Placing Agreement with Silence Therapeutics plc

10 April 2013

Antisoma plc ("Antisoma")

Placing Agreement with Silence Therapeutics plc ("SLN")

The Directors announce that on 9 April 2013, Antisoma entered into a placing agreement to subscribe for 2,000,000 new ordinary shares in SLN under SLN's proposal to raise approximately £19.0m before expenses by means of a placing of 9,512,500 new ordinary shares at an issue price of 200p per share. As announced by SLN on 10 April 2013, SLN intends to effect a share capital consolidation on the basis of 1 Consolidated Ordinary Share for every 50 Existing Ordinary Shares held. Immediately following the share consolidation, the placing of 9,512,500 new ordinary shares is expected to occur. Both the share consolidation and the placing of new ordinary shares are conditional upon approval by SLN shareholders at a General Meeting that will be held on 29 April 2013.

Antisoma's agreement with SLN to subscribe for 2,000,000 new ordinary at 200p per share represents a total commitment of £4 million. The 9,512,500 new SLN ordinary shares would represent approximately 20.2 per cent. of the Enlarged Share Capital of SLN. Following the placing, Antisoma will have an interest over approximately 4.25 per cent. of the issued share capital of SLN.

Further information on the SLN share consolidation and placing is set out in the Share Capital Consolidation and Proposed Placing and Notice of General Meeting announcement by SLN of 10 April 2013 and in the notes to editors below.

Contacts:

Antisoma plc

Mike Bretherton, Chairman 020 7099 7268

WH Ireland Limited (Nominated adviser)

Chris Fielding, Head of Corporate Finance 020 7220 1650

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Notes to Editors

About Silence Therapeutics plc

Silence Therapeutics plc (LSE: SLN) is a leader in the discovery, development and delivery of novel RNA interference (RNAi) therapeutics for the treatment of serious diseases. The company possesses one of the most comprehensive and sophisticated RNAi therapeutic platforms comprised of proprietary delivery technologies, potent small interfering RNA (siRNA) sequences and innovative siRNA structural features - the three areas the company believes to be critical to building, protecting and commercialising RNAi therapeutics. This platform is protected by Silence's strong intellectual property portfolio which includes more than 200 issued and pending patent applications worldwide. Additionally, Silence is a clear leader in the development of RNAi clinical candidates, possessing a pipeline that includes a total of five different internal and partnered programs in the clinic. With at least half of the siRNA programs currently in clinical development worldwide based on Silence's technology, the company's clinical pipeline validates not only the strength of the company's proprietary technology but also the team of researchers that has guided the development path. A final key validation of Silence's leadership position in RNAi is the company's multiple major partnerships with global pharmaceutical companies (AstraZeneca, Pfizer/Quark Pharma and Dainippon Sumitomo).

Atu027, for the treatment of solid tumours, is Silence Therapeutics' most advanced internal drug candidate. Atu027 combines Silence Therapeutics' proprietary drug delivery system AtuPLEX with AtuRNAi, the Company's proprietary RNAi chemistry. Atu027 specifically targets PKN3, a protein, implicated in metastases which is the process responsible for the vast majority of cancer deaths. Atu027 has a novel metastatic effect, preventing the spread of cancer cells into and out of blood vessels. Pre-clinical studies have indicated that Atu027 works by inhibiting blood supply to solid tumours and has a particular profound impact on the prevention and growth of metastases.

Silence Therapeutics intends to use the net proceeds of the Placing to carry out further cancer studies using Atu027. Whilst the Company is exploring a number of alternatives, it is expected that these further studies will be in head and neck cancer and breast cancer. The Company also has two projects, in acute lung injury and hypercholesterolaemia, at pre-clinical stage. Work in six other indications, also targeting the liver and lung, is at proof of concept stage. The Company expects to use the net proceeds of the placing of approximately £18.7 million together with its current cash resources to fund a Phase Ib/IIa programme in Atu027 and to develop its non-cancer projects and broaden its clinical expertise.