Clinical trial update

23 March 2015

Silence Therapeutics plc

Clinical trial update

Silence Therapeutics plc, AIM: SLN ('Silence' or 'the Company'), a leader in the development and delivery of novel RNA therapeutics, provides a draft interim analysis of Atu027-I-02 Phase IIa study in pancreatic cancer. The primary objective of this trial was to assess safety and pharmacokinetics, and the secondary objective was to evaluate efficacy, including Progression Free Survival (PFS).

This study was open label in 23 patients with incurable pancreatic cancer and included two treatment arms with Atu027 in combination with the standard of care, gemcitabine. Treatment arm 1 delivered one dose per week for three weeks, followed by one week of no treatment, giving a total of 6 administrations in 8 weeks. Treatment arm 2 delivered 2 doses per week during 4 weeks, followed by 4 weeks of no treatment, a total of 8 administrations in 8 weeks. Arm 2 therefore received 33% more Atu027 during the same treatment period. The presented results are preliminary but have been generated by an independent clinical research organisation.

Tolerability and platform validation

There was no difference in safety events leading to discontinuation between the two arms, with one subject withdrawing because of an adverse event in each arm. Atu027 was generally well tolerated. In addition, the study results are an important further validation of Silence's two-component drug -a short interfering RNA (siRNA) and a delivery system. Over 400 patients have now been treated with the Company's proprietary modified siRNA (AtuRNAi®), with excellent tolerability. In regards to delivery, this data gives further evidence of the favourable safety profile of Silence's delivery platforms, which are the core components of the Company's 'multiple shots at goal' strategy.

Progression free survival

A preliminary analysis of this open label study indicates that the subjects who were exposed to a 33% higher total dose of Atu027 had a longer duration of PFS (median of 5.33 months) than patients on the lower exposure regimen (median of 1.81 months). This suggests that in this study, a dose-dependent effect was seen for Atu027.

Ali Mortazavi, CEO of Silence Therapeutics, said:

"Even allowing for the small number of patients in the trial, these results show a clear signal which requires further investigation. Atu027 has the potential to become a new therapeutic modality in oncology. This is an excellent outcome both in terms of Atu027 and validation of our RNA therapeutics platform. In light of this data, we are reviewing the protocol for the planned Phase Ib head and neck cancer study.

"In addition to the clinical development of Atu027, Silence Therapeutics has a wide range of pre-clinical projects based on its ability to modulate gene expression both on and off. We look forward to the future with great confidence."

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About Silence Therapeutics (www.silence-therapeutics.com)

Silence Therapeutics is a leading RNA therapeutics company. It has developed proprietary modifications to improve the robustness of RNA sequences together with advanced liposomal chemistries to enhance the delivery of its therapeutics. Its technology can selectively silence or replace the expression of any gene in the genome, modulating expression up as well as down in a variety of organs and cell types, in vivo. This allows the development of therapeutics for diseases with high unmet clinical need.