Jab using body's painkillers could help 500,000 in pain

Hope for cancer patients whose suffering can no longer be eased by morphine.

Ian Sample
Washington DC

Doctors in the US have begun a clinical trial of a gene therapy that uses the body's natural painkillers to bring relief to patients who cannot be helped with conventional drugs. They hope that a single injection could provide relief for up to six months in people whose pain is so severe that morphine and other frontline drugs have little effect or cannot be used because of their side-effects.

The trial was launched after a pilot study this year of people with intractable cancer pain showed the therapy was safe. The therapy smuggles a gene into sensitive nerves beneath the skin that makes the cells release natural chemicals that alleviate pain.

Dr David Fink, who is leading the research at the University of Michigan, said that the trial was the first to investigate if the technique was effective in humans.

"We have started with people who are in pain from terminal cancer, but the approach is applicable for intractable pain from inflammatory conditions, such as arthritis of the hip and any number of other situations," he said.

Half a million people in the UK experience chronic pain, often when their nerves are damaged by cancer, diabetes, surgery or disease, according to the Neuropathy Trust. The constant pain leads to sleeplessness and depression that can be devastating. The therapy uses a form of herpes virus that is modified to prevent it from replicating and causing illness when injected into the body. The virus is engineered further to carry a gene that produces a natural painkiller called enkephalin.

When the virus is injected into the skin, it finds its way into nearby peripheral nerves – those outside the brain and spinal cord – and makes them produce enkephalin for a month to six weeks. Other work by Fink's team suggests this could be extended by up to six months.

The injection allows doctors to target specific parts of the body that are in pain, rather than prescribing a drug that affects the whole body. Patients given high doses of morphine for severe pain can suffer broad and debilitating side effects, including lethargy, confusion and constipation. Fink reported a small trial to investigate the safety of the treatment in April this year. Ten patients with intractable pain were given injections. Those who received high doses reported feeling less pain than those who had medium doses. Those who had low-dose injections felt no benefit.

The latest trial will compare tens of patients who have the injections with a control group that receives a placebo jab. Fink, who outlined the trial at the Society for Neuroscience conference in Washington, expects to have results at the end of the year.

Andreas Beutler, a specialist in chronic pain at the Mayo Clinic in Minnesota, said Fink's work was impressive. "There is a clear clinical need in patients with intractable chronic pain and other diseases involving the peripheral nervous system, such as hereditary neuropathies, where current treatments, while helpful, are failing," Beutler said.

Scientists will be particularly interested to see if the herpes virus used manages to evade the human immune system indefinitely. The latest version was designed to stay active for only a few weeks and has been tested only in a small group of patients at full dose. Long-term effects involving the immune system may not have been apparent.

If the gene therapy is found to ease pain without causing serious side-effects, the virus that Fink has developed could potentially be used to deliver other genes to the nervous system.

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