Merck to buy siRNA specialist Silence Therapeutics for $1.3 billion

The deal: The purchase price is $20 per American Depositary Share (ADS) in cash. This corresponds to an equity value of approximately $1.3 billion and an enterprise value of about $1.1 billion. The transaction is expected to close in the first quarter of 2027, subject to customary conditions, including approval by Silence shareholders and regulatory clearances. It is to be financed through new debt.

Why it matters: The biggest immediate value driver is divesiran, an siRNA drug candidate for polycythemia vera (PV). In this chronic myeloproliferative disorder, the bone marrow produces too many red blood cells. Among other consequences, this increases the risk of thrombosis and other cardiovascular complications. Many patients require regular phlebotomies to keep their hematocrit — the proportion of red blood cells in the blood volume — under control.

How it works: Divesiran does not act directly on blood cell production in the bone marrow, but on the regulation of iron metabolism. The drug is designed to suppress the production of the protein TMPRSS6 in liver cells. This protein normally inhibits the hormone hepcidin, which regulates iron availability in the body. When hepcidin levels rise, less iron is available for red blood cell production. Through this mechanism, Silence aims to curb blood cell production and reduce the need for phlebotomies.

Zoom in: The acquisition follows positive results from the Phase 2 SANRECO trial, which Silence presented in August 2026. The randomized, double-blind, placebo-controlled trial enrolled 48 patients with PV who depended on phlebotomies. The primary endpoint was met: 88% of patients treated with divesiran responded, compared with 19% in the placebo group. A response was defined as requiring no phlebotomy between weeks 18 and 36 while maintaining a hematocrit below 45%.

• The number of phlebotomies also fell significantly. During the first 36 weeks, patients receiving divesiran required an average of 0.2 phlebotomies, compared with 2.1 among those receiving placebo. Both dosing intervals studied — every six weeks and every 12 weeks — also showed response rates. According to the company, the drug was well tolerated, with no new safety signals. Two cases of mild anemia were classified as possibly treatment-related.

Worth watching: These are promising data for a drug that may need to be injected under the skin only once every three months. However, the analysis comes from a comparatively small Phase 2 trial with a follow-up period of 36 weeks. Whether efficacy and safety will be confirmed in a larger trial, and whether treatment will have a long-term effect on complications and quality of life, remains to be established.

What’s next: Silence had announced plans to begin a Phase 3 trial with dosing every 12 weeks in the first half of 2027. Merck should be able to provide the resources needed for precisely this development step, as well as the infrastructure for subsequent commercialization. For the Darmstadt-based group, the acquisition also represents an entry into hematology with a candidate whose mechanism of action has a sound biological basis and whose clinical data already show a clear effect.

A second candidate with substantial market potential: Divesiran is not the only clinically advanced program from Silence. The company is also developing zerlasiran, formerly known as SLN360, an siRNA drug targeting lipoprotein(a), or Lp(a). Elevated Lp(a) levels affect a substantial proportion of the population and are associated with an increased risk of heart attack, stroke and other cardiovascular diseases. The drug is designed to reduce the production of this partly genetically determined cardiovascular risk factor.

• Zerlasiran has undergone early- and midstage clinical trials and the company had completed preparations for a Phase 3 trial. However, Silence intended to begin a large cardiovascular outcomes trial only once it had found a partner. The program therefore represents a potential additional value driver for Merck, but should not be equated with a Phase 3 program that is already underway.

Other candidates are at earlier stages of development: These include SLN548, targeting complement factor CFB; SLN365, targeting GPR146, a potential target for lowering cholesterol; and SLN098, targeting INHBE, which is associated with obesity. These programs are still considerably further from becoming potential products.

Yes, but: The development history of another candidate, SLN312, also shows that a compelling platform alone does not automatically lead to further clinical development. AstraZeneca tested the candidate targeting ANGPTL3 in a Phase 1 trial. According to the company, the results showed dose-dependent and sustained changes in ANGPTL3 and various lipid levels. Nevertheless, AstraZeneca decided in 2026 not to advance the program beyond Phase 1. Silence is to regain worldwide rights and is assessing the next steps. The collaboration with AstraZeneca on other projects remains unaffected.

The Berlin connection: While Silence Therapeutics is headquartered in London, Berlin is an important research location. Scientists there work on developing and optimizing the siRNA molecules that may subsequently enter preclinical and clinical programs as drug candidates.

• The Berlin research is therefore directly linked to the development of the proprietary mRNAi-GOLD platform. This platform is designed to create siRNA molecules that recognize a specific messenger RNA and trigger its degradation. The cell then produces less of the protein for which that messenger RNA provides the blueprint. Unlike genome editing, this approach does not permanently alter DNA. Its effect is temporary, meaning the drugs must be administered again at appropriate intervals.

Also notable: For many of its programs, Silence uses GalNAc technology to deliver siRNA specifically to liver cells. This is pharmacologically relevant: The liver is a suitable target for numerous systemic diseases, for example when a disease-related protein is produced there or a metabolic process needs to be regulated. The platform is also being developed further with the aim of eventually reaching cell types outside the liver. This is an important technical challenge for the entire siRNA industry.

Backstory: The Berlin unit has its roots in German siRNA research, which Silence gained access to through its acquisition of Atugen in 2005. The site was therefore not simply added later as a German subsidiary, but is part of the company’s technological development history. According to available information, Silence employs around 80 people across sites in the U.K., the U.S. and Germany.

The big picture: The Merck deal also signals the growing importance of RNA interference as a therapeutic class. siRNA therapeutics use a natural cellular mechanism to selectively reduce the production of specific proteins. This enables them to address targets that are difficult to influence with conventional small-molecule drugs or antibodies.

• The technology has long since moved beyond being merely a research promise. Several siRNA medicines are approved, including treatments for certain inherited metabolic disorders, acute hepatic porphyria and elevated cholesterol levels. Inclisiran, an siRNA drug targeting PCSK9 that lowers LDL cholesterol levels, is also on the market. Alnylam is among the pioneers of commercial RNAi therapeutics; other companies, such as Arrowhead and AstraZeneca, are advancing their own or jointly developed programs.
• The companies most likely to benefit initially from the acquisition are those that can already demonstrate clinical data and a robust drug platform. The deal confirms that large pharmaceutical companies are prepared to pay substantial sums for siRNA technology and clinically advanced candidates. This could strengthen the negotiating position of other RNAi developers in partnerships and acquisitions.
• For smaller developers, the deal could also underscore the value of platform technologies — provided they can show that their molecules reliably reach the right cells, act there and can be safely administered repeatedly. Alongside selecting the target gene, this is one of the central challenges facing RNA therapeutics. For Pramomolecular, a company also based in Berlin-Buch with siRNA technology that extends beyond the liver, however, the renewed momentum comes too late: It had to file for insolvency in May this year.