UK drug major GlaxoSmithKline has lent its support to a new type of gene-targeted therapeutic strategy known as RNA interference by pledging $712 million to Sirna Therapeutics, one of the leading companies in the field.

RNA interference is a naturally occurring mechanism within cells that controls the function of genes, and companies such as Sirna have developed small interfering RNA (siRNA) strands that can be used to switch off - or silence – specific genes within the cell.

GSK has formed a strategic alliance with Sirna focused on the discovery, development and commercialisation of RNAi-based therapeutics for respiratory diseases, such as asthma and chronic obstructive pulmonary disease. It will pay the latter $12 million upfront to secure rights to the programme. A further $700 million could be forthcoming, based on clinical and developmental milestones, and Sirna would also receive royalties on any eventual sales of products that reach the market, as well as contract manufacturing revenue.

RNAi has some similarities to antisense which while operating by a similar mechanism has failed to emerge as a major treatment option, mainly because of problems associated with delivering the therapeutics into the target cells. RNAi has some advantages in this regard as the therapeutics themselves tend to be smaller and more stable than antisense oligonucleotides.

Last year, Sirna claimed a first by demonstrating for the first time that an siRNA drug could exert a therapeutic effect after systemic delivery. The study, involving an siRNA targeted against the hepatitis B virus, was published in the journal Nature Biotechnology.

Meanwhile RNAi is already becoming widely-used in drug discovery and disease research. Sales of RNAi reagents reached $1 billion in 2004, and are tipped to increase to $2.5 billion in 2010, according to a just-published report from Business Insights.

RNAi therapeutics are forecast to generate sales of around $1 billion by 2015, according to the report, which says this market has significant potential, should companies be able to overcome delivery constraints.