The impact of biotechnology on medicine has been profound. Researchers now approach drug design in completely novel ways, leading to exciting therapies. Says Jurgen Drews of Hoffmann-La Roche, "Molecular biology has invaded all areas of biology and pharmacology and there is hardly any drug research project that does not somehow benefit from recombinant DNA work."

Several avenues of research have opened up. One, how to make larger amounts of proteins usually produced by the body and put them to therapeutic use. Two, how to put together new proteins that are not found naturally and use them to block or enhance the body's normal functions. Three, how to get a person's body itself to produce deficient proteins. Four, how to use pieces of ribonucleic acid (RNA), which is very similar to DNA, to stop the production of certain proteins by blocking the process that translates the message carried in the DNA to the protein. Scientists are exploiting this "antisense" approach to treat diseases like leukemia. Five, exploring options to produce safe and more effective vaccines. Six, using DNA probes to develop quicker diagnostic tests.

Marketing the revolution
The mainstay of the genetic engineering industry is the production of recombinant proteins. In 1978, Genentech researchers genetically engineered bacteria to make human insulin. And, in 1982, the protein became the first product of the "DNA revolution" to reach the market.

Since then, therapeutic proteins have become one of the biggest money-spinners. Today, 20 recombinant proteins and about 40 products, ranging from blood-clotting enzymes and hormones to interferon proteins that stimulate immune cells, are on sale and seven times that number are in clinical development.

Cytokines -- substances produced by the immune system to mediate defence against disease -- are a group of proteins on which molecular biologists are concentrating. At least 50 types of cytokines have been identified, each of which acts in a complex manner on different target cells. The dysfunction of cytokines can lead to pathological disorders. Genetic engineers are now able to clone and produce these substances in the lab in quantities greater than those found in the body. It was virtually impossible to isolate them in sufficient quantities using conventional procedures.

One genetically engineered cytokine was interleukine 2, which could stimulate the proliferation of certain immune-system cells known as T-cells and showed promise as a wonder drug capable of killing tumour cells. Another cytokine, the tumour necrosis factor, also showed similar promise.

However, both did not live up to expectations because they turned out to be extremely toxic when present in doses higher than those found naturally in the body. "But scientists are still trying to develop new complex combination therapies that they hope will improve the clinical efficacy of cytokines to treat diseases that are currently incurable," says Anthony Mire-Sluis of the National Institute for Biological Standards and Control in the UK.

Scientists can also induce cells to produce completely novel proteins. This is done by stringing together a series of nucleotides -- the basic letters of the genetic code -- in combinations that do not occur in nature. Of the 150 or so novel proteins -- also known as oligonucleotides -- being developed across the world, says Drews, at least 30 are likely to be marketed as products in the next five years.

Monoclonal antibodies -- chemicals produced in the spleen to help the body neutralise certain foreign substances -- produced in rats are being modified or "humanised" using recombinant DNA technology. These humanised antibodies are further modified so that the human body does not recognise them as foreign. Scientists predict they will find increasing applications in targeting drugs to fight diseases like cancer, because they are capable of attacking specific target cells or proteins.

But proteins are big and cumbersome molecules that tend to get chewed up by enzymes in the bloodstream. So, scientists are combining 20 years of experience in recombinant DNA and traditional drug research techniques and looking at small molecules to solve problems that large complex proteins are unable to handle. Tularik, a San Francisco firm, for example, is concentrating on finding small molecules to clear cholesterol and treat viral diseases.

In both cases, researchers are examining transcription factors -- proteins that behave like molecular switches, turning genes on and off. These are vital for viral replication and researchers are looking for molecules to subvert their action. In the case of cholesterol, they are looking for mimics of transcription factors that stimulate cells to produce certain receptor molecules -- compounds that can mop up cholesterol in the blood.

"Antisense"
Also, using bits of an RNA sequence that is complementary to a particular gene, scientists can sabotage the production of an unwanted protein. The RNA sequence can bind to and neutralise the gene that codes for the protein. This is known as the "anti-sense" approach.

Molecular biologists have been able to stifle the production of problematic proteins -- such as those that help in the replication of viruses -- in the test-tube. One of the pioneers is a California-based company called Gilead.

Trials for antisense therapy have barely started, says Michael Riordan, president of Gilead. The University of Nebraska is just beginning trials of an antisense treatment for leukemia and a Californian company is evaluating antisense for genital warts.

In tropical countries like India, recombinant DNA technology can be put to relatively low-tech applications. The technology can be used for quicker and more reliable diagnostic tests for such diseases as hepatitis and typhoid. Routine tests for these diseases involve culturing pathogens before they can be identified and can take more than a week. Predicts Tore Goddal, director of the tropical disease research programme of WHO, "The short-term effect of biotechnology will be diagnostics."

Using radioactively labelled DNA probes that combine with DNA sequences of particular pathogens alone, researchers can detect pathogens in body fluids. Kanuri Rao and his colleagues at the International Centre for Genetic Engineering and Biotechnology (ICGEB) in New Delhi have developed an AIDS diagnostic kit based on DNA sequences of the HIV virus, which they claim will save the Indian government thousands of dollars. And, M R Das and his team at Hyderabad's Centre for Cellular and Molecular Biology are extremely excited about a kit they have developed to detect hepatitis C.