Silence Therapeutics Receives Allowance from United States Patent and Trademark Office for its Core RNAi Patent

LONDON, July 31 /PRNewswire/ -- Silence Therapeutics plc (AIM: SLN), a leading European RNAi focused biotechnology company, today announced that the United States Patent and Trademark Office has allowed the Company's core RNAi patent application. The Patent Office issued a 'Notice of Allowance' for patent application 10/633,630, "Interfering RNA Molecules," which covers stabilized, small interfering RNA (siRNA) molecules with defined positional modifications. The claims cover siRNA molecules that are "blunt ended," as well as molecules with one or more "overhangs" and specifically cover Silence Therapeutics' proprietary siRNA molecules, known as "AtuRNAi".

The company also announced today it has received a Notice of Acceptance from the Australian Patent Office for patent application No. 2003260370 entitled "Further novel forms of interfering RNA molecules." The European equivalent of the US and Australian patent applications was granted by the European Patent Office in January 2007.

Iain Ross, Chairman & CEO of Silence Therapeutics, said, "This is a major milestone for Silence, our partners and investors. This patent allowance protects our AtuRNAi technology and our proprietary siRNA molecules in the United States, the largest pharmaceutical market in the world. Silence already has a strong, proprietary position in the RNAi space and this allowance builds further on our global patent portfolio. With the U.S. patent allowance, we are now significantly better positioned to achieve our goal of becoming one of the leading companies in the field of RNAi therapeutics and delivery."

Silence considers its AtuRNAi to be best-in-class siRNA molecules based on important advantages over conventional siRNA molecules, including increased stability against nuclease degradation and an increased serum half-life, while retaining therapeutic activity. AtuRNAi molecules form the basis of Silence's therapeutic research and development collaboration with AstraZeneca, as well as the Company's license and collaboration agreements with Quark Pharmaceuticals Inc. In addition, Silence is developing an internal, proprietary pipeline of systemically delivered AtuRNAi molecules that are initially focused on oncology indications.

Silence's intellectual property portfolio includes patents and patent applications covering essential chemical modification to stabilize siRNA molecules in vitro and in vivo, as well as systemic siRNA delivery systems. These include AtuPLEX, Silence's proprietary systemic delivery system that enables the functional delivery of novel siRNA therapeutic molecules to targeted tissues and cells.

About Silence Therapeutics plc (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 therapeutic 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.

SOURCE Silence Therapeutics plc