GSK plc ( GSK ) on Wednesday agreed to acquire Boston Pharmaceuticals’ lead asset, efimosfermin alfa.

Under the agreement, GSK will pay up to $2 billion in total cash consideration. This includes $1.2 billion upfront, with the potential for additional success-based milestone payments totaling $800 million.

GSK will also be responsible for success-based milestone payments and tiered royalties for efimosfermin owed to Novartis Pharma AG.

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Efimosfermin is a phase 3-ready, investigational specialty medicine for treating and preventing the progression of steatotic liver disease (SLD).

Efimosfermin is a novel, once-monthly fibroblast growth factor 21 (FGF21) analog therapeutic in clinical development for metabolic dysfunction-associated steatohepatitis (MASH), including cirrhosis, and future development in alcohol-related liver disease (ALD), both forms of SLD.

SLD affects approximately 5% of the global population with limited therapeutic options.

ALD affects about 26 million patients globally. Together with MASH, it is the leading cause of liver transplants in the U.S.

In November 2024, Boston Pharmaceuticals shared results from a Phase 2 study evaluating efimosfermin alfa (formerly known as BOS-580) at the American Association for the Study of Liver Diseases The Liver Meeting.

Treatment with efimosfermin led to significant improvements in fibrosis ≥1 stage without worsening of MASH, and MASH resolution without worsening of fibrosis over 24 weeks.

Study participants treated with efimosfermin showed rapid and significant improvement in fibrosis biomarkers and reductions in non-invasive markers of liver injury and liver fat over the study period.

Participants with type 2 diabetes also had significant and clinically meaningful improvement in HbA1c values.

In the study, efimosfermin demonstrated a favorable tolerability profile.

Over 24 weeks of treatment, efimosfermin-treated study participants had low discontinuation rates due to adverse events, and an overall low incidence of gastrointestinal side effects and injection site reactions.

Price Action: GSK stock is up 1.98% at $37.07 during the premarket session at the last check on Wednesday.

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