Silence Therapeutics plc, a leading European RNA interference (RNAi) focused biotechnology company, announced 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, CEO 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."

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.