Researchers advance drugs that treat pain without addiction
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.”
A few days before Christmas 2015, Paige Alexandria, a 28-year-old counselor at the Austin Women's Health Center in Texas, found out she was pregnant.
Alexandria had missed the cutoff for a medication abortion by three days.
"It was an unplanned pregnancy, and instantaneously I knew I needed an abortion," Alexandria recalls. Already a mother of two children, one with special needs, a third child was not something Alexandria and her husband felt prepared to take on. "Mentally, I knew my limit. I wasn't prepared for a third and I didn't want one," she says.
At an ultrasound appointment one week later, scans showed she was a little over eight weeks pregnant. Alexandria opted to have an abortion as soon as possible, and preferably with medication. "I really wanted to avoid a surgical abortion," she says. "It sounded a lot more invasive, and I'm already uncomfortable with pap smears and pelvic exams, so I initially went in wanting to do the pill."
But at the time, medication guidelines stipulated that one of the pills, called Mifepristone, could only be prescribed to end a pregnancy at eight weeks gestation or earlier – Alexandria had missed the cutoff by three days. If she wanted to end the pregnancy, she would need to undergo a surgical abortion, otherwise known as a vacuum aspiration abortion.
With a vacuum aspiration abortion, doctors dilate the cervix and manually aspirate out the contents of the uterus. Medication abortion, on the other hand, consists of the patient taking two pills – Mifepristone, which blocks the hormones that help the pregnancy develop, and Misoprostol, which empties the uterus over a period of days, identical to a miscarriage.
Alexandria was upset about the change of plans but resolute in her decision to end the pregnancy. "The fact that I didn't really have a choice in how my procedure was performed has made the experience just a little more sensitive for me," she says. She scheduled the earliest available appointment for a surgical abortion.
Paige Alexandria would have chosen to terminate her pregnancy with medication if the regulations were less stringent.
(Photo courtesy of Alexandria)
Like Alexandria, many people looking to terminate a pregnancy opt to do so with medication. According to research from the Guttmacher Institute, medication abortions accounted for nearly 40 percent of all abortions in the year 2017 – a marked increase from 2001, when medication abortions only accounted for roughly five percent of terminations. Taken 24-48 hours apart, Mifepristone and Misoprostol have a 95-99 percent success rate in terminating pregnancies up to 63 days – or nine weeks – of gestation, according to the American College of Obstetrics and Gynecology (ACOG).
But even though the World Health Organization (WHO) considers medical abortion to be highly safe and effective, the medication is still carefully guarded in the United States: Mifepristone is only available for terminating pregnancies up to 10 weeks gestation, per the FDA, even though limited research suggests that both are safe and effective at terminating pregnancies between 12 and 20 weeks.
Additionally, a separate set of regulations known as a Risk Evaluation and Mitigation Strategy (REMS) means that patients can only take Mifepristone under specific circumstances. Mifepristone must be distributed in person by a healthcare provider – usually interpreted in most states as a doctor or nurse practitioner – who has registered with the drug's manufacturer. The medication cannot be distributed through a pharmacy, so doctors who wish to provide the drug must stock the medication in-office, and both the provider and the patient must sign a form that warns them of the "risk of serious complications associated with Mifepristone," according to the FDA.
"REMS is a set of restrictions that the FDA puts on the distribution of drugs it considers dangerous or risky in some way," says Dr. Elizabeth Raymond, an OB-GYN and senior medical associate at Gynuity Health Projects. Although not always called REMS, these restrictions have been imposed on Mifepristone since the medication was approved by the FDA in 2000, Raymond says.
Raymond is part of a growing number of physicians and researchers who want to eliminate the REMS requirements for Mifepristone, also known by its brand name Mifeprex. In 2017, Raymond and several other physicians authored a paper in the New England Journal of Medicine (NEJM) arguing that Mifepristone is extremely safe and needlessly over-regulated.
"When the FDA first approved [Mifepristone] and imposed these requirements, they might have made sense 19 years ago when there was limited information about the use of this treatment in the United States," says Dr. Daniel Grossman, director at Advancing New Standards in Reproductive Health at UCSF and co-author of the 2017 report in the NEJM. "Now, after 19 years, it's clear that this medication is very safe, and safer than a lot of others available in a pharmacy."
