GSK plc, a leading clinical-stage biopharmaceutical company developing precision therapies for patients with serious liver disease, and Boston Pharmaceuticals have announced that they have entered into an agreement under which GSK will acquire Boston Pharmaceuticals' lead pipeline drug, efimosfermin alfa. Efimosfermin is a Phase III-ready, potential best-in-class specialty drug for the treatment and slowing of progression of SLD. Under the agreement, GSK will make an upfront payment of $1.2 billion upon closing, plus potential future milestone payments of up to $800 million.

Efimosfermin is a novel once-monthly fibroblast growth factor 21 (FGF21) analogue being developed for the treatment of metabolic dysfunction-associated steatohepatitis. In addition to MASH, which includes cirrhosis, it is also planned to be developed for alcohol-related liver disease (ALD), both of which are types of SLD. By utilizing efimosfermin's direct anti-fibrotic mechanism of action and the data-based knowledge gained from GSK's research in human genetics and disease phenotyping, it is expected that efimosfermin will be able to treat more advanced stages of SLD, and in combination with GSK's siRNA drug GSK'990, it is expected that treatment opportunities will expand to other patient populations with SLD.

The acquisition of efimosfermin is highly aligned with GSK's R&D focus on immune system related science and further underlines the company's focus on leveraging its deep understanding of fibrosis and auto-inflammation to develop precision therapies to halt and reverse disease progression.

SLD is an area of ​​significant unmet medical need affecting approximately 5% of the world's population and continues to have limited treatment options. 1 SLD, including MASH and ALD, are characterized by the accumulation of fat in the liver (steatosis) with associated inflammation and fibrosis. ALD affects approximately 26 million patients worldwide and, along with MASH, is the leading cause of liver transplants in the United States. These represent a devastating group of diseases that place a significant burden and cost on healthcare resources. 1,3 End-stage liver disease is associated with significant and disproportionate healthcare costs. Interventions that reduce moderate to advanced fibrosis and prevent progression to cirrhosis, liver cancer, hospitalization, and transplant could reduce costs to the U.S. healthcare system by $40-100 billion over the next 20 years. 4

Updated data from a Phase II study of efimosfermin evaluated the efficacy and safety of monthly subcutaneous administration in patients with biopsy-confirmed moderate-to-severe (F2 or F3) MASH. The study demonstrated that efimosfermin rapidly and significantly reduced liver fibrosis and inhibited its progression with a manageable tolerability profile. These data suggest that efimosfermin may be more effective at reducing fibrosis compared to other therapeutic approaches, with or without concomitant glucagon-like peptide-1 (GLP-1) therapy. Additionally, efimosfermin may reduce triglycerides and improve glycemic control, important therapeutic considerations for MASH patients, who often have cardiometabolic comorbidities. Efimosfermin has unique properties, such as low immunogenicity and a long half-life, and is expected to be administered on a monthly dosing schedule, providing greater convenience for patients. Detailed data from this study were presented at the American Association of Clinical Oncology for Liver Diseases (AASLD) in November 2024.5

Tony Wood, Chief Scientific Officer, GSK, said: "The FGF21 class of drugs has shown very promising data in MASH, including first evidence of improvement in cirrhosis. With once-monthly dosing and a favourable tolerability profile, efimosfermin has the potential to establish a new standard of care and significantly expands our liver disease pipeline, providing an opportunity to develop a potentially best-in-class new medicine, targeted for launch in 2029. Efimosfermin is also complementary to our development pipeline in ALD and MASH, GSK's development options for both monotherapy and potential combination therapies to improve outcomes for patients."

Elias Zerhouni, MD, Chairman of Boston Pharmaceuticals, said, "We are extremely proud of this agreement with GSK, whom I know and respect well, and extremely grateful to the Boston Pharmaceuticals team for their excellent work under the leadership of Sophie Kornowski, PHARMACOLOGY. In particular, this was made possible thanks to the Bertarelli family's outstanding, sustained, long-term strategic commitment to cutting-edge science and biotechnology, which has enabled us to develop efimosfermin alfa, a potentially best-in-class treatment in its therapeutic area, and we are extremely pleased that a global leader like GSK has recognized efimosfermin's potential to address a growing public health challenge and unmet medical need worldwide. We look forward to continuing our journey with GSK to position efimosfermin as a best-in-class treatment for patients with SLD."

