Phase 1 Clinical Trial to Test Gene Therapy for Chronic Pain

Scientists from the University of Michigan are beginning a phase 1 clinical trial for the treatment of cancerrelated pain that uses a novel gene transfer vector-an agent used to carry genes into cells-injected into the skin to deliver a pain-relieving gene to the nervous system.

Investigators are using a vector created from the herpes simplex virus (HSV) to deliver the gene for enkephalin, an opioid peptide. The enkephalin peptide will be released selectively in the spinal cord at a site involved in transmitting pain from the affected body part to the brain. Opioid peptides exert their pain-relieving effects by acting at the same receptor as morphine and related opiate drugs.

David Fink, MD, who helped develop the vector and will direct the study, noted: “In preclinical studies, we have found that HSV-mediated transfer of enkephalin can reduce chronic pain. After almost 2 decades of development and more than 8 years of studies in animal models of pain, we have reached the point where we are ready to find out whether this approach will be effective in treating patients.”

One key problem in treating pain is that the areas targeted by traditional analgesics are often widely distributed in the CNS. This can result in adverse effects that prohibit the use of those drugs at fully effective doses.

This is the first human trial of gene therapy for pain, and it is the first study to test the use of a nonreplicating HSV-based vector to deliver a therapeutic gene to humans. If proven, this technique may also help treat other types of chronic pain, including pain from nerve damage in persons with diabetes.

Although the trial looks promising, Fink warned, “A treatment is at least several years off.”