SLN.L Regulatory News (SLN)

Silence Therapeutics and AstraZeneca Extend

siRNA Development Collaboration

--One-year extension to collaboration for the development

of five siRNA programs with AstraZeneca --

London, July 14 2010 - Silence Therapeutics plc (AIM: SLN) ("Silence" or the "Company") is pleased to announce a one-year extension of its ongoing research and development collaboration with AstraZeneca. Under the terms of the agreement, which has progressed well since being signed in July 2007, Silence and AstraZeneca are jointly collaborating in the identification and optimization of five novel siRNA therapeutic molecules addressing respiratory and oncology indications.

Silence's team interacts closely with several of AstraZeneca's operational units including Medimmune in the US and AstraZeneca teams in Sweden, the UK and China to progress the development of the siRNA molecules identified as a result of the collaboration. Under the terms of the agreement, AstraZeneca will retain full responsibility for clinical development and commercialization of the siRNA molecules. As announced previously, in addition to the initial £7.5 million access fee paid to Silence in July 2007, the collaboration may generate up to £200 million in fees and milestone payments plus royalties on product sales. The terms of this collaboration agreement are independent of Silence's siRNA delivery collaboration with AstraZeneca which was also extended in April this year.

Commenting on today's announcement, Philip Haworth, Ph.D., Chief Executive Officer of Silence, said: "The extension of our development collaboration with AstraZeneca is testament to the successful relationship and the progress made in this collaboration. Both teams are working closely together to optimize the five therapeutic programs based on Silence's leading siRNA technology, in addition to our collaboration investigating new delivery approaches for RNA interference. AstraZeneca is a strong endorsement of our technology and we are delighted to continue working together."

Thomas Eichholtz, Vice President Respiratory and Inflammation Research Area of AstraZeneca, commented: "AstraZeneca remains committed to the development of new therapeutic technologies that have the potential to create novel therapies. We are very pleased with the progress we have made in our collaborative agreement with Silence Therapeutics."

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

Silence Therapeutics plc (AIM: SLN) is a leading global biotechnology company dedicated to the discovery, development and delivery of targeted, systemic RNA interference (RNAi) therapeutics for the treatment of serious diseases. The company possesses multiple proprietary short interfering RNA (siRNA) delivery technology platforms including AtuPLEX™, a system that enables the functional delivery of siRNA molecules to targeted diseased tissues and cells, while increasing their bioavailability and intracellular uptake. A second, complementary delivery technology known as PolyTran™ uses a library of novel peptide-based biodegradable polycationic polymers for systemic siRNA administration. Additionally, the company has a platform of novel siRNA molecules, AtuRNAi, which provide a number of advantages over conventional siRNA molecules, including increased stability against nuclease degradation. Silence's unique RNAi assets also include structural features for a next generation of RNAi molecules and additional proprietary siRNA sequences against more than 50 highly valued oncology and other disease targets.

The company's strong and diverse intellectual property portfolio includes exclusive licenses from the University of Massachusetts Medical School on three patent families associated with the Zamore "Design Rules," which cover broad structural features of siRNA design for more potent next generation siRNA sequences.

Silence Therapeutics is headquartered in London, UK, with research and development activities in Berlin and operations in Redwood City, CA.

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.

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