They’re found huddling in the soil near the roots of coca plants and swimming in the industrial waste from pharmaceutical factories. They’re a bacteria called Stenotrophomonas maltophilia. And they eat cocaine.
Cocaine overdoses send half a million people to emergency rooms in the United States every year—but once they get there, there’s not much doctors can do beyond alleviating the symptoms. Opiate overdoses can be treated with naloxone, which dulls opiate action by competing with the drug for binding sites; addicts can be given safer alternatives like methadone. But there aren’t any approved medications for cocaine toxicity, and addiction treatment is mostly limited to behavioral and psychological approaches.
So Lei Fang, a postdoctoral researcher at the University of Kentucky’s College of Pharmacy, turned to S. maltophilia, which produces an enzyme called cocaine esterase that breaks down cocaine into inactive molecules. Split up into its constituent parts, cocaine can’t provide its characteristic high—or the risks associated with it. You can’t just inject the bacterial enzyme into humans, though. Cocaine esterase molecules need to be in pairs to work, and because protein structure is so temperature-sensitive, the natural enzyme can’t stay paired up for longer than about 12 minutes at human body temperature.
Bethany Brookshire, writing for Science News:
Fang and colleagues set about trying to make cocaine esterase a more stable dimer at body temperature. They carefully switched out the building blocks of the protein, amino acids, at the site where two enzymes become a matched pair. The scientists have already been able to create a version of cocaine esterase that can withstand human body temperature for six hours. And it’s already in a phase II clinical trial to treat cocaine overdose.
But Fang was hoping to do more than just treat overdoses—he wanted to find a drug that could treat addiction. To do that, you’d need cocaine esterase to function for a lot longer than six hours. So he and his colleagues used computer models to watch exactly what happens when heat unravels the enzyme. That helped them find the enzyme’s weak spots, and with just two more mutations they produced a new form that can stay paired up and active for more than 100 days. Injecting mice with this reinforced enzyme protects them from lethal cocaine overdoses for more than three months—the longest lasting effect that’s ever been demonstrated.
The reinforced enzyme is more active, too—it metabolizes cocaine a thousand times faster than the human body does on its own. If cocaine esterase could digest cocaine faster than addicts could get high, it might be able to disrupt the reward circuits that feed addiction. It would be an entirely new tool for helping the country’s more than one million cocaine addicts get clean—all from a little bacterium that lives in dirt and wastewater.