A novel therapy based on the plant-derived molecule resiniferatoxin could be a safe and effective agent for patients with difficult-to-control cancer pain, according to a recent study published by Mannes et al in NEJM Evidence.
Background
Resiniferatoxin is derived from Euphorbia resinifera, a cactus-like plant native to North Africa. For 2,000 years, Euphorbia extract has been known to contain an irritant substance, which researchers identified how to use for patients through basic research on living cells observed through a microscope. Resiniferatoxin is an activator of the transient receptor potential vanilloid 1 (TRPV1) ion channel and a super-potent equivalent of capsaicin. The ability of resiniferatoxin to open the channel pore in TRPV1 allows calcium to flood into the nerve fiber and block its ability to transmit pain signals, explained investigators.
Unlike current approaches that use heat, cold, chemicals, or surgery to nonselectively interrupt nerves in order to block pain, resiniferatoxin targets the specific sensory pathways of tissue damage pain and heat. Other sensory pathways such as touch, pinprick, pressure, proprioception, and motor function remain intact. The treatment is not designed to cause a generalized numbing like that which occurs with local anesthetics.
“Basically, [resiniferatoxin] cuts the pain-specific wires connecting the body to the spinal cord, but leaves many other sensations … intact,” explained senior study author Michael Iadarola, PhD, a senior research scientist in the NIH Clinical Center Department of Perioperative Medicine. “These TRPV1 neurons are really the most important population of neurons that [we] want to target for effective pain relief,” he continued.
Study Methods
In the first-in-class human clinical trial, researchers examined the safety and efficacy of a single injection of small quantities of resiniferatoxin into the lumbar cerebral spinal fluid via lumbar puncture of patients with end-stage cancers who were among the 15% of patients unable to find pain relief from standard-of-care pain interventions such as opiates.
A single injection of resiniferatoxin provided patients with durable relief, and their quality of life improved. The researchers found that resiniferatoxin reduced the patients’ reported worst pain intensity by 38% and their use of pain-relieving opioids by 57%. They no longer reported needing to spend significant time being sedated with opioids and were able to reengage with their family, friends, and communities following treatments.
“The effects are immediate,” highlighted lead study author Andrew Mannes, MD, Chief of the National Institutes of Health (NIH) Clinical Center Department of Perioperative Medicine. “This is a potential new therapy from a new family of drugs that gives [patients] with severe cancer pain an opportunity to return some normality to their lives,” he added.
The researchers noted that resiniferatoxin wasn’t addictive and didn’t cause a high. Instead, it prevented pain signals from reaching the brain by inactivating a specific subgroup of nerve fibers that transmit heat and pain signals from damaged tissue.
Conclusions
The researchers suggested that resiniferatoxin could have the potential to treat many other conditions, including other types of cancer pain, chronic pain from neuromas, postsurgical pain, trigeminal neuralgia, and chronic oral inflammatory issues following head and neck radiation therapy.
“What makes this unique from all the other [pain relievers] that are out there is this is so highly selective,” Dr. Mannes underscored. “The only thing it seems to take out is heat sensation and pain,” he indicated.
“Targeting specific nerves brings many pain disorders into range of [resiniferatoxin] and allows physicians to tailor the treatment to the patient’s pain problem. This interventional approach is a simple path to personalized pain medicine,” concluded Dr. Iadarola.
The researchers plan to conduct additional, larger-scale clinical trials to move resiniferatoxin toward eventual approval by the U.S. Food and Drug Administration and clinical availability.
Disclosure: The research in this study was supported by the Intramural Research Program of the NIH Clinical Center and the NIH’s National Institute of Neurological Disorders and Stroke. For full disclosures of the study authors, visit evidence.nejm.org.
