GSK has entered into an agreement to acquire efimosfermin alfa, a phase III-ready investigational medicine for steatotic liver disease (SLD), from Boston Pharmaceuticals for $1.2 billion upfront. The deal includes potential additional success-based milestone payments totaling $800 million, highlighting GSK's strategic expansion in the hepatology space.
Efimosfermin is a novel fibroblast growth factor 21 (FGF21) analog therapeutic administered as a once-monthly subcutaneous injection. The drug is being developed primarily for metabolic dysfunction-associated steatohepatitis (MASH), including cirrhosis, with plans for future development in alcohol-related liver disease (ALD).
Addressing a Significant Unmet Medical Need
SLD represents a substantial global health burden, affecting approximately 5% of the world's population with limited therapeutic options currently available. The condition is characterized by fat accumulation in the liver (steatosis), accompanied by inflammation and fibrosis.
ALD affects about 26 million patients globally, and together with MASH, constitutes the leading cause of liver transplantation in the United States. The economic impact is considerable, with interventions that reduce moderate-to-advanced fibrosis potentially saving the US healthcare system between $40-100 billion over the next two decades by preventing progression to cirrhosis, liver cancer, hospitalizations, and transplantation.
Promising Clinical Data
Recent phase II trial results for efimosfermin have demonstrated the drug's ability to rapidly and significantly reverse liver fibrosis and halt its progression in patients with biopsy-confirmed moderate-to-advanced (F2 or F3) MASH. The treatment showed a manageable tolerability profile and potentially greater fibrosis improvement compared to other therapeutic approaches.
The data suggests benefits independent of background glucagon-like peptide-1 (GLP-1) therapy, which is significant as many MASH patients are already receiving GLP-1 medications. Additionally, efimosfermin could offer triglyceride reduction and improved glycemic control—important considerations for MASH patients who frequently have cardiometabolic comorbidities.
Tony Wood, Chief Scientific Officer at GSK, emphasized the drug's potential: "The FGF21 class has shown some of the most exciting data in MASH including first-in-disease evidence of cirrhosis reversal, and efimosfermin has the potential to define a new standard-of-care with its monthly dosing and tolerability profile."
Strategic Fit in GSK's Portfolio
The acquisition aligns with GSK's R&D focus on immune system-related science and builds on the company's understanding of fibrosis and auto-inflammation. Efimosfermin complements GSK'990, a siRNA therapeutic also in development for ALD and MASH, offering the company options to develop both monotherapy and potential combination treatments.
"Efimosfermin will significantly expand our hepatology pipeline and provide us the opportunity to develop a new potential best-in-class medicine with first launch expected in 2029," Wood added.
Mechanism of Action and Unique Properties
Efimosfermin is designed to regulate key metabolic pathways to decrease liver fat, reduce liver inflammation, and reverse liver fibrosis in patients with MASH. Its unique properties include low immunogenicity and an extended half-life, enabling a convenient monthly dosing regimen that could improve patient adherence compared to more frequently administered alternatives.
The drug's direct antifibrotic mechanism of action, combined with GSK's data-driven insights from human genetics and disease phenotyping, suggests potential efficacy in addressing more advanced stages of SLD.
Boston Pharmaceuticals' Perspective
Elias Zerhouni MD, Chair of the Board at Boston Pharmaceuticals, expressed pride in the agreement: "I am very proud of today's agreement with GSK, a company I know and admire with proven expertise in liver disease, and the outstanding work of the Boston Pharmaceuticals team."
Zerhouni acknowledged the Bertarelli family's commitment to leading science and biotechnology ventures, which facilitated the development of efimosfermin as a potential best-in-class therapy.
Financial and Regulatory Considerations
Under the terms of the agreement, GSK will acquire BP Asset IX, Inc., a subsidiary of Boston Pharmaceuticals, to access efimosfermin. In addition to the upfront and milestone payments to Boston Pharmaceuticals, GSK will also be responsible for success-based milestone payments and tiered royalties owed to Novartis Pharma AG.
The transaction is subject to customary conditions, including applicable regulatory agency clearances under the Hart-Scott-Rodino Act in the United States. GSK will account for the transaction as a business combination.
Market Potential and Future Outlook
With a potential first launch expected in 2029, efimosfermin represents a significant addition to GSK's hepatology pipeline of specialty medicines. The company is positioning itself to address both viral (chronic hepatitis B) and steatotic (SLD) drivers of fibrotic liver diseases.
The acquisition reflects the growing recognition of liver disease as a major global health concern and the substantial market opportunity for effective treatments. As the prevalence of metabolic disorders and alcohol-related conditions continues to rise globally, the demand for innovative therapies like efimosfermin is expected to grow correspondingly.
For patients with SLD who currently have few treatment options, the development of efimosfermin offers hope for a therapy that could not only halt disease progression but potentially reverse some of the damage already done—a significant advancement in the management of these challenging conditions.
