Discovery Could Speed Creation of Less-Addictive Painkillers
Chemists have developed receptors that can be used to study addiction and design less expensive and less addictive pain drugs.
By Mollie Bloudoff-Indelicato
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FRIDAY, June 14, 2013 —A new discovery could speed development of less-addictive pain medications, lower the costs of treating chronic pain, and open up a whole new area of pain drug research.
The finding is a big deal for doctors and pharmaceutical companies because the discovery relates to 70 percent of the opioids on the market, which means there's the potential to apply this technology to many areas of research.
Studying painkillers is difficult because the receptors in the brain that process these drugs are few in number and almost impossible to work with outside the body. Now, scientists at the University of Pennsylvania have built a model of a receptor, called mu opioid, that responds to painkillers and contributes to drug addiction.
“The idea going forward is can you get large quantities of these to work with so you can rapidly screen new pain medication candidates,” said Jeff Saven, PhD, a chemist at the University of Pennsylvania Department of Chemistry and author of the study.
Painkiller receptors have vexed the scientific community for years. The receptors are important because the opioids that bind to them can help reduce pain, and they play a big role in drug addiction. The receptors are exceptionally hard to study because not every cell contains a painkiller receptor. They have been found in the brain, the central nervous system and, surprisingly, the gastrointestinal tract. (No one quite knows what purpose those gut receptors play, Dr. Saven said.)
To run tests and trials on new drugs requires thousands of painkiller receptors, but harvesting them directly from a patient isn’t practical. Resourceful researchers often make their own cells, using yeast cultures or bacteria like E. Coli, which, though normally a health hazard, can generate the needed biological matter for testing.
The problem for drug manufacturers, however, is that these painkiller receptors are too fat to replicate. Their high fat content makes the receptors slippery, like a microscopic slip-and-slide. In the body, this water-repelling action is crucial for cell membranes, keeping the cell’s organs from falling out while still allowing nutrients in, said Patricia Pade, MD, an addictionologist at the University of Colorado School of Medicine. In the lab, however, this hydrophobia – or fear of water – is a disaster.
Researchers can’t just tell the painkiller receptors to eat healthier, exercise, and shed some fat. By getting rid of the fat, you get rid of the receptor’s structure. It’s like what would happen if someone removed all of your bones. The receptors would “come out as a blob, and you can’t do anything with it,” said Jean Bidlack, PhD, a pharmacologist at the University of Rochester School of Medicine and Dentistry.
So Saven and his team toiled over the answer. They redesigned the protein to create a painkiller receptor that was water-friendly. More than 50 models later, the scientists successfully generated the receptor that interacts specifically with naltrexone, an anti-addiction drug.
Paving the Way for New Pain Drugs
“I treat both pain and opioid dependence,” Dr. Pade said. “There’s this huge problem with opiates and the way they operate. Some people can go on opiates and never get addicted, and other people, they’re off to the races; they get addicted very quickly.”
“Down the road, we’ll be able to take a look at these receptors and develop therapies that maximize the potential to treat the pain and minimize the addiction potential,” she added.
Of course, there's still work to be done. The next step is to apply the computer model to generate other types of receptors – a practice that may ultimately help map the brain for pain. Now that there's a working receptor model, the research could be streamlined.
“It may result in the ability of chemists to design better painkillers, longer-acting painkillers, and drugs for treating addiction, too,” Bidlack said.
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