How stem cells, CRISPR and skin grafts could help combat cocaine addiction
Extremely addictive and prone to being abused, cocaine is one of the most dangerous illicit drugs out there. Now, researchers at the University of Chicago have developed a novel form of treatment that could help cut back on a person's desire for the drug and reduce its damaging effects in the body. The method involves removing a small patch of skin, introducing genes that produce cocaine-degrading enzymes, and then grafting it back onto the patient.
According to the 2016 National Survey on Drug Use and Health, about 1.9 million people in the US were current users of cocaine, or about 0.7 percent of the US population. It's a particularly nefarious substance, as regular use builds up a person's tolerance to the point where bigger doses are required to get the same high. Once addiction sets in it's hard to beat, since there are no approved medications to treat it, and it's easy to relapse even after years of staying clean.
To find new ways to treat addiction and overdose, scientists are getting creative. In recent years, new treatment ideas have included using laser light pulses or magnetic brain stimulation to reduce patient's desire for drugs, and identifying a membrane protein that at higher levels seems to prevent drug-related "pleasant memories" from sticking.
The new study takes a completely different approach, combining three techniques that individually have proven successful in the past.
"We had an effective enzyme that can degrade cocaine with high efficiency," says Ming Xu, co-lead author of the study. "We had CRISPR, a genetic tool that enabled us to introduce a gene of interest inside the cell without affecting other genes. And, most importantly we had technology, developed by my colleague Xiaoyang Wu, to put genetically modified skin cells back into an immunocompetent recipient. That saved us a lot of trouble."
In tests on mice, the UChicago team started by removing a small section of skin, to collect epidermal stem cells. Using CRISPR, these were then edited so they have a gene that expresses the enzyme butyrylcholinesterase (BChE), which is effective at breaking down cocaine.
BChE is naturally found in the body, but not in levels high enough to prevent the worst of cocaine's effects. Directly injecting the enzyme into the muscle has proven ineffective, because it doesn't last long enough.
The researchers got around this by turning those stem cells into BChE-producing factories. From the relative safety of the skin, these genes are able to effectively deliver the enzyme into the bloodstream. In the tests, the team found that this treatment prevented the mice from seeking out cocaine, and even managed to prevent mice from dying from what would normally have been a lethal dose of the stuff.
The mice also responded well to the stem cells and the skin graft. The introduced skin cells functioned as normal healthy cells would, and the mice continued to express BChE at high levels for more than 10 weeks, without the immune system launching an attack. One year on, the oldest mice are still alive and healthy, the researchers report.
"We demonstrated key evidence that engineered skin transplants can efficiently deliver hBChE in vivo and protect against cocaine-seeking and overdose," say the authors. "Taken together, our results show promise of cutaneous gene therapy as a safe and cost-effective therapeutic option for cocaine abuse in the future."
The researchers say this method could potentially be adapted to help people with addictions to other substances, such as alcohol, nicotine and opioids.
The research was published in the journal Nature Biomedical Engineering.
Source: University of Chicago