GSK secures rights to Boston Pharmaceuticals’ efimosfermin alfa, which the pharma plans to develop for fatty liver diseases such as metabolic dysfunction-associated steatohepatitis and alcohol-related liver disease.
GSK is fronting $1.2 billion to acquire Boston Pharmaceuticals’ investigational FGF21 analog efimosfermin alfa, which it will develop for steatotic liver diseases such as metabolic dysfunction-associated steatohepatitis, the pharma announced on Wednesday.
Aside from the upfront payment, GSK is also putting up to $800 million on the line in additional success-based milestones, resulting in a potential maximum deal value of $2 billion. GSK will also assume the responsibility of paying certain milestones and royalties to Novartis, the original owner of efimosfermin alfa.
Designed to be administered via a subcutaneous injection once per month, efimosfermin alfa is an analog of the FGF21 hormone. The drug regulates metabolic processes in the liver. Through this mechanism of action, efimosfermin alfa can reduce levels of fat in the liver while also tamping down on inflammation and reversing fibrosis in patients with metabolic dysfunction-associated steatohepatitis (MASH), subsequently stopping disease progression, mid-stage studies have shown.
GSK in its statement touted efimosfermin alfa’s “best-in-class” potential and said that the candidate is primed for Phase III development. “These data suggest potentially greater fibrosis improvement compared to that seen with other therapeutic approaches and with benefit expected independent of background [GLP-1] therapy,” GSK wrote in Wednesday’s release.
The pharma also called efimosfermin alfa’s tolerability profile “manageable.” A Phase II readout of the drug in November 2024 showed adverse effects like injection site reactions and gastrointestinal toxicities.
In pushing efimosfermin alfa forward, the pharma also has plans of combining it with GSK’990, its investigational siRNA therapy that the company is also proposing for other types of fatty liver diseases.
According to its pipeline page, GSK’990 is GSK’s only other MASH candidate. The siRNA therapy is in Phase II development and is also being studied for alcohol-related liver disease (ALD). The pharma on Wednesday announced that it is eyeing “future development” of efimosfermin alfa in ALD.
With Wednesday’s deal, GSK pushes ahead in the MASH race, which is currently led by Madrigal Pharmaceuticals. In May 2024, Madrigal won the FDA’s clearance for its THR-beta agonist Rezdiffra, the first-ever drug approved for this disease. Rezdiffra made $137.3 million in the first quarter, a 33% year-on-year increase.
No company has yet been able to replicate Madrigal’s success, but many are trying. Among them are 89bio and Akero Therapeutics, both of which are developing FGF21 analogs similar to efimosfermin alfa. Akero’s efruxifermin hit a snag in October 2023 with disappointing Phase IIb data, though the biotech was able to turn the tables around in March 2024 with promising 96-week data. Both Akero and 89Bio are in Phase III clinical trials, with 89Bio presenting strong Phase IIb findings in March 2023 and Akero sharing its 96-week Phase 2b SYMMETRY data last week at the EASL Congress 2025, showing for the first time, reversal of cirrhosis in a clinical trial.
Editor’s Note (May 14) : This story was updated to include mention of new data on Akero’s efruxifermin.
