SLN.L Regulatory News (SLN)

19 May 2011 07:00

FOR IMMEDIATE RELEASE

Silence Therapeutics to Present New Data from Phase I Study with Atu027 at 2011

ASCO Annual Meeting Data Highlights Disease Stabilization and Potential Antitumor Activity in Cancer Patients with Advanced Solid Tumors

London, May 19, 2011 - Silence Therapeutics plc (AIM: SLN) ("Silence" or the "Company"), a leading global RNA interference (RNAi) therapeutics company, announces that it will present new data from its ongoing Phase I study of Atu027, its lead internal therapeutic candidate, at the 2011 American Society of Clinical Oncology ("ASCO") Annual Meeting on 06 June 2011.

Top-line data includes results for 21 patients who received the study's first seven escalating doses of Atu027 and show that six of these patients experienced stable disease after three months. One patient with neuroendocrine cancer had disease stabilization for nine months, a second neuroendocrince cancer patient experienced partial regression of pulmonary metastases, and a patient with breast cancer demonstrated regression of liver metastases.

More data from the ongoing Phase I Atu027 clinical study will be the subject of a poster presentation at ASCO with the following details:

Abstract Title: First-in-human phase I study of Atu027, a liposomal small interfering RNA formulation, targeting protein kinase N3 (PKN3) in patients with advanced solid tumors Abstract #: 3057 Poster Session: General Poster Session: Developmental Therapeutics - Experimental Therapeutics

Presentation Date/Time: Mon, June 06, 2011 / 8:00am - 12:00pm

Location: Hall A - Poster Board #13F Presenters: Klaus Giese, Ph.D., chief scientific officer of Silence, and Dr. Dirk Strumberg, Professor of Medicine and Director, Department of Hematology and Medical Oncology, University of Bochum, Marienhospital Herne, the study's principal investigator

Silence's open label, single-centre, dose-finding Phase I study of Atu027 in subjects with advanced solid cancer is ongoing with dose escalation continuing. The study is designed to evaluate a total of 11 escalating doses of Atu027 and enroll approximately 33 patients. Across the first seven completed dose levels, Atu027 was generally well tolerated with no dose-limiting toxicities observed. Additionally, as consistent with preclinical data, preliminary Phase I pharmacokinetic (PK) data showed dose-dependent increase in plasma siRNA and lipid levels, suggesting no evidence of drug accumulation during repeat treatment.

Silence expects to complete the ongoing Phase I clinical trial of Atu027, one of the most clinically advanced RNAi therapeutics in the area of oncology, in the second half of 2011. The full ASCO abstract for the Phase I Atu027 study is now available online at: http://chicago2011.asco.org/.

"This positive data to date is very encouraging and we believe the disease stabilization and antitumor activity, in particular, are suggestive of a potential therapeutic benefit for extremely ill patients who have no other treatment options," said Philip Haworth, Ph.D., chief executive officer of Silence Therapeutics. "This data marks Silence's continued progress in the area of RNAi therapeutic development, and we look forward to sharing more complete findings from the ongoing Phase I study at ASCO in June."

About Atu027

Atu027 is a liposomal siRNA formulation targeting PKN3 for the treatment of advanced solid cancer. PKN3 is a key regulator during angiogenesis and lymphangiogeneis, while also acting as a major regulator of metastasis and motility during pathological processes. Accordingly, Silence believes that inhibition of PKN3 with Atu027 may lead to a reduction in nutrient and oxygen supply to solid tumors, as well as interfering with tumor formation, endothelial cell motility and metastasis.

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For further information, please contact:

Silence Therapeutics Singer Capital Markets Phil Haworth/Max Herrmann Shaun Dobson/Claes Sp¥ng +1 (650) 855-1514/+44 20 7491 6520 +44 20 32057500 p.haworth@silence-therapeutics.com shaun.dobson@singercm.com m.herrmann@silence-therapeutics.com claes.spang@singercm.com Vida Communication (US) M:Communications (Europe) Tim Brons (media)/Stephanie Diaz Katja Toon / Emma Thompson

(investors) +44 20 7920 2345 / +44 20 7920 2342 +1 (415) 675-7400 healthcare@mcomgroup.com tbrons@vidacommunication.com sdiaz@vidacommunication.com Notes for editors

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 AtuPLEXâ„¢, 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 PolyTranâ„¢ 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 reduced cytokine induction and decreased manufacturing costs. 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 lead internal drug candidate is Atu027, a liposomal AtuRNAi formulation in clinical development for systemic cancer indications and one of the most clinically advanced RNAi therapeutics in the area of oncology. 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 administration. The study is expected to be completed in the second half of 2011.

The Company's RNAi therapeutic platform has received key validation through multiple partnerships with pharmaceutical companies including AstraZeneca, Dainippon Sumitomo, Pfizer, and Quark. Silence is actively pursuing the establishment of additional partnerships.

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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