New Technology May Permit Drug Delivery to the Brain

Scientists may have finally figured out how to safely open and close the blood-brain barrier so that therapies to treat Alzheimer’s disease, multiple sclerosis, and cancers of the central nervous system might effectively be delivered.

The researchers revealed that adenosine, a molecule produced by the body, could modulate the entry of large molecules into the brain. For the first time, the researchers discovered that when adenosine receptors are activated on cells that comprise the blood-brain barrier, a gateway into the blood-brain barrier can be established.

Although the study was performed on mice, the researchers have also found adenosine receptors on these same cells in humans. They also discovered that an existing US Food and Drug Administration (FDA)-approved drug called Lexiscan, an adenosine-based drug used in heart imaging in very ill patients, can also briefly open the gateway across the blood-brain barrier.

The blood-brain barrier is composed of the specialized cells that make up the brain’s blood vessels. It selectively prevents substances from entering the blood and brain, only allowing such essential molecules as amino acids, oxygen, glucose, and water through. The barrier is so restrictive that researchers could not find a way to deliver drugs to the brain--until now.

“The biggest hurdle for every neurological disease is that we are unable to treat these diseases because we cannot deliver drugs into the brain,” said Dr. Margaret Bynoe, associate professor of immunology at Cornell University’s College of Veterinary Medicine (Ithaca, NY, USA) and senior author of an article published September 14, 2011, in the Journal of Neuroscience. Aaron Carman, a former postdoctoral associate in Dr. Bynoe’s lab, is the article’s lead author. The study was funded by the US National Institutes of Health (Bethesda, MD, USA).

“Big pharmaceutical companies have been trying for 100 years to find out how to traverse the blood-brain barrier and still keep patients alive,” said Dr. Bynoe, who with colleagues have patented the findings and have started a company, Adenios, Inc. (Ithaca, NY, USA), which will be involved in drug testing and preclinical trials.

Researchers have tried to deliver drugs to the brain by engineering them so they would bind to receptors and “piggyback” onto other molecules to get across the barrier, but up to now, this modification process leads to lost drug effectiveness, Dr. Bynoe reported. “Utilizing adenosine receptors seems to be a more generalized gateway across the barrier. We are capitalizing on that mechanism to open and close the gateway when we want to.”

In the article, the researchers described successfully transporting such macromolecules as large dextrans and antibodies into the brain. “We wanted to see the extent to which we could get large molecules in and whether there was a restriction on size,” Dr. Bynoe stated.

The researchers also effectively delivered an anti-beta-amyloid antibody across the blood-brain barrier and observed it binding to beta-amyloid plaques that cause Alzheimer’s in a transgenic mouse model. Similar research has been initiated for treating multiple sclerosis, where researchers hope to tighten the barrier instead of open it, to prevent destructive immune cells from entering and causing disease.

Although there are many known antagonists (drugs or proteins that specifically block signaling) for adenosine receptors in lab mice, future studies will try to identify such drugs for humans, according to the investigators.

The researchers also plan to explore delivering brain cancer drugs and better understand the physiology behind how adenosine receptors modulate the blood-brain barrier.

Related Links:
Cornell University’s College of Veterinary Medicine
Adenios