Are living organisms a suitable way to make new pharmaceuticals?

Most drug production is based on chemical expertise. But some are produced through biological routes - such as erythropoietin (EPO), which is made by genetically modified mammalian cells grown in culture.

Proteins are large, chemically complex molecules that would not be easy to make synthetically. But nature has been making them for millions of years, interpreting the information stored in DNA.

It was originally hoped that genetically engineered bacteria might be able to produce therapeutically useful proteins. Unfortunately, it is hard to get mammalian proteins folded properly in bacteria. And they cannot add the multitude of sugars that many proteins have attached to them. Yeast cells and cultured mammalian cells have been used instead.

An ambitious attempt has been made to speed up production of the antimalarial drug artemisinin in yeast. Currently, it has to be extracted from the sweet wormwood plant. Researchers engineered genes from its biosynthetic pathway into yeast, enabling it to produce a precursor, artemisinic acid, which is relatively easy to convert into artemisinin. This may provide a route to increase the supply of a key antimalarial at an affordable price.

A neat solution would be to engineer animals so that they produced medicines in their milk - 'pharming'. This could be extracted easily and the animal could go on making the medicine throughout its life.

About the only successful example, however, is Atryn - anti-thrombin, a protein that inhibits blood clotting - which is produced in genetically modified goats. The product was given the go-ahead in Europe in 2006. A small number of companies in Europe and the USA are experimenting with a variety of domesticated animals to produce medicinal products.

Companies are also exploring the use of genetically modified plants to produce therapeutic proteins. Several vaccines are currently being grown in plants. Products have progressed as far as phase II trials in Europe, and commercial products could be on the market elsewhere within a couple of years.

However, these products will present another regulatory challenge. The use of GM plants also raises the controversies associated with GM food crops (although the scale of pharming would be tiny compared with food production). The main fears are about contamination of non-engineered crops and their escape into the environment. And the question of public acceptability may also be significant.