As Stephen Brimijoin, Ph.D. speaks, his cupped hands approach you and pull away in imitation of the action of an enzyme that may transform cocaine addiction. Nestled among the scientific tomes and stacks of research papers on a shelf above sits a silent observer in the form of a gray rodent. Eyes open and intent, it appears to be paying close attention, but nary a whisker moves. It is a plush toy rat, perhaps a fitting talisman for its master.

A long path to a miraculous recovery

Two years ago Dr. Brimijoin was holding a real rat in his hands. Dying of a cocaine overdose, it had less than a minute to live. While he watched, Yang Gao, his assistant, skillfully inserted an intravenous line and administered an experimental compound. Then the two scientists held their breath. Within seconds the convulsions stopped. Within minutes the rat was back on its feet, sniffing and scurrying about—rescued, alive and healthy. Dr. Brimijoin sat back, his own heart pounding. He and Yang Gao looked at each other and the rat. Had they found an antidote to cocaine overdose? And if so, might it also be useful in treating cocaine addiction?

Answers to these questions are the focus of a $1.5 million grant from the National Institutes of Health (NIH) awarded this year to Dr. Brimijoin as principle investigator, and Marilyn Carroll, Ph.D., at the University of Minnesota. The path to their discovery represents a fine example of the fusion of pure science and clinical research. It began 40 years ago when a young Dr. Brimijoin, fired with a commitment to the new field of neuropharmacology, was fortunate to join the laboratory of Julius Axelrod, Ph.D. at the NIH. Dr. Axelrod won a Nobel Prize for his contributions to unraveling the mysteries of neurotransmission, the means by which nerves communicate with one another. It was a subject that would remain a major theme in Dr. Brimijoin’s research.

Signals in the nervous system are carried by by substances called neurotransmitters. The chemical reactions that create and break down neurotransmitters are driven by catalysts known as enzymes. When he came to Mayo Clinic in 1971, Dr. Brimijoin focused on these enzymes. Years and many discoveries later, one of them would set him on the trail toward treatment for cocaine abuse and overdose.

Cocaine’s addictive and toxic properties

Cocaine, a white powder extracted from the plant Erythroxylon coca, produces a powerful euphoria and is among the most addictive of all substances. It can also be highly toxic. Whether sniffed through the nose or injected into a vein, it reaches the bloodstream with immediate consequences. In some first-time users a single dose can cause stroke, heart attack, respiratory failure or lethal convulsions. Prolonged use can induce paranoia and fulminant psychosis. Over time, most addicts require stronger and more frequent doses to reach their original ”high.” At the same time, addicts may become increasingly sensitive to cocaine’s physical effects—abnormal heart rhythm, respiratory difficulty, seizures, abdominal pain, and nausea—and even low doses may induce deadly reactions without warning.

Cocaine’s addictive power comes from neurochemical changes deep within the brain. These deep brain structures, designed to drive us to search for food, water, and opportunities for procreation, act together as an elegantly coordinated reward system. Cocaine causes the build-up of the neurotransmitter dopamine at the junction between two nerves, helping to create the short-lived state of euphoria. But it has dangerous long-term effects, laying down un-erasable memories of the “high” in the brain’s reward centers. These memories are easily triggered by environmental cues and translate into overpowering cravings—cravings that can occur long after one becomes abstinent. Thus it is that relapse occurs in more than 80 percent of those who try to give up the drug.

Re-engineering a natural defense

Most efforts at blocking cocaine have focused on restoring dopamine’s natural balance in the brain. Dr. Brimijoin focused instead on a natural enzyme in the blood, which breaks down many plant poisons, including cocaine, into harmless byproducts. He calls it “one of our key defenses in the eternal war between plants and animals.”

Might a modified version of this enzyme destroy or “metabolize” cocaine molecules before they could begin to act? Dr. Brimijoin set out to “re-engineer” the enzyme, taking it down to its atomic structure, realigning its components (amino acids) and its three-dimensional shape. This process, called “structure-based mutagenesis,” has only been possible in the last 10 years. Yuan-Ping Pang, Ph.D., a key Mayo collaborator, lent his critical expertise in protein structure to Dr. Brimijoin’s efforts (Read a story about Dr. Pang’s research). The years of study on enzymes paid off, and soon they had converted the enzyme into a new, more powerful cocaine-eating enzyme that they called CocH (cocaine hydrolase).

