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New technique for delivery of genes may treat epilepsy

25 March, 2003

A new technique for delivering genes to the brain may be of use in treating a number of brain conditions including epilepsy, according to research published in New Scientist.

William Pardridge, leader of the research team at the University of California in Los Angeles, explained that treating the brain is very difficult because of the "blood-brain barrier" created by the tight junctions between the cells lining the capillaries. Only molecules recognised by the cell receptors can get in, unless they are very small. The viruses most gene therapists use to deliver genes are too big, and have to be injected directly instead.

The new method, dubbed a "molecular trojan horse", is a way to get genes into the brain hidden inside fatty spheres called liposomes. The researchers coated the liposomes with a polymer called polyethylene glycol (PEG), without which they would be purged from the blood within minutes. Next, antibodies that latch on to some of the brain-capillary receptors are tethered to a few of the PEG strands. The antibodies trick the receptors into letting the liposomes pass, where they can deliver their cargo to brain cells.

Pardridge's team has already shown that the technique works in rats and have tested the liposomes in rhesus monkeys. The liposomes do not appear to have any toxic side effects, though they do deliver genes to other organs besides the brain. But the team has shown that by choosing the right switch to turn on the gene, the gene will be active only in the desired tissues.

Because the genes are not integrated into the genome, weekly or monthly injections would be needed for long-term treatment. However Pardridge sees this as an advantage as there's no risk of genes lodging permanently in the wrong place and triggering cancer - a worry with some gene therapy viruses.