13 May 1998

Hitching A Ride In A Virus

Remember that movie Fantastic Voyage? Where Raquel Welch gets shrunken along with a submarine and a homicidal maniac? Good, then you're ready for this story.

Viruses get a lot of bad press but professors at Temple University and Montana State University suggest the humble virus may be elevated to the dizzy height of drug delivery agent in the fight against disease. Reported in Nature this week, Trevor Douglas and Mark Young have demonstrated a method by which viruses may be taken apart, purged of genetic material, reassembled and used as couriers for selected substances.

The researchers loaded an organic substance similar to heparin, commonly used to treat coronary thrombosis, into cowpea chlorotic mottle virus. Douglas and Young explain: "In their native state, viruses are protein assemblies which act as host containers for nucleic acid storage and transport. We have subverted this natural function." The process utilizes a "gating mechanism", or "reversible structural transition", in the protein coats of some simple viruses which allows admission and expulsion of organic and inorganic material.

Using this technique, technicians will be able to remove the DNA or RNA of a virus, and use the remaining protein coat to contain and deliver other substances.

"Gating" is possible for a large number of viruses of different shapes and sizes. This suggests that drug delivery by this method would not be limited to any particular class of medicines. The simple protein coats can be "easily and routinely modified by design," and could therefore be altered to target certain cell types, such as cancer cells. There is also the possibility of delivering drugs to specific sites.

Douglas and Young point out that the viruses used pose no threat to humans: they are relatively simple plant viruses which do not use animals as hosts, are safe to eat and have had their genetic material removed.