By Elizabeth Norton
A single dose of a century-old drug has eliminated autism symptoms in adult mice with an experimental form of the disorder. Originally developed to treat African sleeping sickness, the compound, called suramin, quells a heightened stress response in neurons that researchers believe may underlie some traits of autism. The finding raises the hope that some hallmarks of the disorder may not be permanent, but could be correctable even in adulthood.
That hope is bolstered by reports from parents who describe their autistic children as being caught behind a veil. “Sometimes the veil parts, and the children are able to speak and play more normally and use words that didn’t seem to be there before, if only for a short time during a fever or other stress” says Robert Naviaux, a geneticist at the University of California, San Diego, who specializes in metabolic disorders.
Research also shows that the veil can be parted. In 2007, scientists found that 83% of children with autism disorders showed temporary improvement during a high fever. The timing of a fever is crucial, however: A fever in the mother can confer a higher risk for the disorder in the unborn child.
As a specialist in the cell’s life-sustaining metabolic processes, Naviaux was intrigued. Autism is generally thought to result from scrambled signals at synapses, the points of contact between nerve cells. But given the specific effects of something as general as a fever, Naviaux wondered if the problem lay “higher up” in the cell’s metabolism.
To test the idea, he and colleagues focused on a process called the cell danger response, by which the cell protects itself from threats like infection, temperature changes, and toxins. As part of this strategy, Naviaux explains, “the cells behave like countries at war. They harden their borders. They don’t trust their neighbors.” If the cells in question are neurons, he says, disrupted communication could result—perhaps underlying the social difficulties; heightened sensitivity to sights, sounds, and sensations; and intolerance for anything new that often afflict patients with autism.
The key player may be ATP, the chief carrier of energy within a cell, which can also relay messages to other nearby cells. When too much ATP is released for too long, it can induce a hair-trigger cell danger response in neighboring neurons. In 2013, Naviaux spelled out his hypothesis that autism involves a prolonged, heightened cell danger response, disrupting pathways within and between neurons and contributing to the symptoms of the disorder.
The same year, he and his colleagues homed in on the drug suramin as a way to call off the response. The medication has been in use since the early 20th century to kill the organisms that cause African sleeping sickness. In 1988, it was found to block the so-called purinergic receptors, which bind to compounds called purines and pyrimidines—including ATP. These receptors are found on every cell in the body; on neurons, they help orchestrate many of the processes impaired in autism—such as brain development, the production of new synapses, inflammation, and motor coordination.
To determine if suramin could protect these receptors from overstimulation by ATP, Naviaux’s team worked with mice that developed an autism-like disorder after their mothers had been exposed to a simulated viral infection (and heightened cell danger responses) during pregnancy. Like children with autism, the mice born after these pregnancies were less social and did not seek novelty; they avoided unfamiliar mice and passed up the chance to explore new runs of a maze. In the 2013 paper, the researchers reported that these traits vanished after weekly injections of suramin begun when the mice were 6 weeks old (equivalent to 15-year-old humans). Many consequences of altered metabolism—including the structure of synapses, body temperature, the production of key receptors, and energy transport within neurons—were either corrected or improved.
In the new study, published online today in Translational Psychiatry, the researchers found equally compelling results after a single injection of suramin given to 6-month-old mice (equivalent to 30-year-old humans) with the same autism-like condition. Once again, previously reclusive animals approached unknown mice and investigated unfamiliar parts of a maze, suggesting that the animals had overcome the aversion to novelty that’s a hallmark of autism in children. After the single injection, the team lowered the levels of suramin by half each week. Within 5 weeks most, but not all, of the benefits of treatment had been lost. The drug also corrected 17 of 18 metabolic pathways that are disrupted in mice with autism-like symptoms.
Naviaux cautions that mice aren’t people, and therapies that are promising in rodents have a track record of not panning out in humans. He also says that prolonged treatment with suramin is not an option for children, because it can have side effects such as anemia with long-term use. He notes that there are 19 different kinds of purinergic receptors; if suramin does prove to be helpful in humans, newer drugs could be developed that would target only one or a few key receptors. The researchers are beginning a small clinical trial in humans of a single dose of suramin that they hope will be completed by the end of the year.
The study is exciting, says Bruce Cohen, a pediatric neurologist at Akron Children’s Hospital in Ohio. “The authors have come up with a novel idea, tested it thoroughly, and got a very positive response after one dose.” He notes, however, that the mice with a few characteristics of autism don’t necessarily reflect the entire condition in humans. “Autism isn’t a disease. It’s a set of behaviors contributing to hundreds of conditions and resulting from multiple genes and environmental effects. Great work starts with a single study like this one, but there’s more work to be done.”