Washington

Biotechnology companies are edging closer towards taking a promising gene-silencing technique called RNA interference (RNAi) into clinical trials.

The technique can be used to inhibit viruses in animals, such as hepatitis in mice. But it has not yet been tested in people, although companies are consolidating their intellectual property positions and filling their bank accounts in the hope of launching clinical trials, possibly this year.

RNAi relies on a natural mechanism in which animal cells target and destroy foreign genetic material (see Nature 425, 10–12; 2003). Injecting small pieces of RNA into a cell seems to trigger the destruction of any pieces of RNA matching the injected sequence. This creates the enticing prospect of ‘knocking down’ expression of RNA in viruses such as HIV or hepatitis, as well as correcting neurological problems or muscle disease.

One firm pioneering the approach was founded by biologist and Nobel laureate Philip Sharp of the Massachusetts Institute of Technology. His company, Alnylam Pharamceuticals, based in Massachusetts, went public in May, raising $30 million.

Alnylam merged last year with Ribopharma, a company based in Kulmbach, Germany, which owns a European patent on RNAi. It is working in diseases such as macular degeneration (progressive vision loss) and aims to test an RNAi technology in AIDS patients with the condition next year.

Benitec, a firm based in Queensland, Australia, has emerged as Alnylam's main rival. Last year, the US Patent and Trademark Office granted Benitec a patent that seems to cover a large range of clinical applications of RNAi. And the firm has just acquired the company Avocel, founded by Stanford geneticist Mark Kay. Co-founder Sara Cunningham says the company hopes to be listed on the US NASDAQ stock exchange by the end of the year.

Benitec also plans to fund a clinical trial for geneticist John Rossi at the City of Hope in Duarte, California. Earlier this month, Rossi said he hoped to begin as early as this July. His trial will aim to treat children infected with HIV. The children's bone-marrow stem cells will be removed and treated with an RNAi molecule. The cells will then be implanted back into the children. It is hoped that the treated cells will resist HIV infection better than untreated cells. This could be the first RNAi clinical trial to be submitted to the US Food and Drug Administration.