CRISPR-based gene therapy alleviates pain in mice

CRISPR-based gene silencing technique may relieve pain in mice, study finds¹. Although the therapy is still a long way from being used in humans, scientists say it’s a promising approach to alleviating chronic pain that lasts for months or years. Chronic pain is usually treated with opioids such as morphine, which can be addictive.

“It’s a real challenge that the best drugs we have to treat pain give us another disease,” says Margarita Calvo, pain doctor at the Pontifical Catholic University of Chile, in Santiago, who has no participated in the research. This is why the CRISPR-based technique is exciting, she says.

Scientists are already evaluating CRISPR therapies that alter a person’s genome as treatments for blood diseases and some forms of inherited blindness. The new version of CRISPR does not edit genes directly – it prevents them from expressing themselves – and therefore should not cause permanent changes, although it is not known how long its effects last.

A new way to target pain

Some studies estimate that a large proportion of the population in Europe and the United States – up to 50% – suffer from chronic pain^2,3. This pain can become debilitating over time by limiting a person’s activity and having a negative effect on their mental health. Despite the prevalence of the disease, few options exist to provide long-term relief without side effects. Despite this, doctors have moved away from prescribing opioids due to the risk of addiction, which has narrowed their options even further.

This situation prompted bioengineer Ana Moreno and her colleagues at the University of California at San Diego to seek an alternative treatment.

Pain enters the brain when a stimulus – such as touching a hot pan or being pricked with a sharp object – triggers neurons to send an electrical signal through nerves in the spinal cord and to the brain. . This happens when pore-like openings along the neuron – called ion channels – open and close to allow ions to pass, which carries current along the nerve. With chronic pain, parts of this pathway can become overactive.

Although there are many types of ion channels, studies have suggested that a sodium channel called Na_v1.7 could play a central role in chronic pain. When people have mutations in the gene encoding this channel, they experience extreme and constant pain or feel no pain at all.

Moreno and his team therefore thought that they might be able to stop the pain signals traveling to the brain by preventing the neurons from producing Na._v1.7. Chemists tried to block Na_v1.7 with drugs and small molecule antibodies, but struggled because these therapies also interact with structurally similar sodium channels in the body causing side effects including numbness and poor coordination. But with CRISPR, which precisely targets genes, the researchers thought they might be able to reach Na_v1.7 directly, without any off-target effect.

Harnessing the precision of CRISPR

The team started with a modified version of the Cas9 protein which is normally part of the CRISPR gene editing system. It could target, but not cut, the DNA sequence encoding Na_v1.7. The researchers attached a second “ repressor ” protein to the modified Cas9 that shuts down Na_v1.7 gene to be expressed. The researchers wrapped this system in a small, inactive virus called an adeno-associated virus that could carry it into cells.

They gave mice a spinal injection of gene silencing therapy, then tried to induce chronic pain by injecting the animals with chemotherapy drugs or inflammatory agents. These mice were more tolerant of painful stimuli. And mice that were already suffering from chronic pain benefited from the therapy, the team showed. For example, mice that received doses of chemotherapy became very sensitive to pain, but lost that sensitivity after a single injection of gene therapy. The results were published in Scientific translational medicine March 10¹.

Pain relief seemed to last, in some cases, for up to 44 weeks after the injection. “It’s quite remarkable,” says Sulayman Dib-Hajj, a neuroscientist at Yale University in New Haven, Connecticut.

Above all, Calvo says, the treatment seems to have reversed Na’s expression_v1.7 without shutting off the other sodium channels – the mice did not lose any sensation apart from pain and showed no other side effects.

Despite their enthusiasm, the scientists warn that these results are still preliminary and do not know whether the pain relief seen in mice will translate into humans. “This gives us hope that gene therapy approaches can work in humans” to treat chronic pain, says Dib-Hajj, “but there is still work to be done.”

Moreno is now managing director of Navega Therapeutics in San Diego, which plans to continue to develop the treatment in the hopes of one day testing it in humans.