GSK plc and Boston Pharmaceuticals, a clinical-stage biopharmaceutical company, have entered into an agreement under which GSK will acquire Boston Pharmaceuticals’ lead asset, efimosfermin alfa, a phase III-ready, potential best-in-class, investigational specialty medicine to treat and prevent progression of steatotic liver disease (SLD).

Under the agreement, GSK will pay $1.2 billion upfront, with potential for additional success-based milestone payments totaling $800 million.

Efimosfermin is a novel, once-monthly fibroblast growth factor 21 (FGF21) analog therapeutic in clinical development for the treatment of metabolic dysfunction-associated steatohepatitis (MASH), including cirrhosis, and future development in alcohol-related liver disease (ALD), both forms of SLD. It has potential to address more advanced stages of SLD and opportunity in combination with GSK’990, a siRNA therapeutic in development for other subsets of patients with SLD.

Data from Clinical Trials

Recent data from a phase II trial of efimosfermin, designed to assess the efficacy and safety of a monthly subcutaneous dose in participants with biopsy-confirmed moderate-to-advanced (F2 or F3) MASH, showed that efimosfermin rapidly and significantly reversed liver fibrosis and stopped its progression, with a manageable tolerability profile. These data suggest potentially greater fibrosis improvement compared to that seen with other therapeutic approaches and with benefit expected independent of background glucagon-like peptide-1 (GLP-1) therapy.

In addition, efimosfermin could offer triglyceride reduction and improved glycaemic control, important considerations for MASH patients who frequently face cardiometabolic co-morbidities. Efimosfermin’s unique properties, including low immunogenicity and an extended half-life, also offer the potential for a monthly dosing regimen and improved patient convenience.

Tony Wood, Chief Scientific Officer, GSK said: “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. 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.”

Elias Zerhouni MD, Chair of the Board, Boston Pharmaceuticals, said: “We are delighted that GSK, a global leader, recognized efimosfermin’s potential to address a growing global public health concern and unmet medical need. Together, we look forward to efimosfermin’s ongoing journey to become a best-in-class treatment for patients with SLD.”

The addition of efimosfermin further strengthens GSK’s hepatology pipeline of specialty medicines aimed at addressing both viral (chronic hepatitis B) and steatotic (SLD) drivers of fibrotic liver diseases.