Silence Therapeutics Reports Full Year 2023 Financial Results and Recent Business Highlights

Silence also announced positive topline 36-week data from ongoing phase 2 study of zerlasiran in patients with high lipoprotein(a)

Company to host conference call and webcast today at 8 a.m. EDT / 12 p.m. GMT

Silence Therapeutics plc, Nasdaq: SLN ("Silence" or "the Company"), an experienced and innovative biotechnology company committed to transforming people's lives by silencing diseases through precision engineered medicines, today reported its financial results for the full year ended December 31, 2023, and reviewed recent business highlights.

"2023 was a year of strong execution across Silence as we advanced our proprietary pipeline in the clinic," said Craig Tooman, President and CEO of Silence. "That's clearly bearing fruit today with the positive topline 36-week data we announced from the ongoing phase 2 study of zerlasiran in patients with high Lp(a). We are excited about these data and the potential for zerlasiran to address the needs of up to 1.4 billion worldwide living with high Lp(a). In addition to zerlasiran, we've made excellent progress advancing divesiran in PV and remain on-track to report phase 1 data by June. On the partnering side, we were pleased for AstraZeneca to enter the clinic with the first product candidate under our collaboration last month, further highlighting the productivity of our mRNAi GOLD™ platform. We look forward to more clinical data unfolding in the coming year from our proprietary programs and building recognition of Silence as a true platform company."

Recent Business Highlights

Zerlasiran for cardiovascular disease

• In November 2023, reported positive topline data in multiple dose portion of the APOLLO phase 1 study of zerlasiran in patients with high Lp(a).
• Today announced positive topline 36-week data from the ongoing ALPACAR-360 phase 2 study of zerlasiran in patients with a median baseline Lp(a) of approximately 215 nmol/L. Zerlasiran was administered at 300 mg subcutaneously every 16 or 24 weeks and 450 mg every 24 weeks.
  • Study demonstrated highly significant reductions in Lp(a) compared with placebo to week 36 (primary endpoint)
  • Median percentage reduction in Lp(a) of 90% or greater were observed for both doses at week 36
  • No new safety concerns were identified during this treatment period
  • The 60-week study is ongoing and secondary endpoints, including change in Lp(a) from baseline to week 48 (end of treatment period), week 60 (end of study) and potential effects on other lipids/lipoproteins, will be evaluated
  • 48-week topline data expected in the second quarter of 2024

Divesiran for hematological diseases

• Advanced enrollment in the SANRECO phase 1/2 study of divesiran in PV patients.
  • Emerging data from the ongoing phase 1 open label portion of the study continue to look promising
  • On-track to report phase 1 data in the second quarter of 2024

Collaborations

• In February 2024, achieved a $10 million milestone following the initiation of a phase 1 trial of the first product candidate under AstraZeneca collaboration.
• In March 2024, Mallinckrodt notified Silence that they will not pursue further development of SLN501 following the completion of the phase 1 clinical trial. This will conclude all activities and commitments under the collaboration agreement.

"We ended December 2023 with approximately $68.8 million and significantly increased our cash position in early 2024 to over $200 million," said Rhonda Hellums, Chief Financial Officer of Silence. "We are excited to have multiple programs advancing in the clinic, supported by a substantial cash position that extends our estimated runway into 2026. We also continue to evaluate partnering opportunities that could provide additional non-dilutive funding and further extend our cash runway. Looking ahead, we remain committed to responsibly investing in initiatives that will advance our pipeline and expand our platform into new targets where there is clear unmet need and opportunity to deliver value to patients."

Financial Highlights for Year End 2023

• Cash Position: Cash and cash equivalents of £54.0 million ($68.8 million) as of December 2023, compared with £71.1 million as of December 31, 2022.
• Collaboration Revenue: Collaboration revenue was £25.4 million for the year ended December 31, 2023, and £17.5 million for the year ended December 31, 2022, and related to research services performed under the collaboration agreements with AstraZeneca, Hansoh and Mallinckrodt.
• R&D Expenses: Research and development (R&D) expenses were £44.0 million for the year ended December 31, 2023, compared to £35.6 million for the year ended December 31, 2022. The increase is a result of additional clinical studies and an increase in contract manufacturing activities for Silence's proprietary programs.
• G&A Expenses: General and administrative (G&A) expenses were £20.6 million for the year ended December 31, 2023, compared to £19.6 million for the year ended December 31, 2022. The increase is primarily due to non-cash stock compensation costs.
• Net Loss: Net loss was £43.3 million, or 38.9 pence basic and diluted net loss per share for the year ended December 31, 2023, compared to a net loss of £40.5 million, or 41.9 pence basic and diluted net loss per share for the year ended December 31, 2022.

Post-Period Financial Highlights

• In January 2024, received total proceeds of approximately $30 million (includes approximately $20 million from ADS sales under Silence's Sales Agreement and approximately $10 million in R&D tax credit).
• In February 2024, announced a private placement of ADSs with gross proceeds of approximately $120 million (£94.5 million).
• In February 2024, achieved a $10 million clinical milestone under AstraZeneca collaboration. This will be received in April 2024.
• Total ADSs outstanding were approximately 46,502,272, as of March 1, 2024.

Cash and Liquidity Update

As of December 31, 2023, we had cash and cash equivalents of £54.0 million ($68.8 million). With the addition of gross proceeds from our private placement in February 2024 of $120 million (approximately £94.4 million) before deducting fees and estimated offering expenses, the $30 million from proceeds from sale of ADSs under our ATM and receipt of our UK R&D tax credit, and the receipt of the AstraZeneca $10 million milestone in the second quarter of 2024, we believe that our cash of over $200 million and anticipated milestones from current collaborations will be sufficient to fund our operating expenses and capital expenditure requirements into 2026. We may also achieve further milestones from our current collaboration partners which will further extend our cash runway.

Conference Call & Webcast Details

Company management will host a conference call and webcast today, Wednesday, March 13, 2024, at 8 a.m. EDT / 12:00 p.m. GMT.

Webcast link: https://edge.media-server.com/mmc/p/rkramk2y

Conference call registration link: https://register.vevent.com/register/BIa97253e879ff493bb6fe3a99a6ba3532

The conference call and webcast will also be archived on the Company's website at www.silence-therapeutics.com.

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 zerlasiran (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 divesiran (SLN124) designed to address hematological diseases. Silence also maintains ongoing research and development collaborations with AstraZeneca 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 cash runway and forecast operating cash flow, 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 "anticipate," "expect," "intend," "plan," "believe," "seek," "estimate," 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 on the date hereof. 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.

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