– Positive SLN360 data to be presented in late breaker at the American College of Cardiology (ACC) Annual Meeting on April 3, 2022

– SLN124 phase 1 study in thalassemia now fully enrolled; on-track for topline data in Q3 2022

– SLN124 granted FDA orphan drug designation in polycythemia vera; on-track to start phase 1 study in H2 2022

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 reported its financial results for the fourth quarter and full year ended December 31, 2021 and reviewed recent business highlights.

“2021 was a remarkable year for Silence,” said Craig Tooman, President and Chief Executive Officer at Silence. “We successfully delivered the first clinical data from our proprietary mRNAi GOLD™ platform, advanced two wholly owned programs in the clinic and made excellent progress across both our proprietary and partnered pipelines. This momentum has continued into 2022 with the positive SLN360 data and we look forward to the late breaking presentation at ACC on April 3^rd. With clinical data now demonstrated in two separate programs, we are optimistic about what we can deliver from our platform and look forward to a very exciting year ahead.”

Rhonda Hellums, Chief Financial Officer at Silence commented, “We continued to benefit from our hybrid business model in 2021, receiving around $58 million in non-dilutive capital from our collaborations. We moved exclusively to the Nasdaq and significantly expanded our global shareholder base. We ended the year with £73.5 million in cash, cash equivalents and term deposits and we will continue to prioritize non-dilutive financing solutions.”

Fourth Quarter 2021 Business Highlights

mRNAi GOLD™ Proprietary Program Updates

SLN360 Lp(a) Lowering Program

• Extended follow-up period in the single-ascending dose cohorts up to 365 days to further assess the duration of action.
• Established therapeutic dose range based on single-ascending dose cohorts 1-4 to proceed to the multiple-ascending dose portion.

SLN124 Hepcidin Regulation Program

• Presented clinical data from the SLN124 healthy volunteer study at the 2021 American Society of Hematology Annual Meeting. Key data included:
  • All 3 dose levels were well tolerated with no serious or severe treatment emergent adverse events (TEAEs) or TEAEs leading to withdrawal.
  • Average hepcidin, a key endogenous regulator of iron balance and distribution, increased up to ~4-fold after a single dose with effect sustained for at least 2 months.
  • Serum iron reduced by ~50% after a single dose with effect sustained for at least 2 months.

mRNAi GOLD™ Partnered Program Updates

• Secured new collaboration with Hansoh Pharma to develop therapeutics leveraging the Silence mRNAi GOLD™ platform, providing the Company with exclusive rights to two undisclosed targets in all territories except the China region (Greater China, Hong Kong, Macau and Taiwan). Hansoh received an exclusive option to license rights to those two targets in the China region and global rights to a third undisclosed target.

Post Year-end Highlights

• Announced positive topline data in the SLN360 phase 1 single-ascending dose study in 32 healthy adults with high Lp(a) (≥ 60 mg/dL or 150 nmol/L). Topline data included:
  • SLN360 was well tolerated with no clinically important safety concerns identified.
  • SLN360 reduced Lp(a) in a dose dependent manner from 46% up to a maximum of 98% with up to an 81% reduction persisting at 150 days.
• Detailed results from the SLN360 phase 1 single-ascending dose study will be presented in a late-breaker at the American College of Cardiology (ACC) Annual Meeting on April 3, 2022.
• Started dosing in the SLN360 phase 1 multiple-ascending dose study in adults with high Lp(a) that have a confirmed history of stable atherosclerotic cardiovascular disease (“ASCVD”).
• Completed enrollment in the SLN124 phase 1 single-ascending dose study in thalassemia patients and remain on-track to report topline data in the third quarter of 2022.
• SLN124 granted FDA orphan drug designation in polycythemia vera (PV) and the Company remains on-track to start a phase 1 study in PV in the second half of 2022.
• Discontinued further enrollment in the myelodysplastic syndrome (MDS) arm of the SLN124 phase 1 program due to recruitment challenges in this population and the decision to prioritize spend in thalassemia and PV indications where the Company believes it can derive the most value in the near term.

2021 Financial Results

For the twelve-month period ending December 31, 2021, the net loss after tax was £39.4 million, or weighted average loss per share 44.3 pence compared to the same period in 2020 of £32.5 million, or weighted average loss per share 39.8 pence. The increase in net loss was primarily related to increase in R&D expenditures as the Company continues to further advance and expand its pipeline of novel medicines.

Revenue

Revenue recognized for the year ending December 31, 2021 was £12.4 million, compared to £5.5 million for the year ending December 31, 2020. The Company records revenue from collaborations based on percentage of contract completion and the increase was driven by the advancement of current collaboration programs, as well as the execution of new collaboration agreements in 2021. Therefore, as the Company’s current collaboration programs progress and additional programs are initiated revenues are also expected to increase over time.

Cost of sales

The cost of sales increased for the twelve months ending December 31, 2021 to £7.5 million from £3.8 million in the period ending December 31, 2020. Cost of sales includes research and development expenditure that is directly related to work carried out on revenue generating contracts. The increase was largely due to the further advancement and initiation of new collaboration programs.

Research and Development

During the year ending December 31, 2021, research and development expenditures increased by £10.6 million to £30.8 million from £20.2 million in the year ending December 31, 2020. The increase is a result of additional clinical studies and an increase in contract manufacturing activities for Silence’s proprietary programs, as well as an increase in personnel costs to expand the internal capabilities and expertise to further advance the Company’s siRNA platform.

General and Administrative

General and administrative expenses increased by £6.0 million to £20.0 million for the year ending December 31, 2021 from £14.0 million for the same corresponding period in 2020. This increase was predominantly related to requirements for public company compliance and support of the R&D portfolio including personnel.

Liquidity, cash and cash equivalents

As of December 31, 2021, the Company had £73.5 million of cash and cash equivalents. During 2021, the Company received $40.0 million or £30.8 million from its partner AstraZeneca, and milestones totaling $4.0 million or £2.9 million from its partner Mallinckrodt. The Company also received a $16.0 million upfront payment, or £10.7 million net of taxes, from the execution of a collaboration agreement with Hansoh in the fourth quarter of 2021. Since 2019, Silence has received over $100 million in upfront and milestone payments from its collaboration partners. These proceeds provide non-dilutive capital for the continued development and advancement of the Company’s proprietary and partnered product candidates. The Company believes that its cash and cash equivalents of £73.5 million as of the end of December 2021 is sufficient to fund its operations through early 2023.

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 https://www.silence-therapeutics.com/.

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, the initiation or completion of the Company’s clinical trials, the anticipated timing or outcomes of data reports from the Company’s clinical trials and the Company’s anticipated cash runway. 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 to be 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.

Conference Call

Company management will host a live webcast to discuss its fourth quarter and full year 2021 results and recent business performance today at 8:00 a.m. EDT / 12:00 p.m. GMT.

Webcast link: https://edge.media-server.com/mmc/p/k2gmhpy6

Dial-in details:

New York, United States: +1 646 741 3167

United States: 1 877 870 9135

London, United Kingdom: +44 2071 928338

United Kingdom: 08002796619

Passcode: 3055614

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