Quark Signs Exclusive Option Agreement with Novartis for QPI-1002

Silence Therapeutics (“Silence” or the “Company”) Silence Therapeutics’ partner Quark signs exclusive option agreement with Novartis for development and commercialisation of QPI-1002 --An siRNA drug which incorporates Silence Therapeutics’ AtuRNAi technology-- London, August 1 9 2010 – Silence Therapeutics Plc (AIM: SLN) , a leading international RNAi therapeutics company, is pleased to note that its partner, Quark Pharmaceuticals, Inc. (“Quark”), has announced the grant of an option to Novartis to obtain an exclusive worldwide license to develop and commercialise QPI -1002, a p53 temporary inhibitor siRNA drug which incorporates Silence’s AtuRNAi technology. Quark is currently conducting a Phase II clinical trial of QPI -1002 in the prophylaxis of delayed graft function in kidney transplant patients and a Phase I trial in the prevention of acute kidney injury in patients undergoing cardiac surgery. Based on the announcement issued by Quark on 18 August 2010, and under the terms of Silence’s agreemen t with Quark, Silence anticipates that its future milestone payments from this program could potentially exceed $65 million. Commenting on today’s announcement, Phil Haworth, CEO of Silence, said: “We are delighted that Novartis has chosen to take this development option for QPI-1002. This serves as further validation of Silence’s leading AtuRNAi technology and we look forward to receiving the significant milestones as the development of QPI-1002 continues.” -Ends- For further information, please contact: Silence Therapeutics Phil Haworth +1 (650) 855-1514 [email protected] Nomura Code Securities Richard Potts / Jonathan Senior +44 20 7776 1200 Vida Communication (US) Tim Brons (media)/Stephanie Diaz (investors) +1 (415) 675-7400 [email protected] [email protected] M:Communications (Europe) Mary-Jane Elliott / Emma Thompson +44 20 7920 2345 / +44 20 7920 2342 [email protected] 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 intracellul ar 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 ne xt 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 developm ent activities in Berlin and operations in Redwood City, CA.

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