How Do You Get Drugs to the Brain? Maybe Try a Parasite

In a new study, a global team of researchers hijacked the system Toxoplasma uses to secrete proteins into its host cell. The team genetically engineered Toxoplasma to make a hybrid protein, fusing one of its secreted proteins to a protein called MECP2, which regulates gene activity in the brain—in effect, giving the MECP2 a piggyback ride into neurons. Researchers found that the parasites secreted the MECP2 protein hybrid into neurons grown in a petri dish as well as in the brains of infected mice.

A genetic deficiency in MECP2 causes a rare brain development disorder called Rett syndrome. Gene therapy trials using viruses to deliver the MECP2 protein to treat Rett syndrome are underway. If Toxoplasma can deliver a form of MECP2 protein into brain cells, it may provide another option to treat this currently incurable condition. It also may offer another treatment option for other neurological problems that arise from errant proteins, such as Alzheimer’s and Parkinson’s disease.

The Long Road Ahead

The road from laboratory bench to bedside is long and filled with obstacles, so don’t expect to see engineered Toxoplasma in the clinic anytime soon.

The obvious complication in using Toxoplasma for medical purposes is that it can produce a serious, lifelong infection that is currently incurable. Infecting someone with Toxoplasma can damage critical organ systems, including the brain, eyes, and heart.

However, up to one-third of people worldwide currently carry Toxoplasma in their brain, apparently without incident. Emerging studies have correlated infection with increased risk of schizophrenia, rage disorder, and recklessness, hinting that this quiet infection may be predisposing some people to serious neurological problems.

The widespread prevalence of Toxoplasma infections may also be another complication, as it disqualifies many people from using it for treatment. Since the billions of people who already carry the parasite have developed immunity against future infection, therapeutic forms of Toxoplasma would be rapidly destroyed by their immune systems once injected.

In some cases, the benefits of using Toxoplasma as a drug delivery system may outweigh the risks. Engineering benign forms of this parasite could produce the proteins patients need without harming the organ—the brain—that defines who we are.