Company Announcements

Silence Announces Mallinckrodt Exercise of Options for Two Additional Complement Targets

Silence eligible to receive up to ~$700m milestones per target

Double-digit royalties on net sales

16 July 2020

LONDON, Silence Therapeutics plc (LON: SLN) ("Silence" or "the Company"), a leader in the discovery, development and delivery of novel RNA therapeutics for the treatment of serious diseases, today announces that Mallinckrodt plc has exercised the option, under the collaboration agreement announced in July 2019, to obtain exclusive worldwide licenses for two additional complement-targeted RNAi assets from Silence. Silence will receive a $2 million milestone payment upon initiation of work for each asset, the parties anticipate starting work on both programmes in due course.

The collaboration between Silence and Mallinckrodt is aimed at the development and commercialisation of RNA therapeutics designed to inhibit or 'silence' the complement cascade, a group of proteins that are involved in the immune system and that play a role in the development of inflammation. These proteins are known to contribute to the pathogenesis of many diseases, including autoimmune diseases.

Under the terms of the collaboration agreement, Silence will be responsible for preclinical activities and for executing the development programme of each asset until the end of Phase 1, after which Mallinckrodt will assume clinical development and responsibility for the global commercialisation of the assets. Mallinckrodt will fund Phase 1 clinical development including GMP manufacture. Silence will fund all other preclinical activities. Including the $2 million milestone outlined above, Silence is eligible to receive up to $10 million in research milestones for each asset, and up to $703 million per asset in clinical, regulatory and commercial milestones. Silence will also receive tiered, low double-digit to high-teen royalties on net sales for each asset.

In addition to the two new targets announced today, Mallinckrodt and Silence are already collaborating on the development of a RNAi therapeutic designed to target C3. IND enabling activities have been initiated for the C3 targeted programme (SLN500).

Iain Ross, Executive Chairman of Silence Therapeutics commented: "Over the last year we have made great progress in our collaboration with Mallinckrodt and we are very pleased that they have exercised their option over two further complement targets. Alongside our other recent deals with large pharma companies, this is a further validation of our science; a testament to the quality of our data and our dedication to treat serious diseases with high unmet need."

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About Silence Therapeutics plc

Silence Therapeutics is developing a new generation of medicines by harnessing the body's natural mechanism of RNA interference, or RNAi, within its cells. Its proprietary technology can selectively inhibit any gene in the genome, specifically silencing the production of disease-associated proteins. Silence's proprietary RNA chemistries and delivery systems are designed to improve the stability of molecules and enhance effective delivery to target cells, providing a powerful modular technology well suited to tackle life-threatening diseases. The Company has secured high value research and collaboration agreements with AstraZeneca, Mallinckrodt Pharmaceuticals and Takeda. For more information, please visit: https://www.silence-therapeutics.com/

About Mallinckrodt plc

Mallinckrodt is a global business consisting of multiple wholly owned subsidiaries that develop, manufacture, market and distribute specialty pharmaceutical products and therapies. The company's Specialty Brands reportable segment's areas of focus include autoimmune and rare diseases in specialty areas like neurology, rheumatology, nephrology, pulmonology and ophthalmology; immunotherapy and neonatal respiratory critical care therapies; analgesics and gastrointestinal products. Its Specialty Generics reportable segment includes specialty generic drugs and active pharmaceutical ingredients. To learn more about Mallinckrodt, visit www.mallinckrodt.com.