When they applied CocH to cocaine in a test tube, it destroyed the drug 50 times faster than the natural enzyme. Once the findings went public, in 2002, Mayo’s team and other research groups found ways to increase the power of CocH until it was 1000 times faster. Would it be fast enough to destroy cocaine in the bloodstream in the few seconds before it reached the brain? The answer turned out to be a resounding “Yes!” Blood samples taken from CocH-treated rats just seconds after intravenous cocaine injection showed the drug had already vanished.

Preventing toxic overdose

But what if cocaine molecules had already reached the brain as is the case in toxic overdose? Was there a way to prevent their lethal effects? Many experts thought that once attached, cocaine molecules were tightly bound to their brain targets. And it seemed unlikely that the CocH enzyme could help because it was too large to pass from blood vessels into the brain itself.

Yet there was the overdosed rat, minutes before in the throes of life-threatening seizures, now waddling happily about. How had cocaine’s effects in its brain been shut down? What Dr. Brimijoin had discovered, before the amazing rescue, was that cocaine molecules were not so tightly bound to the brain. In fact, they vibrated on and off their targets at a rapid rate. As CocH eliminated all the cocaine molecules in the rat’s bloodstream, those in the brain were quickly drawn back into the bloodstream where they, too, were destroyed. So the rat lived, as did every one of the dozen others tested. Dr. Brimijoin thinks the enzyme would work just as well in people. He and Dr. Carroll anticipate a clinical trial to test this possibility. It may involve emergency medical service (EMS) teams applying the CocH antidote right at the scene of suspected overdose or life-threatening response to cocaine.

Preventing Drug Relapse

With the laboratory studies of cocaine overdose rescue behind them, the team turned to the issue of cocaine addiction. Cocaine use has risen steadily over the past 30 years. In 2005, according to the National Institute on Drug Abuse, over 2.5 million people in the U.S. were current users. Between 1995 and 2002, cocaine-related emergency room visits rose 33 percent. Dr. Carroll is well aware of these facts. She has devoted her career to behavioral and pharmacological interventions to prevent the devastation that drug abuse causes in addicts, their families, and their communities.

The Minnesota Partnership for Biotechnology and Medical Genomics brought Drs. Carroll and Brimijoin together to test the idea that CocH would reduce relapse in addicted subjects. Their work was based on Dr. Carroll’s sophisticated behavioral model of “reinstatement.” The model accurately predicts that addicted rats that have learned to press levers for drug reward, will abandon lever pressing after forced withdrawal from the drug. However, when re-exposed to a single dose, they return to lever pressing with a vengeance. Their behavior resembles that of addicts who, after long periods of sobriety, succumb to a single temptation that then stimulates a fully reawakened addiction. To their delight, the investigators found that CocH completely abolished this relapse-reinstatement behavior in laboratory animals.

CocH has no known side effects and it is hoped it can be used to prevent drug relapse in humans. For example, it might be administered on a regular basis to former addicts, so that when cravings trigger cocaine use, cocaine molecules would be cleared from the blood before the drug can take effect. Dr. Brimijoin is also working on a gene therapy that would make injections unnecessary.

From theory to practice

Mayo Clinic prides itself in providing an atmosphere in which clinical questions stimulate experiments in the lab, and the theoretical questions of basic science affect clinical practice. The best science supports both ends of the spectrum of inquiry. When Julius Axelrod, received his Nobel Prize four decades ago, the presenter said that his discoveries in neurotransmission might be thought of as being of “strictly theoretical interest.” However, he noted, they led to “extensive practical advances.” One example he chose was how ancient intoxicating substances, from mushrooms to coca leaves, were finally understood, not as the effect of “mystical forces,” but of poisons on the chemical transmission of nerve impulses in the brain. So, too, Dr. Brimijoin’s research may seem at first glance to have been “strictly theoretical.” How fitting that his original theoretical questions led to an antidote for the poisonous and lethal effects of the coca plant.

— Penelope Duffy, September 2008