Dream of gene therapy comes a step closer

Doctors of the future may use gene therapy routinely to cure cancer. A new trial from Canada may offer some hope. Charles Arthur, Science Editor, unravels the blueprint for a new cure.

The elusive promise of "gene therapy", in which cancers and inherited genetic defects could be treated by injecting replacement functional genes, may have begun to be fulfilled.

A conference in Paris next week will hear that a Canadian company has successfully managed to get new genes to seek out secondary tumours in laboratory animals. There, the replacement genes take over from the faulty genes which are allowing uncontrolled growth.

Although the technique is in its early stages - it has only so far been demonstrated with "marker" genes, rather than anti-cancer genes - and would have to pass a number of clinical hurdles before being used in humans, it suggests that the multi-pronged approach to gene therapy may begin to pay off in a few years.

That in turn would mean relief, and perhaps even a cure, for thousands of people both with cancers and inherited disorders such as cystic fibrosis.

The new system has been developed by a Canadian company, Inex Pharmaceuticals of Vancouver, and uses artificial "packages" to carry the new genes to the disease site. The packages, called transmembrane carrier systems, are made up essentially of fat droplets and are injected into the bloodstream. They contain a package of genes: in Inex's trials, these were tumour suppressor genes, which carry the code to make proteins which stop cells from reproducing wildly. The trials found that the genes' proteins were being produced in secondary tumours.

If the findings are confirmed, and can be carried over to humans, it will be an important step forward for the technique. So far, human clinical trials of gene therapy have promised much but delivered little. The first ailment to be attacked was cystic fibrosis (CF), in which a faulty gene causes overproduction of mucus in the lungs, with fatal results.

One of the first trials attempting to use gene therapy to replace a faulty CF gene was carried out in Britain. It incorporated the gene into a modified retrovirus - the class of viruses including HIV, which causes Aids - because retroviruses add their genetic material to that of their target cells. The hope was that the working CF gene would be incorporated into the lung's lining, and prevent the overproduction of mucus. However, the results have been disappointing, and success using retroviruses has remained elusive.

But the Inex technique of using fats, which is being followed by a number of other gene therapy companies, may eventually show more promise, even though it relies on an artificial package for the genes. Dr John Warner, head of Inex's gene therapy division, said: "Today, one of the main limitations in gene therapy is the inability to get genes to metastatic or widespread disease. Our technology has the potential to do just this."