LONDON, July 11 /PRNewswire/ --

Silence Therapeutics plc (London AIM: SLN), a leading European RNA interference (RNAi) focused biotechnology company, announced today the successful opposition of a fundamental Alnylam Pharmaceuticals, Inc. European patent resulting in the patent being revoked in its entirety.

The Opposition Division of the European Patent Office, following a three day hearing, announced its decision to revoke European Patent EP 1 230 375, exclusively licensed to Alnylam Pharmaceuticals from Cancer Research Technology, Ltd (UK). The Patent, commonly referred to as the "Glover" patent, broadly relates to medicaments comprising an RNA interference mediating RNA molecule.

Opposition briefs to the Glover patent had been filed by Silence Therapeutics AG, Sanofi-Aventis Deutschland GmbH, Quark Biotech, Inc., Sirna Therapeutics, and Nucleonics, Inc. In the course of the oral hearing which lasted from July 08 to July 10, 2008, Cancer Research Technology Ltd. filed a total of seven auxiliary requests so as to defend the patent in a limited manner. None of these requests was able to overcome the concerns of the Opposition Division that the patent was legally invalid. Cancer Research Technology and Alnylam are expected to appeal the decision.

Jeff Vick, Chief Executive Officer of Silence Therapeutics, said, "The Glover patent was arguably Alnylam's broadest patent and the successful opposition represents an important victory for us in allowing us to maintain our Freedom to Operate. We have long believed that this patent would be revoked and are very pleased with the outcome. This decision by the European Patent Office further strengthens our leading position in the field of RNA interference."

Notes to Editors:

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

Silence Therapeutics plc (AIM: SLN) is a leading European RNAi focused biotechnology company. RNAi can selectively 'silence' genes linked to the onset of disease. RNAi is a Nobel Prize winning technology and one of the most promising areas of drug discovery and development today.

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.

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 (LSE: AZN) 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.

In July 2007, Silence Therapeutics formed its first research and development collaboration with AstraZeneca to develop novel AtuRNAi therapeutics against five specific targets, including those in respiratory indications. 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 the clinic in early 2007. 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. In May 2008 the U.S. Food and Drug Administration (FDA) approved an Investigational New Drug application (IND) from Quark for another siRNA product based on Silence's unique proprietary chemistry. The product, DGFi, which uses the same AtuRNAi molecule as AKIi-5, was discovered and is being developed by Quark for use in prevention or treatment of delayed graft function in kidney transplantation.

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

About RNAi

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.

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.

Web site: http://www.silence-therapeutics.com

Jeff Vick, Chief Executive Officer, or Melvyn Davies, Finance Director, both of Silence Therapeutics plc, +44-0-20-7307-1620; or European Contacts, Citigate Dewe Rogerson, David Dible or Heather Keohane, +44-0-20-7638-9571; or Nominated Advisers, Nomura Code Securities Limited, Chris Collins, +44-0-20-7776-1200; or U.S., LaVoie Group, +1-978-745-4200, Donna LaVoie, ext. 103, or Lisa Rivero, ext. 106