Novartis has joined the ranks of those companies that are developing treatment strategies for avian flu, teaming up with Alnylam Pharmaceuticals, which specialises in an emerging drug class that acts via a mechanism known as RNA interference.

RNA interference is a naturally occurring mechanism within cells and potentially forms the basis for a new class of therapeutic products, commonly referred to as small interfering RNA (siRNA). These selectively switch off – or silence - genes within the cell.

Since many diseases are caused by the inappropriate activity of specific genes, the ability to regulate such genes selectively through RNAi could provide a means to treat a wide range of human diseases.

But, as with antisense before it – which while operating by a similar mechanism has failed to emerge as a major treatment option - the main obstacle to using siRNAs as therapeutics lies in delivery inside the cell. Alnylam says it has developed a technology that improves this delivery.

Under the terms of the agreement, Novartis will throw its weight behind a pandemic flu programme that was started by Alnylam last December. The two companies said in a joint statement that they intend to advance candidates into clinical trials, without giving a timeframe.

Mark Fishman, president of the Novartis Institutes for BioMedical Research, said: "An RNAi therapeutic could be an innovative modality, crippling the virus through incapacitating several genes. In addition, such drugs might be adapted to new strains as they emerge.” Current treatments for influenza rely on blocking enzymes involved in the replication of the virus, but there is a pressing need for new treatment options that can work in combination to boost efficacy and tackle resistant strains.

The RNAi sector is difficult to define at present, as the major use of siRNA reagents is as tools in basic research and drug discovery.

But a market report published in 2004 by Research and Markets estimated that the basic research market was valued at around $300 million and would increase to $850 million by 2010. Similarly, siRNA reagents used in drug discovery could double from its 2004 level and reach $1 billion in the year 2010. But if only a few RNAi therapeutics reach the market by the year 2010, overall sales of these compounds could expand to $3.5 billion.