Opponents of Tuschl I patent succeed in limiting scope and ambiguity in patent

FOR IMMEDIATE RELEASE Silence and other opponents of Tuschl I patent succeed in limiting scope and ambiguity in the patent -- Silence notes Tuschl I patent has no impact on its freedom to operate and has no negative effect on the Company London, UK , 9 March, 2012 – Silence Therapeutics plc (AIM: SLN) (“Silence” or “the Company”), a leading RNA interference (RNAi) therap eutics company , responds to comments that the Tuschl I (EP 1309726) patent has been upheld in European Opposition Proceedings without any modification. Concluding on 1 March 2012, t he European Patent Office held oral opposition hearings in Munich, Germany to discuss the Tuschl I patent. Silence opposed the original patent in order to remove any ambiguity in the original claims. Silence observes this and makes the following three main points: 1. The patent under review does not impact on the freedom to opera te of Silence and does not negatively affect Silence (or its Atu027 product or any of the Company’s candidates) in any way. 2. The claims as originally granted were modified during the hearing held by the Opposition Division of the EPO. 3. The effect of the amendments is to reduce ambiguity in the original patent claims, clearly excluding claims for human therapeutic use. The hearing also restricted the claims to double stranded RNAs between 21 and 23 nucleotides only. --Ends-- For further information, please contact: Silence Therapeutics Tony Sedgwick / Max Herrmann +44 20 7491 6520 [email protected] [email protected] Singer Capital Markets Shaun Dobson / Claes Spång +44 20 3205 7500 [email protected] [email protected] M:Communications Mary-Jane Elliott / Claire Dickinson +44 20 7920 2330 [email protected] Notes for editors About Silence Therapeutics plc (www.silence-therapeutics.com) Silence Therapeutics plc (AIM: SLN) is a leading biotechnology company dedicated to the discovery, development and delivery of targeted, systemic RNA interference (RNAi) therapeutics for the treatment of serious diseases. Silence offers one of the most comprehensive short interfering RNA (siRNA) therapeutic platforms available today based on a strong intellectual property portfolio and large clinical safety database. Silen ce’s clinical siRNA product pipeline is one of the broadest in the industry. The Company possesses multiple proprietary siRNA delivery technology platforms including AtuPLEX™ , DACC and DBTC. AtuPLEX enables the broad functional delivery of siRNA molecules to targeted diseased tissues and cells, while increasing their bioavailability and intracellular uptake. The DACC delivery system allows functional delivery of siRNA molecules selectively to the lung endothelium with a long duration of target mRNA and prot ein knock -down. The DBTC delivery system enables functional delivery of siRNA molecules selectively to liver cells including hepatocytes. Additionally, the Company has a platform of novel siRNA molecules based around its AtuRNAi chemical modification techn ology, which provides a number of advantages over conventional siRNA molecules. Silence’s unique RNAi assets also include structural features for RNAi molecules and specific design rules for increased potency and reduced off-target effects of siRNA sequences. The Company’s lead internal drug candidate is Atu027, a liposomal formulation in clinical development for systemic cancer indications and one of the most clinically advanced RNAi therapeutic candidates in the area of oncology. Atu027 incorporates two of the Company’s technologies, AtuRNAi and AtuPLEX™. Silence is currently conducting an open-label, single- centre, dose-escalation Phase I study with Atu027 in patients with advanced solid tumors involving single, as well as repeated, intravenous administ ration. Encouraging interim safety and pharmacokinetic data were presented at the American Society of Clinical Oncology Annual Meeting in June 2011. The study is expected to be completed in the first half of 2012. The Company’s RNAi therapeutic platform has received key validation through multiple partnerships with pharmaceutical companies including AstraZeneca, Dainippon Sumitomo, Pfizer/Quark, and Novartis/Quark. Silence is actively pursuing the establishment of additional partnerships. Silence Therapeutics has operations in both Berlin and London.

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