Silence Therapeutics Announces Issuance of New U.S. Patent Broadly Covering Methods for Enhancing Silencing Activity of RNAi Therapeutics

Patent Covers Structural Modifications Associated with Innovative Zamore 'Design Rules'

LONDON, June 9, 2010 - Silence Therapeutics plc (AIM: SLN) ("Silence" or the "Company")
announces the issuance of United States patent 7,732,593, titled Methods and
Compositions For Controlling Efficacy of RNA Silencing, by the United States
Patent and Trademark Office (USPTO). The issued patent, which is based on the
seminal research of Phillip D. Zamore, Ph.D., Howard Hughes Medical Institute
Investigator, the Gretchen Stone Cook Chair of Biomedical Sciences, and
Professor of Biochemistry & Molecular Pharmacology at University of
Massachusetts Medical School, generally claims methods of enhancing the RNA
silencing activity of RNA interference (RNAi) agents through certain
structural modifications. The issued claims not only cover enhancing the
efficacy of silencing gene expression using short interfering RNA (siRNA) but
also include specific claims directed to micro RNA (miRNA), pre-miRNA, and
short hairpin RNA (shRNA).

Silence owns exclusive licenses to three Zamore patent families from the
University of Massachusetts Medical School, where Zamore is the co-director
of the RNA Therapeutics Institute. These patent families disclose various
efficacy-enhancing methods and structural elements for RNAi therapeutics,
informally known as the "Zamore design rules" and based on Dr. Zamore's work
at UMass. The company expects additional U.S. patent issuances related to
this Zamore intellectual property portfolio in the coming months.

"Today's patent issuance continues to highlight the powerful synergies
created by the combined assets of Silence and Intradigm. In this case, the
exclusive licenses originally owned by Intradigm to the Zamore patent
families have provided Silence with valuable structural modification
technology that will contribute to further strengthening and expanding the
company's comprehensive RNAi therapeutic platform," stated Philip Haworth,
Ph.D., chief executive officer of Silence Therapeutics. "There is a growing
consensus within the industry regarding the important role of optimized siRNA
structure for developing more potent next generation RNAi therapeutics. With
exclusive access to the industry leading technology in this area, Silence
continues to position itself as the partner-of-choice for pharmaceutical
companies with interest in the RNAi space."

Silence Therapeutics is executing a proactive strategy to continue to
build and strengthen a diverse and competitive intellectual property
portfolio that provides the company and its partners with a strong
proprietary position in the RNAi therapeutics space. The company believes
that it will continue to make significant progress in these efforts
throughout 2010 as it expects a number of additional valuable RNAi patents to
be issued in both the United States and Europe during the year. This
consistent and meaningful IP portfolio growth reinforces Silence's belief
that the company can sustain its position as a preferred partner in RNAi
therapeutics. At present, Silence's global patent portfolio contains issued
patents and pending applications covering strategic areas of RNAi therapeutic
development including multiple proprietary siRNA delivery technologies,
potent siRNA sequences specific for high-value disease targets and key RNAi
sequence and chemical modifications.

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(TM), 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(TM)
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 operations in Berlin and Palo Alto, 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.

Phil Haworth of Silence Therapeutics, +1-650-855-1514, p.haworth at silence-therapeutics.com; or Richard Potts or Jonathan Senior, both of Nomura Code Securities for Silence Therapeutics, +44-020-7776-1200; or media, Tim Brons, tbrons at vidacommunication.com, or investors, Stephanie Diaz, sdiaz at vidacommunication.com, both of Vida Communication for Silence Therapeutics, +1-415-675-7400