GSK Acquires Phase III-Ready Efimosfermin for $1.2 Billion in Bid to Transform Steatotic Liver Disease Treatment
GSK has announced a major strategic acquisition in the field of hepatology, entering into a definitive agreement to acquire efimosfermin alfa, a potential best-in-class investigational therapy from Boston Pharmaceuticals. The deal reflects GSK’s growing commitment to advancing specialty medicines in areas of high unmet need, particularly in the treatment and prevention of steatotic liver disease (SLD).
Under the terms of the agreement, GSK will make an upfront payment of $1.2 billion to Boston Pharmaceuticals. The transaction also includes the potential for an additional $800 million in success-based milestone payments, bringing the total deal value to as much as $2 billion.
Efimosfermin is a Phase III-ready analog of fibroblast growth factor 21 (FGF21), a hormone involved in regulating metabolic and inflammatory processes in the liver. The candidate is being developed for metabolic dysfunction-associated steatohepatitis (MASH) — a progressive form of SLD that includes inflammation and fibrosis — as well as future indications including alcohol-related liver disease (ALD). Both MASH and ALD represent serious, potentially life-threatening conditions with limited treatment options and increasing global prevalence.
Unlocking the Potential of FGF21 in Liver Disease
FGF21 analogs have emerged as one of the most promising therapeutic classes in metabolic and liver diseases, particularly for their anti-fibrotic and metabolic regulatory properties. Efimosfermin stands out among its peers due to its long half-life, low immunogenicity, and monthly subcutaneous dosing schedule, potentially offering better tolerability and convenience for patients.
According to Tony Wood, Chief Scientific Officer at GSK, the addition of efimosfermin strengthens the company’s R&D capabilities in immune-driven and fibrotic diseases, which remain a core focus of its pipeline strategy. “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,” Wood said. “This acquisition will significantly expand our hepatology pipeline and provide the opportunity to develop a new best-in-class medicine, with the first commercial launch expected around 2029.”
Efimosfermin complements GSK’s existing investigational therapy GSK‘990, a small interfering RNA (siRNA)-based candidate also in development for subsets of SLD patients, including those with ALD and MASH. The combined portfolio positions GSK to pursue both monotherapy and combination treatment strategies, offering more tailored therapeutic options based on individual disease progression and patient profiles.
SLD: An Urgent and Growing Public Health Challenge
Steatotic liver disease — an umbrella term that encompasses MASH, ALD, and non-alcoholic fatty liver disease (NAFLD) — affects an estimated 5% of the global population, equating to hundreds of millions of individuals worldwide. While often asymptomatic in its early stages, SLD can progress to cirrhosis, liver failure, and hepatocellular carcinoma (HCC) if left untreated.
ALD alone is estimated to impact 26 million people globally and, together with MASH, constitutes the leading cause of liver transplantation in the United States. The societal burden of these diseases is staggering. In the U.S., advanced liver disease leads to excessive healthcare utilization and high treatment costs, particularly at end-stage. According to recent health economic models, therapies that can halt or reverse fibrosis may help avert the need for transplantation, reduce liver-related complications, and potentially save between $40 billion to $100 billion in healthcare costs over the next 20 years.
Despite this need, approved treatments for SLD remain sparse. The FDA approved resmetirom in early 2024 as the first drug for MASH with fibrosis, but industry analysts agree that multiple approaches targeting different mechanisms will be essential to managing this heterogeneous disease. Efimosfermin could become an important addition to that therapeutic toolkit.
Clinical Data Supports Best-in-Class Potential
Efimosfermin’s potential is underpinned by robust results from a Phase II clinical trial, which evaluated its efficacy and safety in patients with biopsy-confirmed moderate-to-advanced MASH (fibrosis stage F2-F3). The study assessed a monthly subcutaneous dose of efimosfermin and demonstrated rapid and significant reversal of liver fibrosis, a hallmark of advanced SLD. Notably, the therapy also halted fibrosis progression, suggesting both therapeutic and preventive value.
The trial also highlighted several favorable characteristics, including a manageable safety profile, triglyceride reduction, and improved glycemic control — benefits particularly relevant for MASH patients, many of whom also suffer from obesity, type 2 diabetes, and cardiovascular disease.
These data, which were presented at the American Association for the Study of Liver Diseases (AASLD) meeting in November 2024, sparked considerable interest across the hepatology community. Experts have noted that the fibrosis improvements observed with efimosfermin may exceed those seen with other agents, including GLP-1 receptor agonists and THR-β agonists, particularly because its efficacy appears to be independent of GLP-1 background therapy.
Strategic Fit for GSK’s Expanding Hepatology Portfolio
The acquisition of efimosfermin aligns with GSK’s broader strategy to grow its portfolio of specialty medicines targeting chronic inflammatory and fibrotic diseases. Over the past two years, the company has been expanding its focus beyond infectious disease and oncology to include immunology, metabolic disease, and hepatology.
With chronic hepatitis B virus (HBV) infection already a key area of focus — GSK is developing both functional cure strategies and therapies to suppress HBV-related inflammation — the addition of efimosfermin represents a natural extension into non-viral liver diseases. The company’s strategy includes using genomic data and disease phenotyping to identify the right patient populations for targeted interventions, which could further enhance the clinical utility and market success of efimosfermin.
Boston Pharmaceuticals’ Role in Efimosfermin’s Development
The announcement also marks a significant milestone for Boston Pharmaceuticals, the clinical-stage biopharmaceutical company that has shepherded efimosfermin through early and mid-stage development. Backed by strategic investment from the Bertarelli family, Boston Pharmaceuticals has focused on leveraging translational science and cutting-edge biotechnology platforms to develop targeted therapies for liver and metabolic diseases.
Dr. Elias Zerhouni, Chair of the Board at Boston Pharmaceuticals, praised the deal and GSK’s leadership in liver disease. “I am very proud of today’s agreement with GSK, a company I know and admire with proven expertise in liver disease,” he said. “This would not have been possible without the impressive, sustained and long-term strategic commitment to leading science and biotechnology ventures from the Bertarelli family, and the expertise of Ernesto Bertarelli, which led to the development of efimosfermin as a potential best-in-class therapy.”
The deal, which is expected to close in the second half of 2025 subject to customary regulatory approvals, underscores the intensifying pharmaceutical race to bring novel therapies for SLD to market. With efimosfermin potentially entering Phase III trials later this year, GSK is aiming for first commercial launch in 2029. If approved, efimosfermin would offer a long-acting, once-monthly treatment that could transform the care landscape for patients with liver fibrosis caused by MASH or ALD.
In summary, this acquisition reflects GSK’s confidence in the fibroblast growth factor 21 pathway, its ability to leverage precision medicine and human genetics, and its ambition to deliver disease-modifying therapies in areas of high unmet need. By adding efimosfermin to its pipeline, GSK takes another strategic step toward becoming a global leader in the treatment of fibrotic liver diseases.
