Approximately 86 million Americans currently suffer from chronic pain stemming from a variety of sources from muscle aches to arthritis to severe burns and cancer. For some people, the cause of pain is unknown, and for others, pain medications may not be effective. According to the National Institutes of Health (NIH), about 45 percent of Americans visit a doctor because of pain. Long-term use of potent pain relievers (such as the commonly used morphine) has severe side effects, including sedation, tolerance, dependence, enhanced pain sensitivity, constipation and respiratory depression.
SIU Professor of Pharmacology Louis Premkumar, Ph.D., believes that a highly potent compound called Resiniferatoxin (RTX)—a substance that stems from a desert plant — can be used to treat chronic pain. He has been working for ﬁve years to control pain with RTX, a cousin of the chile pepper that contains a naturally-occurring
chemical related to capsaicin (the ingredient that makes chile peppers spicy). Capsaicin already is an ingredient in some topical pain relievers for arthritis. RTX activates the same receptor as capsaicin, but research shows RTX is a thousand times more potent.
Last year, Dr. Premkumar received a $1.4 million, five-year federal grant from the National Institute of Drug Abuse, a division of the NIH, for his RTX project. He has filed a patent for using low doses of RTX to relieve pain. How does it work? In animal models, RTX is administered using small, yet extremely potent doses directly into the spinal cord, (called an intrathecal injection) blocking pain transmission to the brain. RTX selectively binds to pain-sensing nerve endings and desensitizes them to provide pain relief. Dr. Premkumar explains that RTX causes localized, selective ablation of the nerves, and that provides long-lasting pain relief. He continues to build on his existing research to find the basic mechanism for how RTX works. His research is aimed at eliminating the nerve terminal, not the whole neuron, which will preserve the other neuronal functions (including acute pain and lower levels of pain). The central terminals do not regenerate as quickly in the spine as peripheral terminals, meaning that fewer doses would be needed to sustain pain relief. Dr. Premkumar is determining the optimal dosage range in the nanomolar and picomolar levels.
Dr. Premkumar believes RTX has the potential as a treatment for chronic, debilitating, and terminal pain in patients such as those with bone cancer or large mass abdominal cancer where other drugs are not effective. RTX could also one day treat arthritis, pain from burns, and neuralgias. The National Institute of Dental and Craniofacial Research is sponsoring a clinical trial of using RTX for the treatment of cancer pain.