately 30% risk of developing the disorder. The BrightFocus Foundation estimates 11 million people in the U.S. currently have one of three forms of the disease.
Recently, ophthalmologists including Daniel Palanker at Stanford University published research showing advances in the PRIMA retinal implant, which could help people with advanced, age-related macular degeneration regain some of their sight. In a feasibility study, five patients had a pixelated chip implanted behind the retina, and three were able to see using their remaining peripheral vision and—thanks to the implant—their partially restored central vision at the same time.
Should people with macular degeneration be excited about these results?
“Every week, if not every day, patients come to me with this question because it's devastating when they lose their central vision,” says retinal surgeon Lynn Huang. About 40% of her patients have macular degeneration. Huang tells them that these implants, along with new medications and stem cell therapies, could be useful in the coming years.
“The goal here is to replace the missing photoreceptors with photovoltaic pixels, basically like little solar panels,” Palanker says.
That implant, a pixelated chip, works together with a tiny video camera on a specially designed pair of eyeglasses, which can be adjusted for each patient’s prescription. The video camera relays processed images to the chip, which electrically stimulates inner retinal neurons. These neurons, in turn, relay information to the brain’s visual cortex through the optic nerve. The chip restores patients’ central sight, but not completely. The artificial vision is basically monochromatic (whitish-yellowish) and fairly blurry; patients were still legally blind even after the implant, except when using a zoom function on the camera, but those with proper chip placement could make out large letters.
“The goal here is to replace the missing photoreceptors with photovoltaic pixels, basically like little solar panels,” Palanker says. These pixels, located on the implanted chip, convert light into pulsed electrical currents that stimulate retinal neurons. In time, Palanker hopes to improve the chips, resulting in bigger boosts to visual acuity.
The pixelated chips are surgically implanted during a process Palanker admits is still “a surgical learning curve.” In the study, three chips were implanted correctly, one was placed incorrectly, and another patient’s chip moved after the procedure; he did not follow post-surgical recommendations. One patient passed away during the study for unrelated reasons.
University of Maryland retinal specialist Kenneth Taubenslag, who was not involved in the study, said that subretinal surgeries have become less common in recent years, but expects implants to spur improvements in these techniques. “I think as people get more experience, [they’ll] probably get more reliable placement of the implant,” he said, pointing out that even the patient with the misplaced chip was able to gain some light perception, if not the same visual acuity as other patients.
Retinal implants have come under scrutiny lately. IEEE Spectrum reported that Second Sight, manufacturer of the Argus II implant used for people with retinitis pigmentosa, a genetic disease that causes vision loss, would no longer support the product. After selling hundreds of the implants at $150,000 apiece, company leaders announced they’d “decided to pursue an orderly wind down” of Second Sight in March 2020 in the wake of financial issues. Last month, the company announced a merger, shifting its focus to a new retinal implant, raising questions for patients who have Argus II implants.
Retinal surgeon Eugene de Juan of the University of California, San Francisco, was involved with early studies of the Argus implants, though his participation ended over a decade ago, before the device was marketed by Second Sight. He says he would consider recommending future implants to patients with macular degeneration, given the promise of the technology and the lack of other alternatives.
“I tell my patients that this is an area of active research and development, and it's getting better and better, so let's not give up hope,” de Juan says. He believes cautious optimism for Palanker’s implant is appropriate: “It's not the first, it's not the only, but it's a good approach with a good team.”