Silence Therapeutics Issued Novel RNAi Patent Covering High-Value Cancer Target in United States

Company Supplements Broad RNAi IP Portfolio and Strengthens Growing Position in Oncology

LONDON, May 26, 2010 - Silence Therapeutics plc (AIM: SLN) ("Silence" or the "Company")
announces the issuance of United States patent 7,723,316, titled Compositions
and Methods of RNAi Therapeutics For Treatment of Cancer and Other
Neovascularization Disease, by the United States Patent and Trademark Office
(USPTO). The issued patent, which deepens the Company's diverse portfolio of
RNA interference (RNAi) intellectual property, is broadly directed to a
double-stranded short interfering RNA (siRNA) sequence that targets vascular
endothelial growth factor receptor 2 (VEGFR2). VEGFR2 has been demonstrated
to play an important role in the vasculogenic and angiogenic activities that
contribute to the development and progression of tumors associated with a
broad range of cancers. The issued subject matter is not limited to the
VEGFR2 compositions and also includes methods for reducing tumor growth.

"Silence is compiling a powerful portfolio of intellectual property with
value tied to the unique scope of its issued claims and not simply a large
number of owned patents. Today's patent issuance fits perfectly with this
strategy, as in our opinion, there are few disease targets with IP value
comparable to VEGFR2," stated Philip Haworth, Ph.D., chief executive officer
of Silence Therapeutics. "With its demonstrated connection to a broad host of
cancers, among other disease areas, VEGFR2 is a target that we expect to help
drive the expansion of Silence's RNAi therapeutics pipeline. We view today's
milestone as more than just another patent issuance; it is a development that
significantly enhances the fundamental usefulness and functionality of our
growing RNAi IP estate."

The specific composition of matter and method claims for the issued
patent include but are not limited to:

    - A double stranded, double blunt ended siRNA molecule against VEGFR2
    - The siRNA associated with nucleic acid delivery vehicle
      optionally including PEG and/or targeting moiety
    - The siRNA associated with one or more additional nucleic
      acid molecules
    - The siRNA including at least one chemically modified nucleotide for
      stabilization
    - Methods for reducing neovascularization

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 partner-of-choice 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 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 short interfering RNA (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 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 media, Tim Brons, tbrons at vidacommunication.com, or investors, Stephanie Diaz, sdiaz at vidacommunication.com, both of Vida Communications, +1-415-675-7400, for Silence Therapeutics; or Richard Potts or Jonathan Senior both of Nomura Code Securities, +44-020-7776 1200, for Silence Therapeutics