STAINES-UPON-THAMES,?United Kingdom?and?LONDON,?July 18, 2019?/PRNewswire/ --?Mallinckrodt plc?(NYSE: MNK), a global biopharmaceutical company, and?Silence Therapeutics plc?(LON: SLN), a leader in the discovery, development and delivery of novel RNA²?interference (RNAi) therapeutics for the treatment of serious diseases, today announced a collaboration that will allow the companies to develop and commercialize RNAi drug targets 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 agreement, Mallinckrodt will obtain an exclusive worldwide license to Silence's C3³?complement asset, SLN500, with options to license up to two additional complement-targeted assets in Silence's preclinical complement-directed RNAi development program. Silence will be responsible for preclinical activities, and for executing the development program of each asset until the end of Phase 1, after which Mallinckrodt will assume clinical development and responsibility for global commercialization. Mallinckrodt has agreed to provide Silence with an upfront payment of?$20 million. Silence is also eligible to receive up to?$10 million?in research milestones for SLN500 and for each optioned asset, in addition to funding for Phase 1 clinical development including GMP⁴?manufacturing. Silence will fund all other preclinical activities. The collaboration provides for potential added clinical and regulatory milestone payments of up to?$100 million?for SLN500, as well as commercial milestone payments of up to?$563 million?for SLN500. Should Mallinckrodt opt to license one or two additional assets, Silence could receive up to?$703 million?in similar clinical, regulatory, and commercial milestone payments per asset. Silence would also receive tiered, low double-digit to high-teen royalties on net sales for SLN500 and each optioned asset. "We are very excited by the significant potential offered by Silence's RNAi technology to meet the needs of underserved patients in a number of serious and critical conditions, and we look forward to collaborating with them to advance development of complement-targeted assets as new therapeutic options," said?Steven Romano, M.D., Chief Scientific Officer and Executive Vice President of Mallinckrodt. "This license provides Mallinckrodt with an expansion of early development opportunities and the value of applying RNA technology therapeutically to target a range of rare diseases as well as conditions of immune dysregulation," adds?Ulrich H. von Andrian, M.D.,?Edward Mallinckrodt Jr.?Professor of Immunopathology, Microbiology and Immunobiology,?Harvard Medical School?and Member of the?Mallinckrodt Pharmaceuticals Scientific Advisory Council. "This collaboration combines?Silence Therapeutics'?knowledge and world-class research and development in the field of RNAi with Mallinckrodt's expertise and resources as a global biopharmaceutical company with years of experience solving complex challenges," said?Dr.?David Horn Solomon, President and Chief Executive Officer of?Silence Therapeutics.?"The increasing number of clinical conditions and pathologies that involve the complement system has generated significant interest in the development of therapeutic options to inhibit complement activation, which holds great promise in treating a range of diseases. We look forward to working closely with Mallinckrodt to extend our capabilities with RNAi therapies that have the potential to transform patients' lives." The companies will work together to develop and commercialize this RNAi therapeutic target, with the possibility of additional assets, and will form a Joint Steering Committee to guide the asset's development program. Silence's proprietary technology is a highly specific and modular platform designed to inhibit or 'silence' the expression of disease-causing genes. The technology is appropriate to target any number of genes; however, the collaboration focuses on the complement cascade, which is implicated in a number of autoimmune diseases. Silence Call with Investors Dr.?David Horn Solomon, Chief Executive Officer of?Silence Therapeutics, will host a conference call accompanied by a live presentation for analysts and investors today at?13.00pm BST?