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Silence Therapeutics Announces FDA Fast Track Designation for SLN124, a Novel Investigational siRNA Therapy for the Treatment of Polycythemia Vera

Designation provides potential for expedited drug development path

Silence Therapeutics plc, Nasdaq: SLN (“Silence” or “the Company”), a leader in the discovery, development and delivery of novel short interfering ribonucleic acid (siRNA) therapeutics for the treatment of diseases with significant unmet medical need, today announced that the U.S. Food and Drug Administration ("FDA") has granted Fast Track Designation to SLN124, a novel siRNA targeting the TMPRSS6 gene, for the treatment of polycythemia vera (“PV”). The Company plans to start a phase 1/2 study in PV patients this year.

SLN124 is designed to address a range of hematological diseases by targeting TMPRSS6 to increase endogenous hepcidin, the body’s master regulator of iron balance and distribution. SLN124 demonstrated proof of mechanism and was well tolerated in a healthy volunteer study completed last year.

"The granting of Fast Track Designation represents an important recognition by the FDA of SLN124’s potential to address a significant unmet need in the treatment of PV," said Craig Tooman, President and Chief Executive Officer of Silence. "We plan to leverage Fast Track to expedite our development path as we seek to provide an important new treatment option to those suffering from this very serious and chronic genetic disease.”

Fast Track designation aims to facilitate the development and accelerate the review of new therapeutics that are intended to treat serious or life-threatening conditions and that potentially address an unmet medical need. Drugs that are granted this designation are given the opportunity for more frequent interactions with the FDA, as well as potential pathways for expedited approval.

In addition to PV, SLN124 is being evaluated in a phase 1 study in patients with thalassemia. SLN124 has orphan disease designations for PV, thalassemia, and myelodysplastic syndrome as well as a rare pediatric disease designation for thalassemia.

About Silence Therapeutics

Silence Therapeutics is developing a new generation of medicines by harnessing the body’s natural mechanism of RNA interference, or RNAi, to inhibit the expression of specific target genes thought to play a role in the pathology of diseases with significant unmet need. Silence’s proprietary mRNAi GOLD™ platform can be used to create siRNAs (short interfering RNAs) that precisely target and silence disease-associated genes in the liver, which represents a substantial opportunity. Silence’s wholly owned product candidates include SLN360 designed to address the high and prevalent unmet medical need in reducing cardiovascular risk in people born with high levels of lipoprotein(a) and SLN124 designed to address rare hematological diseases. Silence also maintains ongoing research and development collaborations with AstraZeneca, Mallinckrodt Pharmaceuticals, and Hansoh Pharma, among others. For more information, please visit

Forward-Looking Statements

Certain statements made in this announcement are forward-looking statements within the meaning of the U.S. Private Securities Litigation Reform Act of 1995 and other securities laws, including with respect to the Company’s clinical and commercial prospects, regulatory approvals of the Company’s product candidates, potential partnerships or collaborations or payments under new and existing collaborations, the initiation or completion of the Company’s clinical trials and the anticipated timing or outcomes of data reports from the Company’s clinical trials. These forward-looking statements are not historical facts but rather are based on the Company's current assumptions, beliefs, expectations, estimates and projections about its industry. Words such as 'anticipates,' 'expects,' 'intends,' 'plans,' 'believes,' 'seeks,' 'estimates,' and similar expressions are intended to identify forward-looking statements. These statements are not guarantees of future performance and are subject to known and unknown risks, uncertainties, and other factors, some of which are beyond the Company's control, are difficult to predict, and could cause actual results to differ materially from those expressed or forecasted in the forward-looking statements, including those risks identified in the Company’s most recent Admission Document and its Annual Report on Form 20-F filed with the U.S. Securities and Exchange Commission (the “SEC”) on March 17, 2022. The Company cautions security holders and prospective security holders not to place undue reliance on these forward-looking statements, which reflect the view of the Company only as of the date of this announcement. The forward-looking statements made in this announcement relate only to events as of the date on which the statements are made. The Company will not undertake any obligation to release publicly any revisions or updates to these forward-looking statements to reflect events, circumstances, or unanticipated events occurring after the date of this announcement except as required by law or by any appropriate regulatory authority.



Silence Therapeutics plc

Gem Hopkins, Head of IR and Corporate Communications

Tel: +1 (646) 637-3208

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