SLN.L Regulatory News (SLN)

26 Sep 2008 11:55

European Patent Office raises serious concerns about legal validity of

fundamental RNA interference patent

London 26 September 2008 - On September 22, 2008, the Technical Board of Appeal of the European Patent Office issued a preliminary, non-binding opinion about the legal validity of a patent which is generally regarded as fundamental to the field of RNA interference.

The patent under discussion is European patent EP 1 144 623, which is owned by Alnylam Europe AG and originally issued in 2002. The Technical Board of Appeal is due to hold a hearing on December 9, 2008 before its final ruling on the legal validity of the patent.

The Technical Board of Appeal has stated, based on issues to be discussed at the hearing, that the amendment of the originally granted claims during opposition proceedings was inadmissible. The amendment of the original claims which resulted in a reduced scope of protection has been the basis for maintaining the patent during the opposition proceedings in 2006. The Board of Appeal is of the opinion that the disclosure of the patent does not allow a claim to a double-stranded RNA of 15 to 21 base pairs in length.

Dr. John Lucas, General Counsel & Vice President, Intellectual Property, at Silence Therapeutics, said:

"The Board of Appeal's preliminary opinion is in keeping with Silence's long-standing views on this fundamental patent . In first instance opposition proceedings, Alnylam had to reduce the scope of its claim from 15 to 49 base pairs to 15 to 21 base pairs. The patent was then maintained in this amended and restricted form."

"Silence felt this decision was in error and, along with other opponents, has sought to have the amended patent revoked through appeal. In view of this preliminary opinion, the Company believes that this patent is not legally valid. It believes the same is true of any further patents which have or might emerge from this patent as divisionals."

Iain Ross, Chairman and Chief Executive of Silence Therapeutics, said:

"This is an important event not only for Silence, but for the entire industry. While we are confident that this patent is not legally valid, we look forward to a definitive ruling on this issue in the coming months."

"Silence already has freedom to operate because we are developing short interfering RNA molecules (siRNA) that lie outside the scope of the patent's claims. Based on our core AtuRNAi patent we can provide exclusivity to our partners who wish to work in that space. "

ends

Enquiries:

For further information, please contact the following:

Silence Therapeutics plc Powerscourt +44(0)20 7307 1620 +44(0)20 7250 1446 Iain Ross, Chairman & CEO Paul Durman Melvyn Davies, Finance Director Kay Larsen Nominated Advisers Nomura Code Securities Limited +44(0)20 7776 1200 Chris Collins

About Silence Therapeutics plc (www.silence-therapeutics.com)

Silence Therapeutics plc (AIM: SLN) is a leading European RNAi-focused biotechnology company.

RNA interference (RNAi), is a Nobel Prize winning technology and one of the most exciting areas of drug discovery today. It represents a completely new approach to selectively 'silence' or inactivate disease relevant genes and as such it has the potential to create a new class of therapeutic products. RNAi could therefore offer a therapeutic approach to a broad range of diseases (cancer, infectious diseases, inherited diseases), many of which have been regarded as incurable and are not addressed by current therapeutics, therefore providing a large market opportunity.

Silence Therapeutics has developed a platform of novel short interfering RNA ('siRNA') molecules, AtuRNAi, which provide a number of advantages over conventional siRNA molecules, including increased stability against nuclease degradation. In addition, the Company has developed a proprietary systemic delivery system, AtuPLEX. This system enables the functional delivery of siRNA molecules to targeted diseased tissues and cells, while increasing their bioavailability and intracellular uptake.

Following the granting of its patents in Europe, the USA and Australia, Silence Therapeutics is one of only two companies worldwide with a proprietary position on composition of matter for siRNA therapeutics.

Silence's lead internal product, Atu027, is a proprietary AtuRNAi molecule in preclinical development for systemic cancer indications. Atu027 has successfully completed single and repeat dose toxicology and geno-toxicology studies, as well as a 28-day toxicology study using multiple dosing regimens. Silence plans a regulatory filing in 2008 to commence clinical trials for Atu027.

In March 2008 Silence Therapeutics announced a collaboration with AstraZeneca focused on the development of a range of novel delivery approaches for siRNA molecules. Under the terms of the agreement both Silence Therapeutics and AstraZeneca will be allowed to commercialize the truly novel delivery systems that the two partners develop together.

Silence Therapeutics has granted a licence to AstraZeneca to develop novel AtuRNAi therapeutics against five specific targets. This collaboration was the first industry validation of the potential application of Silence Therapeutics' proprietary AtuRNAi molecules and solidified the Company's leadership position in field of RNAi therapeutics.

The Company's AtuRNAi technology also has been sublicensed to Pfizer via Quark's license to them of the compound RTP-801i-14 for the treatment of age-related macular degeneration (AMD) and a number of other indications. This compound entered a phase II clinical study in July 2008. Silence Therapeutics also has licensed to Quark rights to the AtuRNAi structure for Quark's proprietary compound, AKIi-5, which is in a Phase I human clinical study for treatment of acute kidney injury.

Forward-Looking Statements

This press release includes forward-looking statements that are subject to risks, uncertainties and other factors. These risks and uncertainties could cause actual results to differ materially from those referred to in the forward-looking statements. All forward--looking statements are based on information currently available to Silence Therapeutics and Silence Therapeutics assumes no obligation to update any such forward-looking statements.

Silence Therapeutics is based in London, UK, and Berlin, Germany, and is listed on AIM.