(8.00am EDT). Link to the live webcast:?https://edge.media-server.com/mmc/p/d4noa4jd. Dial-in details are: Participant UK dial-in: +44 (0) 2071 928000; Participant; US Dial-in: +1 631 510 7495 Conference ID: 1576453.? A presentation to accompany the call will be made available to download from?https://www.silence-therapeutics.com/investors/results-reports-presentations. ABOUT SILENCE 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-causing proteins. Using its enabling delivery systems, it has achieved an additional level of specificity by delivering its therapeutic RNA molecules exclusively to target cells. Silence's proprietary RNA chemistries and delivery systems are designed to improve the stability of our molecules and enhance effective delivery to target cells, providing a powerful modular technology well suited to tackle life-threatening diseases.?Silence Therapeutics?remains focused and is determined to be responsive to creating shareholder value as well as the appropriate growth and development of its business.?Silence Therapeutics?continues to assess a number of options in addition to its organic plan which it believes would be additive to the Company's future growth prospects and shareholder value, which may include equity fundraisings as well as other strategic licensing and collaboration opportunities. For more information, please visit?https://www.silence-therapeutics.com/. ABOUT MALLINCKRODT 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. Mallinckrodt uses its website as a channel of distribution of important company information, such as press releases, investor presentations and other financial information. It also uses its website to expedite public access to time-critical information regarding the company in advance of or in lieu of distributing a press release or a filing with the?U.S. Securities and Exchange Commission?(SEC) disclosing the same information. Therefore, investors should look to the Investor Relations page of the website for important and time-critical information. Visitors to the website can also register to receive automatic e-mail and other notifications alerting them when new information is made available on the Investor Relations page of the website. Cautionary Statements Related to Forward-Looking Statements Mallinckrodt This release includes forward-looking statements concerning Mallinckrodt's collaboration with Silence, including expectations regarding future research and development plans, potential milestone payments and commercial arrangements and the potential impact on patients. The statements are based on assumptions about many important factors, including the following, which could cause actual results to differ materially from those in the forward-looking statements: uncertainties inherent in research and development, including clinical trial results; satisfaction of regulatory and other requirements; actions of regulatory bodies and other governmental authorities; changes in laws and regulations; issues with product quality, manufacturing or supply, or patient safety issues; and other risks identified and described in more detail in the "Risk Factors" section of Mallinckrodt's most recent Annual Report on Form 10-K and other filings with the?SEC, all of which are available on its website. The forward-looking statements made herein speak only as of the date hereof and Mallinckrodt does not assume any obligation to update or revise any forward-looking statement, whether as a result of new information, future events and developments or otherwise, except as required by law. Silence The information contained within this announcement is deemed by the?Silence Therapeutics plc?to constitute inside information as stipulated under the Market Abuse Regulation (EU) No. 596/2014. Upon the publication of this announcement via the Regulatory Information Service, this inside information is now considered to be in the public domain. CONTACTS MALLINCKRODT Investor Relations Daniel J. Speciale, CPA Vice President, Investor Relations and IRO 314-654-3638 daniel.speciale@mnk.com Media Daniel Yunger Kekst CNC 212-521-4879 mallinckrodt@kekstcnc.com SILENCE THERAPEUTICS Dr.?David Horn Solomon, Chief Executive Officer Mr.?Iain Ross, Non-Executive Chairman +44 (0) 20 3457 6900 Peel Hunt/LLP (Nominated Adviser and Broker) James Steel/Oliver Jackson +44 (0) 20 7418 8900 European IR Consilium Strategic Communications Mary-Jane Elliott/Chris Welsh/Angela Gary silencetherapeutics@consilium-comms.com +44 (0) 20 3709 5700 US IR Westwicke Partners Peter Vozzo Peter.vozzo@westwicke.com 442-213-0505 Mallinckrodt, the "M" brand mark and the?Mallinckrodt Pharmaceuticals?logo are trademarks of a Mallinckrodt company. Other brands are trademarks of a Mallinckrodt company or their respective owners.?^??2019 Mallinckrodt. 7/19 ¹?British Summer Time ²?Ribonucleic acid ³?The C3 protein is part of the complement system. There are nine major complement proteins, labeled C1 through C9.?https://medlineplus.gov/ency/article/003539.htm?Accessed?June 27, 2019. ⁴?Good manufacturing practices

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