Since 2000, Mifepristone has been implicated in 19 deaths, making its mortality rate 0.00063 percent.
According to their research, over three million people have taken Mifepristone since it was approved in 2000. Since then, Mifepristone has been implicated in 19 deaths, making its mortality rate 0.00063 percent. Even then, the risk is inflated, Grossman says.
"The requirement is that practitioners need to report any deaths that occur after taking these medications, and so you'll see deaths included in that figure which are homicides or suicides or something unrelated to taking Mifepristone," says Grossman. In contrast, Acetaminophen – better known as Tylenol – was associated with 458 overdose deaths between 1990 and 1998, as well as 56,000 emergency room visits and 26,000 hospitalizations. Sildenafil, better known as Viagra, was linked to 762 deaths in the first twenty months after it was approved by the FDA. Yet neither Tylenol nor Viagra have been burdened with the same REMS restrictions as Mifepristone.
"It's clearly about more than just the safety of the medication at this point," says Grossman. "It's more about stigma related to abortion and politics."
For people who want a medication abortion, the REMS requirements mean they often need to take off work to schedule a doctor's appointment, arrange for transportation and childcare, and then arrange an additional doctor's appointment days afterward to take the second dose of medication. While surgical abortion procedures are quicker (usually a one-day outpatient procedure, depending on gestation), many people prefer having the abortion in the comfort of their home or surrounded by family instead.
Paige Alexandria, who counsels people seeking abortions at her job, says that survivors of sexual violence often prefer medical abortions to surgical ones. "A lot of time survivors have a trauma associated with medical instruments or having pelvic exams, and so they're more comfortable taking a pill," she says.
But REMS also creates a barrier for healthcare providers, Grossman says. Stocking the medication in-office is "a hassle" and "expensive," while others are reluctant to register their name with the drug manufacturer, fearing harassment or violence from anti-choice protestors. As a result, the number of practitioners willing to provide medical abortions nationwide is severely limited. According to Grossman's own research published in the journal Obstetrics and Gynecology, 28 percent of OBGYNs admitted they would administer medication abortions if it were possible to write a prescription for Mifepristone rather than stock it in-office.
Amazingly, the restrictions on Mifepristone have loosened since it first came on the market. In 2016, the FDA updated the guidelines on Mifepristone to allow its use until 10 weeks gestation, up from eight weeks. But doctors say the REMS restrictions should be eliminated completely so that people can obtain abortions as early as possible.
"REMS restrictions inhibit people from being able to get a timely abortion," says Raymond, who stresses that abortion is generally more comfortable, more affordable, and safer for women the earlier it's done. "Abortion is very safe no matter when you get it, but it's also easier because there's less risk for bleeding, infections, or other complications," Raymond says. Abortions that occur earlier than eight weeks of gestation have a complication rate of less than one percent, while an abortion done at 12 or 13 weeks has a three to six percent chance of complications.
And even for people who want a medication abortion early on in their pregnancy, REMS restrictions make it so that they may not have time to obtain it before the 10-week period lapses, Raymond says.
"If you're seven weeks pregnant but it takes you three weeks to figure out travel and childcare arrangements to go into the doctor and take this medication, now you're at the cutoff date," she says. "Even if you manage to get an abortion at nine weeks, that's still a later gestational age, and so the risks are increased."
In 2016, at a little over nine weeks gestation, Alexandria completed her abortion by having a D&E. But because she didn't have anyone to drive her home after the procedure, she wasn't able to have sedation throughout, something she describes as "traumatic."
"I had the abortion completely aware and coherent, and paired with the fact that I hadn't even wanted a surgical abortion in the first place made it harder to deal with," Alexandria says.
"When you're just a day or two past eight weeks and you want an abortion – why is medication not immediately available?"
Today, Alexandria shares her story publicly to advocate for abortion care. Although she doesn't regret her surgical abortion and acknowledges that not everyone experiences surgical abortion the same way she did, she does wish that she could have gone a different route.
"If I had to do it over, I would still try to do the pill, because [the surgical abortion] was such a terrifying experience," she says. "When you're just a day or two past eight weeks and you want an abortion – why is medication not immediately available? It just doesn't make sense."
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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.