Sophie Kornowski, PHARMA, Pharm.D., CEO of Boston Pharmaceuticals, said, "This announcement marks an important milestone for Boston Pharmaceuticals and efimosfermin alfa as we begin a new chapter with GSK, a global company with proven expertise in liver diseases and a shared strong commitment to patients. This achievement is made possible thanks to the dedicated team at Boston Pharmaceuticals, who have brought a strong sense of urgency to our mission to develop efimosfermin. We are especially grateful to Ernesto Bertarelli for his unwavering support and generous expertise over the past few years."

The addition of efimosfermin further strengthens GSK's liver disease pipeline with speciality medicines to address both viral (chronic hepatitis B) and SLD causes of fibrotic liver disease.

Financial arrangements

Under the terms of the agreement, GSK will acquire BP Asset IX, Inc., a subsidiary of Boston Pharmaceuticals, for the purpose of acquiring efimosfermin. GSK will pay total cash consideration of up to $2 billion, comprised of an upfront payment of $1.2 billion at closing and up to $800 million in future milestone payments based on achievement of certain conditions. GSK will also be responsible for success-based milestone payments and tiered royalties to Novartis Pharma for efimosfermin.

GSK will implement a business combination and account for the transaction, which is subject to customary conditions, including receipt of relevant regulatory approvals under the Hart-Scott-Rodino Act in the United States.

Evercore Partners International LLP is acting as exclusive financial advisor and Cleary Gottlieb Steen & Hamilton LLP is acting as legal advisor to GSK.

Centerview Partners LLC is acting as exclusive financial advisor and Sullivan & Cromwell LLP is acting as legal advisor to Boston Pharmaceuticals.

About efimosfermin alfa

Efimosfermin is an investigational, once-monthly subcutaneously administered, long-acting FGF21 (fibroblast growth factor 21) variant designed to reduce liver fat, improve liver inflammation and reverse liver fibrosis by modulating key metabolic pathways in patients with MASH. Efimosfermin is currently in clinical trials for moderate to severe fibrosis (including cirrhosis) and is not approved for prescription anywhere in the world.

About Boston Pharmaceuticals

Boston Pharmaceuticals is a clinical-stage biopharmaceutical company. Leveraging an experienced and dedicated drug development team, the company is advancing the development of highly differentiated therapeutics that address significant unmet medical needs in serious liver diseases. Boston Pharmaceuticals is a portfolio company of B-Flexion, a private entrepreneurial investment firm that manages capital and investments associated with the Bertarelli family. Boston Pharmaceuticals also seeks to make a positive contribution to society by working with sophisticated capital partners with a common goal of creating exceptional value across generations.

About GSK

GSK is a global biopharmaceutical company whose mission is to combine science, technology and people to fight disease. For more information please visit gsk.com.

Caution Regarding Forward-Looking Statements

GSK cautions investors to read this announcement and any other forward-looking statements or projections made by GSK, including without limitation, statements made by GSK that are subject to risks and uncertainties that may cause actual results to differ materially, including, but not limited to, those factors set out in the "Risk Factors" section of GSK's Annual Report on Form 20-F for 2024 and its First Quarter 2025 Financial Report.

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Reference Information

1. Global Burden of Disease Study 2017 Cirrhosis Collaborative Report. 2020.
2. Allen et al. Postgraduate Medicine. 2024, Volume 136, Number 3, pages 229-245.
3. Younossi et al. Hepatology Communications. December 22, 2023, Volume 8, Issue 1, e0352.
4. Wallace, Carolyn et al. Journal of Hepatology, Volume 0, Issue 0
5. "Hepatology" (2004) Late Breaking Abstracts Special Issue, pages 28-30, TLM2024LBA_20241115A.pdf

The official version of this press release is the original language version. The translated language versions are provided for the convenience of readers and have no legal effect. When using the translated version as a reference, please refer to the original language version, which is the only version that has legal effect.

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